Note: Descriptions are shown in the official language in which they were submitted.
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HIGH FRE4UENCY INDUCTIVE LAMP AND POWER OSCILLATOR
Certain inventions described herein were made with Government support
under Contract Nos. DE-FG01-95EE23796 and / or DE-FC01-97EE23776 awarded
by the Department of Energy. The Government has certain rights in those
inventions.
CROSS REFERENCE TO RELATED APPLICATIONS
This application is related to co-pending applications nos. 09/006,171,
60/071,192, 60/071,284, and 60/071,285, all filed January 13, 1998,
60/083,093,
filed April 28, 1998, 60/091,920, filed July 7, 1998, 60/099,288, filed
September 4,
1998, 60/102,968, filed October 2, 1998, and 60/109,591, filed November 23,
1998,
each of which is herein incorporated by reference in its entirety.
1. BACKGROUND
Field of the Invention
The invention relates generally to discharge lamps. The invention relates
more specifically to inductively coupled electrodeless lamps. The invention
also
relates to novel lamp configurations, coupling circuits, bulbs, aperture
structures,
starting aids, and excitation coils for inductively coupled electrodeless
lamps. The
present invention also relates to an improved electrodeless aperture lamp, and
to an
improved method of manufacturing an electrodeless aperture lamp. The invention
also relates generally to a novel high power, high frequency solid state
oscillator.
Related Art
In general, the present invention relates to the type of lamp disclosed in
U.S.
Patent No. 5,404,076, as well as U.S. Patent Application No. 08/865,516 (PCT
Publication No. 97/45858), each of which is herein incorporated by reference
in its
entirety.
Electrodeless lamps are known in the art. Such lamps may be characterized
according to the type of discharge they produce. Electrodeless discharges may
be
classified as either E discharges, microwave discharges, travelling wave
discharges,
or H discharges. The invention relates to those discharges preponderantly
characterized as H discharges.
Fig. 1 is a schematic diagram of a conventional electrodeless lamp which
produces an E discharge. A power source 1 provides power to a capacitor 2. A
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gas-filled vessel 3 is placed between the plates of the capacitor 2. E
discharges in
electrodeiess lamps are similar to arc discharges in an electroded lamp,
except that
current is usually much less in an E discharge. Once breakdown of the gas to
its
ionized -or plasma state is achieved, current flows through the capacitance of
the
vessels walls between the plates of the capacitor 2, thereby producing a
discharge
current in the plasma.
Fig. 2 is a schematic diagram of a conventional electrodeless lamp which
produces a microwave discharge. A microwave power source 11 provides
microwave energy which is directed by a waveguide 12 to a microwave cavity 14
which houses a gas-filled bulb 13. The microwave. energy excites the fill in
the bulb
13 and produces a plasma discharge. In a microwave discharge, the wavelength
of
the electromagnetic field is comparable to the dimensions of the exciting
structure,
and the discharge is excited by both E and H components of the field.
Fig. 3 is a schematic diagram of a conventional electrodeless lamp which
produces a travelling wave discharge. A power source 21 provides power to a
launcher 22. A gas-filled vessel 23 is disposed in the launcher 22. The gap
between the electrodes of the launcher 22 provides an E field which launches a
surface wave discharge. The plasma in the vessel 23 is the structure along
which
the wave is then propagated.
Fig. 4 is a schematic diagram of a conventional electrodeless lamp which
produces an H discharge. Electrodeless lamps which produce an H discharge are
also referred to as inductively coupled lamps. Inductively coupled lamps were
first
described more than 100 years ago. Experiments by J. J. Thomson are described
in
the article "On the discharge of Electricity through Exhausted Tubes without
Electrodes," printed in the London, Edinburgh, and Dublin Philosophical
Magazine
and Journal of Science, Fifth Series, Vol. 32, No. 197, October 1891. More
recently,
D. O. Wharmby, PhD surveyed the state of the electrodeiess lamp art in the
article
entitled "Electrodeless lamps for lighting: a review," IEEE PROCEEDINGS-A,
Vol.
140, No. 6, November 1993, pages 465 to 473.
Certain aspects of the operation of inductively coupled lamps are well
understood and have been characterized analytically, for example, in articles
by R.
B. Piejack, V. A. Godyak and B. M. Alexandrovich entitled "A simple analysis
of an
inductive RF discharge," Plasma Sources Sci. Technol. 1, 1992, pages 179-186,
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and "Electrical and Light Characteristics of RF-Inductive Fluorescent Lamps,"
Journal of the Illuminating Engineering Society, Winter 1994, pages 40-44.
Inductively coupled lamps having various bulb and coil configurations are
described in U.S. Patent No. 843,534, entitled "Method of Producing Electric
Light."
More recently, inductively coupled lamps having novel excitation coils are
described
in U.S. Patents 4,812,702, 4,894,591, and 5,039,903 (hereinafter, "the '903
patent").
As shown in Fig. 4, one example for a conventional inductively coupled lamp
includes a low frequency power source 31 providing power to a coil 32 which is
wound around a gas-filled vessel 33. The alternating current around the coil
32
causes a changing magnetic field, which induces an electric field which drives
a
current in the plasma. In effect, the plasma can be analyzed as a single turn
secondary to the coil 32. See Piejack et al., referenced above. An H discharge
is
characterized by a closed electrical field, which in many examples forms a
visible
donut-shaped plasma discharge.
Other geometries have been disclosed for inductively coupled lamps. For
example, Figure 1 of the Wharmby article set forth examples (a) - (e),
including a
high inductance coil wound on a ferrite toroid, internal {or optionally
external) to the
bulb. See Wharmby at p. 471.
As used herein, "low frequency" with respect to an inductively coupled lamp is
defined as a frequency less than or equal to about 100 MHz. For example, a
typical
operating frequency for conventional inductively coupled lamps is 13.56 MHz.
For
example, the '903 patent discusses an operating frequency range of 1 to 30
MHz,
with an exemplary operating frequency being 13.56 MHz. Most, if not all, of
the
developments relating to known inductively coupled lamps provide lamps
operating
at low frequency (i.e. less than or equal to about 100 MHz).
Referring again to Fig. 4, during the starting operation of an inductively
coupled lamp, an E field ionizes the fill in the gas-filled vessel 33 and the
discharge
is initially characteristic of an E discharge. Once breakdown occurs, however,
an
abrupt and visible transition to the H discharge occurs. During operation of
an
inductively coupled lamp, both E and H discharge components are present, but
the
applied H discharge component provides greater (usually much greater) power to
the plasma than the applied E discharge component.
As used herein, "high frequency" with respect to an electrodeless lamp is
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defined as a frequency substantially greater than about 100 MHz. The prior art
describes electrodeless lamps operating at high frequency, including lamps
exhibiting coil structures. However, none of the "high frequency"
electrodeless
lamps in the prior art are, in fact, inductively coupled lamps.
For example, U.S. Patent No. 4,206,387 describes a "termination fixture"
electrodeless lamp which includes a helical coil around the bulb. The
"termination
fixture" lamp is described as operating the range from 100 MHz to 300GHz, and
preferably at 915 MHz. As noted by Wharmby, "termination fixture" lamps have a
size-wavelength relationship such that they produce a microwave discharge, not
an
inductively coupled discharge.
U.S. Patent No. 4,908,492 (hereinafter "the '492 patent") describes a
microwave plasma production apparatus which includes a helical coil component.
The apparatus is described as operating at t GHz or higher, and preferably at
2.45
GHz. As disclosed, however, the coil need not be terminated and a large
diameter,
multi-tum coil is preferred to produce a large diameter plasma. In such a
configuration, the dimension of the exciting structure is comparable to the
wavelength of the microwave frequency power and the discharge appears to be a
travetling wave discharge, a microwave discharge, or some combination thereof.
In
any event, the resulting structure apparently does not operate by inductive
coupling.
U.S. Patent No. 5,070,277 describes an electrodeless lamp which includes
helical couplers. The lamp is described as operating in the range of 10 MHz to
300
GHz, with a preferred operating frequency of 915 MHz. The helical couplers
transfer
energy through an evanescent wave which produces an arc discharge in the lamp.
The arc discharge is described as very straight and narrow, comparable to an
incandescent filament. Hence, this lamp apparently does not operate by
inductive
coupling.
U.S. Patent No. 5,072,157 describes an electrodeless lamp which includes a
helical coil extending along a discharge tube. The operating range for the
lamp is
described as 1 MHz to 1 GHz. The discharge produced by the lamp is a
travelling
wave discharge. The effect of the helical coil is discussed as enhancing the
light
output and providing some RF screening.
Japanese publication No. 8-148127 describes a microwave discharge light
source device which includes a resonator inside the microwave cavity which has
the
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shape of a cylindrical ring with a gap. The resonator is described as a
starting aid
and microwave field concentrator.
A number of parameters characterize highly useful sources of light. These
include -spectrum, efficiency, brightness, economy, durability (working life),
and
others. For example, a highly efficient, low wattage light source with a long
working
life, particularly a light source with high brightness, represents a highly
desirable
combination of operating features. Electrodeless lamps have the potential to
provide a much longer working life than electroded lamps. However, low wattage
electrodeless lamps have found only limited commercial applications.
2. SUMMARY
The invention provides a high frequency inductively coupled electrodeless
lamp. In particular, the present invention provides an efficient, high
frequency
inductively coupled electrodeless lamp.
An object of one aspect of the present invention is to provide an ultra
bright,
low wattage electrodeless lamp which has many commercially practical
applications.
Specifically, an object of one aspect of the present invention is to describe
an
electrodeless aperture lamp which is powered by a solid state RF source in the
range of several tens to several hundreds of watts. The lamp of the present
invention represents the first of a revolutionary new family of lighting
products. With
its spectacular brightness, spectral stability, and long life time, the
present invention
provides an excellent light source for such diverse applications as projection
display,
automotive headlamps and general illumination.
Fig. 6 is a schematic, conceptual diagram of a high brightness electrodeless
lamp according to the invention. As shown in Fig. 6, an electrodeless lamp
bulb 4 is
covered with a reflective covering 5 which defines an aperture 6. An inductive
coupling loop 7 is driven by a solid state RF source 8 to power the lamp.
The lamp of the present invention improves on earlier work done in
connection with microwave-powered sulfur lamp technology. The power
consumption has been reduced from thousands of watts to tens or hundreds of
watts. The magnetron RF generator has been replaced with solid state
electronics.
A simple inductive coupling structure replaces the cavity structure used to
transfer
the RF power to the electrodeless bulb. The size of the bulb may be reduced to
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than 7mm in diameter. Lamp brightness may be enhanced by optical elements
built
directly into the lamp providing a nearly ideal two dimensional light source.
Preferably, the lamp according to invention is extremely compact in size.
Advantageously, the lamp can be conveniently packaged into a variety of
configurations. For example, the bulb, RF source and DC power supply can be
packaged together or each of these modules can be packaged and located
separately. Fig. 7 is a perspective view of a lamp according to the invention,
wherein the bulb, RF source, and DC power supply are located in a single
housing
16. Fig. 8 is a perspective view a lamp according to the present invention,
wherein
the bulb is located in a first housing 17 and the RF source and DC power
supply are
located in a second housing 18. The bulb receives the RF energy through
suitable
transmission means (e.g., a coaxial cable).
The lamp of the present invention offers other unique system level
advantages. For example, in certain applications, all of the photons emitted
from a
source may not be useful. With a conventional light source, 'rays of an
undesired
wavelength or polarization must be treated simply as waste light. However, as
shown in Fig. 9, an optical system which utilizes the lamp of the present
invention
may include an optical element 24 which directs waste light 25 back, to be
"recaptured" by the aperture bulb 26. Some of these returned photons interact
with
the plasma and are converted to useful light 27, before being re-emitted,
increasing
the overall efficiency of the lamp. Such light recapture is described in more
detail in
U.S. Patent No. 5,773,918 and PCT publication WO 97/45858 (assigned in common
with the assignee of the present invention), both of which are herein
incorporated by
reference in their entireties.
Long life is a fundamental characteristic of electrodeless lamps. The
elimination of all metal components in the bulb such as the filaments and
electrodes,
and the elimination of the accompanying glass to metal seals remove the
dominant
determinants of conventional lamp life times. The selection of specific bulb
fills
minimizes and in some cases eliminates the chemical interactions between the
plasma and the bulb envelop. Such interactions can significantly affect the
life time
and color stability of conventional high intensity discharge~lamps. Further,
the lamp
of the present invention is made more reliable through the use of all solid
state
electronics.
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Color stability in conventional discharge lamps is a function of the chemical
interaction between the bulb fill and the electrodes, the interaction between
the bulb
fill and the bulb envelope, and the interaction of the various components of
the bulb
fill with each other. Advantageously, the lamp of the present invention can be
configured with a minimally reactive single element bulb fill and no
electrodes
assuring an output spectra that is stable over the life time of the lamp.
Applications
Applications for a long lived high brightness electrodeiess light source such
as
the lamp of the present invention are both numerous and readily apparent to
persons skilled in the use of light sources. In general, the lamp of present
invention
may be configured as an effective light source in virtually any application
which
requires or benefits from artificial light. It is instructive to review some
of the some
of the applications that take special advantage of the unique properties of
such a
light source.
One of the most important applications of the lamp of the present invention is
to projection displays. A variety of imaging technologies are currently being
used to
modulate beams of light to create still or moving images. Technologies such as
Texas Instrument's DMD devices, as well as reflective and transmissive LCDs,
require a focused collimated beam of light. The unique characteristics of the
of the
lamp of the present invention lamp, long life, high brightness, optical
efficiency, color
stability, and excellent RGB ratios make the lamp of the present invention an
excellent source for this application.
The same characteristics are also desirable for applications that are based
upon the use of fiber optics. Before light can be transmitted in an optical
fiber it
must enter the end of the fiber within a critical angle of the fiber axis.
Light that does
not enter the end of the fiber within the critical angle is lost. To a very
large extent
the total efficiency of a fiber optic illumination system is determined by the
coupling
efficiency of the light into the end of the fiber bundle. The two dimensional
lamp of
the present invention source significantly enhances this coupling efficiency.
In fact,
the two-dimensional source provided by the lamp of the present invention
allows for
direct coupling to large core or bundled fiber optics. Fiber optic
illumination can be
advantageously used in a variety of applications including medical devices,
automotive lighting, and general illumination.
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Fig. 10 is a perspective view of the lamp of the present invention utilized in
conjunction with a tapered light pipe (TLP). Fig. 11 is a perspective view of
the lamp
of the present invention utilized in conjunction with a compound parabolic
concentrator (CPC). Fig. 12 is a perspective view of the lamp of the present
invention utilized in conjunction with a ball lens. Fig. 13 is a perspective
view of the
lamp of the present invention directly coupled to a large core fiber optic.
Fig. 14 is a
schematic diagram of the,lamp of the present invention used in an automotive
lighting system with fiber optic distribution. Fig. 15 is a perspective view
of the lamp
of the present invention used in a projection display.
The present invention can be used with both imaging and non-imaging optics
to produce spot and flood type lighting as well as general illumination
products.
The present invention can be paired with various optical films such as 3M's
optical lighting film (OLF) to produce such lighting schemes as light pipe
systems
and light boxes which substitute for conventional fluorescent fixtures.
Most of the examples of the lamp of the present invention described
hereinafter are scaled to power a small screen display, a medical instrument,
a
vehicle headlamp or other application requiring a bright source with an output
of one
to three thousand lumens. However, the lamp of present invention may be scaled
up in power and / or size to provide a bright source capable of emitting tens
of
thousands of lumens. Applications as diverse as theater projectors, large
screen
display TV, theater spot lights and lighthouse beacons are further
contemplated
uses of the present lamp.
Use of lama to cure adhesives
Many adhesives can be cured by intense visible light. Because of the small
spot size and high lumen intensity, the lamp of the present invention is an
excellent
source for adhesive curing. In some processes, selective curing is preferred
over
"flood" light type-curing. It may also be more cost effective from an energy
point of
view to only expose the adhesive to light. Light shielding is also simplified
if only a
selected work area needs to be illuminated. As noted below in section 4.2.2,
the
aperture may be shaped to match a desired area and / or shape of illumination.
A partial listing of some of the applications for the lamp of the present
invention includes the following:
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Projection Applications Architectural Accent Lighting
- Fiber Optics - Fiber optic distribution
- Automated Lights (Gate / Shutter)- Plastic Frenel lens with mirror
- Slide Projector between source and lens to project
- Display projector beam
- Overhead ro'ector - S of / Wash li htin
Automobile Theatrical lighting
- Head lamps - Film / television
- Interior lamps - Stage / studio
Fiber optic distribution - Frenel lens (variable beam
s otli ht
Hazard lighting Signage
- Rugged nature of invention - Neon sign replacement
- Strobe / wamin li ht
Personal head lamp Street light
- Surgeon's light - Full cutoff
- Miner's li ht
Traffic light LCD backlighting
Fiber o tic distribution - Da li ht readable dis la
Landing light Inspection light
- Runway - Flashlight
- Ai lane
General Lighting Residential lighting
- Up lights - Safety
- Down lights - Indirect lighting
- Spot lights - Wall wash
- Flood lights - Outdoor controlled flood light
(no
spill)
- Landsca a li htin
Beam projector Underwater lighting
- Search li ht - A uarium
Materials processing Light house
- Curing light
- Intensity and near UV
- Re ro ra hic Li htin
Cold stora a li htin Shi board li htin
Instrument li htin Horticultural
Table 1
A table of headings is provided below.
1.BACKGROUND
2. SUMMARY
3. BRIEF DESCRIPTION OF THE DRAWINGS
4. DESCRIPTION
4.1 High Frequency Inductive Lamp
4.1.1 First Coupling Circuit
4.1.2 Novel Wedding Ring Shaped Excitation Coil
4.1.3 Second Coupling Circuit
4.1.4 Field Concentrating Conductive Surface
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4.1.5 Ceramic Heatsink for Cooling the Excitation Coil
4.1.6 Lamp with Improved Thermal Characteristics
4.1.7 Novel Omega Shaped Excitation Coil
4.1.8 Integrated Lamp Head
4.1.8.1 Omega Coil
4.1.8.2 Pre-formed Coil Connection for Lamp Head
4.1.8.3 Tunable High Voltage Capacitor
4.1.9 Exemplary Fills
4.2 Bulb and Aperture Structures
4.2.1 Blow Molded Bulbs
4.2.2 Aperture Structures
4.2.3 Exemplary Processes for Filling Aperture Cup
4.2.3.1 Hand gupping
4.2.3.2 Solid Casting
4.2.3.3 Use of Centrifuge to Pack Cup
4.2.4 Exemplary Performance Data
4.2.5 Spectral Distribution
4.2.6 Ball Lens
4.2.7 Ceramo-quartz lamp
4.2.8 Design Feature for Alignment of the Aperture Cup
4.2.9 Flanged Aperture Cup
4.2.10 Starting Aid
4.3 High Power Oscillator
4.4 Lamp and Oscillator
4.4.1 Cantilevered Oscillator Board
4.4.2 Separate Lamp Head Housing
4.4.3 Exemplary Lamp Head Soldering Processes
4.4.4 Improved Solderability Inserts
4.4.5 Separate RF Source
4.4.6 Oscillator Control Circuits
5. CLAIMS
6. ABSTRACT
3. BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood with reference to the accompanying
figures, wherein:
Figs. 1-4 are schematic diagrams of conventional electrodeless lamp systems
which produce various types of discharge.
Fig. 5 is a graph of Q versus frequency.
Figs. 6-9 are conceptual representations of lamps according to the invention.
Figs. 10-15 are depictions of various applications for a lamp according to the
invention.
Fig. 16-32 are related to a novel coupling circuit according to the invention
and various lamp configurations employing the same.
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Figs. 33-37 are related to a washer-shaped excitation coil.
Figs. 38-57 are various schematic views, sectional views, and perspective
views, respectively, of a novel excitation coil and some exemplary alternative
structures of the same according to the invention.
Figs. 58-62 are schematic diagrams showing different circuit arrangements
which are suitable for utilizing the novel excitation coil according to the
invention in
an electrodeless lamp.
Figs. 63-78 are various perspective, schematic, and cross-sectional views,
respectively, of exemplary electrodeless lamps utilizing the novel excitation
coil
according to the invention.
Figs. 79-82 are related to alternative structure for the novel excitation coil
according to the invention which resembles an uppercase Greek letter omega
(S2).
Figs. 83-106 are related to an integrated lamp head according to the invention
and various electrodeless lamps utilizing the same.
Figs. 107-120 are related to a high voltage capacitor arrangement according
to the invention.
Figs. 121-132 are related to a blow molded bulb according to the invention.
Figs. 133-154 are related to various aperture structures according to the
invention.
Figs. 154-159 are related to various performance aspects of an example of
an electrodeless lamp according to the invention.
Figs. 160-171 are related to an alternative bulb / aperture structure and a
method of manufacturing the same.
Figs. 172-175 are related to an aperture cup according to the invention with
features for radial and axial alignment.
Figs. 176-180 are related to an aperture cup with a flanged face for thermal
management.
Figs. 181-186 are related to a ceramic covering for a bulb with embedded
wires to improve lamp starting.
Figs. 187-209 are related to a preferred solid-state high power oscillator
according to the invention for providing high frequency energy to the lamp.
Figs. 210-222 are related to an lamp and oscillator integrated in a single
assembly.
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Figs. 223-255 are related to a separate lamp assembly.
Figs. 256-265 are related to a separate RF source assembly.
4. DESCRIPTION
4.1 High Frequency Inductive Lamp
Embodiments of the present invention can provide a highly efficient, low
power light source with a long working life, particularly a light source with
high
brightness, which represents a highly desirable combination of operating
features.
Low power, as used herein with respect to a light source, is defined as less
than
about 400 watts (W). Brightness, as used herein, is defined as the amount of
light
per unit solid angle per unit of light source area. The present invention
provides
electrodeless lamps that have the potential to provide a much longer working
life
than electroded lamps. Conventional low power electrodeless lamps heretofore
have found only limited commercial applications.
The present invention provides an efficient, iow power electrodeless lamp
with intense brightness, capable of serving in many commercially practical
applications.
Although high frequency power sources and inductively coupled lamps are
known, the prior art does not appear to teach the combination of a high
frequency
power source with a lamp configured for inductive coupling. The present
invention
resolves both practical barriers and technological barriers that have
heretofore
prevented such useful combinations.
In a capacitively coupled lamp system (i.e. an E discharge lamp) the
impedance of the coupling circuit is inversely proportional to frequency.
Thus, at
high frequencies the impedance decreases and the lamp may be run at higher
current and thus more efficiently. Hence, reduced impedance and higher
efficiency
offers a motivation for those skilled in the art to develop higher frequency
capacitively coupled lamps.
In an inductively coupled lamp system (i.e. an H discharge lamp), the
impedance of the circuit would be expected to vary in direct proportion to
frequency.
Thus, at sufficiently high frequencies, the impedance would so increase such
that an
inductively coupled lamp would not operate with any reasonable efficiency, if
at all.
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By way of illustration, the quality factor Q of a coil is an indication of the
coil's
operating efficiency, i.e. efficiency in transferring energy to a device {e.g,
a
secondary coil coupled thereto). Q may be represented by the equation:
Equation (1)
where L is the inductance of the coil, R is the resistance of the coil, and w
is the
radian or angular frequency {w = 2n x f, where f is the operating frequency).
Fig. 5
shows a typical plot of Q versus frequency for a given coil. As can be seen
from the
plot, Q increases proportional to the square root of frequency up to a point,
beyond
which Q declines. One reason that Q declines or "rolls off" from its peak
value is
that, at higher frequencies, "parasitics" or untoward factors are present
which affect
the coil performance by increasing the coil losses (i.e. the impedance of the
coil). At
these higher frequencies, the coil losses increase proportionately greater
with
increasing frequency, thereby causing Q to roll off.
For example, the "proximity effect" is a known phenomenon which describes
how, as the coil turns get closer together, the Q rolls over sooner due to
inter-turn
capacitance. Other factors, such as skin depth and eddy current effects, may
also
contribute to increasing the effective resistance of.the coil at higher
frequencies.
Increasing the effective resistance (i.e. R in equation 1 ) of the circuit may
cause the
roll off to accelerate. Thus, at higher frequencies, the proximity effect
(inter-turn
capacitance) and other parasitic effects which degrade coil performance become
significant obstacles to efficient coil operation.
A further technological barrier to operating an inductively coupled lamp at
high frequencies is that parasitic effects, such as those which affect coil
performance, are also present in the coupling circuit, i.e. the circuitry
operatively
linking the power source to the lamp. Such effects would be expected to
complicate
the circuit design of the coupling circuit. For example, at high frequencies
even
straight wires take on inductive characteristics; a mutual inductance may
occur
between one straight wire and another straight wire. Further, stray
capacitances of
certain parts of the coil to other parts of the coupling circuit are also
present.
Thus, in light of both practical and technological barriers, persons skilled
in
the art apparently have not heretofore configured electrodeless lamps as
inductively
coupled lamps connected to a power source operating at high frequency. For
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example, considerations relating to the coil Q factor and high frequency
coupling
circuits suggest that a very high frequency {e.g. above about 1 GHz)
inductively
coupled lamp would be very inefficient, if operable at all.
The devices in accordance with the present invention overcome one or more
of the problems presented in the prior art through the design of the lamp and
circuit
elements, i.e. through the size of the exciting structure and the physical
size of the
circuit elements. Because physically large circuit elements are more
susceptible to
the above discussed parasitics, the device of the present invention overcomes
this
deficiency by making the circuit elements sufficiently small (e.g., as small
as
practically possible) to permit efficient operation.
Preferably, an effective electrical length of the coil is less than about a
half
wavelength of a driving frequency applied thereto. More preferably, the
effective
electrical length of the coil is less than about a quarter wavelength. Most
preferably,
the effective electrical length of the coil is less than about one eighth
wavelength.
The driving frequency is preferably greater than 100 Mhz and may be greater
than
about 300 MHz, 500 Mhz, 700 Mhz, or 900 MHz.
The devices of the present invention optimally operate with coils in which the
number of turns is preferably less than about 2 turns and, in certain
examples, less
than one turn. At high frequencies, fewer turns minimize and/or effectively
eliminate
inter-turn capacitance. Also, at high frequencies, the present devices use a
coil with
fewer turns to minimize energy transfer losses due to the phase lag around the
coil.
Accordingly, the present invention encompasses coils having less than one turn
to
coils having up to about six turns. (Jptionally, for example at operating
frequencies
of less than about 150 MHz, more than 2 turns are employed. At progressively
higher frequencies, about 2 turns or less is especially preferred.
In general, for a given diameter bulb, and a given diameter coil, the
preferred
number of turns depends on frequency, with fewer turns or less than one turn
being
preferred for lamps operating at the higher frequencies.
4.1.1 First Coualinp Circuit
First examale of a high frequency inductively cour~~led lamp
As used herein, the first example refers generally to an inductively coupled
electrodeless lamp according to the invention in which the coupling circuit
comprises
a "diving board" structure (as hereinafter described) and a helical excitation
coil.
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Description of a first example of the invention will be made with reference to
Figs. 16-18, wherein like elements are referenced by like numerals. Fig. 16 is
a
perspective view of the first example of an electrodeless lamp according to
the
invention. Fig. 17 is a top, schematic view of the first example of an
electrodeless
lamp according to the invention. Fig. 18 is a partial section view of the
first example
of an electrodeless lamp according to the invention, taken along line 18-18 in
Fig.
