US3544840A - Voltage multiplier power supply for gas-discharge lamps - Google Patents

Description

G. P. SAIGER Dec. 1, 1970 VOLTAGE MULTIPLIER POWER SUPPLY FOR GAS-DISCHARGE LAMPS Filed Sept. 26, 1968 -V INVENTOR seems I. swam US. Cl. 315-205 11 Claims ABSTRACT OF THE DISCLOSURE A compact power supply system for a gas-discharge lamp such as a xenon tube, employs a transformerless voltage multiplier of the capacitor-rectifier type and a pulse trigger circuit to provide continuous light emission from the lamp.

The present invention relates to gas-discharge type light sources, and particularly to a power supply for operating such light sources to provide continuous light emission therefrom.

The general use of gas-discharge type light sources or lamps, such as xenon tubes, for various strobe and other illuminating functions is well known. For example, in the photography field, such lamps are commonly em: ployed in conjunction with a trigger-pulse power supply to provide high intensity light flashes of extremely short duration. However, in certain types of photography work it is sometimes necessary or desirable to maintain such a high level of illumination continuously rather than in the form of a short duration flash. Although continuously illuminated xenon lamps have been employed for such purposes, the power supplies necessary to satisfactorily operate such lamps were typically extremely large and heavy, weighing up to 100 pounds, because of the large for various kinds of color photography work, since their spectral emissions are generally characterized by certain predominant color wavelengths which are not suited for this purpose. For such color photography work an emission spectrum producing more nearly White light is preferred, and the spectrum of a xenon discharge lamp is satisfactory and a desired source of illumination but for the serious power supply disadvantages normally attendant its use. Additionally, this light emission is useful for other purposes as well.

Accordingly, it is an object of the present invention to provide an improved power supply for operating light sources of the gas-discharge type which is of relatively small size and weight so as to form an inexpensive and compact unit which can be disposed within the housing typically utilized for such a lamp itself.

It is a further object of the invention to provide such a power supply which may be reliably operated from a relatively large range of line voltages and line frequencies.

These and other objects of the invention are more particularly set forth in the following detailed description and in the accompanying drawings, of which:

FIG. 1 is a schematic diagram showing a circuit in United States Patent 0 accordance with a preferred embodiment of the present invention; and

FIG. 2 is a schematic diagram of multiple light source assembly which may be used in conjunction with the power supply of FIG. 1 for operation at a higher line voltage.

Generally, referring to FIG. 1, there is shown a power supply system 10 for operating a gas-discharge light source, illustrated as xenon lamp 12, from an A.C. source on lines 14 and 16, representing a conventional supply main. The system 10 comprises non-inductive, i.e, transformerless, voltage multiplier means, illustrated as a voltage quadrupler circuit 18, having input and output terminal leads 20-21 and 22-23 for respective connection to the A.C. source on lines 14 and 16 and the gas-discharge lamp 12. The voltage multiplier means includes circuit means for providing a DC. no-load or substantially open voltage at the output terminals 22 and 23 which is sufliciently high to cause a current discharge through the lamp 12 subsequent to an initial ionization thereof, but not so high as to cause this current discharge absent such initial ionization of the lamp. Triggering means, illustrated as circuit 24, generates and applies, via trigger electrode 26, a trigger pulse field to the lamp 12 for producing the initial ionization to start the current discharge therethrough, and a pulse generator circuit 27 is provided for firing the triggering circuit 24. The multiplier means 18 provides a further output at terminal leads 28 and 29 which supplies an operating voltage to both the triggering and pulse generator circuits 24 and 27 prior to the current discharge through the lamp 12, but which automatically disables these circuits after the current discharge occurs by a reduction in the operating voltage to approximately zero or some other disabling value.

A double-pole main power switch 30 is serially connected in the A.C. lines 14 and 16 for selectively applying the line voltage to the power supply system 10 by means of internal A.C. leads 32 and 34, and protective fuses 36 and 38 in each respective lead. A ground lead 39 may be provided for reasons of safety. A fan or blower 40 is desirably connected across the A.C. leads 32 and 34, and upon closure of the main power switch 30, the blower 40 is energized to provide forced convection cooling of the xenon lamp 12. A single-pole light control switch 42 is connected in series in the A.C. lead 34, and controls the application of the line voltage to the voltage multiplier circuit 18 which supplies the required high voltage DC at terminals 22 and 23 for operating the lamp 12 subsequent to its being initially ionized or triggered, and which also supplies the operating DC. voltage across leads 28 and 29 for the lamp triggering circuit 24 and for the firing or pulse generator circuit 27 which actuates the trigger circuit 24. Consequently, upon the closing of the light control switch 42, the firing circuit 27 actuates or fires the trigger circuit 24, which, in turn, applies the appropriate high voltage impulse or transient at its output terminal 43 to the trigger or tickler electrode 26 located adjacent or in proximity to the lamp 12. The electric field produced by the trigger electrode 26 causes suflicient ionization of the xenon gas within the lamp 12 to permit the high DC. voltage across terminals 22 and 23 to provide a current discharge through the lamp, producing the light emission therefrom. Once the lamp 12 is conducting, the voltage thereacross at terminals 22 and 23 decreases to a substantially lower value, as determined by the voltage break down characteristics of the lamp, and the operating voltage across supply leads 28 and 29 decreases to approximately zero, automatically deactivating the firing circuit 27 and the trigger circuit 24 so that no further trigger impulses are supplied to the trigger electrode 26. Thus, the xenon lamp 12 remains in its illuminating or lighted condition until it is turned off, at will, by opening of the light control switch 42, which cuts off the current supply to the lamp 12 so that the gas therein becomes deionized to its normal state.

