Note: Descriptions are shown in the official language in which they were submitted.
1156302
M-8376
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SYSTEM FOR ENERGI~ING AND DIMMING GAS
DISCHARGE LAMPS
BACKGROUND OF THE INVENTION
This invention relates to the energization of
gas discharge lamps, and more specifically relates to
novel energy conservation circuits for eneTgizing and
controlling the illumination output of gas-filled lamps
and high intensity discharge lamps.
To conser~e energy in lighting applications
using gas discharge lamps, it is known that the lamps
should be energized from a relatively high frequency
source, and that the lamps should be dimmed if their
output light is greater than needed under a given
situation. For fluorescent lamps, the use of a fre-
quency of about 20 kHz-will reduce energy consumption
by more than about 20~, as compared to energization at
60 Hz. For high intensity discharge lamps, such as
those using mercury vaporj metal halide and sodium, the
saving in energy exis~s ~ut is somewhat less than for a
fluorescent lamp. Numerous publications deal with the
desirability of high frequency energization of gas
discharge lamps, inciuding, for example:
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Federal Construction Council, High-Frequency
Lighting, Technical Report No. 53, National Academy
of Sciences Publication No. 1610, 1968, p. 6-30;
Campbell, J.H., New Parameters for High Frequency
Lighting Systems. Illuminating Engineering, V. 55, May
1960, p. 247-254; discussion, p. 254-256;
Campbell, J. H., Schultz, H.E., and Schlick,
J. A., A New 3000-Cycle Fluorescent-Lighting System.
IEEE Transactions on Industry and ~eneral Applications,
Vol. IGA-l, Jan.-Feb. 1965, p. 19-24;
Campbell, J. H. Schultz, H. E. and Schlick,
J. A., Characteristics of a New 300Q-CPS System for
Industrial and Commercial Use. Illuminating Engineering,
~. 60, March 1965, p. 148-152;
Dobras, Q. D., ~tatus of High Frequency
Lighting. General Electric Architects and Engineers
Conference, April 1963, p. 17-24;
Northern Illinois ~as Company, High Frequency
Lighting at our General Office, June 1970; and
Wolfframm, B. M., Solid State Ballasting of
Fluorescent and Mercury Lamps. IEEE Conference Record
of 4th Annual Meeting of the Industry ~ General
Applications Group, October 12-16, 1969, p. 381-386.
Energy saved by dimming gas discharge lamps
depends on the degree of dimming which is permitted in
a gi~en situation. The iight output of a lamp is
roughly proportional to the power expended. Thus, at 50%
; light output, only about ~Q% of the full rated power is
expended.
Many applications exist where it is accept-
~ able or desirable to decrease the amount of light from
¦ a lamp. For example, light in a building might be
decreased uniformly or locally in the presence of
~unlight coming through a window to maintain a constant
~1¦ 35 or acceptable illumination a~ a work surface. Thus,
during 8 normal work day, an energy saving of about 50g
may be experienced. Light might also be decreased
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during non-working hours and maintained at a low level for
security purposes. Light output might also be decreased,
either from local controls or from signals from a generating
station during periods of overload on the utility lines.
Energy savings may also be obtained by dimming
lamp output when the lamps are new and have a light output
much higher at a given input power than at the end of their
life. Since a lighted area must be properly illuminated at
the end of lamp life, energy can be saved by dimming the
lamps when they are new, and then reducing the dimming as
the lamps age. Energy saYings of 15% for fluorescent lamps
and 2Q% to 3Q~ for high intensity discharge lamps can be
obtained in this fashion.
One system used at the present time to obtain
the benefits of high frequency energization of gas
discharge lamps distributes power at low frequency C60
Hz~ to each of the fixtures of a lighting system. Each
fixture could commonly contain several lamps in parallel
or series connection. Each fixture is also provided
with an inverter to produce the high frequency energiz-
ing power and contains the necessary ballast circuits
for the lamp. Circuits used in the individual fixture
for the above type circuit are typically shown in
United States Patents 3,422,309, 3,61~,~16; 3,731,142;
25 and 3,824,428, each in the names o Spira and Licata;
and 3,919,592 in the name of Gray, each of which is
assigned to the assignee of the present invention.
i Systems of this type are aYailable from the Lutron
Electronics Co., Inc. of Coopersburg, Pennsylvania
under the trademark Hi-Lume.
While the above arrangement performs well, a
complete inverter circuit and controls therefor must be
placed in each fixture. Thus, the system is costly and
the reliabilit~ problem is repeated for each fixture.
Since esch fîxture receives the co~plete inverter
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circui~, designers and users are hesitant to use complex and
expensive circuits and control schemes because of cost and
reliability. Furthermore, each circuit exists in the
relatively hot environment of the lamp fixture. The scheme
also requires that four leads go to each fixture; two for
power and two for the dimming signal. A further problem is
that it is difficult to proYide a good 5Q Hz to ~Q Hz power
factor in each fixture since the power factor correction
devices are bulky and expensive.
