Note: Descriptions are shown in the official language in which they were submitted.
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RADIATION EMITTING SYSTEM
Background of the Invention
This invention relates to electrical circuits
and is illustrated and described herein with reference to
a circuit for energizing an emitter of electromagnetic
radiation; however it may be utilized in other applica-
tions and environments and is not limited to use with
` radiation emitters.
Known radiation emitting systems include a
radiation emitter, such as a light emitting diode (LED),
10 an electrical power source for driving the emitter and, in
most practical applications, a switching transistor for
applying power to the emitter in pulse form under control
of appropriate oscillator or switching amplifier circuitry.
Typical systems of this type utilize a direct current power
source, or a direct current source in combination with a
charging capacitor, to drive the emitter with square wave
or generally similar pulses of such width and frequency
that the emitter is pulsed off and on for substantially
equal intervals of time. Refer, for example, to United
20 States Patent Nos. 3,894,229, 3,928,760, 3~657~543/
~- 3,751,671, 3,742,947, 3,909,670, 3,705,986 and 3,486,029.
Another generally similar direc-t current system, disclosed
in United States Patent No. 3,727,185, utilizes a silicon
controll~d rectifier (SCR) to switch the emitter. Still
another system, disclosed in Unlted States Patent No.
3~924,120, converts alternating current electrical power
to 120 ~z square wave, the pulse width of which is control-
lable for information transmission to remote locations.
These and other radiation emitting systems are
-~ 30 of limited power and, hence, tend to be short ranged,
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especially in dust filled or like environments. Al-though
most commercially available semiconductor radiation emitters
are capable of peak power operation for short time inter-
vals, in most practical applications -- both continuous
or pulse operated -- they are operated at average power
levels well below pea]~ power because of fears of excessive
junction temperatures, and othex factors. Thus, the
effectiveness of most radiation systems here-to~ore has
been limited by unacceptably low emitter power levels, or
emitter current limiting devices, or both. The effective-
ness of systems which utilize capacitive emitter charglng
elements is-~further limited by dielectric heating effects
and capacitor charginy time limitations.
Summary of the Invention
This invention provides a circuit for energizing
an electrical element at selected intervals for a predeter-
mined time period, with the frequency at which said inter-
vals occur being sufficient that each interval corresponds
- to at least a plurality of such time periods. Thus, it is
possible, by appropriate selection of these intervals with
respect to the time period of energization, to control
application of electrical current having an amplitude
which varies continuously with time so that the element can
be operated at higher power levels without being overloaded.
As applied to an emitter of radiation in the optical spectrum,
for example, this circuit permits the emitter to be energized
at unparalleled power levels without thermal overload and,
as a consequence, heating of the emitter is controllable
to maintain a desired emitter temperature. Emitter temp-
erature is controllable by adjusting the frequency at which
the lntervals occur while the time period of eneryizationremains constant. In one disclosed, specific example,
the aforementioned intervals occur at a frequency o~ 53,000
` cycles per second with ~he time period of energization
being set at one microsecond~ The element, in this instance
a radiation emitter, may thus be energized at intervals
substantially shorter than one cycle of the alternating
current provided by a standard source of ~C power. In
` the circuit illustrated hereinaf-ter, the frequency at which
these intervals occur is controllable by appropriate
setting of -the output frequency of the square wave pulse
generator as determined by the resistance setting of variable
~` resistor. Thus, it is possible, by controlling the output
frequency of the square wave pulse yenerator, to control the
emitter temperature to suit specific applications. It will
be recognized that this invention may be used to energize
or control energization of other types of energy emitters
and electrical elements subject to overload problems.
According to one preferred embodiment of the
invention suited for but not limited to use with an emitter
of electromagnetic radiation in the optical spectrum, the
emitter is pulse driven by high current, low voltaye
electrical power of continuously varying amplitude, the
frequency and pulse width of which are controlled by pulse
frequency control means and pulse width control means,
respectively~ The pulse frequency control means preferably
include a generator for producing a square wave pulse sig-
nal of desired frequency, and the pulse width control
means preferably include a one-shot pulse ~enerator
- 30 operative in response to positive transition of the square
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wave pulse signal for controlling the duration of each
square wave pulse. The emitter additionally is mounted
by a suitable electrically cond~ctive case which con-
- stitutes one current path between
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a source of rectified direct current electrical power,
preferably a full wave bridge rectifier, and the emitter.