More particularly, the voltage multiplier circuit 18, in the illustrated embodiment, is a rectifier bridge 44 having four rectifier branches with one or more diode rectifiers therein, preferably being of the semi-conductor type, and operated in conjunction with a capacitor network to form a voltage quadrupler. The A.C. input nodes 46 and 48 of the bridge 44 are connected directly across the A.C. line voltage which is applied via leads 32 and 34- when the light control switch 42 is in its closed condition. The bridge 44 has a positive DC. output node '50 which is connected directly to the positive output terminal 22 of the multiplier circuit 18, and a negative DC. output node 52 which is connected directly to the DC. output terminal 23, as well as to the DC. reference leads 28 which supplies the firing and trigger circuits 27 and 24, respectively. Rectifier diodes 54 and 56 are each connected, respectively, between the A.C. input node 48 and the positive and negative D.C. nodes 50 and 52. Series connected rectifier diodes 58 and 60 are connected between the other A.C. input node 4 6 and the positive D.C. node 50, while a further pair of series connected diodes 62 and 64 are connected between the same A.C. node 46 and the negative D.C. node 52. All of the rectifier diodes are poled as shown in FIG. 1 so that the A.C. from the line is rectified to provide the polarities described. The capacitor network is formed by a first pair of capacitors 68 and 70 which are each connected, respectively, from a common junction at A.C. input node 48 to the junction of each pair of diodes 58, 60 and 62, 64, and a second pair of capacitors 72 and 74 which are each connected, respectively, from a common junction at the other A.C. input node 46 to the positive and negative D.C. nodes 50 and 52.

With this circuit configuration, an input line voltage of 120 v. at 60 c.p.s., and with the terminals 22 and 23 effectively open circuited (i.e., prior to the triggering of the lamp 12), the multiplier circuit 18 provides a potential of about 600 volts D.C. across terminals 22 and 23, as shown at 75, and a positive potential of about 100 volts on supply lead 29 to the triggering and firing circuits 24 and 27. This latter voltage on lead 29 is taken between diodes '62 and 64 of the bridge 44 and is applied to the triggering circuit 24 through resistor 76 to a trigger capacitor 78 to charge the trigger capacitor in a time determined principally by the time constant or product of the capacitance and resistance of these components. A trigger transformer 80 has its primary winding 80a connected in series with the load terminals (i.e., the anode and cathode) of a silicon controlled rectifier (SCR) 82, and the series combination is connected in shunt across the trigger capacitor 78. The SCR 82 is poled so that the voltage produced by the charge build-up on the trigger capacitor 78 causes it to be forward biased, although it is normally non-conductive until triggered by an appropriate signal on its gate or control terminal 84. The secondary winding 80b of the transformers 80 has one end connected to the common junction of the anode of the SCR 82 and the primary winding 80a, and the other end of the secondary winding 80b is connected to trigger terminal 43 which is adapted to be connected to the trigger electrode 26 through a connecting lead 86-.

The pulse generator firing circuit 27 is also supplied by the 100 volts on lead 29, which is applied through resistor 88 to capacitor 90. A four-layer or Shockley diode 92 is connected, as shown, between the resistor-capacitor junction and the control terminal 84 of the S'CR 82 so as to be reverse biased by the voltage developed across the capacitor 90. The operating characteristic of the four-layer diode 92 has a negative resistance region which causes this circuit to produce an oscillating sawtooth signal 94 across the capacitor 90, since the circuit functions as a relaxation oscillator. The time constant of the oscillator circuit is determined primarily by the values of the resistor 88 and the capacitor which are preferably chosen to provide an operating frequency of about 1000 hertz. A switching effect is produced by the four-layer diode 92 and thus the output of the firing circuit 27 at the SCR gate 84 is in the form of DC. pulses having a repetition rate of 1000 pulses per second, as shown at 96.

