GB1604888A

GB1604888A - Radiation emitting system

Info

Publication number: GB1604888A
Application number: GB19588/78A
Authority: GB
Original assignee: Wilkins and Associates Inc
Current assignee: Wilkins and Associates Inc
Priority date: 1978-05-15
Filing date: 1978-05-15
Publication date: 1981-12-16

Description

(54) RADIATION EMITTING SYSTEM (71) We, WILKINS & ASSOCIATES, INC., a company organised under the laws of the State of Washington, U.S.A., of 601, Alexander Avenue, Tacoma, Washington 98421, U.S.A., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a radiation emitting system and is illustrated and described herein with reference to a circuit for energizing an emitter of electromagnetic radiation.

Known radiation emitting systems include a radiation emitter, such as a light emitting diode (LED), 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 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 direct current system, disclosed in United States Patent No. 3,727,185, utilizes a silicon controlled rectifier (SCR) to switch the emitter. Still another system, disclosed in United States Patent No.

3,924,120, converts alternating current electrical power to 120 Hz square wave, the pulse width of which is controllable for information transmission to remote locations.

These and other radiation emitting systems are of limited power and, hence, tend to be short ranged, especially in dust filled or like environments. Although most commercially available semiconductor radiation emitters are capable of peak power operation for short time intervals, in most practical applications, both continuous or pulse operated, they are operated at average power levels well below peak power because of fears of excessive junction temperatures, and other factors. Thus the effectiveness of most radiation systems has been limited by unacceptably low emitter power levels, or emitter current limiting devices, or both. The effect tiveness of systems which use capacitative emitter charging elements is further limited by dielectric heating effects and capacitor charging time limitations.

According to a first aspect of this invention a radiation emitting system includes an electrically responsive energy emitter and a circuit for driving said emitter, the circuit comprising: means connected with said emitter for applying electrical power of continuously varying current amplitude to said emitter in pulses while simultaneously therewith determining the frequency and width of said pulses such that the time period during which said emitter is de-energized is sufficiently longer than the time period during which it is energized to maintain a desired emitter temperature.

According to a second aspect of this invention, there is provided a circuit for controlling the application of electrical current to an electrical element, which element has a maximum continuous power rating, the circuit comprising a source of electrical current which varies continuously with time, and a drive circuit including a switching device operable alternately to cause the application of the continuously variable current from the source to the element when the device is conductive, and to prevent current flow when the device is non-conductive, the drive circuit further including control means responsive to a repetitive trigger signal to initiate conduction of the switching device and to terminate the said conduction at a predetermined time period after conduction has begun, wherein the duration of the said time period is sufficiently short compared to the interval between successive trigger signals that the interval corresponds to at least a plurality of the said time periods, the amplitude of the said current being such that the peak power developed in the element is greater than the said power rating without damaging the element.

In a preferred embodiment of the invention the drive circuit includes a pulse frequency control device in the form of a clock pulse generator having an adjustable oscillation frequency. A square wave is fed from the output of this generator to the trigger input of a one-shot pulse generator to produce pulses of predetermined width for actuating the switching device. Alternatively, the clock pulses may be derived by squaring control pulses generated in synchronism with the variations in the supply amplitude, the clock pulses then being fed to a pulse-width determining circuit as described above.In this alternative embodiment, the control pulses, and therefore also the clock pulses, occur at a frequency which is sufficiently greater than the frequency of the supply amplitude variations that one cycle of the alternating current supply corresponds to a plurality of the said intervals between successive trigger pulses.

The invention will now be described by way of example with reference to the drawing, the single Figure of which is a circuit diagram.

The radiation emitting system of this invention as depicted 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 during which it is emissive to maintain a desired emitter temperature. The emitter is pulse driven by full wave rectified direct current electrical power of high current and low voltage, transmitted from a full wave 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 nearinfrared, visible or infrared regions of the optical spectrum, as the case may be. It will be recognized, of course, that other types of radiation emitters may be used in the present invention.

The illustrates 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 associated with line 20 protects the system against internal short circuits and acts as a current limiting means with respect to the incoming line. A voltage transient supresser 26 is connected electrically between lines 20 and 22, as shown. Two step-down transformers 28 and 30 are connected with their primary windings across lines 20 and 21, as shown.