Thus, it will be appreciated from the foregoing
summary that this invention successfully overcomes fears
heretofore associated with peak power radiation emitter
operation. The frequency and width of the emitter drive pulse,
of course, may vary, depending upon the characteristics of the
particular emitter used and the available power source. l`he
selection of pulse frequency further could depend upon
additional factors, such as receiver efficiency (in those
applications in which the radiation emitter is used with a
separate receiver), desireability of pulse encoding with respect
to ambient radiation, etc. The choice of a particular
radiation emlkter likewise will depend upon the particular
application and, although optically emissive diodes which
emit a beam in the near-infrared, visible or infrared regions
of the optical spectrum, as the case may be, are suitable
~ for use in this invention, other types of radiation emitters
may be used, if desired. While pre~erably the emitter power
is deri:Ved from full wave rectified direct current electrical
: power, other power wave forms which yield continuously
varying power levels could be used if desired.
These and other features, objects and advantages
of the present invention will become apparent in the
detailed description and claims to follow taken in conjuncti.on
with -the accompanying drawings.
Brief Description of the Drawings
F.ig. 1 is an electrical circuit schematic of the
radiation emitting system of this invention.
Detailed Description of the Drawings
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The radiation emitting system of this invention
as deplcted schematically in Fig. 1 includes a radiation
emitter 10, and means for pulse driving the emitter with
electrical pulses of such frequency and width that the time
period during which the emitter is nonemissive is sufficiently
longer than the time period durin~ which it is emissive to
maintain a desired emitter temperature. ~he emitter is pulse
driven by full wave rectified direct current electrical power
of high current and low voltage, transmitted from a full wave
.: 10 rectifier bridge 12 via an electrically conductive case 14
which mounts -the emitter in electrically conductive relation
therewith. A power switching amplifier 11 pulses the emitter
on and off in response to control signals representative of
the frequency and pulse width of the drive pulses to be applied
to -the emitter. In the example, the control signals are
generated by a square wave pulse generator 16 and a one-shot
pulse generator 18, as will be described presently. In the
example, the radiation emitter is a commercially available
light emitting diode (LED) which generates an optical beam
in the ~ear-infrared, visible or infrared regions of the
optical spectrum, as the case may be. It will be recogni~ed,
of course, that other types o radiation emitters may be used .
in the present invention.
The illustrated system is designed for use with
conventional current supplies, for example 110 volt AC current
supplies, although it could be modified appropriately for use
with other current supplies, both AC and DC, if desired.
Incoming electrical power from the current source appears at
lines 20 and 22. A fuse 24 associa~ed with 1-ine.20 protects .-.
the system against intern~l short circuits and acts as a current
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l.imiting means with respect to the incoming line. A voltage
transient supresser 26 i5 connected electrically between
lines 20 and 22, as shown. Two step-down transformers
referenced generally by numerals 28 and 30, are connected
with their primary windings across lines 20 and 21, as ~hown.
The emitter is driven by electrical power derived
from transformer 30. The secondary winding of this trans-
former provides high current, low voltage electrical power
to the inputs 32 and 34 of bridge 12 which thereupon converts
10 the ~C power to full wave rectified direct current electrical
power of corresponding h.igh current and low voltage. One
bridge output 36 is connected with system ground 38. System
ground is connected by appropriate means (not shown) with
other grounded elements of the system, the other yround
connections being represented by the same symbol and reference
numeral. The other bridge terminal, and in this case the
positive bridge termlnal, referenced by numeral 40, is
connected electrically with case 14. This case mounts the
emitter and the various illustrated system elements. The
case is, in turn, connected electrically with the emitter
anode, as depicted schematically. In the example, the case
is composed of electrically conductive material and, therefore,
provides the positive current path or the full wave
rectified direct current electrical power from the bridge
terminal 40 to the emitter anode. With this construction,
it is possible to eliminate electrical insulation between
the case and emitter and, in this way, achieve highly
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; efficient heat transfer between the emitter and case.
Transformer 28 also derives alternating current
electrical power from the input lines 20 and 22. A full wave
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rectifier ~2 converts alternatlng current electrical power in
the secondary winding of this transformer to full wave
rectified direct current electrical power which is high
frequency filtered and stabilized in DC level by capacitors
44 and 46, respectivel~. A voltage regulator 48 then produces
an appropriate direct current voltage which is further filtered
and stabilized by capacitors S0 and 52, respectively, to yield
regulated DC control power on line 54. A diode 55 connected
in parallel with the voltage regulaLor, as shown, provides
a bypass ~or reverse voltage transient protection.
