US3662213A - Cascaded thyristor quenching arrangement for a pulsed flash device - Google Patents

Cascaded thyristor quenching arrangement for a pulsed flash device Download PDF

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Publication number
US3662213A
US3662213A US8271A US3662213DA US3662213A US 3662213 A US3662213 A US 3662213A US 8271 A US8271 A US 8271A US 3662213D A US3662213D A US 3662213DA US 3662213 A US3662213 A US 3662213A
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United States
Prior art keywords
flash tube
capacitor
thyristor
current
conduction
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Expired - Lifetime
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US8271A
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English (en)
Inventor
Rolf Dieter Dennewitz
Emil A Exner
Henning Zierau
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US Philips Corp
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US Philips Corp
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Publication date
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    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
    • H05B41/14—Circuit arrangements
    • H05B41/30—Circuit arrangements in which the lamp is fed by pulses, e.g. flash lamp
    • H05B41/32—Circuit arrangements in which the lamp is fed by pulses, e.g. flash lamp for single flash operation
    • H05B41/325—Circuit arrangements in which the lamp is fed by pulses, e.g. flash lamp for single flash operation by measuring the incident light

Definitions

  • ABSTRACT [22] Filed: 1970 A compact, high-speed quenching arrangement is described [2l] Appl. No.: 8,271 for use with a portable flash unit that is required to handle moderately high peak currents during quench. A pair of normally nonconductive cascaded thyristors are connected in Foreign Application Prlomy Data shunt with the flash tube. When a predetermined quantity of June 3 1969 Germany "I9 28 1573 emitted light has been monitored and integrated by the flash unit, the first thyristor is switched into conduction. The resultlsz ⁇ US Cl i I A i m3l5/l49 315/24 ing build-up of current in the transconductive path of the first 511 im. Cl.
  • Such gas discharge quench tubes are not generally suitable for use in portable flash devices since they are bulky in themselves and require heavy-duty ignition circuitry and electrostatic shielding to prevent premature ignition. Additionally, their switching speed is relatively low.
  • control signal developed in the light integrating portion of the flash unit has reached a value sufficient to overcome a predetermined threshold level at the input of the transistor, the latter is switched off and the associated rise in potential at its collector triggers the thyristor into conduction to short-circuit the flash tube and terminate the flash.
  • the transconductive paths of a pair of normally disabled cascaded thyristors are connected across the flash tube through current-limiting resistors.
  • the control electrode of the first thyristor is connected to the output of a light-integrating arrangement that is rendered effective at the start of the flash for generating a control signal proportional to the integrated light energy contained in the flash tube emission.
  • the control signal has reached a value sufficient to trigger the control electrode of the first thyristor, the latter starts to conduct to bypass a portion of the flash capacitor energy from the flash tube.
  • An additional resistor in series with the first thyristor responds to the resulting flow of current therethrough to develop a voltage that is applied to the control electrode of the second thyristor so that the latter is instantaneously switched into conduction to absorb the remaining flash capacitor energy.
  • the total switching time between the triggering of the first thyristor and the full conduction of the second thyristor may be as low as l microsecond.
  • the peak current load that may be handled by the cascaded thyristor quenching arrangement may be adjusted by suitably selecting the magnitude of the current-limiting resistors in the transconductive paths of the thyristors.
  • a pulseexcited flash unit including a conventional flash tube 1 (illustratively a gas filled envelope).
  • the tube 1 is provided with a pair of excitation terminals 21 and 22.
  • a primary winding 2a of a transformer 2 is connected between the terminal 22 and a common terminal 23 of the flash unit.
  • a flash capacitor 14 is connected across the terminals 21 and 23.
  • the capacitor 14 may be selectively charged in a known manner to a relatively high potential of the polarity shown from a conventional DC power source 15.
  • the flash tube 1 is further provided with a trigger electrode 13. While not specifically illustrated in the drawing, the trigger electrode may be coupled to the secondary winding of a conventional ignition transformer whose primary winding may be excited by a synchronizing pulse in a known manner.
  • the voltage of the charged flash capacitor 14 is not normally sufficient by itself to cause emission of light energy from the tube 1. However, as is well known, this tube will emit light upon the concurrent application of an igniting pulse to the trigger electrode 13 through its associated ignition transformer. The resulting flash of light energy produced in the tube 1 is emitted through the walls of the tube envelope to a suitable object (not shown). A portion of the light reflected from the object is detected by a photosensitive element 5 (illustratively a light sensitive resistor) which is connected in a light integrating circuit 24 in the manner described below.
  • the resultant conduction of the flash tube (A) causes light energy to be emitted toward the object to be illuminated, and (B) causes a pulse of current to pass through the primary winding 2a of the transformer 2. A corresponding voltage pulse is thereby generated across a secondary winding 2b of the transformer 2. Such voltage pulse is coupled through a rectifying diode 3 to establish a voltage across a capacitor 4.
  • a voltage divider consisting of the light sensitive resistor 5 and an additional pair of resistors 6 and 7 (the former being adjustable) is connected across the capacitor 4.
  • the resulting potential appearing at a junction 26 of the resistors 6 and 7 (which junction forms the output of the light integrating circuit 24) is coupled, through a diode 8, to the control electrode of a first normally disabled thyristor 9.
  • the transconductive path of the thyristor 9 is connected through a pair of resistors 10 and 13' across the terminals 21 and 23 for shunting the flash tube 1. Such transconductive path is therefore excited whenever the flash capacitor 14 is in its charged state.
  • a second normally disabled (cut-off) thyristor 12 is connected in cascade with the thyristor 9 across the flash tube 1 to absorb a portion of the flash capacitor energy bypassed from the flash tube 1 during a quenching operation, as described below.
  • a junction of the resistor 10 and the cathode of the first thyristor 9 is connected through a second isolating diode 11 to the control electrode of the second thyristor 12.