The emitter is driven by electrical power derived from transformer 30. The secondary winding of this transformer provides high current, low voltage electrical power to the inputs 32 and 34 of bridge 12 which thereupon converts the AC power to full wave rectified direct current electrical power of corresponding high 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 ground connections being represented by the same symbol and reference numeral 38. The other bridge terminal, and in this case the positive bridge terminal, 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 for 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 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 rectifier 42 converts alternating 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, respectively. A voltage regulator 48 then produces an appropriate direct current voltage which is further filtered and stabilized by capacitors 50 and 52, respectively, to yield regulated DC control power on line 54. A diode 55 connected in parallel with the voltage regulator, as shown, provides a bypass for 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 frequency of the square 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 transi 0 tion 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 emitter 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 of the one-shot pulse generator goes low, however, the transistor 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 68 delivers current from line 54 and resistor 64 to the base of the amplifier which, therefore, is now in its conductive 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 of the one-shot pulse. The remaining positive portion of the square wave pulse is thus blocked. It will be recognized, of course, that the inverted or high output of the oneshot is blocked by diode 61, and, hence is not utilized; however, by appropriate modification of the illustrated circuit, 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 providing desired emitter drive current. In the example, a Darlington transistor constitutes amplifier 11, although other appropriate amplifiers could be used.

According to one specific application of the invention, a commercially available radiation emitter manufactured by Texas Instruments Corporation and designated model number TIL-3 1, was pulse driven in the Fig.

1 system. In this application, a square wave pulse generator frequency of 53,000 cycles per second and a one-shot pulse of one microsecond 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. 1 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 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 non-emissive conditions thereof with respect to a desired emitter temperature. Furthermore, the power levels of successive drive pulses will, in the example system, vary continuously with respect to peak 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 or near peak power to obtain acceptable power levels.

WHAT WE CLAIM IS: 1. A radiation emitting system including an electrically responsive energy emitter and a circuit for driving said emitter, the circuit comprising: means connected with said emitter for applying electrical power of continuously varying current amplitude to said emitter in pulses while simultaneously therewith determining the frequency and width of said pulses such that the time period during which said emitter is de-energized is sufficiently longer than the time period during which it is energized to maintain a desired emitter temperature.

2. The system of claim 1, further including electrically conductive case means mounting said emitter and constituting an electrical current path for transmitting said pulses thereto.

3. The system of claim 2, wherein said drive circuit includes means for converting alternating current electrical power to rectified direct current electrical power of high current and low voltage, and means for transmitting said direct current electrical power through said case means to said emitter.

4. The system of claim 3, wherein said

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. tion 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 emitter 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 of the one-shot pulse generator goes low, however, the transistor 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 68 delivers current from line 54 and resistor 64 to the base of the amplifier which, therefore, is now in its conductive 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 of the one-shot pulse. The remaining positive portion of the square wave pulse is thus blocked. It will be recognized, of course, that the inverted or high output of the oneshot is blocked by diode 61, and, hence is not utilized; however, by appropriate modification of the illustrated circuit, 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 providing desired emitter drive current. In the example, a Darlington transistor constitutes amplifier 11, although other appropriate amplifiers could be used. According to one specific application of the invention, a commercially available radiation emitter manufactured by Texas Instruments Corporation and designated model number TIL-3 1, was pulse driven in the Fig.

4. The system of claim 3, wherein said

means for converting alternating current electrical power to direct current electrical power includes a full wave rectifier bridge having two inputs, and a capacitor connected electrically between said bridge inputs.

5. The system of claim 1, wherein said means includes switch means triggerable by a trigger pulse for energizing said emitter while triggered, and control circuit means connected with said switch means for triggering said switch means, said control circuit means including a pulse frequency control device for controlling the frequency at which said switch means are triggered to cause said emitter to be energized at intervals, and a pulse width control device for causing said emitter to be energized commencing at each said interval for a predetermined time period less than one said interval, said pulse frequency control device including means for controlling the frequency at which said intervals occur such that each said interval corresponds to at least a plurality of said predetermined time periods.