In another known system, a single source of
high frequency is used and provides energy for a rela-
tively short distance over relati~ely short power
lines. Dimming is obtained by changing the inverter
frequency to a capacitiYe ballast. An arrangement of
this kind is shown in the publication Federal Con-
struction Council, High-Frequency Lighting, Washington,
D.C.; National Academy of Sciences, 1~68, referred to
above.
This arrangement has several disadYantages.
First it provides relatively poor dimming. The lamps
used in the system require separate filament trans-
formers since, if high frequency is used to power the
filaments, it is difficult to keep the filamen~ vol~age
constant with variable frequency. The separate fila-
ment transformers are costly and further complicate thesystem. It is also difficult to change the inverter
frequency and requires costly and complex controls. A
further problem of these systems is that the load on
the in~erter îs capacitive so that the high frequency
power factor is poor. Thus, excessiYe current flows in
the wires between the in~erter and ballast, creating
additional energy loss.
Other arrangements are known in which 50 Hz
to ~0 Hz power is supplied from a local source directly
to the lamps and theîr ballasts, and dimming is obtained
by changing the current amplitude through the use of an
auto-transformer or thyristor control circuit. While
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this system obviously does not have the advantage of
high frequency excitation for the lamps, it is also
true that bulky components are needed in this fixture
and a good 50/60 Hz power factor is hard to obtain.
5 BRIEF DESCRIPTION OF THE INVENTION
In accordance with the present invention, a
novel arrangement is provided wherein a central high
frequency inverter is provided to energize a plurality
of remote ballasts and associated gas discharge lamps
with an a-c output wave form which may or may not be
symmetrical. Circuits of any desired sophistication
are provided for control of the central inverter and
dimming is obtained by varying the amplitude of the
in~erter output. The connection from the in~erter to
the ballasts and lamps and remote fixtures is preferably
by a novel low-loss transmission line consisting of a
pair of spaced conductors which are each insulated by a
very thick insulating sheath which minimizes their
capacitive coupling to one another and to the grounded
Z0 conduit in which they are located. It also minimizes
magnetic field coupling to an iron or ferrous material
conduit, and thus the iron losses in the conduit.
Moreover, the structure permits use of a ferrous metal
', conduit. Furthermore, magnetic coupling proximity
1 25 effect losses are minimized by the no~el heavily
¦ insulated transmission line.
The ballasts used with the lamps are those
' which preferably use passive and linear components, but
! they could be active and/or non-linea~. A passive
¦ 30 ballast is defined herein as one using only resistors,
¦ inductors, transformers and capacitors. An active
ballast is one using amplifier components such as
transistors, thyristors, magnetic ampli~iers, and the
li~e. A linear component is one having a ~airly linear
relationship between input and output.
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The output current wave shape of the inverter of
the invention is preferably sinusoidal but, in general, it
is a substantially continuous periodic wave form. By a
substantially continuous periodic wave form is meant a
wave form which has an alternating component and may or
may not have a d-c component. By substantially continuous
wave form is also meant one ~hich has no significant
interYal of "zero" curTent during each cycle of the high
frequency output, as is present in some pulsed sources or
in a phase controlled thyristor circult. However, a
continuous wave form shall include wave forms such as
sinusoids; triangular wave forms; square or rectangular
wave forms, each with or without d-c components. The
output amplitude of the inverter may be controlled by:
(a~ Phase control;
(b~ Pulse width modulation with a filtering
ballast; or
~ cl D-c input voltage.
In each of the above, there will always be con-
ti~nuously flowing current. By pulse width modulator aboveis meant fixed frequency and variable pulse width or fixed
pulse width and variable frequency, or combinations
thereof.
In order to maintain a high power factor, the
recti~ier network used i~n converting the frequency at the
mains (5Q Hz to ~Q Hz~ to a d-c input or the high frequency
inverter has a novel structure. Moreover, the ballast
circuits used in the f~xtures have a novel configuration.
Pinally, while any deslred high frequency inverter circuit
3~ can be used, a novel preferred inverter to be described is
particularly use~ul with this ;nven~ion.
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With the in~erter of this invention, the use of
the single inverter permits it to be designed with many
features with high reliability at low cost. Thus, all
complexIty is confined to a single unit rather than being
repeated over many fixtures. The single inverter can be
located to enjoy full air circulation and may be easily
cooled. When dimming with a single inverter, all lamps
track in intensity. Since dimming is obtained by inverter
output amplitude control, simple, low cost and highly
reliable equipment can be used in the fixture. Thus, the
fixture for lamp and ballast has only a small number of
small, low loss, highly reliable capacitive and inductive
and transormer components.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a block diagram showing the essential
components o the present invention.
