US 3309567 A
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Description (OCR text may contain errors)
March 14, 1967 R. A. FLIEDER ETAL 3,309,567
PULSE DISCHARGE LAMP CIRCUIT 3 Sheets-Sheet l Filed Got. 22, 1965 March 14, 1967 R. A. Ful-:DER ETAL PULSE DISCHARGE LAMP CIRCUIT 3 Sheets-Sheet 2 Filed OGt. 22, 1965 INVENTORS ROBERT A, FLM-DEI? United States Patent Oice 3,39,557 Patented Mar. 14, 1967 3,309,567 PULSE DISCHARGE LAMP CIRCUIT Robert A. Flieder, Fords, NJ., and Maksymilian A. Miehalski, Woodside, NX., assignors to Berkey Photo, lne., New York, NX.
Filed Oct. 22, 1965, Ser. No. 511,270 7 Ciaims. (Cl. 315-176) This application is a continuation in part of applications S.N. 45,195, tiled July 25, 1960, now abandoned, and SN. 214,791, tiled July 27, 1962.
The present invention relates to starting circuits for an electric discharge lamp of the type using a pulsed waveform.
The discharge lamp, also called a ashtube, is an elongated quartz tube having self-heating electrodes at opposite ends, and contains an inert rare gas such as xenon at a pressure not exceeding atmospheric. ln order to obtain a high light output in proportion to the energy input, it is important that the lamp have a high instantaneous loading such as by supplying it with alternating current through the main winding of a saturable reactor in series with the lamp. The reactor includes a high permeability high-saturation flux density magnetic core material having a generally rectangular hysteresis loop characteristic. Below saturation a low magnetizinfT current flows through the lamp to continue ionization thereof between high current pulses, and thus the high current pulses may be of the same voltage as that necessary to maintain conduction through the lamp.
The discharge through the lamp is initiated by applying a pulse superimposed upon the voltage applied to the terminals of the lamp. It has been found convenient to apply this pulse to an auxiliary winding on the saturable reactor. Heretofore, the pulse has been produced by a circuit connected to the alternating current supply, and peaked by using a small saturable reactor in series with the supply to the auxiliary winding. A low turn ratio is used in the auxiliary winding; thus there is a large stepup in the voltage ofthe starting pulse.
In accordance with the present invention, the discharge through the lamp is initiated by imposing high frequency damped oscillatory pulses on the auxiliary winding of the saturable reactor. These damped oscillatory pulses are in the kilocycle to megacycle range and may occur at the rate of from two to ten for each cycle of the operating frequency, and thus produce two or more pulses of damped oscillations during each half cycle of the supply voltage.
The system in accordance with the invention is particularly advantageous in the event that the lamp is operated from a low voltage supply such as 250 volts as a more economical construction results with great dependability of starting.
Other objects and advantages of the invention will be apparent from the following description and from the accompanying drawings which show, by way of example, embodiments of the invention.
In the drawings:
In FGURE 1 there is shown diagrammatically a discharge lamp with an operating circuit embodying the invention.
In FGURE 2 there is shown a somewhat modied circuit in accordance with the invention.
ln FIGURE 3 there is shown a waveform ofthe circuit of FIGURE 1.
1n FEGURE 4 there is shown a waveform of the circuit of FIGURE 2.
In FGURE 5 there is shown another embodiment of the invention.
Referring to the drawings there is shown in FIGURE l a circuit for an electrical system in which a discharge lamp or iiashtube 10 is connected in series with a saturable reactor 11 connected in series with a current limiting reactance or impedance 14 across an alternating current supply of generally sinusoidal waveform through a variable tap autotransformer 15, and a capacitor 12 is connected across the series connected saturable reactor 11 and the flashtube 10.