17.
As illustrated, an inductively coupled electrodeless lamp 40 includes an
enclosure 46 housing a helical coil 42 with a bulb 43 disposed in the center
of the
coil 42. The bulb 43 is positioned in the coil 42 by a support 47 (as can best
be
seen in Fig. 18). The support 47 is preferably made of a material which is
capable
of handling the high temperatures of the bulb surface, but which does not
conduct
too much energy away from bulb (e.g. the support 47 should not be too heat
conductive, although some heat conduction may be desirable, as hereinafter
described). For example, a suitable material for the support 47 is quartz. The
coil
42, bulb 43, and support 47 are disposed within a dielectric tube 45. The
dielectric
tube 45 may be made from any suitable dielectric material including, for
example,
quartz or alumina.
Power is provided to the lamp 40 via an input connector 41. The input
connector 41 may be, for example, an N-type coaxial connector having a center
conductor, for receiving the high frequency signal, and a grounded outer
conductor,
the grounded outer conductor being electrically connected to the enclosure 46.
A
first conductive element, hereinafter referred to as a "diving board" 48, is
connected
at one end to the grounded outer conductor of the input connector 41. A second
conductive element, hereinafter referred to as a power feed 49, is connected
at one
end to the center conductor of the input connector 41. As shown in Figs. 16-
18, the
diving board 48 and power feed 49 are connected to each other at their
respective
other ends, near the dielectric tube 45. One end of the coil 42 is positioned
opposite
of the diving board 49, and the other end of the coil 42 is grounded to the
enclosure
46.
As can best be seen in Fig. 18, a first capacitor is formed between a portion
42a of the coil 42 and a portion 48a of the diving board 48, with the
dielectric tube 45
providing the dielectric material for the first capacitor. A second capacitor
is formed
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between a portion 42b of the coil 42 and a portion 49b of the power feed 49,
with
both the dielectric tube 45 and the air in the space between the tube 45 and
the
power feed 49 providing the dielectric material for the second capacitor.
In the figures, coil 42 is illustrated as having about 2 turns, but may be
more
or less turns depending on the bulb diameter, operating frequency, etc., as
discussed above.
Lamps having outer diameter bulb sizes ranging from about 1 inch (25 mm)
down to about 0.2 inches (5 mm), with a typical bulb wall thickness of about
0.02
inches (0.5 mm) were constructed and employed, including bulbs with 5, 6, and
7
mm diameters. Of course, larger or smaller size bulbs can be used in the
electrodeless lamp according to the invention, with corresponding adjustments
of the
frequency; coil size, and circuit design.
For example, efficiency is generally improved if the inside coil diameter is
closely matched to the outside bulb diameter. A power transfer ratio for
inductively
coupled lamps was quantified by David Wharmby, Ph.D., in a 1994 presentation
at
the Gaseous Electronics Conference in Gaithersburg, MD, in the following
equation:
~~ = k
Z~u (1 ~Q z ~ Equation (2)
a
where the subscript a refers to the plasma, the subscript a refers to the
coil, P is
power, Q is the quality factor, and k is the coupling coefficient. The
coupling
coefficient k is a measure of the magnetic flux lines linking the coupling
coil and the
current loop within the bulb. Placing the coil closer to the bulb increases
the
coupling coefficient, thereby increasing the power transfer ratio.
In accordance with the foregoing, an exemplary high frequency, inductively
coupled lamp is constructed with the following dimensions. An enclosure 46 is
constructed as a metal box, about 25 mm (1 inch) tall, 38 mm (1.5 inches)
wide, and
50 mm (2 inches) long, with the top (i.e. one of the 38 by 50 mm walls)
removed. A
conventional N-type connector 41 is installed through an opening at one end
(i.e.
one of the 25 by 38 mm walls) of the enclosure 46. The power feed 49 is a thin
ribbon conductor, about 0.33 mm (0.013 inch) thick, having a width of about 4
mm
(0.16 inch). The power feed 49 traces a curved path, beginning at the center
conductor of the input connector 41, bending downwardly in an extension having
a
length of about 6.5 mm (0.25 inch) to a lower extreme, curving back and
extending
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towards the diving board 48 with an inside radius of about 1.25 mm (0.05
inch), the
distance from the lower extreme to the diving board 48 being about 15.25 mm
(0.6
inch). The curved shape and length of the power feed 49 provides a relatively
high
inductance and a distributed capacitance with respect to the coil 42.
The diving board 48 is a straight ribbon conductor, about 0.65 mm (0.025
inch) thick, having a width of about 8 mm (0.32 inch) and an overall length of
about
26 mm (1.02 inches). One end of the diving board 48 is connected to the outer
conductor of the N-type connector 41. The diving board 48 has a portion 48a
bent
at a right angle approximately 21.5 mm (0.85 inch) from the connector 41 end
to
form a plate having a height of about 4.25 mm (0.17 inch). The power feed 49
was
connected (e.g. soldered) to the diving board 48 at the bend. The straight
section of
the diving board 48 is adapted to provide low inductance and low resistance.
The
bent portion 48a of the diving board 48 provides one electrode of the series
resonant
capacitor.
The dielectric tube 45 is a quartz right circular cylindrical enclosure having
a
height of about 28.75 mm (1.13 inches), an inside diameter of about 10 mm (0.4
inch), and a wall thickness of about 2 mm (0.08 inch). The dielectric tube 45
sits on
the bottom of the enclosure 46 and abuts the bent portion 48a of the diving
board
48.
The series resonant coil 42 is wound two and one half turns in a helix, having
an outside diameter of about 10 mm (0.4 inch), an inside diameter of about 8
mm
(0.32 inch), and a pitch of about 5 mm (0.2 inch). The top most portion of the
coil 42
is positioned opposite of the bent portion 48a of the diving board 48 and
forms the
other electrode of the series resonant capacitor. The other end of the coil 42
is
grounded (e.g. soldered to the bottom of the enclosure 46).
The bulb 43 is made of quartz, having an outside diameter of about 8 mm
(0.32 inch) and an inside diameter of about 7 mm (0.28 inch). The bulb 43 is
filled
with about 4 to 6 mg of selenium and a buffer gas of Xenon to a pressure of
300-
1000 Torr. The bulb rests on a right circular cylindrical quartz support 47
having an
inside diameter of about 6 mm (0.24 inch), an outside diameter of about 8 mm
(0.32
inch) and a height of about 6 mm (0.24 inch).
Fig. 19 is a schematic diagram of a system for operating and evaluating the
lamps described herein. A high frequency signal source 52 is connected to an
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amplifier 53. The output of the amplifier 53 is connected to a circulator 54,
which is
connected through a directional coupler 55 to the lamp 40. The circulator 54
shunts
reflected power to a load 56. The directional coupler 55 provides a plurality
of taps
which may be connected to measurement devices 57.
The above described device is operated, for example, at 915 MHz with 30-
100 watts of power supplied by an amplifier made by Communication Power
Corporation, Brentwood, NY, Model No. 5M-915-1,5E2 OPT 001, connected by a
coaxial cable to a Hewlett-Packard Network Analyzer Model No. 8505A. The
circulator and directional coupler employ commercially available components.
The
output of the directional coupler is connected to the input connector 41 via a
coaxial
cable. The inductively coupled lamp produces up to approximately 80 lumens per
watt (i.e. approximately 8000 lumens with 100 watts of power).
The above-described device is powered by any suitable power source
capable of providing a suitable level of power at high frequency. For example,
a
magnetron may be used as the power source. Preferably, the microwave power
from the magnetron would be coupled through an impedance matching device into
a
coaxial cable for supplying the power to the device.
Fig. 20 is a schematic diagram of the first example of an electrodeless lamp
according to the invention. The circuit which couples the input power to the
bulb is a
series resonant circuit. A series resonant circuit includes, for example, an
inductor
(e.g. a coil) and a capacitor in series, and has an alternating current
ringing in the
circuit during operation. Initially, power is supplied to the circuit and
charges the
capacitor, then the capacitor discharges and the energy is stored in the
inductor. As
the current reaches a peak in the inductor, it recharges the capacitor with an
opposite polarity and the process repeats itself. The ringing would be
perpetual,
except for the fact that there are inevitable losses in the circuit. The power
supplied
to the circuit replenishes the losses to maintain the circuit ringing at its
resonant
frequency. Because much of the current is preserved between the capacitor and
the
inductor, only a fraction of the stored energy is required to be replaced to
keep the
circuit ringing with relatively high current, thereby allowing relatively
efficient
operation of the circuit.
As shown in Fig. 20, a series resonant capacitor CO and a series resonant
coil LO form the main components of a series resonant circuit. A high
frequency
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power source 51 provides a feed current through a feed inductor L1. L1 is
connected to the series resonant capacitor C0. The series resonant capacitor
CO is
connected in series with the series resonant coil L0, which is connected
through a
resistor R1 to ground. A small inductor L2 is connected between ground and the
junction of L1 and C0. A distributed capacitance C1 is shown with dotted lines
connecting the middle of LO and L1.
With respect to the first example shown in Figs. 16-18, the series resonant
coil LO corresponds to the coil 42. The series resonant capacitor CO
corresponds to
the first capacitor formed between portions 42a and 48a of the coil 42 and
diving
board 48, respectively. The feed inductor L1 corresponds to the power feed 49
and
the small inductor L2 corresponds to the diving board 48. The distributed
capacitance C1 corresponds primarily to the second capacitor formed between
portions 42b and 49b of the coil 42 and power feed 49, respectively, but also
includes many small capacitances formed between the feed inductor L1 surface
and
the coil LO surface (i.e. every portion of the coil 42 surface has some
capacitance
with respect to every portion of the power feed 49 surface).
During operation, energy is initially stored on the series resonant capacitor
C0, which then discharges and the current passes through the series resonant
coil
L0, down to ground. The current then passes back through the small inductor L2
(i.e. the diving board 48), which is preferably a low inductance device. Thus,
the
series resonant circuit includes primarily CO and L0, with a small inductance
being
contributed by L2. The feed inductor L1 couples a small amount of energy into
the
series resonant circuit, which makes up for the losses (represented by R1 )
for each
ring. R1 represents, for example, two loss components. One is the plasma
resistance reflected back into the primary circuit (e.g., L2, C0, LO). The
other is the
inherent resistance of any non-superconductive circuit. The distributed
capacitance
C1 (between L1 and LO) may be adjusted to match the input impedance by
altering
the location of L2.
Referring back to Figs. 1 fi-18, the energy is brought in via the N-type
connector 41 through the power feed 49, which is a relatively low current
carrying
element, compared to the series resonant circuit, and it feeds energy into the
series
resonant circuit as the energy is dissipated through the coil 42 and other
elements in
the circuit (some energy is lost in operation, mostly resistively, and a
negligibly small
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amount due to RF radiative losses). In comparison to the power feed 49, the
diving
board 48 is a high current carrying element connected directly to ground, and
is part
of the series resonant circuit. The ringing current passes through the diving
board
48, through the dielectric tube 45, through the coil 42, down to ground, and
around
again.
During operation, a large voltage develops between the diving board 48 and
the coil 42, on the order of 1000 to 10,000 volts. The dielectric tube 45
helps
prevent breakdown of the lamp circuit due to this high voltage. The dielectric
tube
45 may also advantageously enclose an optically reflecting powder, such as
high
purity alumina or silica.
The distributed capacitance C1 is relatively small and its function is to
improve the coupling (i.e. impedance matching). For example, the position of
portion 49b of the power feed 49 may be adjusted during bulb operation, with
respect to the portion 42b of the coil {e.g., bent to be closer, farther,
higher, or
lower), to as closely as practical match the input impedance of the power
source
(e.g. nominally 50 ohms, although other input impedances are possible). Of
course,
in production, the circuit can be readily configured so that the desired
impedance
match is provided without any post-production adjustments.
According to the invention, the schematic circuit components are in fact
formed by the physical structure of the conductive elements themselves. This
circuit
structure provides numerous advantages including reduction of cost and
complexity,
and improved reliability. For example, this circuit structure overcomes
problems with
breakdown of discrete circuit elements at high frequencies.
Fig. 21 is a sectional schematic representation of an H discharge occurring
within a bulb. A simplified description of an H discharge is as follows. A
plasma
(e.g. an ionized gas) is contained inside a bulb (e.g. a vessel made of
quartz). The
series resonant circuit drives an alternating current through the coif that
creates a
time varying magnetic field. The changing magnetic field induces a current
inside
the bulb. The current passes through the plasma and excites the production of
light.
The plasma functions analytically as a lossy single tum secondary coil of a
transformer.
While the bulb shown in most of the examples described herein is shown with
a generally spherical shape, other bulb shapes may be used with the
inductively
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coupled lamp according to the invention. Figs. 22-26 show exemplary
alternative
bulb shapes suitable for accommodating an H discharge. Fig. 22 shows a
perspective view of a generally cylindrical shaped bulb. Figs. 23-26 show
generally
disc shaped bulbs, also referred to as pill-box shaped bulbs. Fig. 23 is a
perspective
view. Figs. 24-26 are cross sectional views through the bulb center, where the
bulb
is rotationally symmetric around a vertical axis through the center. Fig. 24
shows a
pill-box shaped bulb with rounded comers. The bulb shown in Fig. 25 includes a
re-
entrant dimple in the bottom. The bulb shapes shown are for purposes of
illustration
only and not limitation. Other bulb shapes are also possible.
The fill material employed can be sulfur or selenium based, but can include
any other fills suitable for use in electrodeless lamp. Preferably, the fill
in its ionized
state provides a moderately low impedance. Examples of suitable fill materials
include metal halides (e.g. InBr, Nal, Cal, Csl, SnCI). Mercury based fills
may also
be used.
Figs. 27-29 are perspective views of exemplary alternative structures of the
first conductive element (i.e. the diving board) and the second conductive
element
(i.e. the power feed) which are suitable for use by the first example of an
electrodeless lamp according to the invention.
The power feed is a lower current carrying element because the power feed
only needs to carry the feed current, which varies depending on the input
power.
The power feed may have any reasonable shape, and is preferably curved or bent
to
provide a longer length (and therefore a higher inductance) than the diving
board.
The diving board, on the other hand, is preferably a high current carrying,
low
inductance conductive element. The diving board carries all of the current of
the
ringing series resonant circuit because that current passes through the
capacitor,
through the diving board to ground, back up through the coil. The diving board
is
shown thicker in some examples (e.g. Fig. 28), but the diving board need only
be
thick enough to accommodate the skin depth of the ringing current. The skin
depth
varies depending on the material. While the diving board is preferably
straight, it
may have small bends or curves. In Fig. 27, the power feed 59 is a relatively
thick
(e.g. about 12 gauge) wire bent at approximately right angles and connected to
the
diving board 58 a short distance past the center of the diving board 58 (i.e.
spaced
inwardly from the bend). In Fig. 28, the power feed 79 is a relatively thick
wire with
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curved bends. In Fig. 28, the diving board 78 is a thicker ribbon conductor
with a
tapered end connected (e.g. soldered) to a metal plate 78a. In Fig. 29, the
diving
board 88 has a portion 88a which is bent up, rather than down.
Although the first capacitor electrode has been illustrated with specific
shapes
and / or positions, other shapes and / or positions are alternately employed.
For
example, by way of illustration and not limitation, the capacitor electrode
may be
square, rectangular, octagonal, circular, semi-circular, or other shapes. The
electrode may be positioned above, below, centered, or otherwise offset with
respect
to the end of the diving board. One of skill in the art will appreciate that
numerous
other design choices for the power feed, diving board, and the plate of the
capacitor
are alternately employed.
Figs. 30-32 show an alternative structure of the first example of an
electrodeless lamp according to the invention. The main differences between
this
alternative structure and the example shown in Figs. 16-18 is that the
inductively
coupled electrodeless lamp 80 utilizes the diving board 88 / power feed 89
combination shown in Fig. 29 (with the portion 88a bent up instead of down), a
straight dielectric 85 is used instead of the dielectric tube 45, and the coil
82
includes a metal plate 82a (as can best be seen in Fig. 27) as the second
electrode
of the capacitor. Operation of this alternative structure is essentially the
same as
that described above with respect to operation of the lamp 40 shown in Figs.
16-18.
Second example of a hiah freauency inductively coupled lamp
As used herein, the second example refers generally to an inductively
coupled electrodeless lamp according to the invention which utilizes the
diving board
structure coupled to a "washer" shaped excitation coil (as hereinafter
described).
A device encompassing the first example described above (i.e. an inductively
coupled lamp having a diving board structure and a helical coil with about 1
1/2
turns) is hereinafter to compared to several other examples including devices
having
a diving board structure and (1 ) a coil having a trapezoidal cross-sectional
shape (as
disclosed in the '903 patent)and (2) a flat, washer shaped coil (which
approximates
the '903 patent's coil shape).
Figs. 33-35 show a schematic view, a sectional view; and a perspective view,
respectively, of a coil 92 comprising the second example of an electrodeless
lamp
according to the invention. The coil 92 has a fiat, generally washer shaped
structure
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with a slot 93. Comparisons were made with washer shaped coils having the
following dimensions (in mm):
INNER OUTER SLOT AXIAL
DIAMETER DIAMETER WIDTH HEIGHT
9.5 15.9 3.5 1,6
9.5 19.7 3.5 3.3
9.5 22.9 3.5 1.0
9.5 22.9 3.5 0.1
9.5 1 5.9 3.5 1.0
9.5 15.9 3.5 0.3
i adie z
For some comparisons, a metal plate was soldered on the side of the coil,
adjacent to the slot, to form an electrode of the series resonant capacitor
(see Fig.
32). Also, for some comparisons, copper tubing was added to the outside of the
coil
to provide water cooling. Figs. 36-37 show a schematic view and a sectional
view,
respectively, of a water cooled, washer shaped coil 122 utilized in the second
example of an electrodeless lamp according to the invention. The perimeter of
the
coil 122 is in thermal contact with copper tubing 124.
Based on a comparison of the first and second examples, the washer shaped
coils were found to be less efficient than the above-mentioned 1 1/2 tum
helical coil
lamp. Further, the washer shaped coils which had a smaller outside diameter
were
more efficient than the washer shaped coils that had a larger outside
diameter. As
suggested in the '903 patent, the washer shaped coils provided an effective
shape
for less light blockage. fn general, the washer shaped coils also appeared to
provide
good heat handling characteristics.
4.1.2 Novel Wedding Ring Shaped Excitation Coil
Third example of a high freauency inductively coualed iamb
As used herein, the third example refers generally to an inductively coupled
electrodeless lamp according to the invention which utilizes the diving board
structure and a novel "wedding ring" (or split wedding ring) shaped excitation
coil (as
hereinafter described).
Novel excitation coil
Figs. 38-40 show a schematic view, a sectional view, and a perspective view,
respectively, of a novel excitation coil according to the invention. According
to the
invention, a coil 132 has a generally "wedding ring" shaped structure with a
slot 133.
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Several wedding ring shaped coils having the following dimensions (in mm) are
constructed:
INNER RADIAL AXIAL
DIAMETER THICKNESS HEIGHT
9.5 1.3 1,3
9.5 1.3 1.9
9.5 1.3 2.5
9.5 1.3 3.2
9.5 0.6 1.3
9.5 0.6 1,8
9.5 0.6 2.3
9.5 0.6 2,8
9.5 0.6 3.3
9.5 0.6 3.8
9.5 0.6 4.3
9.5 0.6 5.1
9.5 0.6 6.4
i anie ;~
In each of the foregoing examples, the slot width is between about 1.8 and 3.5
mm.
As used herein, a "wedding ring" shaped coil refers generally to a radially
relatively thin and axially relatively tall conductive surface, preferably
less than one
turn, and preferably evidencing a non-helical configuration. in other words a
wedding ring shaped coil has a small radial thickness (i.e. difference between
outer
diameter and inner diameter) and an axial height at least greater than the
radial
thickness.
The wedding ring shaped coils exhibited significantly more efficient operation
than either the helical coil or the washer shaped coils when coupled to
essentially
the same diving board structure.
Fig. 41 is a graphical illustration of current distribution in the excitation
coil
shown in Figs. 38-40, of a well coupled operating lamp at high frequencies. In
Fig.
41, the distance the line 139 is spaced from the coil 142 surface represents
the
amount of current flowing in that area of the coil 142. The current is
distributed
towards the outside edges of the coil 142. As can be seen from Fig. 41,
relatively
little current flows in the middle section of the coil 142. Thus, the current
flowing in
the coil 142 essentially forms two loops of current at opposite outside edges
of the
coil 142.
During operation, the lamp operates more efficiently with two current loops.
One half of the current flows in two rings causes only one fourth the loss in
each
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loop. The total loss in the sum of the loss in each loop, resulting in one
half of the
overall losses for an operating lamp. Therefore, efficiency is greatly
improved.
Generally, more current is distributed on the side facing the bulb (if the
coil is
closely coupled to the bulb). Effectively, the coif current and the plasma
current are
drawn together to achieve energy minimization. The closer the coupling between
the two currents, the greater the forces driving the two currents to be as
close to
each other as possible.
At high frequencies, substantially all of the current is carried in the skin
depth
of the coil material. As is well known in the art, the skin depth depends on
the
material and the operating frequency. For example, the skin depth of copper
(in
inches) at room temperature is about 2.61 divided by the square root of the
frequency. Thus, at about 1 GHz, the skin depth of copper is about 0.0001
inches
(1/l0th mil). Preferably, the radial thickness of a wedding ring shaped coil
according
to the invention is at least several skin depths, and more preferably, the
radial
thickness should be greater than about 10 skin depths.
Preferable examples have a radial thickness less than about 0.8 mm (0.03
inches). For example, devices with an axial height of between about 4.0 and
5.0
mm (0.15 to 0.2 inch) are constructed with a radial thicknesses of between
about
0.18 and 0.54 mm (0.007 to 0.021 inch) and maintain comparable efficiency
within
that range of radial thicknesses. For very thin coils, the coil material is
alternatively
deposited directly on an insulating surface.
The preferred axial height for the wedding ring shaped coil according to the
invention is at least greater than the radial thickness and up to about 2J3 of
the
inside diameter of the coil, with between 1/3 and 2/3 of the inside diameter
of the coil
providing better efficiency.
For example, when the axial height of the coil is about equal to the inside
radius of the coil, the operation of the wedding ring shaped coil approximates
a
Helmholtz coil configuration, i.e. a pair of flat, circular coils having equal
numbers of
turns and equal diameters, arranged with a common axis and connected in
series.
The optimum arrangement for Helmholtz coils is when the spacing between the
two
coils is equal to the radius. Helmholtz coils are known to produce a uniform
magnetic field, with the midpoint between the two coils, along the common
axis,
being the point of nearly uniform field strength. In an inductively coupled
lamp,
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uniformity of field is not generally thought of as a critical operating
parameter.
However, the volume integral of the power density in a wedding ring /
Helmholtz coil
configuration is also at an optimum, thereby providing optimum inductive
coupling to
the volume between the coils.
Thus, with the appropriate axial height, an operating lamp utilizing the
wedding ring shaped coil according to the invention provides two current loops
spaced apart by a distance equal to the inside radius of the coil. Each
current loop
corresponds approximately to one coil of the Helmholtz coil configuration. A
precise
Helmholtz arrangement, however, is not required for acceptable efficiency. As
the
coil height approaches the Helmholtz arrangement, the losses become less; but
decreasing asymptotically. Thus, the axial height of the coil may be somewhat
greater or smaller than the inside radius of the coil with only a small effect
on
efficiency: Accordingly, the wedding ring / Helmholtz configuration provides a
robust
system which allows a wide range of design for other lamp parameters.
Figs. 42-57 are perspective views and schematic views, respectively, of
different examples of the novel excitation coil according to the invention.
Figs. 38 -
40 show a preferred wedding ring shaped coil with an axial height about equal
to the
inside radius.
As illustrated in Fig. 41, little current flows in the middle section of the
wedding ring shaped coil. Accordingly, the middle section may be removed with
little
effect on coil efficiency. A "split wedding ring" shaped coil refers to a
generally
wedding ring shaped coil with at least a portion of the middle section of the
wedding
ring removed. When split wedding ring shaped coils having two or more parallel
rings are compared for efficiency with the wedding,ring shaped coil, no
significant
differences in efficiency are noted.
Figs. 42 - 43 show a preferred structure of a split wedding ring shaped coil
with all but a small portion of the middle one-third of the wedding ring
shaped coil
removed. Figs. 44-45 show an alternative structure with the middle one-third
of the
wedding removed from about one half of the wedding ring shaped coil.
Figs. 46-47 show an alternative structure, where only a thin sliver of each
split
ring remains. More preferably, the split rings are made relatively thicker in
order to
reduce the current density in the coil material, thereby reducing power losses
(e.g.,
heating the coil to a lesser extent) and making the lamp more efficient.
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Figs. 48-49 illustrate that a rectangular cross section is not required and
the
edges may be rounded. Other shapes for the edges are also possible.
Preferably,
the coil cross section shape allows the current to spread out. In general, the
more
the current spreads out the greater the efficiency because localized power
losses
are reduced. Making the radial thickness of the coil too thin (although
minimizing
eddy current losses) increases current density and the corresponding power
losses.
Figs. 50-51 are perspective views and schematic views, respectively, of a
further example of the novel excitation coil according to the invention. In
this
example, leads to the coil do not extend beyond the outside diameter of the
coil, so
that the coil may be positioned inside a torus shaped bulb. Fig. 51 shows a
perspective view of a torus shaped bulb. In the case of Fig. 51, the coil 42
could be
positioned either inside the bulb or outside the bulb, depending on the
application.
Figs. 52-57 show examples of wedding ring and split wedding ring coils with
integral leads for connecting to the rest of the lamp circuit. Note that, as
shown in
Figs. 56-57, the top and bottom coil sections need not be physically connected
as
long the currents passing through the two sections are close in phase and
about
equal in magnitude.
Figs. 58-62 are schematic diagrams showing lamps utilizing different split
wedding shaped coil arrangements according to the invention. In each of Figs.
58-
61, the circuit are configured so that the current in each of the split rings
is close in
phase and about equal in magnitude. in Fig. 58, a single power source drives
both
rings. In Fig. 59, two power sources drive the two rings separately. In Fig.
60, two
power sources separately power the two rings, and the leads of the two rings
are
positioned at opposite directions. In Fig. 61, three power sources separately
power
three rings, with one ring being centrally positioned, and the other two rings
being
symmetrically spaced about the center.
The circuit in Fig. 62 deviates from the above discussed split wedding ring
structure because it does not provide two loops of current precisely in phase.
Rather, the circuit in Fig. 61 illustrates the two rings of the split wedding
ring coil
being connected in series to form a two tum ribbon coil. Ribbon coils
typically have
a higher Q, providing advantages at low frequencies. With the appropriate
spacing
of the current loops, the circuit in Fig. 61 would approximate a Helmholtz
coil
configuration and may provide good efficiency at relatively lower frequencies.
At
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relatively higher frequencies, however, proximity effects and other parasitics
would
adversely affect the efficiency of the circuit shown in Fig. 62 to a greater
extent than,
for example, the circuit shown in Fig. 58.