Figure 2 is a cross-sectional view of a pre-
ferred transmission line for connecting the output of
the in~erter to the ballasts and lamps in Figure 1.
Figure 3 is a circuit diagram of a preferred
inverter which can be used in the diagram of Figure 1.
Figure 4 is a circuit diagram of a ballast and
lamp structure wh~ch can be used in the block diagram
o~ Pigure 1.
Pigure 5 is a circuit diagram o a power
supply rectifier which can be used with the present
invention.
~igure 6 is a block diagram of a novel inverter
circui~t arrangement which can be used in the present
invention.
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DETAILED DESCRIPTION OF THE DRAWINGS
Referring first to Figure 1, there is shown a
relatively low frequenc~ (for example, from 25 to 60 Hz)
source 20 which is connected to a rectifier network 21
which produces rectified output power for a single
central inverter 22. Source 20 and network 21 can be
replaced by any appropriate d-c supply or can be driven
from the d-c battery of an emergency battery which is
charged or energized from a power line. In addition,
although the use of a d-c supply powering an inverteT
is most suitable, it is also possible to use a frequency
converter in a manner similar to that shown in U.S.
Patent 3,731,142 dated May 1, 1973, in the names of
30el Spira and Joseph Licata where, for example, a-c
voltage or an unfiltered rectified d-c voltage is fed
directly to a frequency con~erter. RectifieT network
21 may be of the type shown in Figure 5 which will be
later described, and which has high power factor
characteristics. Inverter 22 will be later described
in connection with Figure 3 and produces a sinusoidal
a-c output wave shape at a frequency of about 23 kHz.
. The output of inverter 22 is preferably higher than
about 20 kHz to be above the audio range, and can be as
high as permitted by semiconductor switching losses,
~ 25 component losses, and the.like which increase with
¦ higher fre~uencies. Note that if the apparatus is
installed in an area where audio noise is not important,
' the in~erter output need be h~gher than only about an
;~ order of magnitude greater than the input line fre-
quency.
n inverter output amplitude control circuit
23 is connected t~ i~verter 22 and, under the influence
~ ~ of a signal from dimming sign~l cont~ol deYice 24, will
.~ ~ ~ increase or ~educe the 'a.mpi~tude of the' wave shape o
the high'fre~uency outp~t of~in~ertex' 22~ The control
device 24 can be a ~BnuBl contrsl or can be derived
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from such devices as photocell controls, time clocks,
and the like which apply some desired condition respon-
sive and/or temporal responsive control to inverter 22.
The output of inverter 22 is then connected
to two leads 30 and 31 of a transmission line which is
particularly well adapted to distribute the high fre-
quency power output of inverter 22 over relatively long
distances with relatively low loss. By way of example,
the lines 30 and 31 could have a length of about 100
feet, and could supply power to about twenty-five
discrete spaced fixtures which each might contain two
lamps. In this use, 1850 watts must be provided to the
system with a power factor of about 0.9.
Note that this installation could consist of
fifty 40-watt fluorescent lamps which require 2500
watts at 60 Hz. Only 1850 watts are needed at the
higher frequency and with the novel system of the
invention for the same ligh~ output.
Note further that only two wires are needed
to carry power to lamp fixtures with the present inven-
tion as contrasted to the need for four wires in fixtures
which locally contain inverter circuits and are connected
to easily transmitted low frequency (50/60 Hz) power.
Pigure 2 shows a preferred form of the novel
transmission line of the invention for distribution of
high frequency high power energy, as contrasted to well
known arrangements for the distribution of high fre-
quency, low power signalling voltages. In Pigure 2, `
lines 30 znd 31 are formed of respective central con-
ductors 32 and 33, respectively, which each consist ofnineteen strands of copper wire having diamete~s of
0.014 inch. The outer diameter o the bundle of strands
is about 0.070 inch. ~ach o~ conductors 32 and 33 are
covered with dielectr~c sheaths 34 and 35, respectively,
3~ which may be o~ any suitable conYentional insulation.
Each of sheaths 34 and 3~ ha~e diameters of 0.235 inch
and are preferably at least about three times the
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diameter of their respective central conductor. Strands
30 and 31 are then contained in a grounded steel con-
duit 36 which may be a so-called 3l4 inch conduit which
has an inner diameter of about 0.825 inch and an outside
diameter of about 0.925 inch. The transmission lines
30 and 31 are confined in conduit 36 for a major portion
of their lengths, as needed by the particular installa-
tion.
Note that the dimensions given above are only
typical and that other dimensions could be selected.
