US2923857A - Power supply for electrical photographic flash unit - Google Patents

Description

Feb. 2, 1960 R. A. BROWN ET AL 2,923,857

POWER SUPPLY FoR ELECTRICAL PHOTOGRAPHIC FLASH UNIT Filed April 30, 1958 INVENTORS mm 7' A. BRO w/v Aw r 2. HA? TM/WZZ United States- Patent i Robert A. Brown, Mil ford, and Robert B. Hartman II,

Bridgeport, Conn., assignors to'Remington Arms Company, Inc., Bridgeport, .Conn., a corporation of Dela- T i t r A i incsn6nribii130,i9ss, Serial No. 731,913

i -2 Claims; crisis- 151 invention relates to the fieldiof high speed electr ic photoflash lamps. More particularly, this invention involves anovel improved power supply system for a high speed photoflash lamp for use primarily in ballistics testing and measurements for firearms and ammunition.

It is a requirement for such systems that the flash duration of the lamp be extremely short.

It is a requirement of electric photoflash circuits for use in ballistic measurement and test work that the firing time be extremely short and that only one light flash be produced for each triggering pulse supplied to the circuit.

It has been found highly desirable that such electric photoflash circuits be sufliciently flexible and controllable to permit use of the most appropriate voltages corresponding to varying atmospheric conditions, such as required to fire certain types of gas-filled flash tubes over the life of such tubes, it being known that the firing voltage required increases over the life of the tube.

It is an object of this invention to provide an improved power supply system for a high speed photoflash lamp which satisfies the above requirement and possesses the desired flexibility indicated above.

It is another object of the invention to provide an improved power supply system for a high speed photoflash lamp, which is simple and economical in construction, eflicient and reliable in operation.

Other objects and advantages will appear from the following specification and claims taken with the accompanying drawings in which Figure 1 is a diagrammatic view of circuits and apparatus arranged and constructed according to one embodiment of the invention.

Referring'to Figure l by characters of reference, the circuit includes a variable resistor 10 and transformer primary coil 11 connected in series across input leads carrying A.C. voltage V The secondary coil 12 of the transformer is center grounded as indicated. One of the leads of the secondary coil 12 is connected through diode 13 to one of the electrodes of photofiash tube 20, preferably a Mullard LSD-2 tube of the gas-filled type capable of producing an intense light when an electrical discharge is passed between its anode and cathode terminals. A trigger or control electrode is provided to be energized to initiate the discharge. Theother lead of secondary coil 12 is connected through diode 14 to the other electrode of flash tube 20. Connected in parallel with the flash tube 20 is a condenser 19.

Also connected in parallel with flash tube 20 and condenser 19 is a series of two condensers 15 and 16. The condensers 15 and 16 are preferably but not necessarily equal. Connected between condenser 15 and condenser 16 is an induction coil 17, such as an automobile spark coil, and a condenser 18 to which is applied the trip or triggering pulse of voltage asindicated by the arrow to initiate the light flash. The trigger electrode of flash tube 20 is grounded through condenser 22 and also connected through resistor 21 to the diode 14.

in the preferred embodiment of my system the power 2,923,857 Patented Feb; 2, 1960 r 2 supply voltage V; is -115 A.C. and variable resistor 10 is adjusted to produce a voltage of about 50 volts across the primary winding 11 of our particular transformer. Condensers 15, 16, 18 and 22 have a capacity of about .05 mfd. Condenser 19 hasa capacity of about .25 mfd. Resistor 21 has a resistance of about 0.5 megohm. Variable resistor 10 was adjusted to produce a voltage V of 7500 volts D.C. At this point the resistance of variable resistor 10 was found to be 400 ohms for the particular transformer used. In operation whenjthe input power supply V is applied to the circuit a voltage drop V of 7500 volts is produced across condenser 19 which becomes charged to that voltage level.