While the novel "wedding ring" shaped excitation coil has been described
above with reference to specific shapes and structures, these examples should
be
considered as illustrative and not limiting. For example, by way of
illustration and not
limitation, elliptical, square, rectangular, kidney, and arbitrary cross-
sectional shaped
coils may alternatively be employed in place of the circular cross sections
exemplified above. Also, while the novel "wedding ring" shaped excitation coil
has
been described above coupled to a diving board structure, the novel excitation
coil
according to the invention may be utilized with other circuit designs. For
example,
depending on the operating frequency, a suitable lamp may be built from
discrete
components (e.g. off the shelf capacitors). Moreover, while the novel "wedding
ring"
coil has been described with respect to high efficiency lamps operating at
high
frequencies and/or very high frequencies (e.g. above about 900 MHz), the
utility of
this configuration is not limited to such high or very high frequency
applications. For
example, the novel excitation coil according to the invention is suitable for
a lamp
operating at about 13.56 MHz, 2 MHz, 1 MHz, or lower frequencies, providing
advantages as set forth above at these lower operating frequencies.
4.1.3 Second Coupling Circuit
Fourth example of a hiah fre4uency inductively coupled lama
As used herein, the fourth example refers generally to an inductively coupled
electrodeless lamp according to the invention which couples a "blade"
structure (as
hereinafter defined) to the wedding ring (or split wedding ring) shaped
excitation coil.
The fourth example of the invention is described generally by reference to
Figs. 63-67, wherein like elements are referenced by like numerals. Fig. 63 is
a
perspective view of the fourth example of an electrodeless lamp according to
the
invention, utilizing an example of the wedding ring shaped excitation coil
shown in
Figs. 38-40. Fig. 64 is a top, schematic view of the fourth example. Fig. 65
is a
fragmented, sectional view of an exemplary capacitor structure utilized by the
fourth
example of an electrodeless lamp according to the invention, taken along line
65-65
in Fig. 64. Fig. 66 is a section view of the fourth example, taken along line
66-66 in
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Fig. 64. Fig. 67 is a section view of the fourth example, taken along line 67-
67 in
Fig. 64.
As illustrated, an inductively coupled electrodeless lamp i 40 includes an
enclosure 146 housing a wedding ring shaped coil 142 with a bulb 143 disposed
in
the center of the coil 142. The bulb 143 may be positioned in the coil 142 by,
for
example, a support as described in connection with the first example. One side
of
the slot of the coil 142 is connected (e.g. soldered) to a first plate 142a
which
extends down and connects to a base 148 which is grounded to the enclosure
146.
The first plate 142a positions the coil 142 within the enclosure 146. The
other side
of the slot of the coil 142 is connected to a second plate 142b, 'which is not
grounded.
Power is provided to the lamp 140 via an input connector 141. The input
connector 141 may be, for example, a coaxial connector having a center
conductor
and a grounded outer conductor. The center conductor carries the high
frequency
signal fi.e. the power). The grounded outer conductor is electrically
connected to the
enclosure 146.
A conductive element, hereinafter referred to as a blade 149, is connected at
one end to the center conductor of the input connector 141. A portion of the
other
end of the blade 149 extends in between the plates 142a and 142b, where it is
sandwiched in between a first dielectric 145a and a second dielectric 145b.
As can best be seen in Figs. 63 and 65, capacitors are formed between the
end portion of the blade 149 and the plates 142a and 142b. A first capacitor
is
formed between the plate 142a and the end portion of the blade 149, with the
dielectric 145a providing the dielectric material for the first capacitor. A
second
capacitor is formed between the plate 142b the end portion of the blade 149,
with
the dielectric 145b providing the dielectric material for the second
capacitor.
Fig. 68 is a schematic diagram of the fourth example of an electrodeless lamp
according to the invention. The series resonant circuit includes two
capacitors C1
and C2 connected in series with each other and connected in series with a
series
resonant coil L0. A power source 151 provides a high frequency signal through
a
small inductance L1 to the junction of C1 and C2. The other side of C1 is
grounded.
The series resonant coil LO is also connected to ground through a small
resistance
R1, which represents the lumped circuit resistance.
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During operation, the circuit operates as a series resonant circuit, in which
LO
is the series resonant inductor and both C1 and C2 operating together are the
series
resonant capacitor. In other words, the two capacitors C1 and C2 tied together
in
series effectively provides one series resonance capacitance C0. The capacitor
CO
and the inductor LO together form the series resonant circuit, which during
operation
has a ringing current. Power is supplied to the series resonant circuit in the
form of
a high frequency alternating current. As the power continues to be supplied,
the
energy moves between the capacitors, C1 and C2, and the coil LO in an
alternating
manner. There are inevitable losses in the circuit, represented by R1 in Fig.
68.
The energy (power) supplied to the series resonant circuit replenishes the
losses,
and the series resonant circuit continues to ring.
The lamp is considered to operate at the applied input power frequency. In
other words, the system operates at the power source frequency, assuming that
the
power source frequency is sufficiently close to the actual series resonant
circuit
frequency. During operation, the bulb plasma reflects a certain amount of
resistance
back into the circuit and there is some natural resistance (represented
collectively by
R1 ). The actual resonant frequency of the series resonant circuit need not
exactly
match the power source frequency. The resonant frequency is preferably about
the
same as the power source frequency, taking into account the Q of the circuit
with the
circuit loaded (i.e. with an operating bulb). Depending on the Q of the
circuit, the
range of effective operating frequencies may be relatively wide. In other
words, the
circuit may operate off actual resonance and still operate efficiently (i.e.
fairly well
matched and fairly well working).
Referring back to Fig. 63, during operation of the fourth example of the
invention, high frequency power is brought in through the connector 141 and is
supplied through the blade 149 to the series resonant circuit. The blade 149
is a
relatively low current carrying element, compared to the rest of the circuit,
and has a
small inductance (i.e. included in L1 along with the connector lead). The
blade 149
feeds energy into the series resonant circuit as the energy is dissipated
through the
coil 142 (i.e. LO) and other lossy elements in the circuit. For example, some
energy
is lost in operation, mostly by resistance {i.e. R1 ). A small. amount of
energy may
also be lost by radiation. The ringing current passes around the coil 142 and
through the first capacitor (fom~ed by the plate 142a, dielectric 145a, and
the end
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portion of the blade 149) and the second capacitor (formed by the end portion
of the
blade 149, the dielectric 145b and the plate 142b). Preferably, the first
capacitor
(i.e. C1) provides a low voltage and a high capacitance and the second
capacitor
(i.e. C2) provides a high voltage and low capacitance.
Thus, in the fourth example, the series resonant circuit is confined in space
to
just around the coil 142 and through the two capacitors. Preferably, the two
capacitors are formed between the slot of the coil 142 to keep the circuit
elements
as small as possible. The two capacitors pertorm a dual function of (1 )
tuning the
resonant frequency and (2) providing impedance matching for the input power
source.
The impedance of the input power source is matched by the impedance of
the coupling circuit (including the blade). The impedance is nominally 50 ohms
because many commercially available power sources are 50 ohms. However, the
circuit may readily be impedance matched to other input sources impedances
including, for example, 10 ohms. The impedance matching depends on the ratio
of
the capacitors C1 and C2, and on I_1. Typically, there is no problem in
choosing
capacitor values which provide both good impedance matching and also the
appropriate resonarit frequency for the series resonant circuit. The resonant
frequency is determined by the equation:
f - 1
2n COx LO Equation (3)
where
1
CO = ~ + ~ Equation (4)
C1 C2
With respect to the series resonant circuit, C1 and C2 can have any ratio as
long as the reciprocal of the sum of the reciprocals equates to the desired
C0.
Preferably, as discussed above, C1 and C2 are split so that C1 provides a high
voltage and low capacitance and C2 provides a low voltage and a high
capacitance.
Thus 1/C2 is a small value compared to 1/C1, and, therefore, C2 has only a
small or
negligible influence on the resonant frequency.
With respect to impedance matching, the ratio of C1 ~ and C2 is the important
factor. Thus to select appropriate values for C1 and C2 which provide both the
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desired resonant frequency and the appropriate impedance, the following
procedure
may be used:
1 ) Determine the value of LO for the specific lamp configuration;
2) Select a value of CO which provides a series resonant frequency
closely matched to the power source frequency (this may be subsequently
adjusted
slightly to take into account the Q of the loaded, operating circuit);
3) Choose L1 (preferably small) and a ratio of C1 and C2 to provide
impedance matching for the signal source (e.g. 50 Ohms);
4) Select a value of C1 close to the value of CO (typically a small
capacitance, for example, on the order of picofarads); and
5) Select a value of C2 which satisfies the ratio for impedance matching
(typically a much larger capacitance, for example, on the order of 50 to 100
times
larger than C1).
The specific dimensions (i.e. how much of a tum the coil makes, the spacing
between the blade and the electrode on one side, and the spacing between the
blade and the electrode on the other side) are determined as a function of the
dielectric material (i.e. its dielectric constant), the operating frequency,
and the
resonant frequency of the circuit (which depends on the inductance of the
coil). The
capacitance depends on the area of the electrode size as well as the
dielectric
material and its thickness. For a particular lamp configuration, the choices
for the
capacitor materials and sizes may be readily determined by one of skill in the
art.
The material of choice is preferably a low-loss tangent material of reasonable
dielectric constant. Preferred dielectric materials include, for example,
alumina and
quartz.
In comparison to the diving board coupling circuit, the blade coupling circuit
is
well confined in space. While both structures include a series resonant
circuit, in the
diving board coupling structure high current passes through the enclosure and
the
diving board itself. This current path produces a series resonant circuit that
is larger
than for the blade coupling circuit, and therefore less efficient. By reducing
the
current path, the blade coupling structure can be made about 1.3 to 2 times
more
efficient than the diving board coupling structure, depending on the
particular lamp
configuration.
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4.1.4 Field Concentrating Conductive Surface
Fifth example of a hi4h freauency inductively coupled lama
As used herein, the fifth example refers generally to an inductively coupled
electrodeless lamp according to the invention which utilizes a blade
structure, the
wedding ring (or split wedding ring) shaped excitation coil, and a "stove
pipe" (as
hereinafter defined).
The lamp enclosure is important for providing RF shielding. The lamp
enclosure may have any reasonable shape which encloses the lamp circuit in a
Faraday cage. In general, radiative losses can occur through electromagnetic
radiation or conduction through the power cord. A Faraday cage prevents
electromagnetic radiation from escaping through the enclosure. Other
conventional
methods may be used to shield the radiation through the power cord.
Further, the choice of enclosure can improve the efficiency of the lamp. For
example, in the absence of an enclosure (e.g. a bottom, but no sides or top)
the
lamp operates less efficiently than with a suitably sized enclosure (sides
included).
Moreover, as the size of the enclosure changes, the relative efficiency of the
lamp also changes. The location of the wedding ring shaped coil above the
ground
plane, and the distance between the coil and the enclosure walls likewise
affects the
efficiency of the lamp. _
Fig. 69 is a perspective view of selected components of the fifth example of
an electrodeless lamp according to the invention. As shown in Fig. 69, an
inductively coupled electrodeiess lamp 150 includes a conductive surface
(hereinafter referred to as a stove pipe 151 ). The lamp 150 is otherwise
similar to
the lamp 140, described above with respect to Figs. 63-68. As shown in Fig.
69, the
stove pipe 151 is a semi-cylindrical conductive surface which is connected
(e.g.
soldered) to the mounting base of the lamp 150 thereby grounding the stove
pipe
151.
The stove pipe 151 is preferably positioned symmetrically around the coil.
However, the stove pipe 151 may be asymmetrically positioned with respect to
the
coil with only a small effect on the efficiency. If the lamp enclosure
includes a top,
the coil is preferably positioned central to the top and bottom. However,
where the
enclosure does not include a top, moving the coil closer to the bottom of the
enclosure improves efficiency, with a preferred spacing being about one coil
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diameter from the bottom. The distance from the coil to the stove pipe walls
also
has an effect on efficiency, with a preferred distance for optimal efficiency
also being
about one half to one coil diameter.
For example, with a wedding ring shaped coil having an outer diameter of
about 7.62 mm (0.3 inch), the height and diameter of the stove pipe 151 is
preferably about 22.86 mm (0.9 inch). In enclosures with an open top, the lamp
is
most efficient if the wedding ring shaped coil was placed about one coil
diameter
(i.e. 7.62 mm) above the ground plane.
The stove pipe according to the invention may have any reasonable shape.
For example, Fig. 70 is a perspective view of an exemplary alternative
structure for a
stove pipe utilized by the fifth example of the invention. In Fig. 70, a lamp
160
includes a stove pipe 161 which is generally box-shaped.
Electrical fields will not penetrate the stove pipe. Mirror currents are
induced
on the stove pipe. The lamp efficiency may be improved because the mirror
currents in the stove pipe can act to concentrate the magnetic and electrical
fields to
the region interior to the bulb. This affects the electrical parameters of the
coil and
may affect the resonant frequency.
4.1.5 Ceramic Heatsink for Cooling the Excitation Coil
Sixth examale of a high frepuency inductively coupled lama
As used herein, the sixth example refers generally to an inductively coupled
electrodeless lamp according to the invention which utilizes a blade
structure, the
wedding ring (or split wedding ring) shaped excitation coil, and a heatsink
(as
hereinafter described).
During operation, the resistance in the coil results in coil power losses and
causes the coil temperature to increase. Elevated temperatures increase the
coil
resistance, thereby commensurately decreasing efficiency. Thus, it is
desirable to
use a heatsink to cool the coil. Conventional heatsink methods for cooling
conventional coils include water cooling, heat pipes, or making the coil
massive (e.g.
the '903 patent coil). Each of these conventional methods, however, requires
making the radial thickness of the coil larger. As discussed above, it is
preferable to
make the coil radially relatively thin, as described above.
Fig. 71 is a perspective view of selected components of the sixth example of
an electrodeless lamp according to the invention. As shown in Fig. 71, an
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inductively coupled electrodeless lamp 170 includes a heatsink 171. The
heatsink
171 is preferably in intimate thermal contact with the coil. The surface of
the
heatsink which contacts the coil should be smooth for good thermal contact.
Preferably, the heatsink 171 is made from a material which has a high
thermal conductivity, but little or no electrical conductivity. For example, a
preferred
material for the heatsink 171 includes a high thermal conductivity ceramic,
such as,
for example, beryllium oxide (Be0). Other materials may also be suitable. For
example, boron nitride (BN) has good thermal characteristics and has an
additional
advantage, in this application, because BN conducts heat laterally (i.e. in a
radial
direction). Thus, the use of BN may allow for more precise control of heat
flow.
Aluminum Nitride (AIN) may also be suitable. However, as discussed in detail
below, a heatsink made from AIN may degrade the lamp performance at high
frequencies.
For example, the addition of a Be0 heatsink results in improved lamp
operation with respect to both stability and operating range.
While the heatsink 171 shown in Fig. 71 is generally cylindrically shaped,
other shapes are possible. For example, Fig. 72 shows a perspective view of an
exemplary alternative structure for a heatsink utilized by the sixth example
of an
electrodeless lamp according to the invention. In Fig. 72, a lamp 180 includes
a
heatsink 181 having a box shape. These examples should be considered as
illustrative and not limiting.
The choice of material and structure of the heatsink has a significant effect
on
lamp operation. At high frequency, phase differences around the coil result in
a less
uniform magnetic field. With the coil surrounded by a dielectric material
(i.e. a
ceramic), the electrical length of the coil increases, depending on the
dielectric
constant of the material. As the electrical length of the coil approaches a
substantial
fraction of the wavelength of the power source, the effects of phase slip
become
more pronounced.
For example, U.S. Patent No. 5,498,937 (hereinafter "the '937 patent")
discloses an electrodeless lamp which utilizes AIN as a support material for a
conventional helical coil. The lamp disclosed in the '937 patent is operating
at 13.56
MHz (i.e. low frequency). However, the relatively high dielectric constant of
AIN
makes it less suitable for high frequency operation.
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For example, AIN has a dielectric constant of about 9, and would lengthen the
electrical length of the coil by a factor of about 3. On the other hand, BeO,
which
has thermal characteristics similar to AIN, has a dielectric constant of only
about 6,
and thus would lengthen the electrical length of the coil to a lesser degree
than AIN.
The dielectric constant of BN is about 4, although BN's thermal
characteristics are
less advantageous than either AIN or BeO.
Seventh example of a hiah fre4uency inductivel coupled lama
As used herein, the seventh example refers generally to an inductively
coupled electrodeless lamp according to the invention which utilizes a blade
structure, the wedding ring (or split wedding ring) shaped excitation coil, a
heatsink,
and a stove pipe.
Fig. 73 is a perspective view of a seventh example of an electrodeless lamp
according to the invention. Fig. 74 is a perspective view of an alternative
structure of
the seventh example of an electrodeless lamp according to the invention. As
can be
seen in Figs. 73 and 74, various aspects of the different examples described
above
may be combined to provide a highly efficient, inductively coupled
eiectrodeless
lamp.
The effect of placing the heatsink in the space between the coil and the stove
pipe is that the thermal resistance between the coil and the thermal sink may
be
dramaticaNy reduced. In general, the stovepipe may be fabricated from a metal
that
is a good thermal conductor, such as copper or aluminum. The large area
contact
between the coil and the heatsink, and the heatsink and the stovepipe,
combined
with the relatively short distance through the heatsink, provides for a better
thermal
contact between the thermal sink and the coil. Consequently, coil temperature
is
reduced, the concomitant increase in coil resistance is reduced, and overall
efficiency is increased.
4.1.6 Lama with Imaroved Thermal Characteristics
E~hth example of a high frectuency inductively coupled lamp
In some applications, the heatsink need not be co-extensive with the coil for
the entire circumference of the coil. To reduce phase slip and keep the
electrical
length of the coil as small as possible, a preferred heatsink arrangement
includes a
single slab of dielectric material positioned opposite to the coil power feed.
Thermal
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sinking of the coil is further enhanced by the use of substantial input and /
or output
contacts, preferably made of metal such as, for example, copper.
Fig. 75 is a perspective view of a eighth example of an electrodeless lamp
according to the invention. Fig. 76 is a top, schematic view of the eighth
example
the invention. Fig. 77 is a cross sectional view of the eighth example taken
along
line 77-77 in Fig. 76. Fig. 78 is a cross sectional view of the eighth example
taken
along line 78-78 in Fig. 76.
Referring to Figs. 75-78, wherein like elements are indicated by like
numerals,
an inductively coupled eiectrodeless lamp 190 includes an enclosure 196
housing a
wedding ring shaped coil 192. A bulb 193 is disposed in the center of the coil
192
and supported by a dielectric 195. Power is brought into the lamp 190 by a
thin wire
lead 191 which is connected to a blade 199. Alternatively, a coaxial connector
may
be affixed to the housing 196 with power being brought in on the center
conductor.
A single dielectric 194 is in intimate thermal contact with a portion of the
coil 192, at
a position opposite to where the power is brought in through lead 191. The
lead 191
is connected to a blade 199 inside the housing 196. The blade 199 extends
between dielectrics 199a and 199b, thereby forming the capacitors of the
series
resonant circuit as described in detail above.
To improve thermal conductivity of the coil 192, the radial thickness of the
coil
is made as thick as possible without significantly reducing efficiency. For
example,
for a coil having a 5 mm inside radius and a 4 to 6 mm axial height, the
coil's radial
thickness should be about 0.25 mm to 0.75 mm. To improve thermal sinking of
the
coil 192, the ground contact is substantial and is connected to the front,
top, and
bottom of the enclosure. Thermal conduction of the lamp 190 is also improved
by
minimizing the coil 192 to enclosure 196 spacing, consistent with efficient
operation
as described above with respect to the stove pipe. For example, for a coil
with a 5
mm inside radius, the enclosure 196 should be a right cylinder with the coil
at its
center. The enclosure 196 should have an outer diameter of about 20-30 mm and
a
height of about 20 mm.
Preferably, the dielectrics 194 and 195 are thermally conductive ceramics
such as, for example, BeO, BN, or AIN. If phase distortion ~is to be
minimized, BN is
a preferred material. The bulb size and the coil diameter may be reduced to
shorten
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the electrical length of the coif. Also, the operating frequency may be
lowered to
reduce the effects of phase slip.
In the eighth example, the bulb 193 is encased by a reflective jacket 198,
examples of which are described in section 4.2.2 below and PCT Publication WO
97/45858. The reflective jacket 198 forms an aperture for emitting light
therefrom.
This aperture lamp configuration provides a high brightness light source. The
lamp
190 may be used with or without a light guide in registry with the aperture.
4.1.7 Novel Omega Shaped Excitation Coil
Ninth example of a high freauencv inductively coupled lama
Figs. 79-80 are schematic and perspective views, respectively, of an
alternative structure for the novel excitation coil according to the invention
which is
utilized in an ninth example of an electrodeless lamp according to the
invention. Fig.
81 is a top, schematic view of the ninth example of the invention. Fig. 82 is
a cross
sectional view taken along line 82-82 in Fig. 81.
As shown in Figs. 79-80, the novel excitation coil 220 has a cross-sectional
shape generally corresponding to the upper-case Greek letter omega (S2). The
"omega" coil 220 has a generally wedding ring shaped excitation portion, but
the
leads 220a and 220b are bent tangential to the excitation portion and parallel
to
each other. As can be seen in Fig. 79, the omega coil 220 may include leads
220a
and 220b that are not symmetrical with each other.
Figs. 81-82 show the omega coil 220 mounted on a printed circuit board 221.
The printed circuit board 221 is a double-sided board with a dielectric layer
222 and
conductive areas 224 and 226a-226c disposed thereon. The manufacture of such
printed circuit boards is well known. Conductive area 226c covers one entire
side of
the printed circuit board 221 and is referred to as a ground plane. Conductive
areas
226a and 226b are electrically connected to the ground plane 226c (e.g. by
plated
through holes or other types of electrical connection). Conductive area 224
forms a
stripline impedance matching circuit with a portion 224a essentially
corresponding to
the blade structure as described in preceding examples.
As can best be seen in Fig. 82, a first capacitor is formed by lead 220a,
dielectric 230, and the blade portion 224a. A second capacitor is formed
between
the blade portion 224a, the dielectric 222 of the printed circuit board 221,
and the
ground plane 226c. The printed circuit board 221 is mounted on a metal plate
232.
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The ground plane 226c is in electrical contact with the metal plate 232. The
metal
plate 232 adds strength to the assembly and provides a mounting location for a
coaxial connector 228. The coaxial connector 228 has a center conductor which
is
connected (e.g. soldered) to the stripline 224. The outer case of the coaxial
connector 228 is grounded to the metal plate 232.
Compared to the preceding examples, the omega coil 220 simplifies the
manufacturing process. For example, the omega coil 220 is directly mounted on
a
printed circuit board in a manner similar to a surface mount component.
Moreover,
the omega coil 220 takes advantage of the dielectric layer 222 of the printed
circuit
board 221, thus requiring only a single additional dielectric 230 during
assembly.
The dielectric 230 can be assembled on the printed circuit board 221 using
conventional automated assembly techniques.
4.1.8 Integrated Lamp Head
Tenth example of a high freauency inductively coupled lamp
Fig. 83 is a perspective view of an integrated lamp head for a tenth example
of an electrodeless lamp according to the invention. Figs. 84-85 are side and
top
schematic views, respectively, of the tenth example. Fig. 86 is a cross
sectional
view of the tenth example taken along line 86-86 in Fig. 85.
As shown in Fig. 83, an integrated lamp head 200 includes an enclosure 206
encasing a ceramic insert 204. Overall dimensions for the lamp head 200 are
approximately 40 mm wide x 50 mm long x 15 mm deep. As can best be seen in
Fig. 86, the enclosure 206 includes aluminum (AI) 206a and aluminum silicon
carbide (AISiC) 206b. The integrated lamp head 200 is a monolithic structure
which
comprises a metal matrix composite holding an electrically insulating ceramic.
The
integrated lamp head 200 may be manufactured, for example, by the fabrication
methods described in U.S. Patents 5,570,502 (entitled "Fabricating Metal
Matrix
Composites Containing Electrical Insulators"), 5,259,436 (entitled
"Fabrication of
Metal Matrix Composites by Vacuum Die Casting"), 5,047,182 (entitled "Complex
Ceramic and Metallic Shapes by Low Pressure Forming and Sublimative Drying"),
5,047,181 (entitled "Forming of Complex High Performance Ceramic and Metallic
Shapes"), 4,904,411 (entitled "Highly loaded, Pourable Suspensions of
Particulate
Materials"), 4,882,304 (entitled "Liquefaction of Highly Loaded Composite
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Systems"), and 4,816,182 (entitled "Liquefaction of Highly Loaded Particulate
Suspensions"), each of which is herein incorporated by reference in its
entirety.
In general terms, the integrated lamp head 200 is fabricated according to the
following process. A silicon carbide (SiC) pre-form and a boron nitride (BN)
insert
204 are appropriately positioned in a die cavity. Liquid phase aluminum (or
aluminum alloy) is forced into the die cavity (e.g. by vacuum pressure),
wherein the
aluminum infiltrates the porous SiC pre-form and fills any otherwise open
spaces in
the die cavity. The liquid phase aluminum is solidified, thereby forming a die
cast
structure having metal matrix composite around and through the porous SiC pre-
form and BN insert 204. Aluminum solidifies in a gap between the BN insert 204
and the AISiC 206b, thereby forming a stove pipe 206c as described above with
respect to the fifth example.
The die cast structure is then machined to form the lamp head 200. For
example, the BN insert 204 is formed with a channel 204a corresponding to the
outer diameter and axial height of the wedding ring shaped excitation coil
202.
During the fabrication process, the aluminum fills the channel and the center
of the
BN insert 204. Subsequently, the center of the BN insert 204 is drilled out
with a drill
bit having a diameter corresponding to the inside diameter of the coil 202,
thereby
forming the wedding ring shaped coil 202. The die cavity may include a pin
which
occupies a substantial portion of the center of the BN insert during the
infiltration
process so as to limit the amount of aluminum which is later drilled out.
Similarly, a slot 205 is machined in the die cast structure to form the leads
to
the coil 202. The width of the machined slot provides the appropriate space
for a
blade and associated dielectrics to be subsequently inserted to form the
series
resonant circuit. Other machining may be done as may be desired for particular
applications. For example, the lamp head 200 includes holes 209 and is
machined
to receive mounting hardware 207.
As shown in Figs. 84-86, a bulb 203 is encased in a reflective jacket 208
which forms an aperture 208a. The bulb 203 is approximately centered axially
and
radially with respect to the coil 202. The bulb 203 and jacket 208 may be
manufactured, for example, as described in section 4.2 below. In general
terms, the
reflective jacket 208 is formed by positioning the bulb 203 in the lamp head
200 and
pouring a liquid solution of micro and nano particulate alumina and silica
around the
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bulb 203. The solution hardens when it dries and the aperture is.subsequently
formed by removing some of the hardened reflective material. Alternatively,
the bulb
203 may be separately encased with the reflective jacket 208 and subsequently
inserted in the lamp head 200 as a unit.
In preferred examples, a bottom portion 206d of the enclosure 206 is
removed (e.g. by milling or otherwise machining the die cast structure). The
BN
insert 204 forms a shoulder 204b with the AISiC 206b which vertically
registers the
BN insert 204 during the infiltration process and secures the BN insert 204 if
the
bottom portion 2064 is removed.
