US2655618A - Electronic flash device - Google Patents

Description

Oct. 13, 1953 H PARKER 2,655,618

ELECTRONIC FLASH DEVICE Filed March 15, 1951 INVENTOR. HARRYL. PA AKER Patented Oct. 13, 1953 Harry L. Parker, St. Albans, N. Y., assignor to American Speedlight Corporation, New "York,

Application March 15, 1951, seria1'No."215;727

11 Claims.

1 The present invention relates to electric apparatus and more particularly an electronic flash device suitable, among other purposes, for photographic illumination.

electronic flash device includes a tube in which light isproduced by a discharge of electric current between electrodes of the tube. Generally the electric energy for the fiashis obtained from-an alternating current supply stepped up to a higher voltageby means of a transformer, then rectified'by a uni-directional conductor to produce pulsating direct current.

The amount of light produced by any specific tube construction depends to a great extent upon the amount of energy in thedischarge, and, thus, is directlyproportional to the charge in the storage capacitor.

It is important, particularly when the flash do v'ice'is used for photographic work, that the discharge be uniferm in nature so that dependable exposures may be obtained under various conditions without the needof experimentation. Furthermore, the uniform'results must be obtainable irrespective of changes in the main electrical supply such as 'caused'b'y frequency or voltage variation. In addition, when the flash device'is of high capacity and the main supply is of comparatively low surge capacity, it is important that the hash device have a controlled chargingrate'so as to'prevent system disturbances and to prevent possible damage to the low capacity supply source. In addition, when excessive peak currents are drawn from a low capacity source, the terminal voltage'will drop excessively thereby causing the malfunctioning of components of the device such as relays, time delay devices, etc.

Heretofore the control systems mcharging large banks of electrical capacitors for the flash devices have depended upon series impedances in either'the primary of secondary circuits'to control the rate of current flow into the capacitor. In such a system, in charging the capacitor from the discharged state, the current flow into the capacitor from thesource starts at a peak current rate controlled by the series impedance and then decays exponentially as the charge is accumulated.

In such a system when it is necessary that the charging period he very short and the power demand high, the instantaneous current required, in many cases, exceeds the capabilities of the normally available and economically feasible power supply. Another 'diiliculty arises from the fact that the charge stored'in the capacitors is'in direct=relationship to the'input voltage, and since energy'storage is proportionate to the square of the voltage, a small variation'in input voltage results in 'a relatively large 'pro=- portionate variation inenergy storage. Another difficulty, with such systems, is that a shift in frequency of the 'inputvoltage will'efiect a-change in the value ofthe series impedance and there'- by affect the rate of charge of the capacitors.

This invention aims to overcome the foregoing 'difliculties and disadvantages by providing an electronic flash device in which the charging current is practically constant or linear and in which the capacitor is automatically charged to its predetermined'desired voltage irrespective of variations in supply system conditions.

Another object of the invention is to provide an electronic flash device which is simple and economical in manufacture, efficient in operation and durable in use.

In accordance withthe invention the foregoing objects are accomplishedby providing an electronic charging device including regulating means for the control of its rate and amount oi charge. The controlling means includes a sat- 'urable reactor bridge for the grid'circuitof the rectifier, the reactance of the bridge component being controlled by direct current supplied in variable amount to one or more direct current windings thereon dependent in amount upon one or more conditions which may varyor for which control is desired such as the supply voltage or frequency shift, the'p'eak Value of current to be drawn by the capacitor under charge, or the amount of charge.

The construction in accordance with the invention is advantageous for use in systems of comparativelylow supply capacity such as portable motor generator units as a comparatively large amount of energy may be stored in the capacitor in a short time by eliminating the peak demand and working the supply over a longer period at a continuous demand within its safe output limit. Furthermore, the control of energy level may be hglci 'to very close tolerances not heretofore availa ie.

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, an embodiment of the invention.