The voltage on the igniter electrode 31 and negative electrode 30 of flash tube 20 is a negative 3750 volts. Re-

sistor 21*maintains them both at the same potential after condenser 22 charges between ground and the negative voltagethrough resistor 2l. i 1

A triggering voltage pulse is then applied through condenser 18 to cause induction coil 17 to apply a change in voltage of about 6000 volts at the connection between condensers 15 and 16. This has the etfect of driving the negative electrode more negative through condenser 16. Since the voltage across a condenser cannot be changed instantly, the trigger electrode is maintained at the original negative voltage by condenser 22. This creates a difference in voltage between the trigger electrode 31 and the more negative electrode 30 which will cause the flash tube 20 to ignite discharging condensers 19, 15 and 16. The value of variable resistance 10 which controls the recharge rate of these condensers by limiting transformer current is adjusted so that the flash tube will flash only once'for each triggering pulse. Variable resistor 10 may be replaced by any appropriate variable impedance, either linear or non-linear, active or passive, as desired.

It can be seen that by designing the system of the present invention with the split voltage arrangement utilizing the total difference between maximum positive and maximum negative levels, a considerable portion of the system will not require design to handle the total resulting voltage.

While we have fully described a preferred embodiment of our invention, in accordance with the patent statutes, modifications will occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

We claim:

1. A light flash producing system comprising in combination, a normally non-conducting luminescent discharge lamp having two principal electrodes between which a discharge may pass when the lamp is conducting to produce light and a control electrode operative when energized to render the lamp conducting, a supply transformer having a primary winding and a secondary winding, said secondary winding connected to ground at its midpoint and having two output terminals, a first rectifier and a second rectifier, a main condenser, means for connecting the main condenser to the output terminals of the transformer secondary winding through the rectifiers to cause the condenser to become charged from the transformer, means connecting the main condenser to the principal electrodes of the lamp, means connecting the negative terminal of the main condenser to the control electrode of the lamp through a bleeder resistor, means connecting the control electrode to ground through a second condenser, a third condenser and a fourth condenser connected in series, means connecting said third and fourth condensers in parallel with said main condenser and said lamp, means for connecting the junction between said third and fourth condensers to ground through an impedance means, means connected through said impedance means to apply "a high' voltage triggering *pulse through said third and fourth condensers to said principal electrodes of said lamp and through said bleeder resistor to said ground-coupled control electrode causing a sharp voltage ditTerence-to-appear-between the control electrode and theprincipalnegativeelectrode to initiate conduction of current through the lamp, th'eiprimary winding of said supply transformer-provided with a variable impedance in-series therewith to vary'the total voltageapplied across the lamp-and to limit the rate of recharging of the main condenser.

2. An electrical light-flash producer system comprising in combination a normally non-conducting luminescent discharge lamp having two-principal electrodes between which a discharge may pass-tozproduce lightand'a control electrode operative when energized to enable the lamp to conduct the discharge, a power supply meansflfor supplying initial charging energyto the system, means for connecting the principal electrodes to the power supply means to cause the initial charging energy to be applied to the principal electrodes when ,thelamp is conducting to produce a flash of light, means-,for connecting said principal electrodes "to source 'of triggering voltage-pulses,

means for connecting said control electrode to said source of triggering voltage pulses through a"ble"e'der resistance means, and means for coupling said control electrode to ground through a capacitance means, so that a triggering voltage pulse from said source combines with the energy from the power supply nieansto cause said control electrodeto :render the lamp conductingrandaa discharge to pass between said principal electrodes to produce light pulse.

References Cited in thefile of this patent UNITED STA'TES 'PATENTS 1,979,692, Knowles Nov. 6, '1934 2,014,957" A Westendorp ;Sept.'l17, 1935 2,310,092 Knowles et al. Feb. 2, 1943 2,331,317 Germeshausen Oct. 12, 1943 2,421,182 7 Bayne May 27, 1947 FOREIGN PATENTS H 267,218,

Switzerland June 1, 1950

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