A starting circuit is provided by a cold cathode tube 16 connected across a triggering capacitor 17 in series with an auxiliary winding 19 of the saturable reactor 11. A keep-alive resistance 2i) is connected to a rst grid 21 of the thyratron 16, and an RC circuit including a resistor 22 in series with a capacitor 24 has its mid-point 25 connected to a second grid 26 of the thyratron 16. The current input to the starting circuit is limited by a series reactance or impedance 27. A direct current power supply is provided by selenium rectiiiers 29 and 30 connected to capacitors 31 and 32 in a voltage doubling circuit. The supply for the voltage doubling circuit is taken from end tap 15a of the autotransformer 15 so that about 350 volts is provided. If desired a time delay switch 34 may be connected in the power supply to disconnect the starting circuit after a predetermined starting interval.
The discharge lamp 10 is formed of an elongated quartz envelope 40 containing an inert rare gas of relatively high atomic weight such as xenon at a pressure not exceeding atmospheric. A pair of self-heating electrodes 41 and 42 are provided at opposite ends of the tube 40.
The saturable reactor 11 is formed of a core of grain oriented silicon steel with a main winding thereon. The saturable reactor is so designed and proportioned with respect to the capacitor 12, as is well known in the art, that the saturable reactor reaches saturation during every half cycle of the supply to energize the lamp with high current pulses and to provide a residual current to maintain ionization of the lamp between the pulses.
The current limiting reactance or impedance 14 is a non-saturating reactor of appropriate impedance. Alternativ-ely, a resistance might be used instead of the reactor, but the etiiciency of the system would be less. The autotransformer 15 is provided with a plurality of taps 44 for connection to systems varying between 200 and 250 volts, it being preferable to select one of the taps 44 for connection to a system so as to provide an output of about 250 volts across the outer terminals of the autotransformer.
In the operation of the electric system it is connected to a source of alternating current, potential being applied across electrodes 41 and 42 of the discharge lamp 10. Inasmuch as the discharge lamp inherently has a characteristic wherein the required starting voltage is greater than the operating voltage, the lamp will not ilash over until ionization of the gas is initiated by a triggering pulse from the starting circuit. In order to provide starting pulses, rectified direct current is applied across the RC circuit of resistance 22 and capacitance 24. The -frequency of oscillation of this circuit may be varied by appropriate selection of the values of the resistance and capacitor as is well known in the art. The RC circuit causes discharges of the cold cathode tube 16 at a pulse rate of approximately -600 pulses per second. The discharges of the cold cathode tube 16 cause the discharge of the capacitor 17 through the winding 19. These discharges are pulses of high frequency damped oscillations superimposed upon the supply voltage at the electrodes of the discharge lamp, and because of the turn ratio of the winding 19 with respect to that of main winding 43 of the saturable reactor 11, a greatly increased peaked starting voltage of high frequency is applied to the electrodes 41 and 42, resulting in ionization of the gas, and continued dashing thereof under the normal potential supplied in series with the winding 44 of the saturable reactor 11. The waveform of the voltage applied to the electrodes 41 and 42 for the circuit of FIGURE l, before the lamp is ionized, is indicated at 50 in FIGURE 3, while the effective envelopes of the damped oscillations is indicated at 51.
It will be seen that the discharge lamp is triggered by imposing a series of high frequency damped oscillatory pulses on the auxiliary winding 19 of the saturable reactor 11. The high frequency oscillatory pulses result from the discharge of the condenser 17 through the thyratron 16 and the auxiliary winding 19. The thyratron is rendered conductive by discharges of the RC circuit at a rate or `frequency determined by its constants, desirably at a frequency of from two to ten times the rate of the lamp operating frequency, the preferred frequency of the RC circuit discharges being from 200 to 400 per second. The lower rate of pulse is preferable because it produces a sutiicient amount of distributed damped oscillations or pulses over the peak of the 60 cycle wave. A higher frequency would be unnecessary and would require a higher capacity direct current power supply.