The control power present on line 54 is delivered
to the square wave generator 16 and to the one-shot pulse
generator 18. Variable resistor 56 and fixed resistor 57
selectively control the ~requency of the s~uare wave pulse
generator. The square wave pulse signal of selected frequency
which appears at -the output of the generator 16 is routed to
the generator 18. Generator 18 operates in response to each
positive transition of the incoming square wave pulse train
from generator 16 to deliver an appropriate control signal
to amplifier 11 for applying a pulse of controlled frequency
and width to emiJ,-ter 10, as will now be described.
A pulse amplifier transistor 58 is connected to the
output of the one-shot pulse generator via line 60 and reverse
blocking diode 61. The base of transistor 58 is connected
by a base pull-up resistor 62 with line 54, its collector
is connected by collector pull-up resistor 64 with line 54,
and its emitter is connected with ground, as shown. With
the illustrated construction, transistor 58 normally is held
in its conductive state in response to the voltage developed
by resistor 62. When the signal which appears at the output
, . . ~ ,. ~ .
o~ the one-shot pulse generator goes low, however, the tran-
sistor is rendered nonconductive, or is turned off. At this
time, the collector pull-up resistor 64 impresses a voltage
upon a capacitor 66 which initially speeds up coupling between
line 54 and -the base (referenced by numeral 67) of amplifier
11 by minimizing current draw and providing a high initial
current for fast turn on of amplifier 11. Thereafter,
resistor ~8 delivers current from line 54 and resistor 64 to
the base of the amplifier which, therefore, is now in its con-
ductive condition for completing the current path from bridge
12, via case 14, to the emitter 10, and thence to ground. An
additional resistor 70 connected to ground, as shown, also
aids in turn on of amplifier 11. Amplifier 11 turns off when
transistor 58 resumes its conductive state upon termination
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; of the one-shot pulse. The remaining posit.ive portion of the
square wave pulse is thus blocked. It will be recognized,
of course, that the inverted or hiyh output of the one-shot
is blocked by diode 61, and, hence is no-t utilized; however,
~ ~ by appropriate modification of the illustrated circuit,
-; 20 amplifier 11 could be switched in response to the high
output of the one-shot.
~ Amplifier 11 is connected with its collector in
- series with the cathode of emitter 10 and with its emitter
connected to ground, as shown. Amplifier 11 preferably is
a two stage power switching amplifier having high collector
current carrying capacity and sufficiently high gain to
allow turn on by very small magnitude currents, while pro-
viding desired emitter drive current. In the example, a
Parlington transistor constitutes amplifier 11, although
other appropriate amplifiers could be used.
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According to one specific application of the
invention, a commercially available radiation emitte~ manu-
factured by Texas Instruments Corporation and designated
model number TIL-31, was pulse driven in the Fig. 1 system.
In this application, a s~uare wave pulse generator frequency
~ of 53,000 cycles per second and a one-shot pulse of one micro-
; second yielded peak power operation of about 15 watts -- more
than ten times the manufacturer's recommended pulse operational
power level rating of the emitter -- for prolonged periods,
even at elevated ambient temperature The emitter range
was increased substantially when pulse driven in the Fig. l
system. The optical beam emitted was detectable at a range
about ten times the manufacturer's rated range. In this and
other applications, a shunt capacitor 72 may be connected
between the input terminals of bridge 12, as shown. In the
specific application enumerated herein, the capacitance of
- capacitor 72 is about .22 microfarads.
As will now be appreciated, the 53,000 cycle per
second pulse frequency produces pulses of widths substantially
` 20 greater than the one microsecond one-shot pulse which, as -
; - described herein, effectively controls the width of the drive
pulses applied to the emitter and in this way, the emissive
and nonemissive conditions thereoE with respect to a desired
emitter temperature. Furthermore, the power levels of
successive drive pulses will,-in the example system, vary
continuously with respec-t to pe~k power -- corresponding to
the full wave rectified power wave form. Thus, peak power
will be applied in only a portion of the drive pulses, the
remaining drive pulses applied being of reduced power levels;
however, sufficient numbers of drive pulses are applied at
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or near pea]c power to obtain acceptable power levels.
Al'~hough one preferred embodiment of the invention
has been illustrated and described herein, variations will
become apparent to one of ordinary skill ln the art.
Accordingly, the invention is not to be limited to the
specific embodiment illustrated and described herein and the
true scope and spirit of the invention àre to be determined
by reference to the appended claims.
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