US3790847A

US3790847A - Arrangement provided with an electronic flash bulb

Info

Publication number: US3790847A
Application number: US00013373A
Authority: US
Inventors: H Hintz
Original assignee: US Philips Corp
Current assignee: US Philips Corp
Priority date: 1969-03-01
Filing date: 1970-02-24
Publication date: 1974-02-05
Anticipated expiration: 1991-02-05
Also published as: GB1292373A; DE1910544A1; NL160142B; DE1910544B2; JPS4831621B1; FR2033094A5; BE746703A; NL7002788A; NL160142C

Abstract

The invention relates to an arrangement provided with an electronic flash bulb which is fed from a main capacitor. In a known arrangement a so-called quench tube is arranged across the bulb. This quench tube is ignited when sufficient light is emitted by the bulb. A drawback of the known arrangement is that the main capacitor is substantially discharged when this quench tube is ignited. The invention provides a solution wherein the bulb is fed through a thyristor which is extinguished after some time by a circuit including a second thyristor. The advantage is that the main capacitor is now less discharged and the arrangement is thus sooner ready for the next flash.

Description

United States Patent [191 Hintz ARRANGEMENT PROVIDED WHTH AN ELECTRONIC FLASH BULB [75] Inventor: Harald Hintz, Hamburg, Germany [73 Assignee: us. Phillips Corporation, New

York, N.Y.

[22] Filed: Feb. 24, 1970 [21] Appl. N0.: 13,373

[30] Foreign Application Priority Data Mar. 1, 1969 Germany P 19 10 544.3

[52] US. Cl. 315/151, 315/159, 315/241 P [51] Int. Cl. H051) 37/00 [58] Field of Search... 315/119, 122, 124, 149, 151, 315/159, 160-162,171,173,178-183,185, 187-190, 192, 200, 202, 205, 207, 208, 233,

241 P, 241 R, 241.5, 323, 340; 307/252 K,

[56] References Cited UNITED STATES PATENTS 3,591,829 7/1971 Murata et a1. 315/159 X 3,497,768 2/1970 Mathisen 315/181 X [11.1 3,790,847 Eeb.5,1974

3,238,419 3/1966 Heft et a1 317/33 3,541,387 11/1970 Ackermann 315/151 3,376,470 4/1968 Stone et a1 315/171 Primary Examiner-H. K. Saalbach Assistant Examiner-Lawrence J. Dahl Attorney, Agent, or Firm-Frank R. Trifari [57] ABSTRACT The invention relates to an arrangement provided with an electronic flash bulb which is fed from a main capacitor.

In a known arrangement a so-c-alled quench tube is arranged across the bulb. This quench tube is ignited when sufficient light is emitted by the bulb. A

drawback of the known arrangement is that the main capacitor is substantially discharged when this quench tube is ignited.

The invention provides a solution wherein the bulb is fed through a thyristor which :is extinguished after some time by a circuit including a second thyristor. The advantage is that the main capacitor is now less discharged and the arrangement is thus sooner ready for the next flash.

13 Claims, 1 Drawing Figure PAIENTEUFEB 5:974 790 847 INVENTOR. HAR AL D HI NT Z l IANtGEMENT POVIDED Wl'lll-ll AN ELECTRONIC FLASH BULB The present invention relates to an improved my ristor switching for an electronic flash bulb, said arrangement including a photosensitve member and a supplycapacitor in which the duration of the flash of the flash bulb is influenced by the quantity of light which is reflected onto the photosensitive member by an object to be photographed.

It is known to connect a so-called quench tube parallel to the flash bulb which tube is rendered conducting at the desired instant by means of an auxiliary control voltage. This auxiliary control voltage is generated by an auxiliary arrangement including a photosensitive member. After the quench tube has become conducting it takes over the current from the flash bulb. The supply capacitor is then short-circuited and the electric energy stored therein is dissipated so that the flash bulb is extinguished.

This known arrangement has the drawback that due to the quench tube becoming conducting, the supply capacitor is entirely discharged so that a part of the comparatively small energy of the battery (for charging the capacitor) is needlessly wasted. In addition it takes longer to. make the flash unit ready for flashing. In fact, after each flash the supply capacitor must be recharged entirely. Also, the number of flashes which can be carried out by means of a battery or a pair of batteries is consequently limited.