A system manufactured commercially and found to operate satisfactorily employs constants for the various circuit elements as follows: The size of capacitor 12 in combination with the supply voltage determines the loading or watt input into the lamp. For a 2000 watt discharge lamp 10, and a voltage of 250 volts 60 cycle A.C., a suitable value for capacitor 12 is 84 mfd. in which event the current limiting impedance 14 may be about 50 millihenries. The saturable reactor includes a main winding (43) of about 200 turns of No. 9 square wire Wound on matching U-shaped core sections of grain-oriented silicon steel, the core having approximate cross sectional dimensions of 2" in width by 1 in thickness, the window of the core being about 4 by 1". The cold cathode thyratron 16 is a Type OA-5. The triggering capacitor 17 is 0.5 mfd. The winding 19 being such as to produce between 5 and 10 thousand volts peak across the electrodes 41 and 42. The keep-alive resistor 20 is 10 megohms, resistor 22 is 5 megohms and the capacitor 24 is 0.001 mfd. The current limiting choke or reactance 27 is between 3 and 5 henries. The capacitors 31 and 32 of the power supply are 2.0 mfd. each. The rectiers 29 and 30 are selenium rectifiers. While the starting circ-uit may be continued in operation continually, in order to increase the life of the tube 16, it may be preferable to insert a time delay switch 34 in the supply for the direct current power supply. This time delay may have any desired operating time although it has been found unnecessary to have the starting circuit operate more than a few cycles. Automatic cut-in means may be provided for the starting circuit if desired.
In FIGURE 2 another embodiment of the invention is illustrated in which corresponding parts are designated generally by the same reference numerals as in FIGURE 1. However, when the system constants have been changed, the element has been identified with the same reference numeral with the addition of a or 11.
The circuit of FIGURE 2 is advantageous in that it does not require the use of a separate direct current power supply, the RC circuit being activated directly by the alternating current source. In addition, in FIGURE 2 dual switching tubes having been provided so that high frequency oscillatory pulses are provided in phase for both halves of the alternating current supply waveform, thus increasing the firing possibility of the discharge lamp.
In FIGURE 2 the switching means for the oscillatory circuit including the triggering capacitor 17 and the auxiliary winding 19 is provided by cold cathode thyratron tubes 16a and 16b. It will be noted that the tubes 16a and 16b are similar excepting that their anodes and cathodes are connected in opposition so that one or t-he other of the tubes 16a or 16h fires during alternate half cycles. Tube 16a is controlled by an RC circuit including a resistance 22a and a capacitance 24a, the mid-point 25a being connected to grid 26a of the tube 16a. Tube 1611 is controlled by an RC circuit including a resistance 2211 and a capacitance 24k, the mid-point 25h being connected to grid 26h of the tube 16b. Both RC circuits together with the triggering capacitator 17 are connected across the alternating current supply as stepped up by the full turn ratio of the transformer by using end tap 15a.
The operation of this circuit is similar to that described for the circuit shown in FIGURE 1. The waveform 50a for the voltage applied to the electrodes 41 and 42 remains the same. However the effective envelope of the damped oscillations as indicated at 51a differs in that the damped oscillations for the negative half of the alternating current supply add to rather than subtract from the alternating current voltage and thus provide a greater likelihood of practically immediate triggering of the discharge tube 10.
In a system manufactured commercially in accordance with FIGURE 2 and found to operate satisfactorily the constants employed were the same as those set out for FIGURE l, excepting that the tubes 16a and 16b were Tungsol CH 1150, resistors 22a and 22b were 100K ohms, capacitors 24a and 24,5 were .033 mfd., and resistors 28a and 28h were 5.6 ohms. Impedance 27a was a resistor of 2K ohms.
In FIGURE 5 another embodiment of the invention is illustrated in -which corresponding parts are designated generally by the same reference numbers as in FIGURE 1 plus 500. The circuit of FIGURE 5 is advantageous in that controlled rectifiers are used instead of the thyratrons of FIGURES 1 and 2.