By using relatively thick insulation sheaths 34 and 35,
the capacitive coupling and thus losses between con-
ductors 32 and 33 and from the conductors 32 and 33 to
conduit 36 are minimized. Thus the transmission line
will have low loss qualities, even if it extends long
distances. Note that any desired connection can be used
if the distance from inverter 22 to its loads is short.
By using maximum thickness insulation sheaths
34 and 35 which can still be conveniently drawn th~ough
conduit 36, the electric field intensity is reduced,
thereby to reduce bulk loss resistivity. In the past,
it was believed necessary to use a minimum dielectric
thickness to minimize dielectric volume and thus di-
electric loss. The present invention departs from this
conventional approach in order to reduce the shunt
capacitive losses between the wires and from the wires
i
to the conduit.
The relatively thick insulation sheaths 34
and 35 also minimize magnetic field losses incurred by
coupling with the ferrous metal conduit. The lower
magnetic loss is due to the greater distance of the
conductoss 32 and 33 from the ferrous metal conduit.
Thb magnet'ic field raries inversely as the distance
`; from a conductor. Ener:gy losses due to the presence of
' 35 fer'rous'~et'al in a magnetic 'field vary di~ectly as a
; ~ s~uare o the~magnetic~fiel'd;intensity. Therefore, it
~ ~s seen tha`t thes'e'losses vary inver'sely as the square
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of the distance between the conductors and the ferrous
metal conduit. This permits use of ferrous conduits,
rather than aluminum or other non-ferrous materials.
Preferably, the characteristic impedance of the trans-
mission line should be matched to that of the load toreduce the V~R loss and variation in voltage along the
line.
The transmission line conductors 30 and 31
extend through a building or along a roadway, or the
like, and are connected to one or more remote fixtures.
Two fixtures 40 and 41 are shown for illustration
purposes, but any number can be used. Fixtures 40 and
41 each contain ballasts 42 and 43, respectively, and
associated gas discharge lamps 44 and 45, respectively.
A typical ballast and lamp assembly will be later
described in connection with Figure 4. Lamps 44 and 45
may be fluorescent OT high intensity gas discharge
lamps or any other desired type of gas discharge lamp.
Ballasts 42 and 43 preferably use passive linear com-
ponents such as reactors (of relatively small sizebecause of the relati~ely high frequency applied to the
ballast) and capacitors which are reliable and inex-
pensive. Note that in a prior high efficiency 60 H2
ballast, there was a ballast loss of about 12 watts in
the fixture so that the ~ixture is quite hot. With the
present invention, the ballast loss in the fixture is
less than 1 watt. Thus the components in the ballast
are not subject to high temperature.
In operation, high frequency power (abore
30 about 20 kHz) is trans~itted from inverter 22 over the
I transmission lines 30-31 with relatively lo~ loss and
; is distributed to the plurality of remotely located and
simple and reliable ballasts 42 and 43 and their asso-
ciated lamps 44 and 45J reSPeCtiYe1Y.
In ~rder to dim the output of all the lamps
44 and 4~ in an identical manner, a signal from signal
source 24 Cwhich can be a manual control, a clock
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control, a control from the electric utility to control
utility loading, a sunlight intensity responsive control,
or the like) causes the inverter output amplitude
contTol circuit to reduce the output amplitude of the
5 a-c output of inverter 22. The light output of lamps
44 and 45 will then decrease roughly proportionally to
the reduction in power from inverter 22.
Any desired inverter circuit having a variable
a-c output can be used for the inverter 22. Pigure 3
shows a novel inverter circuit which can be used with
the present invention. A circuit similar to that of
Figure 3 is shown in the pulication An ~mproved
Method of Resonant Current Puise Modulation for Power
Converters, Francisc C. Schwarz, IEEE Transactions, Vol.
IEC 1-23, No. 2, May, 1976; and are also shown in U.S.
Patent 3,663,940 to Francisc Schwarz. That circuit,
however, does not obtain variable amplitude adjustment
with constant fre~uency as is the case of Figure 3.
In Figure 3, the d-c output of rectifier 21
is applied between-d-c positive bus 50 and the negative
or ground bus 51 which are connected ac~oss series-
connected, high speed thyristors 52 and 53. Thyristors
52 and 53 ha~e turn-on speeds of less than about 1
microsecond and turn-off speeds of about 2 to 3 micro-
seconds. The junction between thysistors 52 and 53 isconnected to series-connected capacitor 54, inductor
55, the primary winding 56 of a step-up transformer 57
and the ground bus 51. Trans$ormer 57 has a high
voltage secondary winding 58 which delivers a high
frequency sinusoidal output voltage of about 2S5 volts
a-c for a d-c input voltage o about 320 volts.