Iii the drawings:

Figure 1 is a schematic wiring diagram of an electronic flash device in accordance with the invention;

Referring to the drawings there is shown in Figure 1 an electronic flash device in accordance with the invention and including a transformer 2 adapted to be connected to an alternating current source to supply grid-controlled thyratron tubes 3 and 4 to provide full wave rectification to a supply capacitor 5 for a flash tube 6. The discharge of the capacitor 5 is controlled by a trigger circuit generally indicated by numeral 1. The control circuit 8 for the thyratrons 3 and 4 is used to regulate the charging of the capacitor 5.

The transformer 2 is provided with a primary winding III, a filament supply winding II and a secondary winding I2 having a midtap I3 and outer terminals I4 and I5. By reason of the use of the control circuit later described the transformer may be designed with low impedance in order to provide good regulation.

The thyratrons 3 and 4 may be of the type known as 5563 and are gas filled and, respectively, have cathodes I6 and I7 heated by the filament transformer winding I2 through leads I9 and 20. The tubes are controlled by grids 2| and 22 interposed between the cathodes I6 and I 1 and anodes or plates and By reason of the construction of the tubes 3 and 4 they are adapted to pass current from their cathodes to their anodes upon the application of a suitable grid potential.

In order that full wave rectification may be had for the charging of the capacitor 5, the transformer secondary terminals I4 and I5 are connected to the plates 24 and 25 by connecting wires 26 and 2! and the cathodes I6 and I! are connected to lead 29. The midpoint I3 of the transformer secondary II is connected to one terminal of the capacitor 5 by a wire 36, the other terminal of the capacitor being supplied by the wire 29.

A negative bias for the grids is provided by a battery 3| across which is connected a potentiometer 32. A series resistor 33 is connected in the lead 34 to the cathode circuit. The potentiometer has its adjustable arm connected to midpoint 35 of a peaking transformer 36 by a lead 31. Terminals 39 and 46 of the peaking transformer 36 are respectively connected to the grids 2| and 22 by leads 4| and 42 through resistances 46 and 45.

The transformer I6 may be of any desired type terminals 46 and 41 of the tube 6 by wires 49 and 50.

The flash tube 6 may be of the type known as an F'T500 and is made with a glass envelope 5| which is gas filled with xenon or other suitable gas, the electrodes 46 and 41 extending into the gas filled chamber. A triggering electrode 52 is wound about the envelope 5| of the tube 6 and is adapted when a voltage surge or pulse of electricity is applied to initiate ionization of the gas within the envelope 5|, thus causing it to become a conductor and permitting the capacitor 5 to discharge between the electrodes 46 and 41.

The trigger circuit I includes a cold cathode tube 55 of the type known as 8N4 having electrodes 56 and 51 and grids 59 and 60. A direct current power supply is taken from a battery 6| by the leads 62 and 64. The electrode 51 is connected to the supply lead 64 by a common connection 58 and to a resistor 65 having its other terminal connected to the grid 60. A capacitor 66 is connected at one terminal to the grid 66 and its other terminal to a resistor 61 through a lead 68 then to the electrode 56 by a lead 64. The supply lead 62 is connected to the grid 59 with a resistor 69 therebetween. Another resistor I6 is connected between the grid 59 and the electrode 56 by a lead I I.

A triggering transformer 14 has one terminal of its secondary I5 connected to the triggering electrode 52 by a lead I6 and its other terminal connected to the supp-1y wire 56 from the capacitor 5 by a lead 11. The primary I9 of the trigger transformer I4 has one lead connected to the common connection 58 between the main electrode 51 and the resistor 65 by a wire 86. The other terminal of the primary winding I9 is connected by a wire 8| to a capacitor 82 in turn connected by a lead 84 to the electrode 56. A switch 96 is connected across the wires 58 and 68 for single flashing of the tube 6. In addition, for alternative use, for the successive flashing of the tube 6, a multicontact switch 9| is connected in parallel with the switch 99. The switch SI has a plurality of contacts 92 adapted to be swept by a spring urged midpoint 93 in any suitable construction to provide a succession of contact of successive make and break connections between the wires 58 and 68 the switch having a time contact to provide a delay between suceessive contacts to allow the deionization of the tube 6, and may be of the type commonly used for telephone machine switching.