According to the invention these drawbacks are obviated in that the supply circuit of the flash bulb includes two parallel arranged thyristors each of which is connected to its own supply capacitor, the capacitances of these supply capacitors being unequal and one thyristor being rendered conducting at the instant an ignition pulse is applied to the flash bulb. The other thyristor is subsequently rendered conducting by a control circuit including the photosensitive member.

The current supply to the flash bulb is not interrupted by the elimination of the charge on the capacitor, but rather by switching off the energy supply to the bulb. An advantage of the present invention is, inter alia, that the current peaks occurring in the unit are comparatively low so that less stringent requirements need be imposed on the supply capacitor.

During experiments with an electronic flash unit at a Leitzahl of the maximum value of the current flowing through the flash bulb was approximately 250 300 A while the maximum value of the current flowing through a quench tube is approximately 800 1000 A.

ure of which shows a preferred embodiment of the thyv ristor switching arrangement.

The drawing shows a circuit diagram of an arrange ment according to the invention. A capacitor 3 is charged with the polarity indicated through a voltage inverter whereof only the transformer l is shown) and through a diode 2. The capacitor also is connected through a thyristor 4 to a flash bulb 5. By activating a switch 6 the flash bulb 5 and the thyristor 4 are both rendered conducting. The exposure then commences.

Subsequently a control signal is generated in a control circuit which is provided, inter alia, with a photosensitive resistor 7 (facing the object to be photographed) and a current source not further shown. This control signal is passed on through a transformer 8 to the electrodes of a thyristor 9. The control circuit renders the thyristor 9 conducting when the object to be photographed has received a desired quantity of light. The thyristor 9 is connected to a capacitor 10. The capacitor W was previously charged with the polarity shown through a second winding 11 of the transformer 1 of the voltage inverter and through a diode 12. The capacitor lll may alternatively be charged by a voltage doubler circuit if, for example, the transformer of the voltage inverter has only one secondary winding. Due to the higher potential on the capacitor 10, the thyristor 9 takes over the supply of current to the flash bulb 5 from the circuit that includes the thyristor 4. If the period during which current flows through the thyristor 9 is longer than the recovery time of the thyristor 4, which is approximately 10 20 tsec, then the thyristor 4 is blocked and the direct current supply to the flash bulb 5 from the capacitor 3 is interrupted. The capacitance of the capacitor 10 is about 10 30 #F, so this may be much smaller than that of the capacitor 3, the characteristic value of which is approximately 500 [.LF. It is true that during the process of switching off, the energy stored in the capacitor 10 is applied to the flash bulb 5. This energy first causes a given increase in the luminance of the flash, but this quantity of energy is relatively small and substantially constant so that it can be taken into account when calibrating the auxiliary arrangement including the photosensitive resistor. The currents flowing through the thyristors 4 and 9 are not higher than the current flowing through the flash bulb.

What is claimed is:

l. An-electronic flash arrangement for an electronic flash bulb comprising, a photosensitive member arranged to respond to the flash bulb light reflected by an object to be photographed, a first supply capacitor, a second supply capacitor, a supply circuit for the flash bulb comprising first and second parallel arranged thyristors and means interconnecting said first and second thyristors with said first and second supply capacitors, respectively, and with the flash bulb, means serially connecting the second capacitor and the second thyristor in shunt with the first thyristor, the capacitance of said first capacitor being substantially larger than the capacitance of said second capacitor, means for coupling said first and second capacitors to a source of charge current so that the second capacitor is charged to a higher potential than the first capacitor, means for triggering the first thyristor into conduction at the instant an ignition pulse is applied to the flash bulb, and a control circuit including the photosensitive member for triggering the second thyristor into conduction after the first thyristor has been triggered whereby the duration of the light flash produced by the flash bulb is influenced by the amount of light reflected onto the photosensitive member by said object.

2. A flash control circuit for a flash tube comprising, a first capacitor for supplying operating current to the flash tube, a first controlled conduction device connected in a first circuit with said first capacitor and said flash tube so as to control the discharge of said capacitor across the flash tube, a second capacitor having a different capacitance than the first capacitor, a second controlled conduction device connected in a second circuit with said first and second capacitors and said flash tube so as to control the discharge of the second capacitor across the flash tube and to apply the voltage on said second capacitor to the first conduction device via said second conduction device and in a sense to turn off said first conduction device, a control circuit coupled to said second conduction device and including a photosensitive element arranged to respond to the flash tube light reflected by an object, means for coupling said first and second capacitors to a source of charge current in a manner such that the second capacitor is charged to a voltage level that is independent of the tube ignition voltage, means for applying an ignition pulse to the flash tube, means for triggering said first conduction device into conduction in synchronism with said ignition pulse thereby to flash the flash tube, said control circuit being operative to trigger the second conduction device into conduction in accordance with the amount of light reflected onto the photosensitive element by said object thereby to control the duration of the light flash as a function of said reflected light. I

3. A circuit as claimed in claim 2 wherein the capacitance of said first capacitor is substantially larger than the capacitance of said second capacitor and wherein said coupling means includes means for charging the second capacitor to a higher potential than the first capacitor.

