US 3591830 A
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United States Patent Inventor Samuel W. Woolsey Los Altos, Calif.
Appl. No. 762,933
Filed Sept. 26, I968 Patented July 6, 197 l Assignee Varian Associates 1 Palo Alto, Calif.
STARTING AND OPERATING CIRCUIT FOR GAS DISCHARGE LAMPS 5 Claims, 1 Drawing Fig.
US. Cl. 315/290, 315/100, 315/209, 315/227, 315/238, 315/241, 315/289 Int. Cl H05b37/00, H05b 39/00, H05b4l/14 Field of Search 315/100,
PULSATING 0.0. I VOLTAGE souncs References Cited UNITED STATES PATENTS 2,504,498 4/1950 Clack et al 315/104 3,471,747 10/1969 Geishen 315/205 2,557,809 6/1951 Willoughby 315/103 2,570,780 10/l95l Duckett et a1. 315/103 Primary Examinerlohn W. Huckert Assistant Examiner-B. Estrin Attorney-Stan1ey Z. Cole ABSTRACT: A starting and operating circuit for a gas discharge lamp is disclosed as comprising a vacuum switch adapted to be connected across a gas discharge lamp, a unidirectional conductor adapted to be connected across a direct current source, and an inductor, the vacuum switch, unidirectional conductor and inductor being connected in series circuit.
SWITCHING STARTING AND OPERATING CIRCUIT FOR GAS DISCHARGE LAMPS BACKGROUND OF THE INVENTION This invention relates generally to power supply circuits for I gas discharge lamps, and particularly to circuits for starting and operating high intensity short are lamps.
High intensity short are lamps typically comprise two electrodes spaced apart some 4 to mm. from each other to form an arc gap therebetween. The are gap is located in a vacuum tight envelope which confines an ionizable gas under pressure. To ionize the gas and breakdown the gap requires the impression of high voltage thereacross such as in the range of 5 to 30 kv. Once breakdown occurs, however, the arc gap impedance drops from infinity to a low value such as in the order of a few ohms. At this point only a relatively low voltage is required to cause sufficient current to flow across the arc gap to flash the lamp or to produce continuous luminescence. The ultimate goal here is to provide a power supply which most efficiently delivers these required voltages to the lamp.
Heretofore power supplies for gas discharge lamps have most frequently employed a spark gap to generate a high voltage pulse in breaking down the lamp. Representative examples of such are disclosed in US. Pat. Nos. 3,189,789, 3,250,953 and 3,323,015. Though capable of delivering a large quantity of pulse energy, such pulse is of radio frequency. This often creates electromagnetic interferences and interface problems between the lamp and power supply. Too fast a pulse rise time, for example, may lead to excessive voltage buildup between conductive elements of the lamps other than the starting electrodes. This may in turn lead to internal arcing between the anode and reflector or between external envelope members. Furthermore, the repeated impression of high voltage RF energy between thecathode and anode rapidly causes them to erode.
It therefore is a general object of the present invention to provide an improved circuit forstarting a gas discharge lamp, and to provide improved, combined circuits for both starting and operating such lamps.
Another object of the invention is to provide a starting circuit for a gas discharge lamp which does not require the use of high voltage RF energy.
Another object of the invention is to provide a small, lightweight power supply for a gas discharge lamp which does not require the use of relatively heavy electronic components such as transformers.
A more specific object of the invention is to provide an operating circuit for a gas discharge lamp which steps down the voltage delivered to the lamp without the use of stepdown transformers.
SUMMARY OF THE INVENTION Briefly described, the present invention is a starting and operating circuit for a gas discharge lamp comprising a vacuum switch, means for opening the vacuum switch, an inductor and a unidirectional conductor, the vacuum switch, inductor and unidirectional conductor being connected in series circuit. The vacuum switch is adapted to be connected across a gas discharge lamp. The unidirectional conductor is adapted to be connected across a direct current source without discharging the source therethrough. When the vacuum switch is closed and connected across the lamp, and the unidirectional conductor is connected across the direct current source, the inductor becomes charged. When the vacuum switch is opened the charged inductor impresses a starting voltage across the lamp. After starting the inductor may serve to integrate the continuous, direct lamp-operating current.
BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic diagram of the preferred embodimentof the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in detail to the drawing, there is schematically illustrated a high intensity short are lamp L such as the I50X8P xenon short are lamp sold by the Eimac Division of Varian Associates, The lamp is connected across capacitor 1 and a vacuum switch S such as the VS-8-type which likewise is manufactured and sold by Eimac. Switch S is in turn connected through switch actuating coil 2 and the switching current regulator indicated in block form across the pulsating direct current voltage source which likewise is indicated in block form.
The pulsating direct current voltage source consists of a pair of input terminal leads 3 and 4 which are connectable, to a source of alternating current which is schematically illustrated as being sinusoidal in waveform. Input terminal leads 3 and 4 are respectively connected to the input terminals of bridge rectifier 5. The bridge rectifier provides full wave'rectified, pulsating DC voltage across output terminal leads 6 and 7 of the source which voltage is smoothed by capacitor 8 which is connected across the output terminal leads.