In operation, as the charge builds up on the trigger capacitor 78, the forward voltage across the SCR 82 increases until a sufliciently high voltage is reached to achieve proper triggering, at which time one of the pulses 96 fires the SCR 82. The charge on capacitor 78 then abruptly discharges through the low impedance path formed by the transformer primary winding 80a and the SCR 82, causing an extremely high voltage transient to be generated by the secondary winding 80b at the trigger electrode 26, the field fromwhich lowers the break-down voltage of the flash tube 12 so that the 600 volts thereacross discharges therethrough to produce a light emission. The lamp 12 then loads the multiplier circuit 18 so that it functions as merely a full-wave rectifier, and a full-wave rectified waveform appears across the output terminals 22 and 23 at a reduced voltage of about 165 volts, as shown at 75. The multiplier circuit supplies sufiicient current from the supply lines to the lamp 12 to sustain conduction, and the lamp 12 remains illuminated until the current supply thereto switched off by the opening of the control switch 42.

Also, upon the occurrence of this initial current discharge, the positive 100 volts DC. on the operating supply lead 29 becomes approximately zero, and this automatically disables the triggering circuit 24 and the firing circuit 27 from operating. Thus, during the condition of lamp conduction, high voltage pulses are not produced at the trigger electrode 26. This materially reduces any potential danger to personnel from the high-voltage pulses, and in addition, eliminates the ozone generation which may occur from the presence of such high voltage pulse potentials.

With respect to the detailed operation of the illustrated voltage-quadrupler circuit 18, the output voltage of 600 volts -D.C. across the terminals 22 and 23 is approximately four times greater than the peak line voltage on input leads 20 and 21. An output voltage of this magnitude is present, however, only with the lamp in its off condition, as previously mentioned. In operation, when the input line voltage on lead 20 is positive and the voltage on lead 21 is negative, a current flows through diode 60 and charges capacitor 68 to a value approximately equal to the peak line voltage. The polarity of the charge on capacitor 68 is such that when the next alternation occurs, i.e., when lead 21 becomes positive and lead 20 becomes negative, the line voltage will then add to the voltage across capacitor '68, causing diode 58 to conduct. Capacitor 72 will then be charged to a value approximately twice the peak line voltage. At the same time, the diode 62 conducts, charging capacitor 7 0 to approximately the peak line 'voltage. On the next alternation, lead 21 is negative and lead 20 is positive, so that the line voltage adds to the voltage across capacitor 70. The cathode of diode 64 then becomes negative with respect to its anode, causing it to conduct and to charge capacitor 74 to a value approximately twice the peak line voltage. Since the anode of diode 60 is now positive, diode 60 conducts and again charges capacitor 68. Thus, the total voltage appearing across the output terminals 22 and 23 of the circuit 18 is the sum of the voltages existing across the capacitors 72 and 74, which is approximately four times the peak line voltage.

The capacitors in the circuit serve effectively to filter the no-load voltage to obtain the constant 600 volt level illustrated at 75; however the output voltage may assume the rectified full-wave reduced voltage waveform once the lamp 12 is conducting, as previously mentioned. In

this connection, the diodes 54 and 56 are alternately conductive until the capacitors 72 and 74 each have the double peak voltage thereacross, after which they may be blocked by these voltages. However, when the lamp 12 conducts, the capacitors are loaded sufiiciently to substantially preclude the voltage addition action, and the diodes 54 and 56 then operate in conjunction with the other diodes to form a full-wave rectifier bridge.

Where a line voltage of 220 volts is to be used instead of the 120 volts previously described, xenon lamps having the same rating as lamp 12 may be employed with the system of FIG. 1 by connecting two such lamps in the circuit configuration illustrated in FIG. 2. As there shown, two lamps 12a and 12b, each identical to the lamp 12 of FIG. 1, are connected in series. Additional capacitors 98 and 100 are each respectively connected in shunt across each of the lamps 12a and 12b. This circuit combination of lamps and capacitors is then adapted to be connected across the output of the multiplier circuit 18 through terminals 22 and 23, shown in FIG. 1. Trigger electrodes 26a and 26b are located in proximity to each respective lamp 12a and 12b and are connected in parallel. The parallel trigger electrodes 26a and 26b are adapted for connection to the trigger terminal 43, via lead 86a.