The operation of the trigger tube circuit is well known in the art and is initiated by a momentary pulse applied to the grid 60. In the static condition the voltage of power supply 6| is applied across the cold cathode tube 55 and the capacitor 82 which is charged to the full voltage of the power supply 6 I. Likewise capacitor 66 is charged through resistors 65 and 61 to the same voltage. The grid 59 is biased to a positive voltage with respect to cathode 51 by the proper ratio of voltage drops across the resistors 69 and 10. Grid 66 is maintained at the same potential as the cathode 51 as it is connected through resistor 65 through which there is no current flow.

When the trigger pulse is desired, terminal 66 is connected to the cathode 65 by actuation of either the switch or, if successive pulses are desired, by actuation of the multiple contact switch 9|. At the instant that terminal 68 of the capacitor 66 is connected to the cathode 51 by one or the other of the switches 99 or 9| the full voltage of the capacitor appears across the resistor 65 thereby applying a voltage pulse to the grid 66. This voltage pulse ionizes the gas in the cold cathode tube 55 allowing the capacitor 82 to discharge through the primary winding I9 of the triggering transformer 14. The discharge of the capacitor 82 through the primary winding I9 induces a high voltage pulse in the secondary winding I5 which, in turn, ionizes the gas in the flash tube 5|.

The control circuit for the thyratrons 3 and 4 is based on a bridge I00 incorporating saturable reactances I Ill and I02 in a bridge connection with resistances I63 and I04. The output of the bridge I06 is connected to the peaking transformer 36 by wires I05 and I66. The bridge I66 is supplied from the alternating current source by a transformer III) having a primary winding III and a secondary winding H2. The secondary winding |I2 has a first terminal connected to a phasing capacitor II4 by a lead II5, the other terminal of the capacitor being connected to one terminal to the bridge kl ll b y a transwire l It The secong 1 qtth Jpfl- .al;e-e aqtly sim a n ima e wit iro s re 9 h? i -r1? rnat.w i additiq i Mee c. eumfiere imt l mu h imiylii i. A d re t lw iedi MA fihrque ,e n -tn ldi te eu t en t m n a qnttsalis i ellitwefiux sie ihetan ie lte .7 tie n u gc v4 --.-t e e, fi ht? wemttqne eetwet itlr .pai :s.Q are provided between windings- I51 A 7 4 9 2 2 e wittfiiaesiflansi Him? wi l 1 ind-19%}? t; -h mn? lieandzbe- ,QQnQW QdJ Qmms t. I. 1e 9. e t9 termi a m e zed J0--th 1ehtt b in I pe tqrmmals n L temfor .the

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2?] Zis'Yfoniitdhij wiir e fifli toterrninaijl?) it} the series coniie'cta coil's l3l -ll 3ii. Timqzfii sidetof oils li-l36 is connected through tier} Ininal 153 by leads 2 H and 2 to the bos itii'e terminal of battery 216. The connection 'is made from the grid-223 through a grid leak resistor-lfl through a wire 228 to the movable top 229 of a rename resistorfifi: One terminal -of:the teister 2301.15 connected to cathode -23 l ot-the-tube 235 and-also through a wire .232'to oneelectrode 233 of aivoltage. regulating tube 234 which may be of thetype knownas No. VR150; The other electrode 235.-.of the tube 23.4.-.is connecteiby-ia lead 236 to the other end of .variable -rresistori2ll a w t, fiendl e a vi e? all wi g th -Wham i veeetli rl n the trek-Ea h ra e al e -e -.;t9r a -mete Renee 12 e K e .l matipqsiq and a tap connection 231 is made to wire 20L By means of the voltage divider 200 a reference voltage is obtained to control the current flow in the appropriate control windings of the reactor bridge. The control is so proportioned that linear current flow is obtained. The voltage across the capacitor is sampled by the voltage divider and carried by wires 201 and 202 to the tube 205 to vary the grid voltage thereof. Tube 205 then acts as a variable resistor which controls the D. C. current through reactance direct current windings l30l3l, thereby providing a control through the bridge to the thyratron for the linear charging of the capacitor 5.