The integrated lamp head 200 provides many advantages. For example, the
lamp head 200 provides a mechanically rigid physical structure to contain and
protect the bulb. The lamp head 200 provides a package which is readily
adapted
for attachment to external optical elements. The integrated lamp head 200 also
provides advantages in thermal management. The lamp head 200 provides intimate
thermal contact between the coil 202 and the heatsink (e.g., BN insert 204)
and
between the heatsink and the lamp body (e.g., enclosure 206). Preferably, the
coefficient of expansion of the coil, the heatsink, and the lamp body are
matched so
that intimate thermal contact is maintained during thermal cycling (e.g. lamp
start up,
steady state operation, and lamp shut down). Preferably, the heatsink material
also
provides a coefficient of thermal conduction which is suitable for operating
the lamp
at the desired temperature. In the ninth example, the coefficient of expansion
of the
BN insert 204 is suitably matched with the coefficient of expansion of the
AISiC 206a
portion of the enclosure 206. With these materials, the lamp head 200
effectively
conducts heat away from the bulb and also conducts heat away from the
inductive
coupling to maintain high RF efficiency of the coupling.
The integrated lamp head 200 advantageously further provides a conductive
screen around the bulb and coupling circuit to reduce the radiation of RF
energy to
the external environment. Moreover, the lamp head 200 provides the above-
described advantages in an integrated package that may be manufactured cost
effectively in volume.
Figs. 87-88 are top and side schematic views, respectively, of a lamp
assembly utilizing the ninth example of the invention. The lamp head enclosure
206
is mounted on a base 2i0. A bracket 212 is connected to one end of the base
210
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and supports a coaxial connector 214. A center conductor of the coaxial
connector
214 is electrically connected to a blade 216 which extends in between the
leads of
the coil 202. As described above with respect to the fourth example, a thin
dielectric
is positioned between the blade 216 and the grounded lead of the coil 202 and
a
relatively thicker dielectric is positioned between the blade 216 and the
other lead of
the coil 202.
The base 210 includes a channel 218 which accommodates a starter wire.
For bulbs which are difficult to start, an insulated wire may be routed
through the
channel 218 so that an exposed end of the wire is positioned proximate to the
bottom of the bulb. A high potential may be applied between the coil and the
starter
wire to generate a sufficient electric field strength to ionize the gas inside
the bulb
and thereby initiate the breakdown process. While a channel for a starter wire
has
been provided in the base 210, for most lamp configurations the use of a
starter wire
is not required.
Integrated lamp heads are built with coils having inner diameters ranging from
about 7 mm up to about 8.5 mm, radial thicknesses ranging from about 0.15 mm
up
to about 0.8 mm with a preferred radial thickness being about 0.5 mm, and
axial
heights ranging from about 3 mm to 5 mm with about 1/2 the inner diameter
being a
preferred axial height. Bulbs are used with the integrated lamp heads
typically
having an outer diameter (O.D.) of about 7 mm and an inner diameter (I.D.) of
about
6 mm. The bulbs are typically spherical, although some optionally have a
flattened
top and some are optionally pill box shaped.
While the examples of an integrated lamp head described herein relate
generally to inductively coupled lamps, the integrated lamp head according to
the
invention may be readily adapted to provide capacitively coupled lamps,
travelling
wave launchers, and even microwave lamps. Other excitation structures may be
integrally formed on the interior surface of the insulating ceramic to provide
differently configured lamps. For example, opposed electrodes may be formed to
provide a capacitively coupled lamp. Other modifications will be apparent to
those
skilled in the art.
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4. i.8.1 Omega Coil
Eleventh example of a high freauency inductively coupled lamp
Fig. 89 is a perspective view of an integrated lamp head for a eleventh
example of an electrodeless lamp according to the invention. Figs. 90-91 are
front
and top schematic views, respectively, of the eleventh example. Fig. 92 is an
enlarged, fragmented view of the circled area 92 in Fig. 91. Fig. 93 is a
cross
sectional view of the eleventh example taken along line 93-93 in Fig. 91. Fig.
94 is a
cross sectional view of the eleventh example taken along line 94-94 in Fig.
91.
The eleventh example utilizes an omega coil 242, but otherwise is similar in
construction to the tenth example. An integrated lamp head 240 includes an
enclosure 246 encasing a ceramic insert 244. A slot 244b separates the leads
242a
and 242b of the omega coil 242. Overall dimensions for the lamp head 240 are
approximately 31 mm wide x 47 mm long X 18 mm deep. From the center of the
ceramic insert 244, the enclosure 246 is substantially semi-circular with a
radius of
about ~3.5 mm. The main body of the enclosure 246 is about 11 mm deep, with an
optional protruding ridge 246c about 7mm deep. The ridge 246c is provided
primarily for application interface purposes. As discussed above with respect
to the
tenth example, and as can best be seen in Figs. 93 and 94, the enclosure 246
includes aluminum (AI) 246a and aluminum silicon carbide (AISiC) 246b and
encases a BN insert 244.
The omega coil 242 is formed according to the following process. The BN
insert 244 is pre-formed with a shoulder 244a corresponding to the outer
diameter
and lower extent of the omega coil 242. The BN insert 244 further includes an
opening 244c positioned centrally along the flat face of the BN insert 244.
During
the fabrication process, the aluminum fills the center of the BN insert 244
and the
opening 244c. Subsequently, the center of the BN insert 244 is drilled out
with a drill
bit having a diameter corresponding to the inside diameter of the omega coil
242.
The BN insert 244 is then counter-bored with a drill bit which has a diameter
slightly
larger than the outside diameter of the omega coil 242 to a depth
corresponding to
the desired height of the omega coil 242. As can best be seen in Fig. 93, the
width
of the machined slot 244b is less than the width of the opening 244c while the
height
of the machined slot 244b is taller than the height of the opening 244c. Thus,
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machining the slot 244b in the die cast structure forms the slot in the
wedding ring
shaped coil and forms the connection from the leads 242a and 242b to the coil
242.
Fig. 92 illustrates a feature of the invention referred to as a locking pin
250.
The BN insert 244 is formed with a recess which fills with aluminum and
solidifies
during the fabrication process. The aluminum solidified in the recess forms a
locking
pin 250 which helps prevent the lead 242a from separating from the BN insert
244.
Preferably, the integrated lamp head 240 is used with a bulb encased in a
reflective jacket and with bulb fills as described above with respect to the
tenth
example.
4.1.8.2 Pre-formed Coil Connection for Lamp Head
In the above-described eleventh example, after infiltration of the aluminum
and subsequent cooling, the coil connection is accomplished by milling a slot
244b
through the BN insert to make blade-type connections on each side of the
wedding
ring shaped coil and isolate the high voltage plate from the ground plate.
This
leaves a relatively thin section 256 of the BN insert (see Fig. 92).
According to the present aspect of the invention, the BN insert is made
relatively stronger in the area of the coil connection by pre-forming the coil
connection in the BN insert to avoid subsequent milling. For example, peg-type
connections to the coil may be utilized instead of blade-type connections.
Fig. 95 is
an enlarged, fragmented view of the lamp head. Fig. 96 is a schematic view of
a BN
insert with pre-formed coil connections. Fig. 97 is a cross sectional view of
the BN
insert taken along line 97-97 in Fig. 96. Fig. 98 is a schematic view of the
BN insert
showing the location of pre-drilled holes used to form a peg-type connection
to the
coil. Fig. 99 is a cross sectional view taken along line 99-99 in Fig. 98. As
shown in
Figs. 95-99, four holes 258 are drilled in the BN insert prior to infiltration
with the
aluminum metal. Once the casting process is complete, the wedding ring shaped
coil is separated by drilling a hole partially through the BN insert in an
area 260 (see
Fig. 95). Thus, the relatively thin area is eliminated and the BN insert is
made
relatively stronger. This approach also improves manufacturability because
less
machining is required after the casting process is complete.
As noted in section 4.1.2 in connection with the split coil examples, using
two
pegs instead of a single blade does not significantly affect circuit
performance
because most of the current spreads to the outside of the conductive elements.
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Figs. 100 and 101 are enlarged, fragmented views of the lamp head showing
alternative arrangements for the pegs. As shown in Figs. 100 and 101, angled
pegs
may also be utilized for one or both of the connections. Using angled pegs
allows
greater separation between the high voltage plate and the various electrically
grounded surfaces of the lamp head to further reduce the possibility of arcing
therebetween. Also, while the illustrated examples utilize round pegs, any
suitable
shape may be used (e.g. square, rectangular, elliptical).
Also, the BN insert may alternatively be pre-formed with blade-type
connections, as shown in Figs. 102-10fi. Because the later milling step is
avoided,
the BN insert is still relatively stronger as compared to the example shown in
Figs.
89-94.
4.1.8.3 Tunable High Voltage Capacitor
Figs. 107 and 108 are schematic views of a lamp head / power feed
assembly. A lamp head 325 is mounted on a power feed assembly 327. A
capacitor assembly 329 is positioned between a high voltage plate of the lamp
head
325 and a power feed pad of the power feed assembly 327. Fig. 109 is an
enlarged,
fragmented view of the area 109 in Fig. 107, showing the relative positioning
of the
capacitor assembly 329 with respect to the lamp head 325 and the power feed
assembly 327.
Further details regarding the construction of the lamp head 325, the power
feed assembly 327 and the lamp 321 are discussed in sections 4.1.8.1 and
4.1.8.3
above and section 4.4.3 below.
Figs. 110 and 111 are schematic views of opposite sides of the capacitor
assembly 329. Conductive pads 331 and 333 are disposed on opposite sides of a
dielectric material 335. For example, capacitor assembly 329 may comprise a
printed circuit board having a dielectric material made of a Teflon4 composite
and
clad with copper plating for the conductive pads. The thickness of the
dielectric
material 335 and the size of the conductive pads 331, 333 are selected to
provide a
desired capacitance value.
A present aspect of the invention is directed to various improvements for the
capacitor assembly.
The lamp 321 is an RF-powered, inductively coupled electrodeless lamp
which utilizes a capacitor stack as part of a series resonant circuit for
coupling the
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RF power to the lamp fill. The capacitor is subject to high voltages during
lamp
operation and is preferably designed to minimize arcing.
A problem with the capacitor assembly 329 shown in Figs. 110 and 111 is
that the capacitance value is fixed and cannot be easily adjusted. It is
sometimes
desirable to tune the final lamp assembly to match a preferred operating
frequency.
It is an object of one aspect of a present aspect of the invention to provide
an
adjustable high voltage capacitor. It is a further object of the present
invention to
provide an adjustable high voltage capacitor which is designed to minimize
arcing.
First examale of a tunable high volta4e capacitor
Figs. 112 and 113 are schematic views of opposite sides of a first example of
a capacitor assembly according to the invention. One side of the assembly is
provided with a conductive pad 341 having a plurality of protruding fingers
343. The
capacitance value of the assembly may be readily adjusted by removing some of
the
conductive material from the fingers 343. For example, a razor blade may be
used
to scrape the conductive material off of the dielectric material. Removing the
conductive material lowers the capacitance value.
Second examale of a tunable high voltacte capacitor
Figs. 114 and 115 are schematic views of opposite sides of a second
example of a capacitor assembly according to the invention. One side of the
assembly is provided with a conductive pad 351 having a plurality of
protruding
fingers 353 and a plurality of isolated conductive areas 355 in close
proximity to the
fingers 353. Fig. 116 is an enlarged, fragmented view of the area 11 fi in
Fig. 115.
The capacitance value of the assembly may be readily adjusted by adding
conductive material between the fingers 353 and the isolated-areas 355. For
example, a solder bridge may be formed across the small gaps between the
fingers
353 and the isolated areas 355. Likewise, conductive material may be added
between additional isolated areas to adjust the capacitance value. Adding
conductive material increases the capacitance value. As compared to the first
example, the second example ameliorates arcing from metal slices associated
with
the cutting technique.
Third examale of a tunable hi h voltage capacitor
Figs. 117 and 118 are schematic views of opposite sides of a third example of
a capacitor assembly according to the invention. One side of the assembly is
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provided with a conductive pad 361 which defines a plurality of voids 363 in
the
conductive pad 361. The voids 363 extend through the conductive pad 361 to the
surface of the dielectric material. The capacitance value of the assembly may
be
readily.adjusted by adding conductive material or dielectric material to cover
the
voids 363. For example, a conductive plate may be soldered across one or more
of
the voids 363. The conductive plate may be disc-shaped, for example.
Alternatively, a conductive film or a dielectric material may be adhesively
bonded
over one or more of the voids 363.
As compared to the first example, the conductive pad 361 has smoothly
rounded comers at one end and a hemispherical shape at the other end. By
maintaining a simple peripheral shape (e.g. omitting the protruding conductive
areas), the third example reduces voltage stresses caused by the more complex
peripheral shapes of the first and second examples. Advantageously, the third
example suppresses arcing to a greater extent than either the first or second
examples.
Figs. 119 and 120 are schematic views of opposite sides of an alternative
configuration for a capacitor assembly of the third example. This preferred
configuration includes a conductive pad 371 which is substantially rectangular
with
smoothly rounded comers. The conductive pad 371 defines a plurality of voids
373.
While the invention has been described with respect to specific examples,
variations will occur to those skilled in the art. For example, the number of
fingers,
isolated areas, and / or voids may be increased or decreased depending on the
amount of adjustment desired. Also, a conductive pad may include a combination
of
fingers, isolated areas, and / or voids. The size and shape and the conductive
pads,
fingers, isolated areas, and / or voids may be configured to suit the
particular
application.
4.1.9 Exemplary Fills
Bulb fills are typically mercury free, and include metal halides) and a noble
gas. Suitable metal halides include indium bromide (InBr), cesium bromide
(CsBr),
praseodymium tri-bromide (PrBr3), and praseodymium tri-chloride (PrCl3).
Exemplary
fills for a 7 mm O.D. x 6 mm I.D. spherical bulb are as follows:
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Fill 1 Fill 2 Fill 3
0.08 mg InBr 0.02 mg PrCl3 0.02 mg Se
0.02 mg CsBr 0.04 mg InBr 0.02 mg CsBr
50 Torr Kr 500 Torr Xe 50 Torr Kr
Table 4
Alternatively, a small amount of mercury (or mercury halide) may be added to
the fill. For example, for a 7 mm O.D. x 6 mm I.D. spherical bulb, about 0.1
to 0.5
mg of mercury iodine (Hgl) may be added.
4.2 Bulb and Aperture Structures
4.2.1 Blow Molded Bulbs
A present aspect of the invention pertains to improvements in envelopes and
the methods for manufacturing envelopes containing fill for use in
electrodeless
lamps and has utility in lamps of the type disclosed herein.
The prior art method for making envelope blanks is gathering of a gob of
molten quartz on the end of a section of quartz tubing and, by means of
manually
changing the internal pressure within the tubing and applying fire to the
exterior of
the tubing and the gob, shaping the end of the quartz tubing and gob into a
thin
walled sphere having an interior volume in communication with the quartz tube.
The shape of the thin walled sphere produced by the prior art method cannot
readily be altered, and it is difficult to repeatabiy, consistently inflate a
gob of flexible
quartz into any desired shape (including a sphere). Additionally, it is
difficult to
process the resulting tube and sphere structures using automated manufacturing
machinery for making electrodeless lamps, or the like.
An electrodeless lamp aperture bulb is a bulb jacketed or enclosed in a highly
diffusely reflective material having a small opening_or aperture through which
light is
emitted. The bulb may be properly characterized as having a multiplicity of
internal
reflection paths. In order for an aperture bulb to function efficiently, a
photon, once
generated, must exit the bulb either directly or after a number of internal
reflections,
possibly after a number of absorptions and re-emissions. Colder regions in a
sulfur,
selenium, or sulfur-like fill material, in which a plasma has been created,
reradiate
the absorbed radiant energy with a temperature characteristic of the
temperature of
the colder region. The absorption and radiation in the colder regions reduce
the
lamp efficacy, because the eye is less sensitive at these wavelengths. In an
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electrodeless lamp having a sulfur fill or the like, the tower radiation
efficacy is a
function of the volume of the colder regions contained within a bulb or
envelope. In
the past, pill-box shaped bulbs or envelopes have been used with inductively
operated high intensity discharge laps (without an aperture in a reflective
jacket or
the like). Examples in the prior art include U.S. Patent No. 4,783,615 {Dakin
et al),
Patent No. 5,367,226 (Ukegawa et al) and U.S. Patent 4,705,987 (Johnson). None
of the pill-box shaped bulbs in the prior art have been used with a sulfur and
selenium fill as part of an eiectrodeless lamp surrounded by a jacket having
an
aperture, however.
A number of problems have been encountered in producing electrodeless
aperture lamps; in particular, some of the conventional bulb shapes are not
well
suited to excitation using a conventional, spiral wound RF coil that has been
wound
on a cylindrical coil former or the like. For spherical bulbs driven by
cylindrical RF
excitation coils having a coil height shorter than the bulb diameter, the
spherical
interior volume occupied by the fill material is not uniformly excited by the
coil, since
top and bottom portions of the spherical bulb extend along the coil cylinder
axis and
project beyond the height of the coil.
Another problem encountered in mass producing aperture lamps with
spherical envelopes is that there is no practicable automated method to
provide the
optically reflective jacket white leaving a uniformly sized aperture. There is
also no
practicable automated method for accurately positioning and attaching a light
guide
member to the spherical surface of the envelope of the prior art. Ordinarily,
jackets
having apertures formed by the insertion of a core in a reflective material
slurry must
be sintered with the aperture defining core held in place. After the
reflective material
is cured or sintered and assumes a solid consistency, the core is removed,
leaving
an aperture having the same cross sectional shape as the core. Problems with
manipulating the core and removing the core include risk of destroying the
lamp
envelope or the reflective material of the jacket around the core. The
envelope must
be manipulated before and after the jacket molding process and it is difficult
to
position and manipulate the envelope within the mold cavity before and after
filling
the mold with the reflective material. Accordingly, several~problems have been
encountered in attempts to develop a practicable method for automated high
speed
fabrication of large numbers of aperture electrodeless lamps.
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It is an object of the present invention to overcome one or more of the
aforesaid problems associated with the prior art.
Another object of the present invention is to provide an eiectrodeless lamp
bulb or envelope adapted for use with cylindrical RF coils or the like.
It is another object of the present invention to provide an envelope having
surface features well suited to receiving an attached light extraction pipe or
aperture
defining member.
Another object of the present invention is to provide a method for
manufacturing an electrodeless aperture tamp using high speed automated
equipment.
Yet another object of the present invention is to provide a pill-box shaped
envelope for overcoming the lower efficacy observed in the bulbs of the prior
art by
eliminating or greatly reducing the volume of the colder regions of the
envelope.
The aforesaid objects are achieved individually and in combination, and it is
not intended that the present invention be construed as requiring two or more
of the
objects to be combined unless expressly required by the claimed attached
hereto.
Surprisingly, it has been discovered that a sulfur plasma exhibits an
extremely
large light absorption in short light wavelengths. The large light absorption
was
observed within a multiply reflecting bulb structure (i.e., an aperture bulb),
and, as a
consequence, lower efficacy was observed. The pill-box shaped electrodeless
lamp
bulb of the present invention, however, has few colder regions in the envelope
interior and the fill was observed to reradiate absorbed energy at a higher
temperature, thereby resulting in a more efficient lamp. By eliminating or
reducing
colder portions of the plasma within the envelope volume, the sulfur aperture
bulb
was observed to exhibit a higher efficacy.
Examples of blow molded bulbs
As illustrated in Figs. 121-125, a bulb blank 410 (see Fig. 125) is
manufactured from a length of quartz tubing 412, preferably, a 3 by 5 mm fused
quartz (e.g., GE 214) tubing section of approximately 150 mm in length. The
quartz
tube 412 has a fire polished end 414 with a minimum opening of 2.5 mm in
diameter. In the first step of the method of the present invention, shown in
Fig. 121,
a selected longitudinal section 41 fi of the tubing is flame heated and caused
to
transversely shrink and close off by means of surface tension and working of
the
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liquid quartz within the flame. A closed off or occluded section 418, shown in
Fig.
122, one and one half mm in length and one and one half mm in outside diameter
is
thereby produced, preferably at a location approximately 15 mm from the tubing
lower end (as tubing 412 is held in a vertical orientation). After the tubing
section
416 is closed off by occluded section 418 and allowed to cool, upper tubing
section
419 (above occluded section 418) is heated until a plastic state is reached
and, as
shown in Fig. 123, a mold 422 having a cavity 424 with a selected
substantially
spherical interior shape including a planar section 426 is closed about the
heated
upper tube section 419. In the particular example illustrated in Figs. 123 and
124,
the cavity portion, other than planar section 426, is generally spherical. Gas
pressure is applied via open upper tubing end 414 to pressurize the tube
interior.
Pressure is increased to a point above atmospheric pressure to deform and
expand
the plastic quartz tube wall section 428 at approximately the mid-point of
upper
tubing section 419. Pressure is applied until the plastic quartz material has
expanded, within mold cavity 424, outwardly or transversely and has come into
contact with, and becomes contoured to match, the mold interior surface 430,
as
shown in Fig. 124. Mold 422 is immediately removed after the tubing blank has
assumed the shape of the mold interior cavity 424. The tubing blank is thereby
molded into a bulb blank 410 having a planar interface area 433 and an upper
bulb
opening 432 located just above the expanded part of the bulb blank. Upper
opening
432 is a short constricted tube section having an inner diameter of between
one half
to one mm over a length of one mm.
Bulb blank 410 is then cooled to a temperature sufficiently low to allow
contact (in a subsequent filling procedure) with sulfur or selenium and gas
mixture fill
materials (and other materials, as discussed in U.S. Patent 5,404,076, cited
above).
During the filling process, the fill materials are injected via top end 414
and through
upper bulb opening 432, after which upper opening 432 is closed using a torch
flame, forming the tip of the bulb 434, as shown in Fig. 126. While the tip
434 of the
bulb is being formed, the 15 mm long lower stub 436 of tubing is used to
support
and position the bulb. After filling, the bulb, supported by lower stub 436,
is
transported to an automated reflective jacket forming machine. An aperture
forming
tool or aperture defining member 440 having an outer contour of the aperture
is then
glued to the flat window formed on the bulb interface area 433 using a hot
melt
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polymer or other bonding agent, as shown in Fig. 127. Once the aperture
defining
member 440 is secured, lower stub 43fi is scored at occluded section 418 and
removed. Scoring is performed with a sharp knife and the stub 436 is then
snapped
off, resulting in the bulb shape illustrated in Fig. 128. The tool 440 is then
used to
manipulate the bulb through the reflective jacket forming operations and
subsequent
stops. During high temperature curing or sintering of the reflective jacket
(not
shown), the hot melt polymer pyrolizes and the bulb is released from the
aperture
defining member or tool 440.
Turning now to Fig. 129 an alternate example of the bulb blank 442 is
illustrated as it appears after removal from a mold (not shown). Bulb blank
442 has
a pill-box-shaped bulb segment 444 with a downwardly oriented, circular,
planar
interface area or flat 446 with a diameter of four and one half mm. Bulb blank
442
also includes an upper bulb opening 447 (having an inside diameter of between
one
half and one mm and a length of one mm) produced just above the shoulders 448
of
the newly formed bulb 444. The bulb height of four mm is measured from the
outside of flat 44fi to the bottom of upper opening 447, and the bulb outside
width
{i.e. extent transverse to the tubing axis) is seven mm. The wall thickness of
bulb
444 is one half mm (with a tolerance of plus or minus one tenth mm), and so
the
inside bulb height is three and one half mm. As above, bulb blank 442 is
manufactured from a length of quartz tubing, preferably, a 3 by 5 mm fused
quartz
(e.g., GE 214) tubing section of approximately 150 mm in length and having a
fire
polished upper end 448 with a minimum opening of 2.5 mm in diameter.
In accordance with another aspect of the present invention, pill-box or
reentrant bulb shapes illustrated in Figs. 130, 131 and 132 are provided to
overcome
lower efficacy caused by having a significant volume of colder gas regions.
The pill-box shaped bulb 450 of Fig. 130 is approximately eight mm in outer
diameter or width (i.e., in the longer, horizontal dimension) and six mm high
(i.e., in
the shorter, vertical dimension), and has an envelope 452 with a wall
thickness 454
of one half to one mm. Envelope 452 encloses an interior volume 456 including
a fill
having approximately 0.05 mg of selenium, 500 Torr of xenon gas (at room
temperature) and a small amount of cesium bromide (typically less than 1 mg),
provided as a plasma forming medium. Bulb 450 is inductively coupled with an
encircling RF coil for excitation of a toroidal plasma 458 in the fill. The
shape of
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toroidal plasma 458 is approximated by a ring or toroid having a central hole
460
and those regions within the interior volume 456 occupied by the plasma are
relatively "hotter" while those parts lying outside the plasma toroid 458 are
relatively
"colder"-. Pill-box shaped bulb 450 is closely contoured to match plasma
toroid 458
and exhibits improved brightness; it is believed that this is due to an
envelope shape
having fewer colder regions within the bulb, and as a result, greater
brightness and
light output (i.e., efficacy) are observed. Pill-box shaped bulb 450
eliminates colder
interior volume regions and the fill reradiates absorbed energy at a higher
temperature, resulting in a more efficient lamp. By eliminating or reducing
the colder
portions of the plasma within the envelope volume, the sulfur aperture bulb
was
observed to exhibit a higher efficacy.
The pill-box shaped bulb 450 is substantially circular in cross section and
shaped as a short cylinder having a diameter which is greater than the
cylinder
height and so is sized to approximate the toroidally shaped plasma 458 in the
bulb
fill. Pill-box shaped bulb 450 includes an outwardly projecting solid quartz
light guide
474, affixed in the center of a substantially circular transparent upper wall.
In an
alternative example illustrated in Fig. 131, an alternate example of a pill-
box shaped
bulb 464 has a reentrant concave downwardly facing indentation 466 roughly
aligned with the central hole 460 of toroidal plasma 458. Bulb 454 also
includes an
outwardly projecting solid quartz light guide 474, affixed in the center of a
substantially circular transparent upper wall. In yet another example
illustrated in
Fig. 132, a pill-box shaped bulb includes a relatively high walled aperture
470 in a
reflective jacket 472, as an alternative to a solid quartz light guide 474, as
in the
examples of Figs. 131 and 132.
4.2.2 Aperture Structures
Electrodeless lamps of the type with which the present invention is concerned
are comprised of a light transmissive bulb having an envelope containing a
plasma-
forming medium. The bulb may be partially or completely covered or jacketed
with a
reflective material" and may, optionally, include an outwardly projecting
light guide
member. A microwave or radio frequency (RF) energy source has its output
energy
coupled to the envelope via a coupling arrangement to excite a plasma,
resulting in
a light discharge. The envelope is embedded in or surrounded by a jacket of
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reflective material over nearly the entire envelope surface, except for a
small area
through which light is permitted to pass.
A number of problems have been encountered in producing electrodeless
aperture lamps; in particular, jackets having apertures formed by the
insertion of a
core in a reflective material slurry have to be sintered with the core held in
place.
After the reflective material is sintered and assumes a solid consistency, the
core is
removed, leaving an aperture having the same cross-sectional shape as the
core.
Problems with manipulating the core and removing the core include risk of
destroying the aperture, lamp envelope, or the reflective material jacket
surface.
Another problem is that it is difficult to accurately position the envelope or
bulb within
the cavity used in molding the reflective material jacket from the slurry.
Finally, with
the molds and methods of the prior art, a distinct mold must be fabricated for
each
desired aperture (and core) cross-sectional shape, since the core must fit
tightly in
the mold to prevent the reflective material slurry from flowing or leaking
around the
core.