Thus, there has been described a lightweight and compact light source power supply system for gas-discharge tubes, having extremely great flexibility of use because of its being operable from a wide range of line voltages at line frequencies from 50 to 400 hertz. This represents a significant advantage over power supplies employing large power transformers to supply the necessary high voltage across the lamp electrodes, while still having the necessary current supply capacity for continuous operation, since operation of such transformer supplies at frequencies substantially different from the rated frequency may result in circuit inoperativeness and, in certain instances, transformer failure. Although the voltage multiplier means in the system of the present invention only provides a high DC. voltage across the lamp prior to its conduction, such high voltage D0. is actually only necessary at this time. and the loss of this high voltage after lamp conduction is no disadvantage since the system has the capability of supplying sutficient current to continuously sustain the gas ionization within the lamp for continuous light emission at a substantially reduced voltage. Additionally, the use of the firing and trigger circuits provide reliable starting of the lamp, since these circuits will provide repetitive trigger pulses to the lamp until the lamp fires. Immedi ately thereafter, however, these circuits are automatically disabled by the action and loading characteristics of the lamp on the voltage multiplier circuit.

Although, the illustrated system utilizes a voltagequadrupler circuit, other multipliers may, of course, be employed, depending generally on the specific lamp ratings and source voltage.

Various modifications of the present embodiment will be apparent to those skilled in the art; and accordingly the present invention should be defined only by the appended claims, and equivalents thereof.

Various features of the present invention are set forth in the following claims.

What is claimed is:

1. A power supply system for continuously operating a gas-discharge lamp from an A.C. line source, comprising a non-inductive type of voltage multiplier means having input and output terminals for respective connection to the A.C. line source and the gas-discharge lamp, said voltage multiplier means including means for providing a DC. voltage at said output terminals which is sufliciently high to cause a current discharge through the lamp subsequent to an initial ionization thereof, but not so high as to cause said discharge absent said initial ionization, triggering means including a trigger electrode disposed in proximity to said lamp for applying a trigger pulse field to the lamp to produce said initial ionization, and said multiplier means including means for supplying to the lamp, after the initial current discharge therethrough, rectified current from said line source of sufiicient magnitude to sustain the discharge at a reduced voltage so as to provide continuous light emission from the lamp.

2. The system of claim 1 wherein said voltage multiplier means has further output terminals, said system further comprising means coupling said triggering means to said further output terminals of said non-inductive voltage multiplier means for operation of said triggering means, said multiplier means comprising means for automatically altering the voltage at said further output terminals to disable said triggering means on the occurrence of the current discharge through the lamp.

3. The system of claim 2 wherein said triggering means comprises charge storage means and switching means coupled to said storage means for causing said triggering pulse field to be produced, said system further comprising a pulse generator for actuating said switching means after sufficient charge has been stored for effective triggering of the lamp.

4. The system of claim 3 wherein said pulse generator comprises means for providing pulses to said switching means at a rate substantially higher than the frequency of the A.C. source.

5. The system of claim 3 wherein said pulse generator is coupled to and energized by said further output terminals of said multiplier means so as to be disabled thereby on the occurrence of the current discharge through the lamp.

6. The system of claim 3 wherein said charge storage means includes a capacitor and said switching means includes a controlled semiconductor switching device having two load terminals and a control terminal, said triggering means further includes a trigger transformer having its primary winding serially connected with the load terminals of the switching device and the combination being conected across the capacitor, and said pulse generator comprises a relaxation oscillator having its output coupled to the control terminal of said switching device.

7. The system of claim 6 wherein said relaxation oscillator is coupled to and energized by said further output terminals of said multiplier means.

8. The system of claim 2 wherein said multiplier means comprises a rectifier bridge having a first rectifier diode forward coupled between one A.C. input terminal and the positive D.C. output terminal, a second rectifier diode reverse coupled from said one A.C. input terminal to the negative DC. output terminal, third and fourth series connected rectifier diodes forward coupled from said other A.C. input terminal to the positive DC. output terminal, fifth and sixth series connected rectifier diodes reverse coupled from said other A.C. input terminal to the negative DC output terminal, and a capacitor network comprising first and second capacitors each respectively connected from said one A.C. input terminal to the junction of the third and further diodes and the junction of the fifth and sixth diodes, and third and fourth capacitors each respectively connected from said other A.C. input terminal to the positive and negative DC output terminals.

9. The system of claim 8 wherein each of said further output terminals comprises, respectively, means connected to the junction between said fifth and sixth diodes and means connected to said negative DC. output terminal.

10. The system of claim 9 further comprising pulse generating means coupled to said further output terminals for firing said triggering means.

11. The system of claim 1 wherein said voltage multiplier means comprises a rectifier bridge and capacitor means interconnected with said rectifier bridge to provide a DC. voltage at said output terminals which is a multiple References Cited UNITED STATES PATENTS Germeshausen 3 15-241 Meyer et a1 321-l5 Edgerton et a1. 315241 Michalski 315'-289X I} 3,259,830 7/1966 Ojelid 321 21 3,466,500 97 1969 Peek '315-289X 3,467,849 9/19619 Wilson 321-15 JOHN KOMINSKI, Primary Examiner C. R. CAMPBELL, Assistant v Examiner .U..s. c1. X.R.

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