The switching current regulator comprises switching transistor 10, the collector of which is connected to output terminal lead 6 of the pulsating direct current voltage source. The emitter of the switching transistor is connected through current sampling resistor I I to regulator output lead 16 which in turn is connected to switch S. The base of the switching transistor is connected to the output of feedback amplifier A which has two input leads l2 and 13 connected across resistor 11. For sake of clarity, the power supply for amplifier A has not been shown.
Output terminal lead 7 of the pulsating direct current source is connected through inductor 1 4 to regulator output lead 17 which in turn is connected to switch S. Output terminal lead 7 is also connected through diode 15 to feedback amplifier input lead 12. 1
When input terminal leads 3 and 4 are connected to source of alternating current with switch 8 closed, the source current is converted by full wave bridge rectifier 5 into pulsating direct current which pulses are smoothed by capacitor 8 and delivered to the switching current regulator. Current flows through switching transistor 10, resistor 11, closed switch S, and inductor 14 of the regulator which thereby becomes charged with energy through the establishment of a strong magnetic field generated by the current in the induction windings. When current through current sampling resistor II of the switching current regulator reaches a predetermined upper level, feedback amplifier A, in sensing voltages across input leads 12 and I3, amplifies the voltage drop across the resister to a level sufficient to send a cutoff signal to switching transistor 10. With switching transistor 10 now open, inductor l4 discharges through the loop consisting of inductor I4, diode l5, resistor 11, switch actuating coil 2 and vacuum switch S. The current through actuating coil 2 is sufficient to cause the vacuum switch to open. When the contacts of the vacuum switch S have separated to such a degree that the current through the contacts is interrupted, the current is diverted to charging capacitor 1. The voltage across parallel elements capacitor I, switch S and lamp L increases with time directly with current and inversely with the value of the capacitance being charged. With switch S open, the voltage induced by inductor 14 across lamp L rises rapidly to that required for lamp gas breakdown to occur. When the gas in lamp L breaks down the resistance between the two lamp elec-- trodes drops drastically. Arcing then occurs between the lamp electrodes and the lamp goes into continuous conduction. Capacitor 1, although not required, has been connected across the lamp to control the rise time of the voltage impressed across the lamp.
It should be appreciated that the illustrated circuit is oneof a complete though basic power supply. Thus inductor 14in the switching current regulator serves the described role of storing and discharging lamp starting energy and also of integrat ing the lamp operating current. Nevertheless, it also should be understood that the scope of the invention is limited solely by the concluding claim herein, and not to conjunctive use with the disclosed or anyother switching current regulator. Where the invention is used solely as a starter or pulser without a complete switching current regulator, a small ballasting resister, having a value such as l ohm, may be required in series with the DC source and lamp. Furthermore, though vacuum switch S has been actuated by means of coil 2 in the described embodiment, alternative switch actuating means may be used, such as those types which are manually actuated,
The actual value of components usedin the illustrated embodiment are listed below in Table 1:
TABLE l Current Source Value in Volts Q rs Bridge Rectifier Type 5 Motorola MDA-952-3 Switching Transister Type l (3,) Delco DTS-430 Diode Type IS IN 3891 Inductor Value in millihenries Capacitor Value in microfarads Resistor Value in Ohms Vacuum Switch Ty e S Eimac VS-E Are Lamp Type L Eimac ISOX 8P lclaim:
l. A current regulating and starting circuit for connection between a source of direct current and an arc discharge device to be supplied with energy from said source, comprising in combination: a first current gating means having first, second and third terminals, said first gating means providing a low impedance between said first and second terminals in response to current from said second to said third terminal when said current is below a first preselected level, and providin a high impedance between said first and second terminals w en said current exceeds said preselected level; a second current gating means having fourth, fifth and sixth terminals, said second gating means providing a low impedance between said fifth and sixth terminals in response to current between said fourth and fifth terminals below a second preselected level and a high impedance between said fifth and sixth terminals in response to current between said fourth and fifth terminals above said second preselected level, said second preselected current level being higher than said first level; an inductor; and a unidirectional conductor means having seventh and eighth terminals and providing a low impedance to currents from said seventh to eighth terminals and a high impedance to currents from said eighth to seventh terminals; said third terminal being connected to said fourth terminal, said inductor being connected between said sixth and seventh terminals, said eighth terminal being connected to said second terminal, said first and seventh terminals being input terminals for connection to said source of direct current, and said fifth and sixth terminals being output terminals for connection to said are discharge device.
2. The circuit of claim 1 wherein said first current gating means comprises a transistor having its collector connected to said first terminal and its emitter connected to said second terminal, a sampling resistor interconnecting said second and third terminals and a feedback amplifier having its input connected across said resistor and its output connected to the base of said transistor.
37 The circuit of claim 1 wherein said second current gating means comprises a switch connected between said fifth and the rate of change of voltage between said fifth and sixth terminals.
5. The circuit of claim 1 further including a full wave bridge-type rectifier circuit having a pair of DC output terminals connected between said first and seventh terminals and having a pair of AC input terminals for connection to a source of alternating current.