4. A circuit as claimed in claim 2 wherein said second capacitor and said second conduction device are serially connected across the main electrodes of said first conduction device.

S. A circuit as claimed in claim 2 wherein said first capacitor and said first conduction device are serially connected with the flash tube in a closed loop circuit and one terminal of said first capacitor is directly connected to a terminal of the second capacitor of opposite polarity.

6. A circuit as claimed in claim 4 wherein said first capacitor and said first conduction device are connected in series with said flash tube and said first and second capacitors are connected in series with said second conduction device and said flash tube to form a separate closed loop circuit.

7. A circuit as claimed in claim 4 wherein said conduction devices each comprise a controlled rectifier having a control electrode, said triggering means and said pulse applying means together comprising a transformer with a primary winding arranged to be selectively connected to a source of voltage and first and second secondary windings coupled to the control electrode of the first controlled rectifier and to a starter electrode of said flash tube, respectively, the control electrode of said second controlled rectifier being coupled to said control circuit which is arranged to trigger said second controlled rectifier into conduction at a point in time subsequent to when the first controlled rectifier and the flash tube are triggered into conduc tion and independently of the current then flowing through the flash tube.

8. A circuit as claimed in claim 4 wherein the capacitance of said first capacitor is substantially larger than the capacitance of said second capacitor and wherein the circuit parameters are chosen so that the voltage on the second capacitor is higher than the voltage on the first capacitor at the instant when said second conduction device is triggered into conduction.

9 A flash control circuit for a flash tube comprising, a pair of terminals, first and second capacitors, means connecting said first and second capacitors in series across said terminals, means coupled to said terminals for electrically charging said capacitors with the same polarity and in a manner such that the second capacitor is charged to a voltage level that can be chosen independently of the volage level to which the first capacitor is charged, first and second controlled conduction devices, first means connecting said first controlled conduction device in circuit with said first capacitor and said flash tube so as to control the discharge of said first capacitor across the flash tube, a second means connecting said second controlled conduction device in circuit with said second capacitor and said flash tube in a manner so as to apply a reverse bias voltage from said second capacitor to said first conduction device when said second conduction device is triggered into conduction, a control circuit coupled to a control electrode of said second conduction device and including a photosensitive element arranged to respond to the flash tube light reflected by an object, means for triggering the first conduction device into conduction to discharge the first capacitor and thereby flash said tube, said control circuit being operative in accordance with the light reflected onto the photosensitive element by said object to trigger the second conduction device into conduction thereby to apply said reverse bias voltage to the first conduction device for a time period that is longer than the recovery time of said first conduction device.

10. A circuit as claimed in claim 9 wherein said first connecting means connects said first conduction device between the junction point of the series connected capacitors and one main electrode of the flash tube and said second connecting means serially connects said second capacitor and said second conduction device in the order named between said junction point and said one main electrode of the flash tube.

1 1. A circuit as claimed in claim 9 wherein the capacitance of said first capacitor is greater than the capacitance of the second capacitor and wherein the plates of said capacitors that form a junction point therebetween are charged with opposite polarity.

12. A circuit as claimed in claim 11 wherein the cirpath including the second conduction device.

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Claims

1. An electronic flash arrangement for an electronic flash bulb comprising, a photosensitive member arranged to respond to the flash bulb light reflected by an object to be photographed, a first supply capacitor, a second supply capacitor, a supply circuit for the flash bulb comprising first and second parallel arranged thyristors and means interconnecting said first and second thyristors with said first and second supply capacitors, respectively, and with the flash bulb, means serially connecting the second capacitor and the second thyristor in shunt with the first thyristor, the capacitance of said first capacitor being substantially larger than the capacitance of said second capacitor, means for coupling said first and second capacitors to a source of charge current so that the second capacitor is charged to a higher potential than the first capacitor, means for triggering the first thyristor into conduction at the instant an ignition pulse is applied to the flash bulb, and a control circuit including the photosensitive member for triggering the second thyristor into conduction after the first thyristor has been triggered whereby the duration of the light flash produced by the flash bulb is influenced by the amount of light reflected onto the photosensitive member by said object.