Suitable bypass diodes 59 and 60 may be con-
nected across thyristors 52 ~nd 53~ respectively. Ca-
pacitoT 54 and inductor 55 have values chosen to be
resonant-~t about~23 kHz. Thus, capacitos ~4 ~ay have
a~Yalue of ~33 mic~ofarads and inductor 55 may have a
value of about 130 microhenrys.
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A~plitude control circuit 23 provides timed
output gate pulses to thyristors 52 and 53 to control
their operation, and these pulses are phase-controlled
by the dimming signal.
In operation, and to start the inverter,
consider that both thyristors 52 and 53 are off. A
gate pulse from control 23 first turns on thyristor 52
to create a current path through components 50, 52, 54,
55, 56 and 51. The gate pulse to thyristor 52 is
removed after a few microseconds and when conduction o~
thyristor 52 is fully established. Since capacitor 54
and inductor 55 are resonant at about 23 kHz, the
current in the above circuit goes through a half cycle
at the resonant frequency and, when it comes close to
zero, thyristor 52 is commutated off, and the current
reverses and flows through the path 51, 56, 55, 54, 59
and 50.
At this point, a pulse from control 23 turns
on thyristor 53 so that the resonant current (and
energy stored in the resonant circuit) can now reverse
and flow through the circuit including components 53,
56, 55 and 54 in a resonant half cycle. The triggering
pulse from circuit 23 is removed after conduction is
established in thyristor 53. Thus, when the current at
the end of this negative half cycle approaches zero,
the thyristor 53 is commutsted off and the current
re~erses into the positive half cycle and flows through
components 60, 54, 55 and 56. The next pulse from
control Z3 turns on thyristor 52 as the resonant current
swings into its positive half cycle to complete a full
; cycle of operation.
Obviously, a high output ~oltage is induced
into output winding 58 during this operation which is
subsequently applied to the transmission line consisting
o~ conductoss 30:and 31.
Amplitude variation is obtained by delaying
the application of the firing signal to thyristors 52
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and 53 and th~s varying the duty cy~le of the in~e~ter.
Thus, the conduction time of t~e th~ristors, during the
half cycle, is reduced and less voltage ;s applied to the
prlmary wind~ng 56. ~o~ever, the voltage to winding 56 is
sinusoidal due to t~e resonsnce of capacitor 54 and in-
ductor 55. Thus the voltage fed to ballasts 42 and 43
(Figure 1) is also sinusoîdal. Ampl~tude variation may be
obtained by var;a61e delar of t~e firing signal to either
or both thyristor switches.
As will be later described, the ballasts 42 and
43 are tuned to the output frequency of inverter 22. The
sinusoidal wave form reduces inefficiency due to harmonics
and also reduces production of electromagnetic inter-
ference. However, as mentioned previously, non-sinusoidal
wave forms can also be used with the invention.
Note that any desired inverter circuit and con-
trol could be used in place of inverter 22 including arrange-
ments for varying the voltage at bus SO; pulse width
modulation techniques; transistorized circuits; and the use
of a high frequency variable ratio transformer, or other
circuits using similar controllably conductive devices.
While some aspects of the particular inverter
circuit of Figure 3 are known, it was never previously used
for gas discharge lamp control purposes. This is because
in ordinary lamp applications, the lamps would go out if
the voltage input is reduced. However, in the present in-
vention, the lamps stay on and dim as input voltage
amplitude is decreased because the lamps are operated at
high freguency and are provided with a special and suit-
1 30 able passiYe linear ballast.
i A novel ballast arrangement such as that shown
¦~ in Figure 4 is pro~ided for each of ballasts 42 and 43.
~j~ The ballast o~ Figure 4 is used for two series lamps 70 and
3-1~ 71 (equi~alent ~o lamps 44 in fixture 40 of Pigure 1), where
lamps 70 and 71 are rapid-start fluorescent lamps which are
~'i véry suita61e for dimming. Other gas discharge lamps
! could have been used.
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The ~allast circui"t for th~ lam~s 7Q and 71 in-
cludes capacitors 72 and 73, transformer 75 and inductor 76.
A winding tap 77 i~s connected to filament 78 of tu~e 70. A
wi`nding tap 79 i~s connected to fi~aments 8Q and 81 of tubes
70 and 71, respectively. A winding 82 is connected to fila-
ment 83 of tube 71. Transformer 75 has a primary winding of
about 235 turns. Taps 77 and 79 and ~inding 82 may be about
9.5 turns. A conventional thermally responsive switch 84
which opens, for example, at 105C is in series with capacitor
72.
The values of capacitors 72 and 73 and inductor
?6 are chosen to ~e resona~t at about 32 kHz while capacitor
72 and inductor 76 resonate close to about 12 kHz. Therefore,
the reactive impedance of inductor 76 is greater than that
of capacitor 72 at 23 kHz. By way of example, capacitor
72 is Q.033 microfarad; capacitor 73 is about 0.0047 micro-
farad; and inductor 76 is about 5.1 millihenrys.