In FIGURE 5 the switching means for the oscillatory circuit including the triggering capacitor 517 and the auxiliary winding S19 is provided by controlled rectifiers 550 and 551. In order that one or the other of the controlled rectifiers 550 or 551 fire during alternate half cycles they are connected in opposition. Control means for the firing of the controlled rectifiers includes oppositely connected blocking diodes 552 and 553 respectively connected through voltage dropping resistors 554 and 555 across the control potential. A unijunction transistor 556 is connected through a current limiting resistor 557 between the anode of blocking diode 552 and the cat-bode of blocking diode 553. A triggering circuit for the unijunction transistor 556 includes a capacitor 558 connected in series with an adjustable resistance 559 and primary winding 560 of a pulse transformer 561 between the anode of blocking diode 552 and the cathode of blocking diode 553. Secondaries 562 and 563 of the pulse transformer 561 are connected to the gates of the controlled rectifiers 550 and 551. An air core inductor 564 may be connected in series with the inverted parallel connected controlled rectifier-s 550 and 551 to limit :1i/dz (rise time) to prevent damage thereto.
The operation of the circuit of FIGURE 5 is similar to that explained for the circuit of FIGURE 2. As is well known in the art the circuit of FIGURE 5 will produce a plurality of pulses for each half cycle of the low frequency supply upon proper selection of system constants.
While the invention has been described and illustrated with reference to specific embodiments thereof, it will be understood that other embodiments may be resorted to without departing from the invention. For example, While the circuit of FIGURE 2 has been shown with two switching tubes 16a and 16h, it is obvious from the specification that satisfactory operation may be had by the use of only one such tube. Also, half cycle operation of the circuit of FIGURE 5 maybe had by omitting one of the controlled rectiiers 550` or 551. Further, while the electronic switches shown in the embodiment of FIGURE 5 are controlled rectitiers which may be silicon controlled rectifiers made by General Electric Company, an alternative system might Iemploy a Triac made by the same company and which is, in eect, a pair of controlled rectiers connected back to back with a single control electrode. In this case one of the secondaries of the pulse transformer 561 might be omitted. Therefore, the form of the invention set out above should be considered as illustrative and not as limiting the scope of the following claims.
1. An electric system comprising an electric discharge lamp, `an operating circuit connected to an alternating current source of relatively low frequency, an operating circuit current limiting impedance, a main capacitor connected in series with the operating circuit current limiting impedance across said low frequency source, a saturable reactor including a main winding connected in series with said lamp across said capacitor, a starting circuit supplied by said source of potential, starting circuit current limiting impedance, an electronic switch having two main electrodes and a control electrode, a resistance-capacitance circuit means supplied by said source of potential operatively connected to said control electrode to effect closing of the electronic switch between two and ten times during at least'each alternate half cycle of the low frequency source, a triggering capacitor, an auxiliary Winding for the saturable reactor, the triggering capacitor and the auxiliary winding connected in series with the starting circuit current limiting impedance across said source of potential for the charging of the triggering capacitor, the electronic switch connected across the series connected triggering capacitor and auxiliary winding whereby upon each closing of the electronic switch, said closing occurring two to ten times during at least each alternate half cycle of the low frequency supply, a pulse is produced in the auxiliary winding each said pulse comprising high frequency damped oscillations, and corresponding pulses are induced across the main winding of the saturable reactor and superimposed upon the low frequency voltage pulses supplied to the discharge lamp.
2. An electric system according to claim 1 in which the electronic switch is a controlled rectifier.
3. An electric system according to claim 1 in which the electronic switch is a thyratron.
4. An electric system according to claim 1 in which a second electronic. switch is included, said second electronic switch being connected in parallel-opposite relationship with said claim 1 electronic switch and likewise Iesistivelycapacitively controlled so that starting pulses are provided for `both half cycles of the low frequency supply.
5. An electric system according to claim 1 in which the starting circuit is connected in parallel with the operating circuit across the low frequency supply.
6. An electric system according to claim 1 in which the requency of the high frequency damped oscillatory pulse is less than one megacycle.
7. An electric system according to claim 1 in which direct current supply means is provided for the resistancecapacitance circuit.
References Cited by the Examiner UNITED STATES PATENTS 2,784,349 3/1957 Anderson 315-176 2,856,563 10/1958 Rively 315-289 X 2,858,481 10/1958 Bird S15-289 X JOHN W. HUCKERT, Primary Examiner'.
D. O. KRAFT, Assistant Examiner.