2. A flash control circuit for a flash tube comprising, a first capacitor for supplying operating current to the flash tube, a first controlled conduction device connected in a first circuit with said first capacitor and said flash tube so as to control the discharge of said capacitor across the flash tube, a second capacitor having a different capacitance than the first capacitor, a second controlled conduction device connected in a second circuit with said first and second capacitors and said flash tube so as to control the discharge of the second capacitor across the flash tube and to apply the voltage on said second capacitor to the first conduction device via said second conduction device and in a sense to turn off said first conduction device, a control circuit coupled to said second conduction device and including a photosensitive element arranged to respond to the flash tube light reflected by an object, means for coupling said first and second capacitors to a source of charge current in a manner such that the second capacitor is charged to a voltage level that is independent of the tube ignition voltage, means for applying an ignition pulse to the flash tube, means for triggering said first conduction device into conduction in synchronism with said ignition pulse thereby to flash the flash tube, said control circuit being operative to trigger the second conduction device into conduction in accordance with the amount of light reflected onto the photosensitive element by said object thereby to control the duration of the light flash as a function of said reflected light.

5. A circuit as claimed in claim 2 wherein said first capacitor and said first conduction device are serially connected with the flash tube in a closed loop circuit and one terminal of said first capacitor is directly connected to a terminal of the second capacitor of opposite polarity.

7. A circuit as claimed in claim 4 wherein said conduction devices each comprise a controlled rectifier having a control electrode, said triggering means and said pulse applying means together comprising a transformer with a primary winding arranged to be selectively connected to a source of voltage and first and second secondary windings coupled to the control electrode of the first controlled rectifier and to a starter electrode of said flash tube, respectively, the control electrode of said second controlled rectifier being coupled to said control circuit which is arranged to trigger said second controlled rectifier into conduction at a point in time subsequent to when the first controlled rectifier and the flash tube are triggered into conduction and independently of the current then flowing through the flash tube.

8. A circuit as claimed in claim 4 wherein the capacitance of said first capacitor is substantially larger than the capacitance of said second capacitor and wherein the circuit parameters are chosen so that the voltage on the second capacitor is higher than the voltage on the first capacitor at the instant when said second conDuction device is triggered into conduction. 9 A flash control circuit for a flash tube comprising, a pair of terminals, first and second capacitors, means connecting said first and second capacitors in series across said terminals, means coupled to said terminals for electrically charging said capacitors with the same polarity and in a manner such that the second capacitor is charged to a voltage level that can be chosen independently of the volage level to which the first capacitor is charged, first and second controlled conduction devices, first means connecting said first controlled conduction device in circuit with said first capacitor and said flash tube so as to control the discharge of said first capacitor across the flash tube, a second means connecting said second controlled conduction device in circuit with said second capacitor and said flash tube in a manner so as to apply a reverse bias voltage from said second capacitor to said first conduction device when said second conduction device is triggered into conduction, a control circuit coupled to a control electrode of said second conduction device and including a photosensitive element arranged to respond to the flash tube light reflected by an object, means for triggering the first conduction device into conduction to discharge the first capacitor and thereby flash said tube, said control circuit being operative in accordance with the light reflected onto the photosensitive element by said object to trigger the second conduction device into conduction thereby to apply said reverse bias voltage to the first conduction device for a time period that is longer than the recovery time of said first conduction device. 10. A circuit as claimed in claim 9 wherein said first connecting means connects said first conduction device between the junction point of the series connected capacitors and one main electrode of the flash tube and said second connecting means serially connects said second capacitor and said second conduction device in the order named between said junction point and said one main electrode of the flash tube.

11. A circuit as claimed in claim 9 wherein the capacitance of said first capacitor is greater than the capacitance of the second capacitor and wherein the plates of said capacitors that form a junction point therebetween are charged with opposite polarity.

12. A circuit as claimed in claim 11 wherein the circuit parameters are chosen so that the voltage on the second capacitor is higher than the voltage on the first capacitor at the instant when said second conduction device is triggered into conduction.

13. A circuit as claimed in claim 9 wherein said second connecting means is arranged to provide only one discharge path for said second capacitor, said discharge path including the second conduction device.