- An important feature of t~e ballasts of the inven-
tion ~s that they only need to provide filament heater power.
- 20 Moreover, the ~allast inductors and capacitors can be con-
tained in the same can or housing, thus contributing to small
size and economy for the ballast. The use of a common
housing also simplifies the installation of the ballast since
it is not necessary to handle many separate parts.
The ballast circuit described above has the
follo~ing desirable characteristics:
~ 1. It will not be damaged by accidental appli-
¦ cation of 50 Hz to 60 Hz power.
2. The inverter 22 will not be shorted if any
one ballast component fails. Thus, the short circuit can
¦ be located more easily sînce the lamps in unshorted
fixtures are still on.
3. The circuit exhib~ts a good power factor to
~! the inverter 22 and transmission lines 30-31.
4. T~ere ls a relat~vely constant filament voltage
¦ over the dim~ing range to a~oid damage to lamps.
~- 5. T~e starting voltage is sufficiently high
to strike the lamps under specified conditions but is
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not so high that the lamps can be damaged.
6. The ballast is small and efficient because
the ballast transformer only handles the filament power
of the lamps.
The operation of the circuit of Figure 4 is ~s
follows: When a-c power is applied to lines 30 and 31,
the 23 kHz power causes components 72, 73 and 76 to
partially resonate at their resonant frequency of
32 kHz. The increase in current flow due to this par-
tiai resonance causes the voltage on capacitor 73
to rise high enough to start lamps 20 and 21. The
partial resonance is important since it affords suffi-
cient but not excessive starting voltage which might
damage lamps 70 and 71. Once lamp 71 starts, capacitor
73 is essentially shorted,so that capacitor 72 and
inductor 76 are resonant below the inverter frequency.
During'operation, capacitor 72 blocks low
frequency voltage of from 50 Hz to 60 Hz, if that vol-
tage is accidentally applied to lines 30 and 31. Thus,
accidental destruction of the ballast by low frequency
power is prevented. Also, since impedance components
including capacitors 72 and 73, transformer 75 and
inductor 76 are connected in series, the failure of any
one component will not appear as a short on the inverte~
22. Thus, all lamps of all fixtures are not extinguished
and the faulty component can be easily located.
, Good power factor is ob,tained wit,h the circuit
of Figure 4 by making the impedance of capacitor 72
close to that of inductor 76 a~ 23 kHz. `Since the '
reactive impedances of components'72 and 76 subtract,
, the ~esultant is small compared,to the series resist'ance
of lamps 70 and 71, Thus, the reactiVe component of
the load is small so that good power factor is o~tained.
A relati~ely constant filament voltage for '
' 3S ~i,1aments 78j 80, 81 and 83 is assured s~ce the
', primaTy winding of transo~mer' 75 is -connected ac~oss
i lamp 70. The ~oltage drop across this lamp is rela-
1 ~ ~
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tively constant even as the lamp is dimmed. Thus, the
filament voltages remain approximately constant. Note,
however, that as the amplitude of the input voltage
from lines 30 and 31 is varied, the current in lamps 70
and 71 varies and the light output of the lamps varies.
The inductor 76, in addition to being a
component of the power factor network, has a larger
reactive impedance than capacitor 72, and thus acts as
a ballasting impedance to limit current in lamps 70 and
71.
Although the arrangement of Figure 4 shows
the invention in connection with fluorescent lamps, it
should be understood that the invention can be applied
to the energization and dimming o any gas discharge
lamp. Indeed, the invention can be used to operate and
dim incandescent lamps if desired to give a user of the
circuit flexibility of application. If one or more
incandescent lamps are used in place of lamps 70 and
71, the ballast circuit can, of course, be eliminated.
Lamps 70 and 71 in Figure 4 could be replaced
by conventional high intensity discharge lamps, such as
mercury ~apor, metal halide, and high and low pressure
sodium lamps. These lamps do not have filaments and
are relatively immune to damage from too high a striking
25 voltage. Thus, the ballast of Figure 4 can be modified
to remove the transformer 75 and its filament heater
windings when applied to a high.intensity discharge
lamp.
The circuit of Figuse 4 can also be modified
to place the inductor 76 across the lamp terminals in
a well known.circuit arrangement. With the transformer
. 7~ remo~ed, the capacitor 72 is designed to block 60 Hz
power and to prevent shut-down of the system in case of
~a shorted co~ponent. Resonance is established between
the inducto.r 76.and..the capacitors in series therewith
near the d~iving freq-uency of the inverter 22. Thus,
be`fore the ~.-I.D. lamp strikes,.the circuit has a high
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Q and a large voltage builds up across the lamp. This pro-
vides sufficient voltage to strike the lamp arc~ and the
lamp becomes a lower impedance, more nearly matched to
the ballast. The ballast then regulates the lamp arc
current as a function of the ballast input voltage.