While it is desirable to charge the capacitor 5 as rapidly as possible, it is necessary that the voltage applied to the capacitor be cut off at a predetermined point so as to assure uniformity of charge on the capacitor which in turn of course will assure uniformity in the brilliance of the flash from the discharged tube. This could be achieved by taking a voltage signal from the resistor 200 which is in parallel with the capacitor 5. However, it is desirable to achieve greater accuracy in determining the peak voltage than is possible with this method. Therefore, the tube 205, which has been previously used as a current control tube, is used also as an amplifier for the voltage signal from the voltage divider 200. A small change of voltage across the portion of the voltage divider 200 between its two connections 0 and b is applied to the grid 204 of the tube 205, thereby causing a change in current through the tube and through the cathode resistor B. resistor 208 is larger than the voltage change between the points a and b of the voltage divider 200, thus, producing a larger signal in relation to the change of voltage across condenser 5.

The amplified voltage signal across 208 is fed 4 through the voltage peak tube 22I into the control tube 224. By reason of its bias, tube 224 is normally cut off and there is no current through control windings l3l-I36. However, when the voltage across 208 builds up to the point that tube 22! conducts and overcomes the bias of the grid 223 of tube 224, the tube suddenly becomes a conductor and passes a current through the windings |3|I38 which offsets the phase advance caused by the current flow through the windings l-l31. Thus, retarding the phase of the potential applied to the grid control thyratron 3 and 4 and thereby stopping further increase in charge on the capacitor 5. The tube 224 is designed with a sharp cutofi and the tube H 22l is used in series with the grid 223 to provide a clipping action so as to assure dependable and uniform control accurately limiting the charge on the capacitor 5.

From the preceding description it will be seen that the present invention provides an electronic flash device having efficient and reliable control means for assuring a uniform charge on the capacitor at a control rate such as to prevent supply source disturbances yet such as to assure rapid recharging as may be required for successive flashes.

While the invention has been described and illustrated with reference to a specific embodiment thereof, it will be understood that other embodiments may be resorted to. Therefore, the form of invention set out above should be considered as illustrative and not limited in scope as to the following claims.

The change in voltage across the I claim:

1. An electronic flash device comprising a flash tube, a capacitor to store energy to flash the tube, a grid-controlled rectifier for charging the capacitor, control means for the rectifier grid including a saturable reactor, a direct current winding for the saturable reactor, a source of direct current, and control means to vary the direct current through the direct current winding, including a feedback circuit obtaining information from across the storage capacitor, whereby the charging rate of the storage capacitor and its maximum voltage is limited to a predetermined value.

2. An electronic flash device comprising a flash tube, a capacitor to store energy to flash the tube, a grid-controlled rectifier for charging the capacitor, control means for the rectifier grid including a saturable reactor, a direct current winding for the saturable reactor, a source of direct current, control means to vary the direct current through the direct current winding including a feedback circuit from the storage capacitor and responsive to the potential thereof, and a frequency sensitive bridge rectifier circuit adapted to provide a varying direct current output responsive to a change of supply frequency, whereby the charging rate of the storage capacitor and its maximum voltage is limited to a predetermined value.

3. An electronic flash device comprising a flash tube, a capacitor to store energy to flash the tube, a grid-controlled rectifier for charging the capacitor, control means for the rectifier grid including a reactor bridge, and direct current control means for the reactor bridge responsive to electrical information from across the storage capacitor to control the rate of charge thereon.

4. An electronic flash device comprising a flash tube, a capacitor to store energy to flash the tube, a grid-controlled rectifier for charging the capacitor, control means for the rectifier grid including a reactor bridge, and direct current control means for the reactor bridge responsive to potential of the capacitor to control the rate of charge and peak voltage thereon.