It is an object of a present aspect of the present invention to overcome one
or
more of the aforesaid problems associated with the prior art.
It is another object of the present invention to enable use of an aperture
having any desired cross-sectional configuration in an electrodeless lamp made
in a
mold receiving an envelope and a flowable reflective material slurry.
Yet another object of the present invention is to properly position the
envelope within the mold cavity to permit proper filling of the mold with
flowable
reflective material slurry.
The aforesaid objects are achieved individually and in combination, and it is
not intended that the present invention be construed as requiring two or more
of the
objects to be combined unless expressly required by the claims attached
hereto.
Examples of aaerture structures
According to a first example of the present invention, illustrated in Figs.
133
and 134, an electrodeless lamp 510 includes an elongate aperture defining
member
or mold insert 512. Aperture defining member 512 includes an aperture or light
passage defining bore 514 defined longitudinally therethrough. The aperture
defining member 512 is made from ceramic or another material having high light
reflectance and sufficient mechanical strength to withstand automated assembly
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machinery handling. The aperture defining member material is capable of
withstanding a wide range of temperatures, e.g., a winter ambient temperature
at
one extreme and a high operating temperature of several hundred degrees
Fahrenheit at the other extreme. Aperture defining member 512 is bonded or
cemented to a light transmissive envelope 516 having an exterior surface 518
including a substantially flat or planar envelope interface area 520. The
cement is
preferably an organic material selected to decompose at the temperature used
in a
subsequent sintering step. Envelope 516 may be ball-shaped or pill-box-shaped
and encloses an interior volume 517 including a fill material having sulfur,
selenium
or another substance or compound producing light when subjected to microwave
or
radio frequency (RF) energy.
As shown in Fig. 133, envelope 516 is disposed within a separable, two-part,
reflective material mold 522 having a first mold segment 524 separably mated
to a
second mold segment 526 to define a mold interior cavity 528 having an
interior
surface 529 therein. Mold segments 524, 526 are preferably made of carbon. As
shown in Figs. 133 and 135, first mold segment 524 includes a mold opening 530
providing access from mold interior cavity 528 to a bottom exterior mold
surface 532.
Aperture defining member 512 is disposed within mold opening 530 and
includes a substantially planar radially extending flange 534 projecting
transversely
from the bore central axis. Turning now to the bottom view of Fig. 135, it is
illustrated that mold opening 530 and aperture defining member bore 514 are
substantially coaxially aligned, thus permitting light to pass through the
transparent
envelope interface area to the mold exterior. In Fig. 135, the bore 514 is
illustrated
as being circular in cross section, however, any aperture cross section can be
used,
such as, for example, the star-shaped aperture cross section of the alternate
example of Fig. 136. Star-shaped aperture 544 is exemplary of many fanciful or
arbitrary aperture shapes which can be defined in an aperture defining member,
thus allowing a single mold to accommodate many aperture shapes.
As shown in Fig. 137, aperture defining member 512 includes a tubular body
536 having a central axis and a distal end 538 opposite proximal transverse
flange
534. Bore 514 is a light transmissive passage extending through the aperture
defining member 512 from the proximal end of tubular body 536 to distal end
538.
In the example of Fig. 137, transverse flange 534 includes an indexing feature
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as a clipped corner 540. In the alternative example illustrated in Fig. 138,
the
aperture defining member transverse flange is circular and includes no
indexing
feature.
In the method of the present invention, reflective material mold 522 is split
into two (or more) parts, allowing access to the mold cavity 528 defined
within. An
aperture defining member 512 is positioned within and projects outwardly from
mold
interior cavity 528 through mold body opening 530. The aperture defining
member
512 includes a proximal, t~adially extending flange 534 projecting in a plane
transverse to the bore center axis. Envelope 16 rests upon flange 534 which
has a
flange thickness 548 (see, e.g., Fig. 137) selected to maintain a desired
separation
between the envelope exterior surface 518 and the inner surface 529 of the
mold
cavity. The mold 522 is closed and a flowable slurry of reflective material is
injected
or poured through a mold injection opening 550, filling the space in the mold
cavity
528 between the envelope outer surface 518 and .the mold interior cavity
surface
529. The reflective slurry material 554 is then dried, sintered or fired to
provide a
rigid or hardened reflective jacket 556, as shown in Fig. 134. The cement
material
used to bond the aperture defining member 512 to envelope exterior surface 518
decomposes, thereby allowing for significant differences in coefficients of
thermal
expansion between the envelope 516 and the aperture defining member 512.
As noted above, the outer perimeter of the aperture defining member can
include a projecting key feature (e.g., a clipped comer), thus indexing (or
controlling
the orientation of) the aperture defining member in the mold body opening
having a
complimentary receiving feature (e.g., a receiving socket having a clipped
corner).
Bore 514 in aperture defining member 512 can have any desired cross-sectional
shape, while the outer perimeter of the aperture defining member body is a
standardized shape (e.g., tubular body 536), thereby allowing a common mold
member to be used in molding aperture lamps having many different aperture
cross-
sectional shapes, with the aperture defining member being indexed in a
selected
location and orientation, regardless of bore shape.
Turning now to Figs. 139 and 141, indexing shape of an alternate example of
aperture defining member 560 includes a stepped flange structure having a
proximal
outer flange segment 562 with a clipped corner indexing feature 564 and an
intermediate stepped flange segment 566 of reduced transverse extent and
having a
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radially aligned clipped corner indexing feature 568. A shown in Fig. 141, a
mold
570 for receiving aperture defining member 560 includes a stepped receiving
socket
572 adapted to receive intermediate stepped flange segment 566 in only one
rotational orientation, due to a socket clipped corner indexing feature
corresponding
in extent to the clipped comer indexing feature 568 of intermediate stepped
flange
segment 566. Indexing feature 568 can also be used in later assembly steps,
for
alignment, positioning or the like, in making an eiectrodeless lamp fixture.
The reflective jacket 576 of the example of Fig. 141 extends over and covers
the portion of outer flange segment 562 projecting radially beyond
intermediate
flange segment 566 and so provides a thin annular layer of jacket material
providing
additional retaining structure for affixing aperture defining member 560 the
bulb.
Fig. 140 illustrates another alternative example including an aperture
defining
member 580 situated within a mold cavity and having a radially transversely
projecting flange 582. The reflective jacket 584 extends over and covers the
radially
projecting flange 582 and so provides a thin annular layer of jacket material
providing additional retaining structure for affixing aperture defining member
580 to
the bulb.
As illustrated in Fig. 142, the external portion 586 of aperture defining
member 512 is employed as a support for an optical element such as a coated
optical reflector 588 for directing light produced in the electrodeless lamp
510.
The mold 522 of the present invention needn't be removed and can be
incorporated in a lamp within an exterior housing, if desired. As shown in
Fig. 143,
mold 522 can be an integral,part of an RF energy coupling circuit or a heat
sink for
the RF excitation coil 500 used to provide RF excitation power to the
electrodeless
lamp 510. Thus, mold 522 need not be a reusable tool solely for determining
the
outer shape of the reflective jacket component molded onto the envelope.
Aperture
defining member 512 defines an aperture of any desired cross-sectional shape,
positioning envelope 516 within the reflective jacket, providing an aperture
reference
or index and eliminating manufacturing requirements for precise tooling for
bulb
shape and jacket shape.
The reflective material mold need not be a two-part.mold For example, as
shown in Fig. 144, a one-piece reflective material mold 590 can be used.
Reflective
material mold 590 includes a mold opening 591 (similar to mold opening 530
shown
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in Fig. 133) providing access from mold interior cavity 592 to a bottom
exterior mold
surface 593. An aperture defining member 512 is disposed within mold opening
591, as described above.
The reflective material mold 590 further includes a mold opening 594 in the
top exterior mold surface 595. Mold opening 594 is sufficiently large to allow
the
light transmissive envelope 516 to pass therethrough and into the mold
interior
cavity 592. For example, as shown in Fig. 144, the mold interior cavity 592
may be
shaped such that the mold opening 594 is approximately the same width as the
widest portion of the mold interior cavity 592, with the mold interior cavity
surface
596 being substantially cylindrical towards the top of the mold interior
cavity 592.
Once the light transmissive envelope 516 is positioned in the mold interior
cavity
592, a flowable slurry of reflective material 554 is poured into the mold
opening 594,
filling the space in the mold cavity 592 between the envelope outer surface
518 and
the mold interior cavity surface 596. The wide mold opening 594 at the top of
reflective material mold 590 eliminates the need for two separate mold parts.
In general, the interface area of the envelope can have any shape which
permits sufficient bonding to the light transmissive envelope, and need not be
flat or
planar. For example, as shown in Figs. 145 and 146, the envelope 501 may have
a
ball-shaped (e.g., substantially spherical or ellipsoidal) exterior surface
with a
rounded envelope interface area 502. The envelope 501 can be bonded to an
aperture defining member having either a non-conforming or a conforming shape.
For example, as shown in cross-section in Fig. 145, a non-conforming aperture
defining member 503 has a flange 504 with a planar upper surface 505. The
aperture defining member 503 contacts the rounded envelope interface area 502
of
the envelope 501 at an edge 506 formed at the juncture of planar upper surface
505
and aperture defining member bore 507. Thus, the planar upper surface 505 does
not conform to the rounded shape of the envelope interface area 502, and the
envelope 501 is bonded to the aperture defining member 503 along a narrow
annual
band at edge 506.
According to an alternative example shown in Fig. 146, an aperture defining
member 508 conforms to the shape of the envelope interface area 502.
Specifically,
the upper surface 509 of flange 511 is cup-shaped, having a curvature
corresponding to that of the rounded envelope interface area 502. The aperture
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defining member 508 is shown in perspective in Fig. 147. The conforming shape
of
the aperture defining member 508 provides a larger surface area over which the
rounded envelope interface area 502 of envelope 501 can bond to the aperture
defining member 508.
In use, an electrodeless lamp (e.g., lamp 510, as shown in Figs. 134, 142 or
143) is electrically coupled to a microwave or RF source and receives energy,
thereby creating a fight emitting plasma in the fill material contained within
the
envelope interior 517. Light created thereby is internally reflected from the
jacket
556 and passes outwardly through the aperture of bore 514.
The method for making electrodeless lamp 510, includes the steps of
providing an envelope 516 with an exterior surface 518 and an interior volume
517
including a fill material; providing a mold 522 having an exterior surface
532, an
interior cavity 528, a first segment 524 and a second segment 526, where the
mold
first segment 524 has a mold opening 530 providing access from the mold
interior
cavity 528 to the mold exterior surface 532; inserting an aperture defining
insert
member 512 into the mold opening 530, where the aperture defining insert
member
512 includes an insert bore 514 which, when the insert member 512 is inserted
in
the mold, provides an internally reflective light passage or aperture from the
mold
interior cavity to said mold exterior surface; placing envelope 516 into the
mold
interior cavity and proximate to the aperture defining insert member 512 upon
flange
534; and filling the mold interior cavity 528 with a flowable reflective
material 554;
and then curing the flowable reflective material 554 to render a solid
reflective jacket
556 which encloses or surrounds, but does not uniformly adhere to or coat
envelope
516. Optionally, one may proceed by removing the envelope 516, with the
aperture
defining member 512 and cured reflective material jacket 556 affixed thereon,
from
mold 522. Alternatively, one may, instead of or in addition to removing the
envelope,
proceed by affixing an external reflector 588 (or some other optical adjunct)
to an
eternal portion 86 of aperture defining member 512. The step of inserting an
aperture defining insert member into the mold opening includes indexing or
orienting
the aperture defining insert member by aligning indexing feature 540 of insert
member 512 with a corresponding indexing feature of the mold.opening which,
when
the insert member 512 is inserted in the mold in a selected orientation, fits
indexing
feature 540 of insert member 512; and inserting the indexed aperture defining
insert
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member 512 into mold opening 530. The step of placing the envelope into the
mold
interior cavity and proximate to the aperture defining insert member includes
placing
substantially planar portion 520 of envelope 516 upon supporting flange 534 of
insert member 512 extending into the mold interior cavity 528, thereby
supporting
the envelope and providing a separation between the envelope exterior surface
518
and the interior surface 529 of the mold cavity. The step of filling the mold
interior
cavity 528 with a fiowable reflective material 554 includes pouring a
reflective
material slurry into the mold interior cavity.
The resulting electrodeless lamp aperture bulb 510 thus includes a light
transmissive envelope 516 having an exterior surface 518 including a first sub-
area
and a second sub-area, where the envelope encloses an interior volume 517
including a fill material. Bulb 510 also includes an aperture defining member
512
affixed to the first sub-area {i.e., the interface area 520) of the envelope
exterior
surface. The aperture defining member 512 has a distal surface 538 and an bore
514 through a tubular body 536; bore 514 provides a light transmissive lumen
or
passage from envelope 516 to aperture defining member distal end 538. Bulb 510
also includes a light reflective jacket 556 covering the second sub-area
{e.g., the
remaining area) of the envelope exterior surface. The jacket 556 preferably
has a
thickness equal to or greater than one half millimeter and is a sintered
solid. The
aperture defining member is preferably ceramic or a material having equivalent
light
reflecting, thermal and structural properties.
As noted above, the electrodeless lamp aperture bulb 510 can include an
integral permanently affixed mold having an interior cavity, an exterior
surface and a
mold opening 530 providing access from the mold interior cavity to the mold
exterior,
where the envelope is disposed within said mold interior cavity providing a
one-piece
assembly as shown in Fig. 142. Alternatively, the one-piece assembly integral
mold
includes RF excitation coils 100 disposed proximate the mold interior cavity
528, as
shown in Fig. 143.
Inasmuch as the present invention is subject to various modifications and
changes in detail, the above description of a preferred example is intended to
be
exemplary only and not limiting. It is believed that other modifications,
variations
and changes will be suggested to those skilled in the art in view of the
teachings set
forth herein. It is therefore to be understood that all such variations,
modifications
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and changes are believed to fall within the scope of the present invention as
defined
by the appended claims.
Fig. 148 is a schematic view of a preferred bulb blank for use in the lamp of
the present invention. Fig. 149 is a cross sectional view of the preferred
bulb blank
taken along line 149-149 in Fig. 148. The bulb is rotationally symmetric about
the
longitudinal axis. The bulb has a general wine glass shape with a
substantially flat
face. A suitable fill material is deposited in the bulb through the opening in
the stem.
An inert starting gas (e.g. xenon, argon, krypton) is applied to a suitable
pressure.
The stem is then heated at the pinched portion to seal off the bulb enclosing
the fill
material and starting gas.
Fig. 150 is an exploded, schematic view of a preferred aperture cup according
to the invention. Fig. 151 is a schematic view of the aperture cup showing
details of
the aperture. Fig. 152 is a cross sectional view taken along line 152-152 in
Fig. 151.
As shown in Figs. 150-152, the bulb is inserted in a reflective ceramic cup
and
positioned approximately symmetric with respect to the aperture. The cup is
then
filled with a reflective material which hardens to encase the bulb and secure
the bulb
in position. Other details of bulb and aperture forming processes are
described
above, in section 4.2.4 below, and in PCT pubiication WO 97/45858. Preferably,
the
reflective cup and the reflective material are low dielectric / high
(relative) thermal
conducting materials to aid in thermal management of the lamp.
According to another aspect of the present invention, the shape of the
aperture is configured to optimize optical efficiency. For example, a round
aperture
is utilized when coupling to the circular end of a fiber optic. A rectangular
optic of
aspect ratio of 3 to 4 or 9 to 16 is utilized when coupling to an LCD display
engine.
Yet more complex shapes are utilized when generating the beam for an
automotive.
headlamp. For virtually any application an optimally shaped aperture can be
designed. Lamps with two or more apertures are also possible. Fig. 153 shows
several examples in which a bulb with a flat face is encased in a reflective
cup with a
variety of apertures shapes.
4.2.3 Exemplary Processes for Filling Aperture Cup
The preferred aperture bulb according to the invention is shown in Fig. 152.
A desired aperture shape is pre-formed in a base of a ceramic cup. A quartz
bulb
having a goblet shape is positioned approximately symmetric with respect to
the
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aperture and with a flat face of the bulb abutting the aperture. The volume of
the
cup not occupied by the bulb is filled with a reflective ceramic material.
Exemplary
processes for constructing the illustrated bulb are described below.
4.2.3. i Hand gupping
A slurry or gup comprising 60% Nichia (part no. 999-42 from Nichia America
Co.) and 40% methanol is prepared. The gup should be flowable such that it can
be
drawn into a 5-l0cc syringe. The cup is placed in methanol and allowed to wet
to fill
the pores in the cup before gupping. A small amount {about 1 cc) of gup is
placed
into the cup near the aperture. The bulb is slid up to the aperture,
displacing some
of the gup through the aperture and around the bulb. The cup is then filled
about
half full with gup and tapped gently on a flat surface to pack the material
(e.g.
remove air bubbles or voids). After several minutes of air drying, the
material is
further packed with a small stick or the like. Additional gup is applied in
several
increments until the cup is filled, with each application being tapped, dried,
and
packed as just described. The gup is then removed from the aperture area and
the
assembly is oven dried at about 100°C for 10 minutes and then baked at
about
900°C for 30 minutes.
4.2.3.2 Solid Casting
A slurry is prepared comprising about 70% Nichia, 27% DI water, and 3%
Darvan 821-A. The slurry is rolled for several hours to fully disperse the
Nichia. The
bulb is glued to the cup from the outside in the area of the aperture and a
latex tube
is placed over the open end of the cup so that the cup can be overfilled by
about 6
mm. The cup is placed in DI water for about 10-20 seconds to saturate the
pores
with water. The cup is removed and excess water is blown out of the inside of
the
cup with compressed air or nitrogen. The slurry is drawn into a syringe and
slowly
dispensed into the cup taking care to avoid air bubbles. A rubber cap is
placed over
the latex tube and the slurry is air dried for 2-3 hours. The rubber cap and
latex tube
are then removed and excess material is trimmed from the end of the cup with a
knife or razor blade. The cup is heated at a rate of 10°C/minute up to
about 900°C
and then held at 900°C for about 30 to 60 minutes.
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4.2.3.3 Use of Centrifuge to Pack Cup
Preferably, the resulting reflective ceramic material is dense and without air
pockets. In the above-described procedures, there is a trade-off between good
flow
characteristics and resulting density. Also, it is time consuming and
difficult to avoid
air pockets using the above procedures. According to a present aspect of the
invention, the cup is packed with gup using centrifugal forces. For example,
using a
centrifuge to pack the cup with the slurry facilitates application of
significant forces
on the slurry which can cause the slurry to flow into small crevices and force
air
pockets out. Prolonged time in the centrifuge can separate the liquids from
the
solids thus changing the solid content of the casting. Controlled
configurations may
be utilized to construct ceramic parts with variable or gradient density.
According to
the present invention, the centrifuge process increases the density of the
resulting
reflective ceramic material with a lesser requirement for good flow
characteristics.
An exemplary centrifuge process is as follows. A slurry is prepared
comprising about 5% Nichia and 95% water or methyl alcohol. The slurry is
milled
for at least about 1 hour before gupping. The bulb is centered about the
aperture
and glued from the outside of the cup. A centrifuge fixture is configure to
hold the
cup so that the aperture end of the cup is radially outward during spinning.
The
ceramic cup is relatively porous and the water / methyl alcohol seeps through
the
face of the aperture cup under sufficient centrifugal forces. The fixture may
be
configured to hold an amount of slurry in excess of the volume of the cups so
as to
reduce the number of processing steps. The fixture and / or cups are then
filled with
the slurry and spun at about 3900 revolutions per minute for about 5 minutes
or until
no further water / alcohol is observed leaking from the fixture. The filling
and
spinning are repeated until the cup is filled. The cups are then removed from
the
fixture, oven dried at about 80-90°C for 30 minutes, and baked at about
900°C for
minutes.
An alternative process is to use a first mixture of 5% Nichia / 95% water and
a
second mixture of 50% Nichia / 50% water. The 5/95 mixture is used at least
until
30 the bulb is substantially covered with the packed ceramic material.
Thereafter, the
50/50 mixture is used to speed processing.
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4 2 4 Exemplary Performance Data
Exemplary performance parameters of the lamp of the present invention are
as follows:
DC Power ApertureBrightness 2D Lumens CCT CRI
Case # 120 W 9 mm2 53 cd/mm2 1500 6800 K >90
1
Case # 120 W 18 mm2 45 cd/mm2 2500 7500 K >90
2
Table 5
where in each case the bulb fill is about 1.8 mg / cc of InBr and the bulb is
a wine
glass shaped bulb with dimensions of about 7 mm outer diameter and 6 mm inner
diameter (bulb interior volume of about 0.1 cc).
An advantage provided by the lamp and aperture structures of the present
invention is a near Lambertian angular distribution of light. Fig. 154 is a
graph of
measured angular distribution of light from the lamp of the present invention
as
compared to a Lambertian distribution of light. The near cosine distribution
of the
light allows for the efficient generation of highly collimated shafts of
light. Both
imaging and non-imaging optical elements can be matched to the aperture to
achieve the desired beam angle.
The aperture lamp topology holds other important advantages. By adjusting
the size of the aperture relative to the size of the bulb, the lamp of the
present
invention can trade lumen efficacy for source brightness. A smaller aperture
port will
yield lower lumen efficacy, but higher source brightness. Conversely, a larger
aperture increases the luminous flux but reduces the brightness of the source.
For
example, an efficient light source which is excellent for general illumination
is
achieved by opening the aperture to match or nearly match the bulb diameter.
In
such a configuration, the lamp of the present invention is readily adapted to
up light
or down light fixtures to provide effective lighting for office environments,
schools,
factories, shops, homes, and virtually anywhere which requires or benefits
from
artificial lighting.
The shape of the bulb can likewise be varied to optimize coupling to the RF
field and to the optical aperture. For example, a bulb shaped like the top of
a wine
glass with a flat face on top works well for a lamp with a single aperture. A
bulb
shaped like a hockey puck could be chosen for better optical coupling when two
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oppositely disposed apertures are desired. The size of the bulb can also be
varied.
In general the size of the bulb is a function of power level and the required
source
brightness. In general, larger bulbs are required for higher power levels. At
a given
power level a small bulb with a smaller aperture will produce a brighter
source.
Bulbs can be constructed from a variety of materials, glass, quartz, alumina,
etc. The
bulb envelop does not need to be transparent, only translucent. Any material
that is
translucent, can withstand the necessary operating temperatures, is chemically
inert
to the chosen fill and does not excessively interfere with the RF wave can be
used.
Traditional light sources emit light in three dimensions. A reflector is
typically
used to redirect and focus the light onto the desired object or plane. For the
illumination of large areas these tried and true techniques work fine.
However, when
a narrow, highly collimated light beam is needed, conventional light sources
are
quite inefficient. Moreover, many conventional lamps provide only a localized
bright
spot, with most of the source lumens emanating from a different, significantly
less
bright portion of the discharge.
In contrast to conventional light sources, light emitted from the lamp of the
present invention aperture is directed in only two dimensions. In other words,
the
brightness is uniform with little deviation between the peak and average
brightness
across a two dimensional area. Fig. 155 is a graph of an exemplary intensity
map of
the lamp of the present invention for a near field distribution. Fig. 156 is a
three
dimensional graph of an exemplary near field distribution of the lamp of the
present
invention.
A low etendue is a necessary but not sufficient feature for efficiently
coupling
of light into small optical systems such as fiber optics or small diagonal
LCDs. The
other necessary feature to maximize coupling is the match of skewness
distribution
between source and target. Unless the source and target skewness distributions
are
well matched, it is difficult to maintain both low 8tendue and high collection
efficiency. Generally, three-dimensional light sources do not provide a good
match
of skewness distribution with planar targets such as fiber optics or LCDs. For
example, it is well known in the art that transferring light from a spherical
source with
axially symmetric optics causes a loss of etendue or collection efficiency or
both.
Advantageously, the lamp of the present invention provides both low etendue
and an excellent skewness match for planar targets. The two-dimensional light
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source provided by the lamp of the present invention maximizes the collection
efficiency for optical systems in which it is also necessary to maintain low
etendue.
The foregoing advantages concerning low etendue, skewness match, and
angular distribution can be effectively utilized by reflective, refractive,
imaging, and
non-imaging optics to create bright and efficient optical systems. For
example, the
angular distribution of the lamp of the present invention is well suited to
all types of
collection optics such as reflective or refractive compound parabolic
concentrators
(CPCs) and light pipes, and a variety of imaging optical solutions.
While the lamp of the present invention uses an inductive RF coupling
structure, the benefits of the aperture lamp technology is broadly applicable
when
used with other coupling structures.
4.2.5 Spectral Distribution
The aperture bulb technology described herein, coupled with selected bulb
fills, delivers full spectral light at high CRI and color temperatures which
are excellent
for many applications. Color temperature and spectral balance can be tailored
by
choice of bulb fill chemistries and dose. The lamp of the present invention
can also
utilize fills and / or filters to produce light of specific color bands. A
full range of bulb
fill materials from conventional mercury and metal halides to sulfur and
selenium can
be used in the lamp of the present invention. Fig. 157 is a graph of spectral
power
distribution for an indium bromide only fill as described above. Fig. 158 is a
graph of
spectral power distribution for a fill including indium bromide and cesium
bromide
(0.8 mg/cc InBr, 0.2 mg/cc CsBr, 50 Torr Kr). Unlike most other discharge
lamps,
the light output of the lamp of the present invention can be readily dimmed.
Fig. 159
is a graph of spectral power distribution for an indium bromide only fill at
varying
levels of RF power.
4.2.6 Ball Lens
As noted above, the angular distribution from the lamp of the present
invention can be configured to be a nearly Lambertian distribution. In other
words,
the light exits the aperture distributed over an angle of 180 degrees or over
a cone
with a half angle of 90 degrees. In certain applications, it is desirable to
focus as
much as possible of the exiting light onto another surface while providing a
maximum concentration.
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With conventional light source, and in general, it is difficult to capture
light
distributed over 180 degrees. However, as shown in Fig. 12, a ball lens may be
utilized in conjunction with the lamp of the present invention to capture
substantially
all of the light exiting the aperture. A ball lens may take the form of a
truncated
sphere or ellipsoid. In this case, the light enters a first surface (the flat
side) of the
ball lens which is placed in contact or near contact with the aperture and
exits a
second surface (the spherical side) of the ball lens. The light exiting the
aperture
enters the ball lens, passing from a region of low refractive index (air) to a
region of
high refractive index (the ball lens). The light is thereby refracted so that
it is
distributed over a cone angle much less than 180 degrees.
Even when passing from air to an optical material with a relatively low
refractive index such as fused silica, the cone angle is less than 90 degrees.
The
ball lens has a convex second surface from which light exits without returning
to an
angular distribution of 180 degrees. With the appropriate choice of center
thickness
and radius, the second surface can reduce the cone angle significantly below
90
degrees.
After exiting the ball lens with a reduced angle of distribution, conventional
lens design can manipulate the light. Significantly, substantially all of the
light exiting
the aperture is utilized by the optical system.
Alternatively, the ball lens may take the form of a complete sphere or
ellipsoid
or other solid arcuate shape. Total utilization of the available light may be
achieved
using a completely spherical ball lens. Also, the first surface of the ball
lens may be
aspheric. Even with a spherical second surface the ball lens may be designed
to be
an aplanat.
For a ball lens without a truncated surface, a round aperture shape is
preferred.