6. The system of claim 5, wherein said pulse frequency control device includes means for generating a square wave pulse signal of desired frequency, and said pulse width control device includes one-shot pulse generating means interposed between said square wave pulse generating means and said switch means and operative in response to positive transition of said square wave signal for generating a trigger pulse which persists for said predetermined time period.

7. The system of claim 6, wherein said switch means include high gain switching amplifier means, and wherein said control circuit means include means responsive to a trigger pulse for switching said amplifier means.

8. The system of claim 7, wherein said control circuit means include means for converting alternating current electrical power to regulated direct current electrical power and applying such power to said square wave pulse generating means, said one-shot pulse generating means, and said switching amplifier means.

9. The system of claim 1, wherein said means includes means for causing said pulses to be applied to said emitter at intervals for a predetermined time period with the frequency at which said intervals occur being sufficient that each said interval correponds to at least a plurality of said predetermined time periods.

10. The system of claim 9, including means for varying the frequency at which said intervals occur.

11. The system of claim 1, wherein said means include means connectable to a source of alternating current electrical power providing electrical drive power in the form of a plurality of unidirectional drive pulses in synchronism with the alternating current for energizing the emitter, means including semi-conductor switch means triggerable by a trigger pulse for applying said drive power to the emitter to effect energization thereof while triggered, means connectable to the power source providing a plurality of unidirectional control pulses in synchronism with the alternating current, means squaring said control pulses to provide a plurality of unidirectional square wave pulses, square wave responsive trigger pulse means providing a plurality of trigger pulses for triggering said switch means at intervals to effect energization of the emitter, each said trigger pulse persisting for a predetermined time period, the frequency at which said intervals occur being sufficient that each said interval corresponds to at least a plurality of said predetermined time periods.

12. The system of claim 11, wherein said trigger pulse means provide a trigger pulse in response to positive transition of each said square wave pulse.

13. The system of claim 11, wherein the frequency at which said intervals occur is sufficiently greater than the frequency of the alternating current that one cycle of the alternating current corresponds to a plurality of said intervals.

14. The system of claim 1, wherein the emitter is an emitter of electromagnetic radiation in the optical spectrum.

15. A circuit for controlling the application of electrical current to an electrical element, which element has a maximum continuous power rating, the circuit comprising a source of electrical current which varies continuously with time, and a drive circuit including a switching device operable alternately to cause the application of the continuously variable current from the source to the element when the device is conductive, and to prevent current flow when the device is non-conductive, the drive circuit further including control means responsive to a repetitive trigger signal to initiate conduction of the switching device and to terminate the said conduction at a predetermined time period after conduction has begun, wherein the duration of the said time period is sufficiently short compared to the interval between successive trigger signals that the interval corresponds to at least a plurality of the said time periods, the amplitude of the said current being such that the peak power developed in the element is greater than the said power rating without damaging the element.

16. The circuit of claim 15, including means for controlling the frequency at which said intervals occur.

17. The circuit of claim 15, wherein said means include clock pulse means providing clock pulses which occur in synchronism with amplitude variations of the electrical current, and clock pulse responsive trigger pulse means for triggering the switch conductive at said intervals by application of a trigger pulse which persists for said time period.

18. The circuit of claim 17, wherein the source of electrical current provides alternating electrical current and further including means providing a plurality of unidirectional control pulses in synchronism with the alternating current, said clock pulse means including means squaring said control pulses to provide a plurality of unidirectional square wave pulses, and said trigger pulse means including means for triggering the switch conductive responsive to positive transitions of said square wave pulses.

19. The circuit of claim 18, wherein said square wave responsive means provide a trigger pulse in response to positive transition of each said square wave pulse.

20. The circuit of claim 18, wherein the frequency at which said intervals occur is sufficiently greater than the frequency of the alternating current that one cycle of the alternating current corresponds to a plurality of said intervals.

21. The circuit of claim 15, wherein the element comprises an emitter of electromagnetic radiation in the optical spectrum.

22. A circuit for controlling the application of electrical current to an electrical element, the circuit being substantially as herein described with reference to the drawings.