5. An electronic flash device comprising a flash tube, a capacitor to store energy to flash the tube, a grid-controlled rectifier for charging the capacitor, negative bias means for the rectifier grid, and a reactor bridge adapted to act in opposition to the negative bias to render the rectifier operative and the bridge variable to control the energy stored in the capacitor.

6. An electronic flash device comprising a flash tube, a capacitor to store energy to flash the tube, a grid-controlled rectifier for charging the capacitor, negative bias means for the rectifier grid, and an alternating current bridge adapted to act in opposition to the negative bias to render the rectifier operative, and direct current control means for the bridge responsive to circuit information to shift the output of the bridge to control the energy stored in the capacitor.

7. An electronic flash device comprising a flash tube, a capacitor to store energy to flash the tube, a grid-controlled rectifier for charging the capacitor, negative bias providing means for the rectifier grid, a reactor-resistor bridge connected to supply a grid potential to act in opposition to the reactor, grid negative bias, and direct current windings for the reactors of the bridge to shift the phase angle of the bridge bias voltage with respect to the rectifier anode-cathode volt- 9 age to vary the charge on the capacitor to control the nergy stored in the capacitor.

8. An electronic flash device comprising a flash tube, a capacitor to store energy to flash the tube, a grid-controlled rectifier for charging the capacitor, negative bias providing means for the rectifier grid, a reactor-resistor bridge connected to provide a grid potential to act in opposition to the reactor, grid negative bias, a first set of direct current windings for the reactors of the bridge to provide a reference direct current flux, and a second set of direct current windings for the reactors responsive to circuit information to control the energy stored in the capacitor and thus to control the energy of the flash.

9. An electronic flash device comprising a flash tube, a capacitor to store energy to flash the tube, a grid-controlled rectifier for charging the capacitor, negative bias providing means for the rectifier grid, a reactor-resistor bridge connected to provide a grid potential to act in opposition to the reactor, grid negative bias, a first set of direct current windings for the reactors of the bridge to provide a reference direct current flux, a second set of direct current windings for the reactors, a direct current information source including an inductance, and a rectifier bridge having its input bridge connected in series with the inductance the output of the bridge connected to the second set of direct current windings to provide direct current flux to act with the reference direct current flux to vary the charge on the capacitor to control the energy stored in the capacitor and thus to control the energy of the flash irrespective of system frequency variations.

10. An electronic flash device comprising a flash tube, a capacitor to store energy to flash the tube, a grid-controlled rectifier for chargin the capacitor, negative bias providing means for the rectifier grid, a reactor-resistor bridge connected to provide a grid potential to act in opposition to the reactor, grid negative bias, a first set of direct current windings for the reactors of the bridge to provide a reference direct current flux, a second set of direct current windings for the reactors, a direct current information source including a potentiometer connected across the capacitor to provide a source of potential drop, and electronic control means to control current through the second windings responsive to said potential drop to provide a flux to coact with the reference flux to provide a grid voltage shift to control the rate of charge of the capacitor.

11. An electronic flash device comprising a fiash tube, a capacitor to store energy to flash the tube, a grid controlled rectifier for charging the capacitor, negative bias providing means for the rectifier grid, a reactor-resistor bridge connected to supply a grid potential to act in opposition to the negative bias, a first set of direct current windings for the reactors of the bridge to provide a reference direct current flux, a second set of direct current windings for the reactors, a direct current information source including a voltage divider connected across the capacitor to provide a source of potential drop, electronic amplifying means responsive to said potential drop to provide an amplified control voltage, and electronic control means responsive to said amplified voltage to provide a flux to coact with the reference flux to cause the rectifier to limit the charge on the capacitor to a predetermined value and thus to control the energy of the flash.

HARRY L. PARKER.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,408,091 Olesen Sept. 24, 1946 2,459,551 Steinitz Jan. 18, 1949 2,478,901 Edgerton Aug. 16, 1949 2,513,396 Beck July 4, 1950 2,555,975 Kellogg June 5, 1951

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