4.2.7 Ceramo-auartz lamp
Electrodeless lamps of the type with which the present invention is concerned
are comprised of a light transmissive bulb having an envelope containing a
plasma-
forming medium. A microwave or radio frequency (RF) energy source has its
output
energy coupled to the envelope via a coupling arrangement to excite a plasma,
resulting in a light discharge. The envelope is embedded in or surrounded by a
jacket
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of reflective material over nearly the entire envelope surface, except for a
small area,
known as an aperture, through which light is permitted to pass.
Section 4.2.2 above discusses a method of manufacturing an electrodeless
aperture lamp which possesses certain advantages over the prior art. In the
aperture
structures from section 4.2.2, a mold cavity is provided, an aperture forming
member
is inserted therein, a lamp envelope is placed therein proximate the aperture
forming
member, and the interior of the mold cavity is filled with a flowable,
reflective material,
which after hardening forms a jacket around the lamp envelope.
A present aspect of the invention is directed to a method of manufacturing an
electrodeless aperture lamp which possesses other advantages over the prior
art.
It is important for certain methods of making electrodeless lamps to be easily
accomplished by mass production so that large production quotas can be readily
filled.
It is also important that the resulting lamp be durable, so that its longevity
is increased.
The electrodeless lamps to which the invention pertain operate at a high
temperature
and become very hot, especially during operation over extended periods. It is
therefore important to remove the heat from the bulb, which is made of quartz,
and will
otherwise melt. To accomplish this, the heat is transmitted from the bulb to a
heat sink
where the heat is dissipated, and it is desirable for the transmission of the
heat from
the bulb to the heat sink to be high.
It is thus an object of one aspect of the present invention to provide a
method
of making an electrodeless aperture lamp which is easy to implement and lends
itself
to the economies of mass production.
It is a further object of one aspect of the invention to provide an
electrodeless
aperture lamp which is durable.
It is still a further object of the invention to provide an electrodeless
aperture
lamp which has a high heat transmission characteristic.
It should be understood that the above objects are achieved individually and
in
combination with each other, so the invention should not be construed as
requiring two
or more of the objects to be combined.
First examale of a ceramo-auartz aperture structure
A lamp bulb in accordance with a first example of the present invention is
depicted in Fig. 160. A lamp envelope 602 is shown which is typically made of
quartz
and is filled with a discharge forming medium which emits light when excited.
By way
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of non-limiting example, a possible fill is a sulfur or selenium based
substance, as
disclosed in the above-mentioned U.S. Patent No. 5,404,076. Also, the envelope
may
be made by the method discussed in section 4.2.1 above.
The envelope is located in a container 610 which has a closed end 611, and a
side wall 609 which opens into a mouth 613. The side wall has an inside
surface 615
and an outside surface 617, and at least the portion of the inside surface 615
which
abuts the lamp envelope is arranged to be reflective. In the preferred
example, the
container 610 is made of reflective, ceramic material, and is cup-shaped
Between the lamp envelope 602 and the container end 611 is a reflective fill
material 612 which, as shown, fills the region between the container end and
the lamp
envelope. In the preferred example, this material is a reflective ceramic
having a lower
density than the ceramic of which the container 610 is made. For example, the
fill
material 612 may be a hardened slurry or powder.
A bulb surface 604, which faces the container mouth 613 has a washer 606, at
least the inside surface of which is reflective, secured thereto, e.g., with a
ring 608 of
bonding material. The washer comprises an aperture-forming member which forms
an aperture 607, and in the preferred example is made of reflective, ceramic
material.
The bulb surface 604 is preferably flat to allow for easy attachment of the
washer 606,
although the washer can be secured to rounded surface portions 601 also.
The inside surface 615 of the container side wall is conical in shape and
tapers
toward the container end. In the preferred example, it has circular cross-
sections of
progressively decreasing diameters in the direction towards the container end.
The
lamp envelope 602 has a side wall 619 in the preferred example which is also
conical
in shape. It is congruent with the inside surface 615 of the container side
wall, and
abuts such inside surface. The outside surface 617 of the container wall is
also
conically tapered, and in the preferred example, tapers in the opposite
direction from
the inside surface.
Fig. 161 shows a lamp which incorporates the aperture lamp bulb of Fig. 160.
An excitation coil 621, which may be in the form of a metallic band, is
disposed around
the container 610, while a heat sink 614, which may be made of a boron-nitride
ceramic material surrounds the bulb and excitation. coil. A plunger 616 which
is biased
by a spring 618, attached to a support 620, prevents movement of the lamp when
it is
turned off and physical contraction takes place due to cooling. tt is noted
that the
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inside surface 622 of the excitation coil 62i is tapered so as to mate with
the taper of
the outside surface 617 of the container wall.
The bulb shown in Fig. 160 and the lamp depicted in Fig. 161 possess many
advantages, which will be described in greater detail below.
Figs. 162 to 165 illustrate an example of the method of the invention.
Referring
to Fig. 162, the washer 606, which may be made of reflective ceramic is first
cemented
to the lamp envelope 602 with cement 623, which is preferably an organic
material
selected to decompose at the temperature used to dry, cure, or sinter the
reflective
material in the present invention.
The ceramic washer may be made of an alumina/silica combination, e.g., 90%
alumina and 10% silica with a desired porosity. As is known to those skilled
in the art,
ceramic technology is available to easily mass produce such washers by mold
pressing ceramic bodies as they are transported on a conveyor belt. To
accomplish
the cementing of the washer 606 to the bulb envelope, lamp envelope 602 is
placed in
a holder 624 which is of a similar shape as the bulb. The holder 624 has a
centrally
located opening 625 in which the bulb tip 626 may be inserted to effectively
hold the
lamp envelope 602 steady during the cementing step.
As shown in Fig. 163, the container 610 is provided, which may be cup-shaped.
The container 610 may be of relatively high density ceramic material, e.g.,
the same
material as the washer. The container 610 may be made in a mold, and is easy
to
mass produce with known ceramics technology. As noted above, the side wall of
the
container has inside and outside surfaces which are conically shaped, with the
inside
surface tapering towards the container bottom while the outside surface tapers
towards the container top.
The next step of the method is to fill the container 610 with a reflective
slurry or
powder 612 to a predetermined level, e.g., with a nozzle 627 which is fed by a
source
of the slurry or powder. The slurry or powder is preferably made of a
relatively low
density ceramic material, e.g., substantially pure alumina mixed with water
and a small
amount of organic additive to prevent sedimentation.
The next step is shown in Fig. 164, and is comprised of inserting the bulb
envelope/ceramic washer combination in the container 610.' A vacuum holder 629
may be used to hold and lower the envelope into the proper position, which is
shown
in Fig. 160. After the lamp envelope is in the correct position, as shown in
Fig. 165,
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the ring 608 of ceramic bonding material is applied to secure the ceramic
washer 606
to the wall of container 610. The ceramobond has a paste-like consistency, and
is
typically made of a combination of alumina and silica powders combined with
organics.
The slurry is allowed to harden by drying, and the next step in the method is
to
cure the lamp bulb in an oven in order to cure the slurry and ceramobond.
Curing of
the slurry may be at a temperature of at least 500°C and may be done
for a period of
to 20 minutes, while curing of the ceramobond may be at about 50°C and
may take
1 to 2 hours to finish. If a powder is used, the powder may be heated and / or
partially
10 sintered.
It can now be appreciated the method of the invention described above
provides an easy way to manufacture an aperture lamp, which can be
conveniently
accomplished by mass production. Additionally, it follows from the method that
the
lamp which is produced is quite durable.
15 Referring to Fig. 160 again, it is seen that the conical side wall 619 of
the lamp
envelope 602 abuts the inside surface 615 of container side wall 609. The
mating
tapered surfaces provide sure contact, which facilitates heat transfer away
from the
lamp envelope, ensuring that the lamp operates at a low enough temperature.
Referring to Fig. 161, it is seen that the inside surface 622 of excitation
coil 621
is tapered so as to mate with the outside surface 617 of the container side
wall. The
inside surface of the annularly shaped heat sink 614 is similarly tapered. The
mating
tapered surfaces provide sure contact therebetween, resulting in high heat
transfer. In
the preferred example, the taper of both the inside and outside surfaces of
the
container side wall is between 0.5° and 2.0°.
Referring again to Fig. 160, it is seen that the washer 606 forms the aperture
607 through which light exits the bulb. The use of a flat washer as an
aperture forming
member is one of the improvements of the present invention, since this part is
standardized and easy to manufacture and install. In some lamp applications,
the
washer would be used as shown, while in other applications, additional light
extraction
members such as fiber optics would be associated with the washer, for
controlling the
light as desired.
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Second example of a ceramo-auartz aperture structure
Referring to Fig. 166, a second example of an aperture lamp bulb in
accordance with the invention is shown. In this example, the entire region in
the
container between the side wall and the lamp envelope is filled with a
reflective fill
material642.
Referring to the aperture lamp of Fig. 167, it is noted that a ceramic washer
638
is wider than in the first example, and is joined to the heat sink 644 with
ceramobond
646. The flange provided by the oversized washer 638 facilitates heat transfer
away
from the bulb. The other components depicted in Figs. 166 and 167 are similar
to the
corresponding components of Figs. 160 and 161.
The method of manufacturing the example of Figs. 166 and 167 is illustrated in
Figs. 168 to 171. Referring to Fig. 168, the first step is comprised of
cementing a
technological ceramic washer 650 to the top flat surface of a lamp envelope
630 with
cement 656, as explained in connection with the prior example. The
technological
washer 650 has a circular channel 654 therein, which leads to an orifice 652.
Referring to Fig. 169, a container 641 is provided, which may be cup-shaped,
and is made of ceramic which may be reflective. A vessel 658 is also provided,
to
which water may be supplied and extracted through an inlet/outlet 661.
The container 641 is inserted in the vessel 658 until its side wall abuts
ledge 664 in the vessel. Water 660 is then caused to flow into the vessel 658
as
shown. Then, container 641 is filled with reflective, flowable material such
as a
ceramic slurry to a predetermined level through nozzle 662. The purpose of the
water
is to exert pressure on the ceramic container 641 and seal its pores. This
prevents
liquid from leaking, which would cause the slurry to dry out.
Then, referring to Fig. 170, the water 660 is evacuated from the vessel 658
and
the lamp envelope/technological washer combination is inserted in the
container 641.
This causes part of the slurry 642 to flow into the channel 654 of the
technological
washer 650. )t is necessary to overfill the container 641 with slung, since in
the
thermal curing step, the slurry will shrink.
After drying of the slurry, the entire assembly shown in Fig. 170 is placed in
tunnel oven 664, shown in Fig. 171, for thermal curing. Supports 668 are
located in
the interior of the oven for holding the assembly of Fig. 170. After curing
the face of
the bulb is cleaned of foreign material.
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In the resulting lamp bulb, the hardened slurry 642 forms a jacket which
covers
the surface of envelope 630, but which does not uniformly adhere to or coat
the
envelope. Referring to Fig. 167, a ceramic heat sink 644, which may be boron
nitride
has an- annular cross section, and is cemented to the container 641 and a coil
643.
The heat sink has an annular channel therein near the top as depicted in Fig.
167, and
ceramobond 646 joining the washer 638 to the heat sink 644 is located in this
channel.
The large size of the washer and ceramobond connection to the heat sink
promote
heat transfer from the bulb.
4.2.8 Design Feature for Alignment of the Aaerture Cup
A preferred aperture cup / bulb assembly is shown in Figs. 150-152. This
assembly is axially, radially, and rotationally aligned in the lamp head, as
shown in
Figs. 213 and 215. According to a present aspect of the invention, the
aperture cup
is provided with structural features for aiding the alignment of the assembly.
Fig. 172 is a schematic view of an aperture cup 671 according to the
invention. Fig. 173 is a cross-sectional view taken along line 173-173 in Fig.
172.
The aperture cup 671 includes several features for aiding alignment, including
a
protrusion 672, notches 673a and 673b, and flattened portions 674a and 674b.
These features may be used individually or in combination as shown.
For example, the protrusion 672 may be sized to fit with the drilled area 260
as illustrated in Fig. 95 to provide rotational alignment of the assembly. As
shown in
Fig. 173, the aperture cup 671 further includes a rim 672a which acts as a
stop (e.g.
abutting the excitation coil) when the assembly is placed inside the lamp head
at a
desired axial alignment.
Fig. 174 is a schematic view of an alternative aperture cup 675 according to
the invention. Fig. 175 is a cross-sectional view taken along line 175-175 in
Fig.
174. The aperture cup 675 includes a raised portion 676 surrounding the
aperture
area. The raised portion 676 includes outside edges 677a-d which form a
polygon.
In the example shown, the polygon is a non-equiangular hexagon. The raised
portion 676 may be readily grasped and aligned by automated component assembly
equipment. For example, a fixture utilizing mating v-shaped fingers which move
synchronously in diametrically opposite directions would be suitable to
capture the
aperture cup 675 in a repeatable rotational orientation. The automated
component
assembly equipment can be readily adapted to position the captured cup axially
and
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radially in the lamp head. The angled orientation of the faces 677a, 667b and
677c,
677d accommodates a certain amount of dimensional variations while still
facilitating
accurate rotational alignment.
4 2.9 Flanged Aperture Cup
Fig. 176 is a schematic view of an alternative, preferred aperture cup 678
according to the present invention. Fig. 177 is a cross-sectional view taken
along
line 177-177 in Fig. 176. Fig. 178 is a perspective view of the aperture cup
678.
The cup 678 includes a flange portion 679 extending from an end of the cup
678.
The cup 678 may be made out of a ceramic material of, for example, fully
densified
alumina. Preferably, the flange cup 678 comprises about 90% alumina, 10%
silica
with a porosity of about 17% to 20%. As illustrated, the flange 679 is semi-
circular
with a flattened portion 680 along its periphery. A preferred bulb for the
flanged cup
is a 6.5 mm OD, 5.5 mm ID spherical bulb filled with 0.16 mg InBr and 30 Torr
Kr.
The flanged cup 678 may be used an integrated lamp head as shown in Fig.
179. Preferably, the BN insert is counter-bored to mate with the flange
portion 679
to provide axial, radial, and rotational alignment of the cup, and to promote
heat
transfer away from the bulb. Thermal putty (e.g. T-putty 502) is applied
between the
flange cup 678 and the BN insert around an outer- periphery of the flange 679.
Fig.
180 is a perspective view of an alternative flanged aperture cup with the
flange at
the end of the cup opposite from the end with the aperture.
4.2.10 Starting Aid
An electrodeless aperture lamp may be inductively excited by a conductive
excitation member which extends around the bulb in the azimuthal direction,
for
example a coil or similar member. However, the field which is coupled by the
excitation coil, while sufficient to sustain a discharge, may not be locally
concentrated enough to start the discharge. This is especially true if the
fill includes
one or more high pressure noble buffer gasses. Also the presence of the
ceramic
jacket may modify the field which penetrates through to the fill. Thus, a
starting
assist member is sometimes desirable to produce a field which is concentrated
enough to trigger ignition.
Many different types of lamp starting assist arrangements are known in the
prior art. However, the prior art arrangements may be unduly complex, contain
parts
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which may break, and/or introduce appreciable additional size to the lamp. For
example, such arrangements, include coils which may be moveable in and out of
starting assist position, and metallic or gas electrodes which are located in
elongated
quartz housings which are attached to the bulb.
It is therefore an object of one aspect of a present aspect of the invention
to
provide a lamp starting arrangement for an inductively coupled aperture lamp
which
is simple, easy to manufacture, and reliable.
In accordance with an aspect of the invention, an electrodeless aperture lamp
is provided which comprises a bulb containing a discharge forming fill, a
ceramic
reflecting jacket encasing the bulb except for an aperture, a conductive
excitation
member for inductively coupling excitation power to the fill which extends
around the
bulb and ceramic jacket in the azimuthal direction, and at least one
conductive
starting element embedded in the ceramic reflecting jacket for coupling a
starting
electrical field to the fill.
In accordance with a further aspect of the invention, the starting element
which is embedded in the ceramic reflecting jacket is not connected to an
electrical
power source, but couples a starting electrical field caused by a voltage on
the
element which is induced by an electric field created by the conductive
excitation
member.
Examines of starting arrangements
Referring to Fig. 181, a first example of the present invention is shown. A
bulb 686 is surrounded by a non-adherent ceramic jacket 687. Light exits via
an
aperture 688 and fiber optic 689. The fill in the bulb 686 is inductively
excited by a
conductive excitation member 690, which in the example depicted' is a helical
coil
which extends around the bulb 686 in the azimuthal direction. The coil 690 is
connected to a power source 691, which typically is time varying electrical
energy at
radio frequency (RF).
The alternating current in the excitation coil produces a time-varying
magnetic
field (H field), which induces an electric field (E field) in the fill. During
steady state
operation, both applied H field and applied E field components are present,
with the
H field component usually being much greater. While it is~the applied E field
which
starts the discharge, the E field produced by the excitation coil by itself
may not be
concentrated enough to ionize the fill and start the lamp. This is
particularly true
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when the fill includes one or more high pressure buffer gases, which may be
present
to increase efficiency.
In accordance with an aspect of the invention, a starting element 692, which
may be~ in the form of a wire, is embedded in the ceramic jacket. The ceramic
jacket
provides a suitable support means for the starting element, so that extra
components such as subsidiary support envelopes are not necessary. The element
may be installed in the ceramic jacket during the early stages of the
sintering
process, so that the sintered solid is formed around the element, firmly
embedding it
in the solid. It is preferably installed so that one end is near the bulb
which is to be
ignited.
In the example shown in Fig. 181 to 183, the starting element is disposed in a
non-azimuthal direction, meaning that it has only axial and/or radial
directional
components. This minimizes "cross-talk" between the excitation coil and the
starting
element, which might decrease power coupled to the fill during steady state
operation. As used herein, the term "the azimuthal direction" represented by
the
symbol q in Fig. 182, refers to the direction of any circular line around the
bulb. The
"axial direction" (Z) refers to the direction of a line which is perpendicular
to the
plane of the area bounded by the circular line, and "the radial direction" (R)
refers to
the direction of any radius of the circular line.
In accordance with a further aspect of the invention, the starting element is
not connected to a separate source of electrical power, but rather couples a
starting
field caused by a voltage on the element which is induced by the electric
field
created by the excitation coil. The helical coil has a dimension in the axial
direction
(top to bottom of coil in Fig. 181 ). It has been recognized by the inventors
that while
the primary field induced by the coil is toroidal in shape, because of its
axial
dimension there is a potential difference between the top and bottom parts of
the
coil, thus creating an electric field in the axial direction, and it is this
electric field
which is coupled to the starting element in the example of Fig. 181. Since the
element has an abrupt termination (the end of wire 692 in Fig. 181 ), it
concentrates
the field near the bulb, aiding ionization of the gas therein, and ignition of
the lamp.
Figs. 182 to 184 are cross-sectional views of alternative examples of the
invention, the coil not being shown in these Figures. In Figs. 182 and 183,
instead
of using a single wire, a plurality of starting wires are used. In Fig. 182,
starting
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wires 693a and 693b are positioned in the axial direction. In Fig. i83, wires
694a,
694b, 694c and 694d are positioned in the axial direction. The number and
position
of wires may be experimented with to provide the optimum starting arrangement
for
a particular lamp.
In addition to having an electric field in the axial direction, the excitation
coil
also has an electric field in the radial (R) direction, although typically,
this will not be
as large the axial field. In Fig. 184, starting wires 695a and 695b, which lie
in the
radial direction are depicted. It is of course possible for the starting
elements to
have directional components lying in both the axial and radial directions,
although in
order to take advantage of the relatively large electric field in the axial
direction of a
helical coil, it is preferred that the starting element have a substantial
directional
component in the axial direction.
The shape of the ceramic jacket 687 in Figs. 181 to 184 is generally an
elongated cylinder. The jacket is relatively thick, which allows proper
insertion and
retention of the starting wire without breaking. The thickness of the jacket
is
preferably in the range of 0.25 - 2 mm. In the above-discussed aperture
structures
(including sections 4.2.2, 4.2.7, 4.2.8, and 4.2.9), the starting elements
disclosed
herein are situated in the ceramic before it hardens.
While the conductive excitation member 690 shown in Fig. 181 is a helically
wound coil, other configurations are possible. For example, Fig. 185 shows a
conductive excitation member 696 which is in the shape of a wedding ring
except for
a gap. Fig. 186 shows a further example of a starting assist arrangement
according
to the invention, which is for use with a wedding ring or similar shaped
excitation
member, such as shown in Fig. 185. In this case, unlike in the examples of
Figs. 181
to 184, it is preferred for the starting elements to lie in the azimuthal
direction.
Referring to Fig. 186, it is seen that azimuthally curved starting wires 698a
and 698b
are embedded in reflecting ceramic jacket 697 and lie in the azimuthal
direction.
The gap of the wedding ring member 696 is a high field area and starting wires
698a
and 698b are located in the ceramic 697, opposite the gap in the wedding ring
structure.
More particularly, it may be advantageous to situate both starting elements at
the same height as the top or bottom edge of the wedding ring structure, with
the
interior ends of the elements extending a little way into a region in the
ceramic which
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is directly opposite the gap, as shown in Fig. 186. The starting elements may
have
the same azimuthal curvature as the wedding ring structure so as to be
congruent
therewith.
The high field in the gap of the wedding ring structure will induce a
relatively
high electric field in the "gap" between the two starting wires, thus
facilitating ignition
of the lamp.
The present invention may be applied to lamps having various specific fills
which, by way of non-limiting example, include sulfur, selenium, and tellurium
based
fills as described in U.S. Patents Nos. 5,404,076 and 5,661,365 or various
metal
halide fills. If necessary to start specific lamps, the starting elements) may
be
connected to a separate source of AC or higher frequency power.
There thus has been described a starting assist arrangement which is
particularly adapted for use with an inductively coupled electrodeless
aperture lamp
having a ceramic jacket. The invention has many advantages and provides a
simple
and effective starting means.
4.3 High Power Oscillator
Microwave solid state oscillators are described in various textbooks including
"Microwave Solid State Circuit Design," written by I. Bahi and P. Bhartia
(Wifey
Interscience Publication, 1988, Chapters 3 and 9) and "Microwave Circuit
Design
Using Linear and Nonlinear Techniques," written by George D. Vendelin, Anthony
M.
Pavio, and Ulrich L. Rohde (Wiley-Interscience Publication, 1990, Chapter 6).
Articles on such oscillators include "Microwave Solid State Oscillator
Circuits,"
written by K. Kurokawa (Microwave Devices, Wiley, 1976) and uAccurate Linear
Oscillator Analysis and Design," written by J. L. Martin and F.J. Gonzales
(Microwave Journal, June 1996 pp. 22-37).
Microwave oscillators utilizing solid state components and strip-line
transmission lines are described in U.S. Patent Nos. Re 32,527, 4,736,454, and
5,339,047. Solid state microwave oscillators having various feedback
structures are
described in U.S. Patent Nos. 4,775,845, 4,906,946, 4,949,053, and 5,483,206.
Conventional solid state microwave oscillators produce relatively low power
output, for example, ranging from a few hundred milliwatts (mW) up to a few
watts
(W) at most. Moreover, conventional solid-state microwave oscillators are
relatively
inefficient, typically less than 40%.
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For higher power applications requiring a high frequency signal, the
oscillator
signal is typically provided to an amplifier to increase the output power. For
example, Fig. 187 is a schematic diagram of a conventional system for
providing a
high power, high frequency signal. An oscillator 702 provides a low power,
high
frequency signal to an amplifier 704 which increases the power level and
outputs a
high power, high frequency signal.
A radio frequency (RF) powered electrodeless light source is one example of
an application which could utilize a high power, high frequency signal source.
For
example, U.S. Patent No. 4,070,603 discloses an electrodeless light source
which is
powered by a solid state microwave power source. The microwave power source
described therein has the general structure shown in Fig. 187. Namely, the
output of
a relatively low power oscillator is applied to a power amplifier to provide a
40 W,
915 MHz signal, at a purported 50% direct current (DC) to RF efficiency.
Summary of a novel high sower oscillator according to the present invention
A number of parameters characterize highly useful sources of high frequency
power. These include power output, oscillating frequency, DC to RF efficiency,
reliability, mean time between failure (MTBF), economy, durability (working
life), and
others. For example, a highly efficient, high power output source with a long
working
life, particularly a power source with long MTBF, represents a highly
desirable
combination of operating features. High power, as used herein, is defined as
greater than about 10 watts (W). Solid state microwave power sources have the
potential to provide a much longer working life than, for example, magnetrons.
However, due in part to relatively low power output and/or relatively low
efficiency,
conventional solid state microwave power sources have found only limited
commercial applications, typically in low power applications.
The present invention provides one or more of the following advantageous
operating features in a high frequency oscillator system:
- Voltage protection of the active element
- High efficiency
- High output power
- Low drift of the oscillating frequency
- Low level of harmonics
- Wide tolerance of load mismatch
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- Linear dependence of output power from DC drain voltage
- Pulse width modulation of output power
- Single active element (lower cost, higher reliability)
- High durability, long working life
- Small physical dimensions
- Low weight
Voltage Protection
An obstacle to achieving a high power, high frequency oscillator with
conventional circuits is that a high level of voltage may be fed back in
excess of the
breakdown limit of the device, thereby causing device failure. The present
invention
overcomes this problem.
According to one aspect of the invention, a high power oscillator includes an
amplifier with a positive feedback loop configured to initiate and sustain an
oscillating condition. The feedback loop comprises an impedance transformation
circuit which transforms a high reflected voltage on the amplifier output to a
proportionately lower voltage on the amplifier input to protect the amplifier
from an
over-voltage condition on its input. The voltage on the input is limited to
less than
the breakdown voltage of the amplifier input.
According to the invention, the feedback circuit utilizes micro-strip
transmission lines and stubs to limit the maximum reflected voltage provided
to the
output side of the feedback circuit to a maximum of two times the voltage on
the
output of the amplifier. With the voltage on the output side of the feedback
circuit
thus limited to a fixed maximum, the feedback circuit is then configured to
reduce
the voltage fed back to the input side of the amplifier to some fraction of
the output
voltage which is within the safe operating limits of the amplifier. For
example, a
lumped capacitor circuit element may be utilized to couple with the output and
reduce the voltage provided to the feedback circuit. As used herein, a
"lumped"
element refers to a discrete electrical component.
Load Tolerance
In some applications, the load driven by an oscillator varies widely during
operation. For example, an electrodeless lamp presents a~ high impedance load
when there is no discharge in the bulb and a low impedance load when the lamp
is
lit. Thus, during lamp ignition, or if the lamp extinguishes, the load changes
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dramatically. These load changes cause high voltage reflections which are
potentially destructive if fed back to the amplifier input. Conventional
oscillator
circuits which include lumped elements in the feedback circuit typically
include
lumped-inductor elements which have a high quality factor (Q) and are thus
more
susceptible to feeding back destructive high voltage from such voltage
reflections.
According to the invention, the oscillator circuit operates without
destruction of
the amplifier element at all phase angles and at all magnitudes from open to
short
circuit. Preferably, the feedback circuit includes only transmission lines and
non-
inductive lumped elements.
According to another aspect of the invention, the feedback circuit comprises
impedance transformation circuits in two feedback loops with reduced feedback
voltage on each loop. For example, two smaller lumped capacitor elements are
utilized (one for each loop) to decrease the coupling between the output and
the
input and thereby reduce the voltage in each loop. This improves load
tolerance
because of improved voltage protection. Preferably, the two feedback loops are
symmetrical so that the voltage provided to each feedback loop is the same.