Any suitable ballast circuit could be used
with the H.I.D. lamp where, however, the ballast is
subject to an energy-conserving dimming operation.
Figure 5 shows a rect~fier network circuit 21
~hich can be used with the present invention, and which
has the adYantage of haY~ng a high power factor so as
not to place an unnecessarily high current drain on the
50~6~ ~z wiring leading to the rectifier network 21.
The circuit consists of a resonant circuit
~nclud~ng inductor ~0 and capacitor Ql connected be-
tween the input low frequency a-c source and the single
phase, bridge-connected rectifier 92. The d-c output
of rectifier Q2 is then connected to an output capacitor
~3, which ma~ be an electrolytic capacitor, and to the
positive bus 5Q and ground bus 51. The values of
i~nductor 9Q and capacitor Qi are critical and are 30
millihen~s and 10 microfarads, respectiYely.
In opération, the LC circuit QQ-~l in front of
rect~fier ~2 causes the current drawn from the S0/60 Hz in-
put to flow for a longer time during each half cycle and tohave a better phase relationship with the ~oltage. The in-
ductor QQ and capacitor Ql are resonant at a period of about
one-fourth of the period of the input circuit frequency
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(usually 5~ Hz to 60 Hz). At one point in the cycle,
the voltage on capacitor 93 exceeds the voltage on
capacitor 91. This back-biases rectifier 92 so that
line current will surge into capacitor 91 rather than
cutting-off. The surging of current into capacitor 91
during reverse-biasing of rectifier 92 causes inductor
90 and capacitor 91 to resonate, thereby causing more
uniform current flow from the a-c mains over each half -
cycle, and thereby substantially improving power factor.
It is understood that the system shown herein
can also be realized with inverter 22 as a multi-phase
inverter such as a three-phase inverteT. In this case,
the high frequency power will be distributed to ballasts
and lamps by means of multi-conductor transmission line,
lS e.g. three conductors for three-phase power. The
ballasts and lamps would be connected conductor-to-
conductor, or conductor to neutral, if a neutral is
provided. Likewise, the low frequency 50/60 Hz supply
20 in Figure 1 can be a multi-phase supply, e.g. three
phase.
An important feature of this invention is the
use of a single central inverter transformer 57 to supply
the proper starting voltage to the lamps. This feature
improves the efficiency of the system. In the conven-
tional system, a transformer is contained in each
fixture to supply proper starting voltage. It is well
known to transformer designers that for a given volt-
ampere size, one large transformer is more efficient
than a number of smaller transformers.
The inverter transformer 57 supplies the
proper starting voltage and the transfo~mers 75 in the
fixture ballasts ~Figure 4~ does not have to carry full
lamp powes, but only carries filament power. ~11 lamp
powe'r is sup~lied rom the single inverteT transformer
57 of Pigu~e 3 which'is more 'efficient than an aggregate
of smaller transformer's for each'ballast and for the
same total volt amper'es rating. Thus higher system
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efficiency is ~btained.
Furthermore, since the ballast transfoTmers 75
only carr~ filament power, the f~xture ~allasts are
smaller, cooler, lig~ter, more e~ficient, less complex and
thus more relia~le than ~allast transformers which must
carry the full lamp power.
The ballast will generate appToximately an ordeT
of magnitude less heat t~an those in which lamp volt
amperes must be ~andled by the ballast transformer.
Therefore the fixture temperature is considerably lower.
When fluorescent lamps are run at this resultant cooler
temperature, their lig~t output for a given input power
~efficacy~ increases. This effect can save an approximate
additional 5~ in power in a given system.
lS In addition to the gain in efficiency by the use
of a central transformer 57, the heat produced by the lamp
power volt-amperes is dissipated in the central inverter
transformer 57 rather than in the individual fixtures.
The central inverter transformer 57 can be efficiently
cooled since it ~ill be in a convenient and accessible
location, and any desired cooling can be used.
One inverter or converter structure which
generally follows the concepts of the arrangement shown in
Figure 3 is shown in ~lock diagram form in Figure 6. In
Figure 6 controls are provided for the circuit of Figure 3
which enable the circuit to be uniquely applicable to a
variable power output type of system such as a lamp
dimming system ~here the inverter is the central high
frequency supply for a plurality of lamp loads which are
connected to the supply over a transmission line or the
like.
The inverter to be described in Figure 6 will
satisfy the ollowing criteria:
The converter output will be a sine wave
3~ w~ich îs believed to ~e th~ ~est for the lowest trans-
mission line loss.
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2. The output amplitude of the sine wave
output of the converter is variable in ordeT to obtain
dimmlng.