Symmetrical dual feedback loops also improve efficiency.
According to another aspect of the invention, a four way junction of micro-
strip
transmission lines (e.g. a microwave cross) is connected to the amplifier
output to
provide distribution of current and minimize inductance at the amplifier
output.
Load sensitivity
According to another aspect of the invention, the oscillator includes an
output
impedance matching circuit connected to the amplifier output and the feedback
circuit is coupled with a high impedance end of the output impedance matching
circuit to reduce sensitivity to the load impedance.
Circuit Size
According to another aspect of the invention, lumped capacitors element are
utilized in the feedback circuit to reduce the circuit size by adding phase
shift to the
feedback circuit without long lengths of transmission line. The circuit size
is further
reduced by selecting suitable dielectric material to reduce the physical
length and/or
width of the transmission lines while maintaining suitable electrical length.
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Pulse Width Modulation
The oscillator examples described below may be configured with a gating pulse
applied to the gate of the active element to turn the oscillator off for some
fraction of a
cycle and thereby reduce the average output power delivered to the load. This
form of
pulse width modulation allows for dimming of the lamp from full brightness
down to
about 30% of full brightness.
Thus, the present invention provides a power source which is suitable for many
commercially practical applications, including high power applications such as
electrodeless lighting. Of course, depending on the application one or more of
the
above features may not be required. The above features are achieved
individually and
in combination, and it is not intended that the present invention be construed
as
requiring two or more of the features unless expressly required by the claims
attached
hereto.
The invention is hereinafter described with respect to seven specific 'circuit
examples. Exemplary part numbers for each of the first through seventh
examples are
as follows:
Example Q1 C1 C2 C3 C4 C5 C6 C7 C8 C9 C10 L1 R1 R2 R3 R4 D1
First 1 9 4 7 8 4 12 14 15 16 20 20 16 23
Second 1 5 5 8 8 5 13 9 15 22 18
Third 1 4 6 4 8 4 8 10 14 13 9 15 16 17 21 24
Fourth 1 4 4 8 8 10 13 14 9 15 16 17 21 24
Fifth 2 5 5 8 8 10 11 14 9 15 16 17 21 24
Six 1 5 5 8 8 10 11 14 9 15 16 17 21 24
Seventh 3 5 5 8 8 5 10 11 14 9 15 22 19 19 17 25
Table 6
where:
1 - Motorola~ MRF184 12 -130 nF surface mount capacitor
2 - Ericson~ E10044-E9584 13 - 150 nF surface mount capacitor
3 - Motorola~ MRF184S 14 - 4.7 NF surface mount capacitor
4 - 0.7 to 2.6 pF surface mount15 - 0.4 NH wire wound inductor
variable
capacitor 16 - 0 to 5.1 K ohm surface mount
variable
5 - 0.6 to 2.5 pF surface mountresistor
variable
capacitor 17 - 2.1 K ohm surface mount resistor
6 - 1.5 to 9 pF surface mount 18 - 2.2K ohm surface mount resistor
variable
capacitor 19 - 5K ohm surface mount resistor
7 - 2.5 to 8 pF surface mount 20 -10K ohm leaded resistor
variable
capacitor 21 -15K ohm surface mount resistor
8 - 22 F surface mount capacitor22 - 100K ohm surface mount resistor
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.9 - 130 pF surface mount capacitor 23 - Varactor diode
- 470 pF surface mount capacitor 24 - Zener diode
11 - 100 nF surface mount capacitor 25 - surface mount Zener diode
Table 7
Exemplary performance characteristics for each of the first through seventh
examples
are as follows:
30 40 50 60 70
Watts Watts Watts Watts Watts
V V V V V
% % % % %
f f f f f
121.4 60 864.023.262 866.025.163 867.027.261 868.0
214.0 71 749.516.071 750.418.071 751.019.969 751.4 21.967 751.6
318.0 67 879.720.767 880.623.266 881.125.fi65 881.6
4- 17.270 763.419.271 764.721.271 765.8 23.271 765.9
516.7 70 771.519.668 773.022.665 774.026.262 775.0
617.8 67 746.420.268 748.922.868 750.025.068 751.0 27.068 752.0
713.9 73 748.516.074 749.517.974 750.319.873 750.7 21.572 751.0
Table 8
5 where the first column corresponds to the example number and:
V - DC Voltage;
- DC to RF Efficiency; and
f - Oscillating frequency in MHz.
Examples of high power oscillators
10 Fig. 188 is a block-level schematic diagram of an oscillator system
according to
the invention for producing a high power, high frequency signal. A power
supply circuit
(not shown) provides a DC voltage to an oscillator 707 and a bias circuit 703.
The bias
circuit 703 provides a suitable DC voltage to the oscillator 707 to bias the
active
element of the oscillator 707. For example, the bias circuit 703 provides
sufficient bias
for the active element to initially operate in its linear region with enough
gain to support
oscillation. The oscillator 707 oscillates at a design frequency which is
tuned by a
tuning circuit 705. The oscillator 707 provides a high power, high frequency
signal to
an output impedance matching circuit 709, which may be connected to a suitable
load.
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Sinctle Impedance Transformation Network Feedback Circuit
Fig. 189 is a block-level schematic diagram of an oscillator 707 according to
the invention utilizing an impedance transformation network in a feedback
circuit.
According to the invention, an output of an amplifier 711 is fed back to an
input of
the amplifier 711 through an impedance transformation network 713.
The impedance transformation network 713 is configured to provide suitable
positive feedback for initiating and sustaining an oscillating condition.
According to
the invention, the impedance transformation network 713 is further configured
to
protect the amplifier input, during high output power operation, from an over-
voltage
condition which would otherwise destroy the device. For example, the voltage
protection is achieved by preventing voltage build up at the output through
controlled
voltage reflections and transforming a high voltage at the output terminal of
the
amplifier 711 to a low voltage at the input terminal of the amplifier 711,
which
assures that the maximum voltage-breakdown rating of the amplifier is not
exceeded.
According to the invention, the impedance transformation network 713 is
preferably further configured to create a matching condition between the
amplifier
input impedance and the feedback circuit to improve efficiency. The amplifier
711 is
preferably biased near cutoff so that the circuit operates efficiently.
Fig. 190 is a block-level schematic diagram of an oscillator system according
to the invention incorporating the oscillator from Fig. 189. In Fig. 190, the
impedance transformation network 713 is not directly coupled to the drain, but
is
instead coupled to the output impedance matching network 709. Preferably,
there is
a relatively high impedance (e.g. greater than about 100 ohms reactance)
between
the point of connection and the drain output. By coupling to the output
impedance
matching circuit 709 at a high impedance point, the feedback loop has less
influence
on the drain output and the oscillator system is less sensitive to the load
impedance.
First example of a high power oscillator
Fig. 191 is a circuit-level schematic diagram of a first example of an
oscillator
system according to the invention. A transistor Q1 has a source terminal S
which is
grounded. An output from a drain terminal D is connected.to an output
impedance
matching circuit including a transmission fine TL1 (with a characteristic
impedance
Z1 ) connected at one end to the drain D and unconnected at the other end, a
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transmission line TL2 (with a characteristic impedance Z2) connected at one
end to
the drain D and to a feedback circuit at the other end, and a transmission
line TL3
(with a characteristic impedance Z3) connected at one end to the junction of
TL1
and TL2 and connected at the other end in series with a first lead of a
capacitor C1,
the other lead of C1 providing an output which may be connected to a load.
The feedback circuit is connected between the end of the transmission line
TL2 and an input of the transistor Q1 at a gate terminal G and includes a
capacitor
C2, a transmission line TL4 (with a characteristic impedance Z4), a capacitor
C3, a
transmission line TL5 (with a characteristic impedance Z5), a capacitor C4,
and a
transmission line TL6 (with a characteristic impedance Z6) connected in
series.
A DC supply voltage Vdc provides power to the oscillator system through an
RF filter circuit, a tuning circuit, and a bias circuit for the transistor Q1.
The RF filter
circuit includes inductor L1 and a filter capacitor C6 and provides a DC
operating
voltage to the drain D of the transistor Q1.
The tuning circuit includes a variable resistor R1 which is a three terminal
device, wherein a first and second terminal are respectively connected to
opposite
ends of a variable voltage divider and a third terminal is connected at the
junction of
the voltage divider. In Fig. 191, the first terminal is connected to Vdc, the
second
terminal is connected to ground, and the third terminal is connected to one
end of a
resistor R2. The other end of resistor R2 is connected to a junction of a
cathode end
of a varactor diode D1 and a capacitor C5. The other end of diode D1 is
grounded.
The other end of capacitor C5 is connected to the transmission line TLS. The
resistors R1 and R2, the varactor diode D1, and the capacitor C5 provide a
tuning
function for the oscillator system.
The bias circuit includes a variable resistor R3 with the first terminal
connected to Vdc and the second terminal connected to ground. The third
terminal
of R3 is connected to one end of a resistor R4. The other end of the resistor
R4 is
connected to the transmission line TL6. The bias circuit provides a DC bias
voltage
to the gate G of the transistor Q1.
Fig. 192 is a printed circuit board layout suitable for use in implementing
the
circuit set forth in the first example. Overall board dimensions are about 102
mm (4
inches) by about 7fi mm (3 inches). The thickness of the dielectric material
is about
1.27 mm (0.05 inch), and the dielectric constant is about 9.2. Fig. 193 is a
cross-
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section view of the printed circuit board taken along line 193-193 in Fig.
192. As can
be seen in Fig. 193, a printed circuit board 715 includes a layer 725 for
conductive
traces, a dielectric layer 727, and a ground plane layer 729. Preferably, the
printed
circuit 715 is further mounted to a metal plate 731 which is electrically
connected to
the ground plane 729. In the first example, the printed circuit board 715
further
includes a cutout portion 721, which is sized to accommodate the active
element of
the oscillator circuit.
The printed circuit board 715 has conductive traces TL1-TL6 disposed
thereon which are transmission lines respectively corresponding to the various
characteristic impedances Z1-Z6. Ground areas 717 are also disposed on the top
layer 725 and are electrically connected to the ground plane 729 by plated
through
holes or other conventional methods. A conductive area 719 is isolated from
the
ground area 717 and provides a connection area for the DC supply voltage Vdc.
Another conductive area 723 provides a connection area for the tuning circuit.
Approximate characteristic impedances and electrical Lengths for each of the
transmission lines are as follows.
TRANSMISSION CHARACTERISTIC ELECTRICAL
LINE IMPEDANCE LENGTH
TL1 Z1 = 25 Ohm 0.154 ~.g
TL2 Z2 = 25 Ohm 0.154 ~,g
TL3 Z3 = 50 Ohm Not applicable
TL4 Z4 = 40 Ohm 0.115 ~,g
TL5 Z5 = 40 to 25 Ohm* 0.23 ~,g
TL6 Z6 = 25 Ohm 0.016 ~,g
~ Table 9
* TL5 transitions from 40 Ohms to 25 Ohms to match the 40 Ohm impedance of TL4
with the 25 Ohm impedance of TL6.
Fig. 194 is an assembly-level schematic diagram of the printed circuit board
from Fig. 192 populated with suitable electronic devices and other parts for
implementing the oscillator system of the first example. Reference designators
in
Fig. 194 corresponds to like circuit elements in Fig. 191. Q1 is preferably a
power
field effect transistor (FET), for example, a metal-oxide semiconductor (MOS)
field
effect transistor (MOSFET) fabricated with laterally diffused MOS (LDMOS)
technology. As set forth in Fig. 194, the source terminal of Q1 provides
mounting
holes through which a screw or bolt is inserted for mounting Q1 to the metal
plate
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731 and making the electrical connection from the source terminal of Q1 to
ground.
The source terminal S of the transistor Q1 is preferably also soldered to the
metal
plate 731 so that Q1 is welt grounded (i.e. RF current flows over a wide area
of the
wave structure). The metal plate 731 also provides a heat sink for the
transistor Q1
and is referred to as a heat spreader. The gate G and drain D terminals of Q1,
and
the remaining electrical components are mechanically and electrically secured
to the
printed circuit board 715 by soldering or other conventional means.
General operation of the circuit is as follows. A DC voltage Vdc is applied to
the circuit. The voltage Vdc is supplied to the drain D of the transistor Q1
through
the RF filter circuit. The drain voltage may be varied from about 20 V to
about 28 V.
The voltage Vdc is also supplied to the gate G of the transistor Q1 through a
voltage
divider circuit which is configured to provide a gate bias voltage to the
transistor near
cutoff which initially places the transistor Q1 at an operating point just
inside its
linear region. For example, for the above-specified Motorola~ MRF184 the gate
voltage is set to about 4V. The voltage Vdc is also supplied to the varactor
diode D1
through a voltage divider circuit. Varying the voltage provided to D1 tunes
the
oscillating frequency.
Once the voltage Vdc is applied to the circuit, the transistor Q1 conducts.
Some amount of random noise is inherent in the circuit. Noise which is present
on
the drain D is fed back through the feedback loop and amplified. This process
initiates the oscillation. Once initiated, the oscillation becomes sustained
at the
design frequency. To sustain oscillation at the design frequency, the time
delay (i.e.
phase shift) in the feedback loop and the transistor Q1 should be
approximately
equal to 1 /(2x f ~), where f os~ is the design frequency.
The transmission lines TL1 and TL2 are stubs configured such that the length
of transmission line between the drain D and the TL1, TL2 stubs' junction
together
with the length of the stubs TL1, TL2 result in an impedance match of drain
impedance to the impedance of the transmission line TL3 (e.g. a characteristic
impedance Z3 of about 50 ohms). Characteristic of the transmission line
arrangement for TL1 is that the maximum reflected voltage seen at any point on
TL1
is at most two times the voltage applied to TL1 from a conjugately matched
source.
Thus, the voltage on the open (i.e. high impedance) end of the stub TL1 (i.e.
the end
of TL1 distal to the drain) is limited to at most two times the voltage on the
amplifier
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output (i.e. the drain RF voltage). This voltage is progressively decreased
through
the feedback circuit so that the voltage at the input side of the active
device (i.e. the
gate) is significantly less than two times the voltage on the drain. The RF
voltage
fed back to the gate G is, however, sufficiently high to produce a large
current in the
transistor Q1.
Moreover, in order to achieve the desired voltage protection under all load
conditions, the feedback circuit is configured such that even if the gate
voltage
instantaneously doubles (e.g. due to a doubling of the voltage at TL1 ), the
doubled
gate voltage is within the safe operating limit of the device. For example,
for the
above-specified Motorola~ MRF184 the gate to source breakdown voltage is about
20V. During operation, the circuit is configured to operate with a gate
voltage of
about 8V plus the DC bias voltage of 4V for a total gate to source voltage of
about
12V. If the operating voltage were to instantaneously double, the gate voltage
would
be about 16V plus the DC bias voltage of 4V for a total of 20V which is within
the
safe operating limits of the device.
Dual Impedance Transformation Network Feedback Circuit
Further improvements in output power, efficiency, and working life are
achieved by an oscillator according to the invention which utilizes two
feedback
circuits. Fig. 195 is a block-level schematic diagram of an oscillator
according to the
invention utilizing dual impedance transformation networks in respective
feedback
circuits. According to the invention, an output of an amplifier 733 is fed
back to an
input of the amplifier 733 through a first impedance transformation network
735 and
a second impedance transformation network 737.
Fig. 196 is a block-level schematic diagram of an oscillator system according
to the invention incorporating the oscillator from Fig. 195. In Fig. i 96, the
impedance transformation networks 735 and 737 are not directly coupled to the
drain, but are instead coupled to the output impedance matching circuit 709 to
improve the load impedance sensitivity as discussed above with respect to Fig.
7 90.
According to the invention, the dual impedance transformation networks 735,
737 are configured to provide suitable positive feedback for initiating and
sustaining
an oscillating condition. As in the first example, the dual impedance
transformation
networks are further configured to protect the amplifier input, during high
output
power operation, from an over-voltage condition which would otherwise destroy
the
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device. Advantageously, the dual impedance transformation feedback networks
provide even greater positive feedback to the amplifier input, as compared to
a
single feedback circuit, and at the same time improve the voltage protection
and
improve efficiency. By utilizing two feedback loops, the feedback current to
the gate
remains high while the feedback voltage in each feedback line is halved.
Because
the destruction of the device is caused largely by over-voltage conditions,
the
voltage protection is significantly improved. In some of the following
examples, full
voltage swing and/or class C operation may be achieved.
Second example of a hi4h power oscillator
Fig. 197 is a circuit-level schematic diagram of a second example of an
oscillator system according to the invention. A transistor Q1 has a source
terminal S
which is grounded. An output of the transistor Q1 is taken from a drain
terminal D
and is connected to an output impedance matching circuit including a
transmission
line TLO (with a characteristic impedance ZO) connected at one end to the
drain D
and connected at the other end between respective ends of two transmission
lines
TL1 and TL2 (with characteristic impedances Z1 and Z2, respectively). The
other
end of TL1 is connected to a first feedback circuit. The other end of TL2 is
connected to a second feedback circuit. The output impedance matching circuit
further includes a transmission line TL10 (with a characteristic impedance
Z10)
connected at one end to the junction of TLO, TL1, and TL2 and connected at the
other end to an end of transmission line TL11 (with a characteristic impedance
Z11 ).
The other end of TL11 is connected to a junction of transmission lines TL12,
TL13,
and TL14 (with respective characteristic impedances Z12, Z13, and Z14). TL12
and
TL13 are matching stubs which are unconnected at their respective other ends.
The
other end of transmission line TL14 is connected in series with a capacitor
C7. The
output of the capacitor C7 may be supplied to a load.
The first feedback circuit is connected between the end of the stub TL1 which
is distal to the drain D and an input of the transistor Q1 at a gate terminal
G. The
first feedback circuit includes a capacitor C1, a transmission line TL3, a
capacitor
C3, and a transmission line TL5 connected in series. The second feedback
circuit is
connected between the end of the stub TL2 which is distal to the drain D and
the
gate G and includes a capacitor C2, a transmission line TL4, a capacitor C4,
and a
transmission line TLfi connected in series.
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A DC supply voltage Vdss provides operating voltage to the drain D of the
transistor Q1 through an RF filter circuit including an inductor L1 and
capacitor C6.
In Fig. 197, one end of the inductor L1 is connected to Vdss and the other end
of the
inductor L1 is connected at the junction of C1 and TL1. One end of the
capacitor C6
is connected to Vdss and the other of the capacitor C6 is connected to ground.
A DC supply voltage Vgs provides bias voltage to the gate G of the transistor
Q1 through a bias circuit including resistors R1 and R2. In Fig. 197, one end
of the
resistor R1 is connected to Vgs and the other end of the resistor R1 is
connected in
series with a transmission line TL7 which is connected to the gate G. One end
of
the resistor R2 is connected to Vgs and the other end of the resistor R2 is
connected
to ground.
The oscillator system illustrated in Fig. 197 further includes a tuning
circuit
comprising a transmission line TL8 (with a characteristic impedance Z8) which
is
unconnected at one end and at the other end is connected in series with a
transmission line TL9 (with a characteristic impedance Z9) and a trimming
capacitor
C5, which is RF-grounded. The junction of the transmission line TL8 and the
transmission line TL9 is connected to the junction' of the resistor R1 and the
transmission line TL7.
Fig. 198 is a printed circuit board layout suitable for use in implementing
the
circuit set forth in the second example. Approximate board dimensions are
about
102 mm (4 inches) by about 64 mm (2.5 inches). The thickness of the dielectric
material is about 1.27 mm (0.050 inch), and the dielectric constant is about
9.2. The
printed circuit board has conductive traces TLO-TL14 disposed thereon which
are
transmission lines respectively corresponding to the various characteristic
impedances ZO-Z14. Approximate characteristic impedances and electrical
lengths
for each of the transmission lines are as follows.
TRANSMISSION CHARACTERISTIC ELECTRICAL
LINE IMPEDANCE ~ LENGTH
TLO ZO = 10 Ohms
TL1 Z1 = 10 Ohms
TL2 Z2 = 10 Ohms
TL3 Z3 = 2x Z1 ~,g/8
TL4 Z4 = 2x Zi ~ ~,g/8
TL5 Z5 = l5~Zin~ 0.075 ~,g
TLfi Z6 = l S~Zin~ 0.075 ~,g
TL7 Z7 = 22 Ohms 0.045 ~,g
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TL8 Z8 = 28 Ohms 0.12 ~.g
TL9 Z9 = 28 Ohms 0.12 ~,g
TL10 Z10 = 10 Ohms >_ 0.07 ~,g
TL11 Z11 = 50 Ohms **
TL12 Z12 = 50 Ohms **
TL13 Z13 = 50 Ohms **
TL14 Z14 = 50 Ohms Not applicable
Table 10
where
* The respective electrical lengths of TLO, TL1, and TL2 are calculated from a
Smith Chart to match the output impedance Zout of the transistor with a ten
(10)
Ohm impedance;
** The respective electrical lengths of TL11, TL12, and TL13 are calculated
from a Smith Chart to match a fifty (50) Ohm impedance with a ten (10) Ohm
impedance;
~.g is the wavelength of the oscillating frequency;
Z,~ is the input impedance of the gate G; and
Zo~t is the output impedance of the drain D.
Ground areas 741 are also disposed on a top side of the printed circuit board
and are electrically connected to a ground plane on the opposite side of the
printed
circuit board by plated through holes or other conventional methods for good
RF-
grounding practices. A conductive area 743 is isolated from the ground area 41
and
provides a connection area for the DC supply voltage Vdss. Another conductive
area 745 provides a connection area for the DC supply voltage Vgs.
The short length of transmission line TLO attached to the drain D
compensates for the capacitance of the drain. The stub lines TL1 and TL2 are
configured to match the output impedance of the drain D. C1 and C2 are used as
trimming capacitors to change the level of feedback for optimized output power
and
efficiency. Preferably, C1 and C2 each have a relatively high impedance of Xc,
_
Xc2 = between about 150 and 250 Ohms. The relatively high impedance of C1 and
C2 limits the RF voltage which transfers to the feedback circuits and creates
an
essentially open circuit condition on the ends of stub lines TL1 and TL2
distal to the
drain. As discussed above, under this condition the RF voltage on the ends of
stub
lines TL1 and TL2 distal to the drain is limited to no more than about two
times the
drain RF voltage. The dual feedback configuration increases the positive
feedback
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(e.g. beta) of the feedback circuits and an increased efficiency of the
oscillator is
observed.
As used herein, a "stub" refers to a branch off of a transmission line,
typically
forming. a "T" junction with the transmission line. A microwave transmission
line
"stub" produces an immittance effect at the branch point in a guided wave
structure
by transforming the impedance seen at the end of the stub through a length of
transmission line of the stub. The length of the stub is selected to have a
particular
characteristic impedance which produces the desired immittance at the branch
point.
In the circuit illustrated in Figs. 197-199, high voltage damage to the
transistor
Q1 is ameliorated by providing low characteristic impedance lines TL5 (Z5) and
TL6
(Z6) to transform the feedback impedance to the complex conjugate of the gate
impedance. TL5 and TL6 are lines which prevent high voltage transients on the
feedback circuit by producing an extra shunt capacitive effect at the gate G,
and
decreasing the peak voltage appearing at the gate G.
Transmission lines TL3 and TL4 provide feedback lines for the signals from
C1 and C2, respectively. Capacitors C3 and C4 provide coupling between the
feedback lines TL3 and TL4 and the protective stubs TL5 and TL6. The impedance
of C3 and C4 is configured to be Xc3 = X~ = between about 8 and 10 Ohms at the
oscillating frequency ~.g.
Transmission line TL7 and tuning stubs TL8 and TL9 decrease the input
impedance at the gate G and provide additional protection for the gate G from
voltage transients on the feedback signal. Tuning stub TL8 may be trimmed
(e.g.
cut) to adjust the input impedance. Preferably, the sum of the lengths of
lines TL7
and TL8 and the sum of the lengths of lines TL7 and TL9 are each about equal
to
one-half wavelength of the third harmonic of the oscillating frequency (i.e.
LT~7 + Ln8
= LT~7 + LTL9 = ~g/6). Maintaining this length relationship increases the
third
harmonic signal in the gate voltage and increases efficiency.
Capacitor C5 is a variable capacitor which may be adjusted to tune the
oscillating frequency. The oscillating frequency may be determined by the
following
equation:
LI L; Ls coC~»Zs I I _
~C ~I+~3-~~5 +aIlCIlil~ 2 ~+(ppl-11'CIal1 ~,I(ZI+Z3~ al'Ctall ~,3~Z3-~Zs~ 7C
~4t
Equation (5)
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where:
L~ is the length of transmission line TL1
L3 is the length of transmission line TL3
L5 is the length of transmission line TL5
~,gi is the appropriate wavelength at the oscillating frequency for the
transmission line TLi
w is the oscillating frequency
Z~ is the characteristic impedance of transmission line TL1
Z3 is the characteristic impedance of transmission line TL3
Z5 is the characteristic impedance of transmission line TL5
cpQ, is the delay phase angle inside the transistor Q1
C;~ is the input capacitance created by the transistor gate capacitance, the
capacitance of transmission lines TL7, TLB, and TL9, and capacitor C5.
Fig. 199 is an assembly-level schematic diagram of the printed circuit board
from Fig. 198 populated with suitable electronic devices and other parts for
implementing the oscillator system of the second example. The transistor Q1 is
mounted to a metal plate which is electrically connected to ground as
described
above with respect to the first example. The other transistor terminals and
electrical
components are mechanically and electrically connected to the micro-strip
lines
andlor printed circuit board by soldering or other conventional means. A
coaxial
connector 747 is provided on the printed circuit board with its center
conductor
connected to the output of the capacitor C7 and its outer conductor connected
to
ground. C7 is referred to as a "blocking" capacitor because it acts to block
the
output from DC bias.
General operation of the circuit is as described above with respect to the
first
example. The drain voltage may be adjusted from about 14V to about 28V and the
gate bias voltage is about 4 volts. The practical operating range for the
second
example is from about 1 OW to about 100W of output power over a frequency
range
of about fi80 MHz to about 915 MHz. Higher efficiencies are typically obtained
at
the lower end of the frequency range. Those skilled in the art will understand
that
the amount of output power obtained is limited by the maximum operating
characteristics of the active element and that higher output power may be
provided
by an oscillator system according to the invention utilizing an active element
with
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correspondingly higher operating characteristics. Moreover, those skilled in
the art
will understand that the effective frequency range and oscillating frequency
may be
adjusted by appropriate sizing of the printed circuit board and transmission
lines
thereon and proper selection of the values for the discrete components.
Fig. 200 is a combination graph of a characteristic I-V curve for the
transistor
and the output signal of the drain of the transistor: As shown in Fig. 200,
the signal
706 on the drain starts as random noise and oscillates with increasing
amplitude
until the transistor Q1 becomes saturated. The circuit then oscillates at a
frequency
where the following conditions are satisfied:
/3 x A >_ 1 Equation (6)
and
rp, = 2n Equation {7)
where
~i is the feedback transfer coefficient;
A is the amplification coefficient for the amplifier element in a linear mode
of
operation; and
cp; is the phase shift of each element in the feedback loop.
Fig. 201 is a combination graph of the output power and efficiency of the
oscillator system in the second example as a function of the DC drain voltage.