3. The inverter operates with high efficiency,
thereby to save energy.
4. The output frequency of the inverter can be
greater than about 20 kHz and above the audio range so
that the converter will not generate annoying audible
noise when used in an environment susceptible to an audio
noise problem.
5. The converter can be reliably started up and
turned of with the switching devices of the inverter
being immediately operated in order to insure proper
converter operation and to insure proper lamp striking.
6. The inverter sine wave output has low
distortion even though there is a relatively large change
in the load current due, for example, to dimming or a
change in the number of lamps in the system which are
conducting load current.
7, The conYerter is protected against fault
load current and is turned o~f and requires an intentional
operation by t~e user to turn it back on if a load fault
is developed.
8. The converter is internally protected with
automaticall~ reset means for temporarily turn~ng off the
converter upon the occurrence of an internal converter
fault and then automatically returning the converter to
duty.
In Figure 6, input power at lines 50-51 are
connected to the block 52-53 labeled CONYERTER POWER
SWITCHI~G ELEMENTS. These power switching elements could
be the thyristor switching devices 52 and 53 of Pigure 3
~and their associated diodes 5~ and 6Q, respectively) or
could be anr other desired type of switching element
including transistors and the like.
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The circuit including switching elements 52 to
53 contains a converter fault detector circuit lO0 which
is operable to produce an output signal in response to a
fault within the converter. By way of example the fault
detector lO0 could consist of a current transformer whose
output winding is connected to a load resistor which
produces a suitable output to a shut-down circuit system
103.
The main current carrying circuit next contains
the sine wave filter 54-55 consisting of previously
described components 54 and 55 and which insures that the
sqllare wave input from the converter power swi~ching
elements 52 and 53 is con~erted to a sine wave with low
distortion. This is obtained because, at the fundamental
frequency, the sum of the impedances of inductor 55 and of
capacitor 54 is zero, so that the fundamental frequency of
the square wave is unattenuated. However, the total
impedance of the tuned circuit 54-55 is different from
zero for other frequency components which form the input
2Q square wave and these frequency components are greatly
attenuated. Consequently, a relatively low distortion
sine wave output is produced by the converter circuit in
view of the tuned circuit including capacitor 54 and
inductor 55. Moreover, the fre~uency of this circuit is
chosen aboYe the audible range and preferably is greater
than 20 kHz so that both criterion 1 and 4 above are met.
The load circuit in Figure 6 is next connected
through a phase-sensitive zero crossing detector circuit
llQ which is operable to time the operation of a syn-
3~ chronizing circuit 111. The phase-sensitive zero crossing
detector can consist of any desired type of circuit. The
circuit could consist of a saturable core transformer
whi~ch is saturated during most of the positive and negative
hal~ c~cles and is unsaturated only for a short time
during each current zero interval. Thus, an output
voltage pulse is produced on a secondary winding and
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across a load resistor each time the main converter
current passes through zero.
The main load current circuit also includes a
load fault detector circuit 120 which may include a load
current transformer having a secondary winding which has
an output connected to a suitable shut-down circuit system
123.
The main load circuit next includes a load
buffer network 130 which can consist of a-Yoltage transformer
and a capacitor which tends to overpower large values of
resistance which might appear due to a very light load,
and preserves the sine wave configuration of the output.
Thus, in the circuit of Figure 3, which does not contain
the abo~e-mentioned capacitor, if the load resistance
becomes too large, the circuit becomes over-damped and the
voltage across the load is no longer a sine wave and the
resonance of members 54 and 55 ceases. The load buffer
capacitor presents an added resonating component which is
in parallel with the load and is used to preserYe criteria
~ listed above.
The block diagram of Figure 6 contains con-
sIderable control circuitry which can ~e conYeniently
constructed and adjusted for use with a single central
inverter and which would be Yery expensive to reproduce at
each fixture of a fluorescent lamp system. Thus, the
circuit of Figure 6 includes a variable amplitude control
circuit 14Q) whic~ receives an input from the synchronizing
circuit 111. The variable amplitude control circuit is
used to change the switching point of the power switching
elements 52 and 53 (to obtain phase control) and is con-
trolled from several inputs. These include the shut-down
circuit lQ3 which is operated from the conYerter fault
detector and the shut-down circuit 123 which is operated
from the load fault detector 12Q. Circuit 140 is also
controlled by a lamp striking sequence circuit 15Q or from
a manual control input 151 which operates through the lamp
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striking sequence circuit 150. A start-up and shut-down
sequence control circuit 152 is also provided.
Although the present invention has been described
in connection with a preferred embodiment thereof, many
variations and modifications will now become apparent to
those skilled in the art. It is preferred, therefore,
that the present invention be limited not by the specific
disclosure herein, but only by the appended claims.
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