As
can be seen from Fig. 201, the output power increases linearly with the DC
drain
voltage from about 30 W at about 14 V Vdss to about 70 W at 22 V Vdss. Over
this
entire range of DC drain voltages, the DC to RF efficiency of the oscillator
system is
over 67%, peaking at about 71 % efficiency at 15 V Vdss.
Fig. 202 is a graph of oscillating frequency as a function of output power. As
can be seen from Fig. 202, the oscillating frequency increases only slightly
(e.g. by
about 0.27%) as output power is increased from about 30W to about 70 W. The
change in frequency is a result of a change in the drain junction capacitance
at the
different DC voltages for the different output powers.
Fig. 203 is a graph of oscillating frequency versus time for an oscillator
system operating at about 50 W with a drain voltage of about 18 V. As can be
seen
from Fig. 203, the oscillator system exhibits low drift of the oscillating
frequency over
about 100 hours of relatively constant temperature operation.
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Thus, the second example of the invention provides a highly desirable
combination of operating features. Namely, a highly efficient, high output
power
oscillator system with low drift of the oscillating frequency. The second
example
also exhibits substantially linear dependence of output power on the DC drain
voltage. Advantageously, these and other features of the invention are
achieved in
an oscillator system having only a single active element, which provides lower
cost
and higher reliability as compared to prior art high power RF generator
systems
which required both a low power oscillator and an external amplifier (i.e. at
least two
active elements) to achieve high output power. The oscillator system according
to
the invention also advantageously provides small physical dimensions and low
weight, thus making the system suitable for many practical applications.
Third example of a high power oscillator
Fig. 204 is an assembly-level schematic diagram of a printed circuit board
populated with suitable electronic devices and other parts for implementing a
third
example of an oscillator system according to the invention. The third example
differs
from the second example in that, among other things, the dual feedback
circuits in
the third example are asymmetrical.
The printed circuit board in the third example has approximate dimensions of
about 102 mm (4 inches) by 64 mm (2.5 inches). The thickness of the dielectric
material is about 1.25 mm (50 mils), and the dielectric constant is about 9.2.
The oscillator system according to the third example is operated in a
frequency range of between about 790 to 920 MHz, with an output power ranging
from about 30 W to about 70 W (corresponding to a DC drain voltage range of 18
V
to 26 V). The circuit exhibits a DC to RF efficiency of between about 56 to
68% with
a frequency stability of +/- 0.5 MHz.
Fourth example of a hiah~ower oscillator
Fig. 205 is an assembly-level schematic diagram of a printed circuit board
populated with suitable electronic devices and other parts for implementing a
fourth
example of an oscillator system according to the invention. The dual feedback
circuits in the fourth example are substantially symmetrical. The fourth
example
differs from the second example in that, among other things, the fourth
example
utilizes a single DC power supply which is connected to the drain through an
RF filter
circuit (L1, C8, C9) and to the gate through a bias circuit (R1, R2, R3, D1).
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fourth example exhibits better load matching and efficiency as compared to the
second example.
The printed circuit board has approximate dimensions of about 102 mm (4
inches) by about 64 mm (2.5 inches). The thickness of the dielectric material
is
about 1.25 mm (50 mils), and the dielectric constant is about 9.2.
Fifth examale of a hicth power oscillator
Fig. 206 is an assembly-level schematic diagram of a printed circuit board
populated with suitable electronic devices and other parts for implementing a
fifth
example of an oscillator system according to the invention. The dual feedback
circuits in the fifth example are substantially symmetrical. The fifth example
is a
variant of the fourth example as modified to match the impedance
characteristics of
a different power transistor.
The printed circuit board has approximate dimensions of about 102 mm (4
inches) by about 64 mm (2.5 inches). The thickness of the dielectric material
is
about 1.25 mm (50 mils), and the dielectric constant is about9.2.
Sixth example of a hiah rower oscillator
Fig. 207 is an assembly-level schematic diagram of a printed circuit board
populated with suitable electronic devices and other parts for implementing a
sixth
example of an oscillator system according to the invention. The dual feedback
circuits in the sixth example are substantially symmetrical. The sixth example
is a
variant of the fourth example as modified for a different dielectric material
and
thickness of the printed circuit board material. The output impedance matching
circuit is reshaped with angled comers to provide the appropriate electrical
length in
substantially the same size printed circuit board.
The printed circuit board has approximate dimensions of about 102 mm (4
inches) by about 64 mm (2.5 inches). The thickness of the dielectric material
(FR-4)
is about 0.8 mm (31 mils), and the dielectric constant is about 4.
Seventh example of a hiah power oscillator
Fig. 208 is a printed circuit board layout suitable for use in implementing a
seventh example of an oscillator system according to the invention. Fig. 209
is an
assembly-level schematic diagram of the printed circuit board from Fig. 208
populated with suitable electronic devices, including a surface mount version
of the
Motorola~ transistor, and other parts for implementing the oscillator system
of the
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seventh example. As shown in Fig. 209, the transistor Q1 is drain justified.
The
dual feedback circuits in the seventh example are substantially symmetrical.
The
seventh example is a variant of the sixth example as modified for a different
dielectric material and reduced printed circuit board size. As compared with
the
preceding examples, the seventh examples provides the highest efficiency and
smallest physical dimensions.
The printed circuit board has approximate dimensions of about fi4 mm (2.5
inches) by about 38 mm {1.5 inches). The thickness of the dielectric material
is
about 0.6 mm (25 mils), and the dielectric constant is about 10.2.
While the invention has been described with respect to specific examples, the
invention is not so limited. Based on the drawings, the detailed description,
and the
teachings set forth herein, numerous other examples will occur to those
skilled in the
art. For example, one of ordinary skill in the art will appreciate that other
circuit
configurations may be utilized to provide appropriate tuning and bias voltages
for the
various examples set forth herein. Moreover, the examples includes variable
resistors and/or capacitors which may be replaced by fixed value components in
production. The preceding examples should therefore be considered as
illustrative
only, with the scope and spirit of the invention being set forth in the
appended
claims.
4.4 Lamp and Oscillator
!n general, the present aspect of the invention refers to an integrated lamp
head as described in Section 4.1.8 powered by an~RF power oscillator as
described
in Section 4.3, and various improvements and / or alterations thereof.
The lamp according to the present invention represents a true revolution in
lighting. Just as the vacuum tube has been replaced by the transistor, first
in niche
applications and later in virtually all applications, the solid state
electrodeless lamp
will push into all aspects of lighting. At the heart of the RF source is the
same silicon
technology that has given us the transistor radio and the computer. By
utilizing a
novel combination of electrodeless bulbs and solid state technology, the
resulting
lamp is reliable, long lived, and is contemplated as being highly cost
effective when
produced in volume. While the lamp of the present invention preferably employs
a
high power oscillator as described in section 4.3, other circuit topologies
can
alternatively be used to generate the reguired RF energy. Lamps have been
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successfully operated with more conventional circuitry employing a low wattage
oscillator followed by one or more stages of amplification. Unlike most RF
applications, linearity is not of paramount importance, and amplifiers of any
class
including class E and F can be used.
As noted above, the RF source preferably uses a commercially available
silicon RF transistor, which meets certain cost and performance targets. Other
suitable choices for the transistor technology include, but are not limited
to,
germanium, gallium and silicon carbide. The same forces that are collapsing
computers from boxes to boards and finally to a single integrated circuit are
also
driving the lamp of the present invention. The lamp of the present invention
contemplates product configurations in which the power supply, power RF
oscillator,
the coupling circuit, and the bulb are integrated into a single device. For
certain
applications, the integration can extend beyond the lamp. For example, an
optical
modulator could be integrated with the lamp device to provide a display
engine.
According to another aspect of the present invention, the lamp head is
mounted directly on the same printed circuit board as the RF oscillator
circuitry. In
some examples, the printed circuit board in mechanically and electrically
connected
to a metal plate, referred to as a spreader plate, which has an opening under
the
printed circuit board in the area of the lamp head in order to allow the
printed circuit
board to flex in response to thermal forces.
According to another aspect of the present invention, a control circuit is
provided for matching the operating characteristics of the lamp to the
operating
frequency of the oscillator at a plurality of different frequencies.
Class E amelifier
Class E RF sources offer the potential for efficiency greater than 80% and
have also been the subject of much development effort at frequencies up to
about
13 MHz. Some development has occurred at frequencies up to about 5 GHz using
GaAs MESFET transistors.
Significantly, an extremely wide range of RF frequencies may be utilized to
power the lamp of the present invention. Operation from a few KHz to several
GHz
and beyond have been demonstrated. Moreover, the Lamp of the present invention
may be operated over a wide range of lamp power. The only significant
practical
limitations on the amount of power applied to the lamp is the availability of
cost
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effective RF energy sources and certain considerations of keeping the bulb
temperature within a suitable operating window.
Examples of Lamp and Oscillator systems
Fig. 210 is an exploded, perspective view of a first example of a high
brightness lamp according to the present invention. A lamp head 820 is mounted
on
an oscillator board 822. A suitable dielectric material 824 is positioned
between a
high voltage plate of tha lamp head 820 and a pad on the oscillator board 822.
The
oscillator board 822 is mechanically and electrically connected to a metal
plate 826,
hereinafter referred to as a spreader plate 826. A ground plate of the lamp
head
820 is mechanically and electrically connected to a ground pad on the
oscillator
board 822. A perimeter portion of the lamp head 820 is also mechanically and
electrically connected to the spreader plate 826. The lamp head 820 and
oscillator
board 822 are enclosed by a first heatsink 828 and a second heatsink 830.
Power is
supplied to the oscillator board 822 from an insulated pin 832 and a ground
pin 834.
The lamp head 820 is constructed as described in detail in section 4.1.8.1
above in connection with Figs. 89-94. As illustrated in Fig. 210, the lamp
head 820
omits the optional protruding ridge. The oscillator board 822 is constructed
as
described in detail in section 4.3 above in connection with Figs. 208-209,
except for
the addition of the ground pad and power feed pad for connecting to the lamp
head
820.
Fig. 211 is an exploded, schematic view of the first example illustrating
various assembly details. The oscillator board 822 is secured to the heatsink
830 by
fasteners 836 (e.g., bolts or screws). The heatsink 828 is secured to the
heatsink
830 by RF sealing adhesive 838 and clips 840. A power cord 842 is connected to
the power pins 832 and 834. An optional clip 844 may be used to provide stress
relief for the power cord 842.
Fig. 212 is an exploded, schematic view of the first example illustrating
assembly details for an end plate 846. The end plate 846 is secured to the
heatsinks 828 and 830 with an RF sealing adhesive. Figs. 213 and 214 are
schematic views of the completed assembly of the.first example. Fig. 215 is a
cross
sectional view taken along line 215-215 in Fig. 213. In general, the lamp of
the
present invention is configured to contains the RF fields generated therein.
The
power line is filtered, metal enclosures are used with openings constricted to
below
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cutoff, and gasketing is employed between surfaces. Gasketing involves glues,
strips of compressible rope, resistive films and associated mechanical design
to
restrict the flow of RF current and associated radiation l coupling.
Fig. 216 is a schematic view of the oscillator board 822 and spreader plate
826. Fig. 217 is a cross sectional view taken along line 217-217 in Fig. 216.
A
groove 848 is formed in the spreader plate 826 to restrict the transfer of
heat from
the lamp head 820 to the oscillator circuitry. The oscillator board 822
includes a cut-
out section 850 and the spreader plate 826 includes a corresponding depression
852 where the active element of the oscillator is directly grounded to the
spreader
plate 826. Fig. 218 is a schematic view of the lamp head 820 mounted on the
oscillator board 822 and spreader plate 826, with the oscillator board 822
populated
with suitable electrical components, such as those described in connection
with Fig.
208-209 in section 4.3 above.
4.4.1 Cantilevered Oscillator Board
Fig. 219 is a schematic view of an alternative structure for the spreader
plate
826. Fig. 220 is a schematic view of the oscillator board 822 mounted on the
alternative spreader plate. Fig. 221 is a cross sectional view taken along
line 221-
221 in Fig. 220. As shown in Figs. 219-221, the spreader plate is provided
with an
opening 862 and the oscillator board 822 is secured the spreader plate with a
portion of the board cantilevered over the opening 862. The lamp head,
including
the capacitor stack is connected the oscillator board at the cantilevered
portion. As
shown in Fig. 221, the oscillator board can flex in the area of the lamp head
connection.
As described in section 4.1.8.1 and 4.1.8.3, a capacitor stack of dielectric
and
conductive plates is positioned between the lamp head and the PCB. The
different
materials utilized therein may have different coefficients of thermal
expansion. For
example, the dielectric material can be either rigid (as in glass or ceramic)
or soft (as
in plastics). The connection from the stack to the other elements is typically
made
with a tin lead solder which may be characterized as a plastic material at the
lamp
operating temperatures.
As the lamp head is heated, it may expand at a greater rate than the
capacitor stack. Moreover, if the capacitor stack is compressed by a pre-load
in
assembly, high stresses may be generated within the rigid materials while
distortions
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are generated in the plastic materials (which may relieve some of the pre-
load).
During thermal cycling of the lamp, the stack assembly may undergo tensile
stresses
which can lead to degradation or failure through delamination of the stack.
According to the present aspect of the invention, the lamp assembly is
configured so that the PCB can flex in the area of the lamp head so that a
small
amount of motion generated by the different rates of thermal expansion can be
accommodated without causing unit failure.
Fig. 222 is a schematic diagram of an alternative, preferred printed circuit
board layout for the oscillator board 822. In the preferred layout, the ground
pad on
the oscillator board is eliminated and the ground plate on the lamp head is
connected directly to the spreader plate.
4.4.2 Separate Lama Head Housing
Fig. 223 is a perspective view of a housing for the lamp head. The housing
includes heatsinks 864 and 866 which are relatively shorter as compared to
heatsinks 828 and 830. RF power is provided to the lamp head via a coaxial
cable
868 from any suitable source of RF energy. Advantageously, the lamp head
assembly is smaller and may be located remote from the RF source. Figs. 224-
226
are schematic views of various assembly details for the separate lamp head
housing.
Fig. 227 is an exploded, schematic view of the lamp head / power feed
assembly. The lamp head 870 is mounted on a power feed assembly 872. A
capacitor assembly 874 is positioned between a high voltage plate of the lamp
head
870 and a high voltage pad 876 of the power feed assembly 872. Figs. 228-230
are
schematic views of various assembly details of the lamp head / power feed
assembly.
Fig. 231 is an exploded, schematic view of the power feed assembly 872. A
power feed printed circuit board 878 is electrically and mechanically
connected to a
spreader plate 880. The spreader plate 880 is formed with a groove 882
configured
to receive a grounded outer conductor 884 of a coaxial cable 886 and to
suitably
position a center conductor 888 of the coaxial cable on the high voltage pad
876 of
the power feed printed circuit board 878. A bracket 889 secures the coaxial
cable
886 to the spreader plate 880 via a fastener 890 (e.g. a bolt or a screw).
Figs. 232-
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234 are schematic views of various assembly details of the power feed assembly
872.
Figs. 110 and 111 are schematic views of opposite sides of an exemplary
capacitor assembly 874. As described in section 4.1.8, the capacitor assembly
874
is of suitable dielectric material and thickness to provide a desired
capacitance. As
shown in Figs. 110-111, the capacitor assembly 874 is laminated with
conductive
pads and provided with through holes for alignment with the power feed
assembly
872.
An alternative, preferred construction of the capacitor stack according to the
invention is shown in' Figs. 235-239. The power feed assembly comprises a
single
sided printed circuit board 871 with a power feed pad 873 on one side and a-
bonding adhesive 871 a on the other for bonding the board to the spreader
plate 880.
The high voltage capacitor assembly comprises a single sided circuit board 875
having a conductive pad 371 as described above in section 4.1.8.3 with respect
to
Fig. 120 on one side and adhesive bonding 875a on the other for bonding the
capacitor assembly to the power feed assembly. This alternative, preferred
construction eliminates a number of solder layers in the capacitor stack. As
compared to the foregoing constructions, this preferred construction
ameliorates
arcing by utilizing a minimum number of well-controlled solder posts. Figs.
238-239
show an alternative preferred arrangement for a single sided printed circuit
board
877 with a power feed pad 879 on one side.
Fig. 240 is an exploded schematic view of the lamp head. An aperture cup
892 (enclosing a bulb) is inserted in an opening in the lamp head 870. Figs.
241-
242 are schematic views of the lamp head from opposite sides. Fig. 243 is a
cross
sectional view taken along line 243-243 in Fig. 242. Fig. 244 is a schematic
view of
a side of the lamp head which is mounted to the power feed assembly 872. As
shown in Figs. 240-244, the aperture cup 892 is positioned in the lamp head
with the
bulb aligned with the wedding ring shaped coil. The aperture cup 892 is
secured in
this position with a high temperature adhesive 894 on the outside of the lamp
head
870. Securing the aperture cup 892 from the outside of the lamp head 870 aids
in
thermal management of the lamp. The lamp head 870 has a high voltage plate 896
and ground plates 898 which are electrically connected to the high voltage pad
876
and spreader plate 880, respectively, of the power feed assembly 872.
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4.4.3 Exemplary Lamp Head Soldering Processes
Any of a number of techniques may be utilized for effecting an electrical
connection between the lamp head and the printed circuit board (PCB) /
spreader
plate assembly. Preferably, the lamp head has a coating of Rabbit metal
applied to
the high voltage pad and ground pads to assist soldering and mechanical
attachment to the PCB assembly. The lamp head connection pads are preferably
grit blasted just prior to spray coating of the Babbit metal.
One method according to the invention is to place solder in the area of the
desired connection and then heat the lamp head and PCB assembly to about
200°C,
for example, with a heating plate. The lamp head is then manually placed in
the
appropriate location and the parts cool together to form a bond.
Another exemplary method for forming an electrical connection between the
lamp head and the PCB assembly is as follows. Solder is pre-applied to the
lamp
head and / or PCB assembly. The lamp head is placed on the PCB assembly and a
high amperage current is run through the lamp head and PCB assembly in the
area
of the lamp head connection. High heat is generated at the contact areas,
causing
the pre-applied solder to melt. The current is then removed and a bond forms
as the
parts cool. For example, a clamping fixture is used which holds the lamp head
and
PCB assembly together. The clamping fixtures includes oppositely disposed
carbon
electrodes through which the high amperage current is passed. The current
heats
the carbon electrodes which in tum heats the lamp head and PCB assembly. This
method has the advantage of heating only a portion of the PCB assembly,
thereby
avoiding reflow of solder on other parts of the PCB assembly. This method is
also
faster because only a portion of the PCB assembly needs to be heated.
4.4.4 Improved Solderability Inserts
According to a present aspect of the invention, the lamp head includes
conductive inserts in the areas) of the high voltage pad and / or ground pads
which
improve solderability as compared to integral aluminum pads. Preferably the
insert
is selected from materials which will not melt in the presence of molten
aluminum.
More preferably, the selected material will form a metalurgical bond between
the
insert and the aluminum portion of the lamp head. Also, the selected material
preferably exhibits an improved solderability for connection to copper areas
on the
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PCB assembly. For example, suitable materials include nickel, nickel plated
with
platinum, and nickel alloyed with a small amount (e.g. less than about 25%) of
iron.
Fig. 245 is a schematic, top view of a lamp head 950 according to the
invention. Fig. 246 is a schematic, front view of the lamp head 950. The lamp
head
950 includes an insert 951 in an area of a high voltage pad of the lamp head
950
and inserts 952a, 952b, and 952c in respective areas of ground pads of the
lamp
head 950.
As described above, the lamp head 950 is integrally formed through a
vacuum injection molding process. The mold, BN insert, and / or silicon
carbide pre-
form are adapted to retain the pad inserts in position during the molding
process.
Fig. 247 is an enlarged, fragmented, cross-sectional view of the insert 951
positioned in a mold 954 prior to infiltration of the aluminum. The insert 951
is
further positioned by the BN insert 956. For the high voltage pad insert 951,
one
end of the insert 951 will make electrical connection with the pegs) 958 which
connects to the excitation coil. The lamp head 950 may be machined, for
example,
along line 960-960 to expose an inner portion of the pad material.
Fig. 248 is an enlarged, fragmented, cross-sectional view of the insert 952a
positioned in the mold 954 prior to infiltration of aluminum. The insert 952a
is held in
place by the silicon carbide pre-form 962.
The inserts 951 and 952a-c may be of any suitable shape and may be of
uniform longitudinal cross-section. Alternatively, the inserts may have a non-
uniform
longitudinal cross-section to aid retention during the molding process and /
or in the
finished integrated lamp head. Figs. 249 - 251 are schematic and perspective
views, respectively of an insert with shortened leg segments 964. Figs. 252 -
254
are schematic and perspective views, respectively, of an insert with through
holes
966. Fig. 255 is a perspective view of an insert with notches.968.
4.4.5 Separate RF Source
Fig. 256 is a perspective view of a preferred RF source 900 for the separate
lamp head described above in connection with Figs. 223-255. An RF power supply
is housed in an enclosure 902 which is secured to a heatsink 904 by fasteners
906.
A coaxial connector 908 is also mounted to the heatsink 904.
Fig. 257 is an exploded, schematic view of the RF source 900. As shown in
Fig. 257, the RF source 900 includes a control circuit 910, an oscillator
assembly
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912, and a circulator 914, connected as described hereinafter. Fig. 258 is a
schematic diagram of a power connection for the RF source 900. Power is
provided
to the RF source 900 through a filter assembly 916, one lead of which is
grounded to
the heatsink 904 and the other of which provides DC power.
Fig. 259 is a partial cross sectional view of the power filter assembly 916. A
capacitor 918, a transient voltage suppressor 920, and a resistor 922 are
connected
in parallel between a DC supply voltage and ground. For example, the capacitor
918 has a value of about 1000 NF and a rating of 50V, the voltage suppressor
920 is
a Motorola P6KE27A, and the resistor has a value of about 6.6K ohms with a
rating
of about 1 /4 watt.
4.4.6 Oscillator Control Circuits
Figs. 260-262 are block level schematic diagrams for various RF circuits
powering a lamp according to the present invention. In the lamp of the present
invention, especially when utilizing an indium halide only fill, the ignited
cold lamp
state has a significantly different electrical condition (e.g. impedance) as
compared
to the ignited hot state of the lamp. In order to improve starting and
operation of the
lamp, it is therefore preferred to provide a plurality of tuning states which
correspond
to various lamp parameters. These parameters include, for example, light
output
level, RF power reflection, and light color.
A feature of the oscillator described in section 4.3 is that the frequency of
the
oscillation may be tuned by adjusting a capacitor value. According to the
present
aspect of the invention, a control circuit is provided to switch the value of
the
capacitor in order to provide a desired frequency of oscillation.
The capacitor value may be switched, for example, by providing a varactor
diode in series with the tuning capacitor, providing two tuning capacitors in
series
with one another which are both switched open or closed with a pin diode, and
two
tuning capacitors in parallel with each other with one being driven by a pin
diode.
The control circuit may include, for example, a timer circuit based on
observed lamp operating characteristics, a DC input current monitor, a light
level
output monitor, and an RF reflected power monitor. .
Fig. 260 is a diagram of an RF circuit including a control circuit 924 which
provides a control signal to an oscillator 926. The output of the oscillator
926 is
directed to though a circulator 928 to an RF powered lamp 930. In the control
circuit
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924, the control signal is provided independent of any feed back from the rest
of the
circuit. For example, the control circuit 924 comprises a timer circuit
configured to
provide a suitable control signal based on timed intervals from when the lamp
is
switched on. The timed intervals are based on, for example, empirical
observation
of the lamp performance.
Fig. 261 is a diagram of an RF circuit including a control circuit 932 which
provides a control signal to an oscillator 926. The output of the oscillator
926 is
directed to though a circulator 928 to an RF powered lamp 930. In the control
circuit
932, the control signal is provided based on feed back received from the
circulator.
For example, the control circuit monitors reflected RF power and adjust the
frequency of the oscillator to obtain a minimum amount of reflected RF power.
Fig. 262 is a diagram of an RF circuit including a control circuit 934 which
provides a control signal to an oscillator 926. The output of the oscillator
926 is
directed to though a circulator 928 to an RF powered lamp 930. In the control
circuit
934, the control signal is provided based on feed back received from the lamp.
For
example, a optical sensor 936 (e.g. a photo-detector) is positioned to monitor
light
output or light to sense light color. The control circuit monitors the
measured
quantity and adjust the frequency of the oscillator accordingly.
Fig. 263 is a schematic diagram of a preferred RF circuit according to the
invention. A timer circuit 942 provides control signals to adjust the
frequency of an
oscillator 944. An output of the oscillator 934 is provided to a circulator
946. The
output of the circulator 946 is connected to the center conductor of a coaxial
connector 948.
The circulator is a non-reciprocal device that reduces the effects of the lamp
load and its changing impedances on the power, frequency, voltages, and
currents
of the oscillator. The circulator improves the ability to perform tuning of
the
oscillator.
Based on empirical observations, the lamp of the present invention operated
better with two tuning states. The oscillator board is constructed as
described in
connection with Figs. 208-209, except that a varactor diode D2 is connected in
series with the tuning capacitor C14. When the varactor diode is off, the
frequency
of the oscillator is adjusted to be somewhat lower (corresponding to a first
tuning
state) as compared to the frequency of the oscillator when the varactor diode
is on
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(corresponding to a second tuning state). The first tuning state is preferred
while the
lamp is igniting and during steady state operation. The second tuning state is
preferred after the lamp has ignited, but before the lamp reaches full output
(also
referred to as run-up).
The timing circuit is configured to begin a first timer when the lamp is
turned
on. Initially, the varactor diode is off and the lamp operates in the first
tuning state.
After a suitable period of time has passed for the lamp to ignite (based on
empirical
observation), the first timer expires and the timing circuit switches in the
varactor
diode to switch the oscillator to the second tuning state. The timing circuit
begins a
second timer which allows a suitable period of time for run-up. After the
second
timer expires, the varactor diode is switched off and the lamp operates in
steady
state in the first tuning state.
Fig. 264 is a schematic diagram of an exemplary printed circuit board layout
for oscillator board described in connection with Fig. 263. Fig. 265 is a
schematic
diagram of a timer circuit according to the invention. Integrated circuit U1
is a quad
2-input nor gate logic device. The timing intervals are determined by the
decay of
the various capacitive elements.
Alternatively, each of control circuit 924, 932, and 934 may comprise a
microprocessor based circuit or a micro-controller programmed to provide a
control
signal to adjust the oscillator frequency. For example, a timer circuit is
readily
implemented using a micro-controller. The above-described circulator feedback
and
/ or sensor feedback may be provided as information to the micro-controller.
The
micro-controller can use the information in an algorithm (e.g. a frequency
dithering
technique) to determine if the frequency needs to be adjusted. For example,
the
micro-controller can periodically make small adjustments to the frequency and
determine the effect on the lamp performance in accordance with the feedback
information. Such techniques provides automatic real-time tuning of the
oscillator
frequency. Other types of feedback (e.g. a bi-directional coupler) may also be
used.
While the invention has been described with respect to specific examples, the
invention is not so limited. Based on the drawings, the detailed description,
and the
teachings set forth herein, numerous other examples will occur to those
skilled in the
art. The preceding examples should be considered as illustrative only, with
the
scope and spirit of the invention being set forth in the following claims.
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