  • the transconductive path of the the thyristor 12 is connected, through a resistor 14', across the terminals 21 and 23 so that the thyristor 12 is also normally energized by the voltage on the flash capacitor 14.
  • the characteristics of the thyristors 9 and 12 and the resistors 10, 13, and 14 may be selected such that the thyristor 12 is immediately triggered into conduction by the voltage developed across the resistor 10 by the current resulting when the thyristor 9 is driven into conduction.
  • Such conduction of the thyristor 9 is initiated by the action of the light integrating circuit 24.
  • the voltage on the capacitor 4 builds up at a rate determined by variations in the resistance of the light sensitive resistor in the shunting voltage divider. Such variations are in turn proportional to the intensity of the light reflected to the resistor 5 from the illuminated object.
  • the voltage across the capacitor 4, and therefore the proportional voltage at the junction 26, is indicative of a quantity proportional to the total integrated reflected light from the object.
  • the thyristor 9 will conduct when the potential at the junction 26 has built up to a point that exceeds the characteristic threshold triggering level at the control electrode of the thyristor 9.
  • the resulting pulse of current through the primary winding 2a will result in a pulse of charging current applied to the capacitor 4 through the secondary winding 2b and the diode 3.
  • the voltage across the capacitor 4 thereupon builds up in a manner determined by the characteristic of the light sensitive resistor 5 in response to the light reflected thereto from the object.
  • the resulting potential at the junction 26 builds up in proportion to the total light energy integrated by the circuit 24.
  • the thyristor When the emission of light from the tube 1 has persisted for a duration long enough to permit the voltage at the control electrode of the thyristor 9 to exceed its threshold trigger value, the thyristor is rapidly driven into conduction to efiectively present a low impedance across the flash tube 1. A portion of the energy from the flash capacitor 14 is thereupon bypassed from the flash tube 1 to the now-conductive thyristor 9 to commence the quenching operation. The resulting surge of current through the transconductive path of the thyristor 9 causes a proportional voltage to be developed across the resistor 10.
  • Such voltage applied to the control electrode of the second thyristor 12 through the diode l 1, drives the thyristor 12 into conduction to further lower the total shunting impedance across the tube 1 thus to absorb the remaining bypassed energy from the flash capacitor 14, thereby preventing overloading of the thyristor 9.
  • the total interval between the triggering of the first thyristor 9 and the full conduction of the second thyristor 12 can be as low as l microsecond and even lower.
  • the quantity of light energy emitted by the flash unit before quench may be regulated, e.g., by suitably varying the value of the adjustable resistor 6 in the light integrating circuit 24. Also, it will be understood that the current load handled by the thyristors 9 and 12 may be varied by suitably selecting the magnitudes of the current limiting resistors 13' and 14'.
  • the cascaded thyristor arrangement of the instant invention avoids the problem of large and bulky gas discharge devices with their accompanying heavy-duty ignition circuitry and electrostatic shields.
  • the associated flash unit may safely operate with objecrto-flashlamp distances so small as to normally cause excessive exposure of the object to be illuminated when prior art gas discharge quench tubes are used.
  • An apparatus for rapidly terminating the output of a pulsed flash tube when a controllable quantity of light energy has been emitted therefrom comprising:
  • first means rendered effective at the start of the flash for generating a control signal that varies in proportion to the light energy emitted from the flash tube;
  • first and second normally disabled thyristors having their respective transconductive paths connected in parallel across the flash tube;
  • the first generating means comprises, in combination, a capacitor, a transformer having a primary winding in series with the flash tube and a secondary winding connected across the capacitor, and a voltage divider including a photosensitive element connected across the secondary winding and the capacitor.
  • the first coupling means comprises a diode connecting a tap point of the voltage divider to the control electrode of the first thyristor.
  • the second generating means comprises an additional resistor connected in the transconductive path of the first thyristor.
  • a flash tube ignition control circuit comprising, a capacitor connected across the flash tube for supplying operating current thereto, means coupled to the flash tube for igniting said flash tube, first and second substantially identical normally nonconductive load sharing semiconductor controlled conduction devices each having a rated current capacity which is insufficient by itself to safely pass the normal expected operating discharge current of said capacitor during a tube quenching operation, means connecting said first and second semiconductor devices in parallel across the flash tube, a light integrating circuit responsive to the flash tube current for generating a control signal upon ignition of the flash tube, said integrating circuit including a photosensitive element arranged to respond to a portion of the flash tube light reflected by an object thereby to cause said control signal to vary as a function of said reflected light, means for coupling said control signal to the control electrode of the first semiconductor device to trigger same into conduction to initiate the quenching operation when the control signal attains a predetermined value, means responsive to the current flow through the first semiconductor device for generating a voltage of a magnitude to trigger the second semiconductor device into conduction, and means for coup
  • said integrating circuit further comprises means for electrically isolating said second capacitor from any electrical energy source so that the second capacitor voltage returns to approximately zero value in the absence of current flow through the flash tube.
  • said charge current supply means comprises a transformer with a primary winding in series with the flash tube and a secondary winding connected across said second capacitor.

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  • Stroboscope Apparatuses (AREA)
  • Discharge-Lamp Control Circuits And Pulse- Feed Circuits (AREA)
  • Exposure Control For Cameras (AREA)
US8271A 1969-06-03 1970-02-03 Cascaded thyristor quenching arrangement for a pulsed flash device Expired - Lifetime US3662213A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE19691928157 DE1928157A1 (de) 1969-06-03 1969-06-03 Schaltungsanordnung fuer Elektronenblitzgeraete mit in Abhaengigkeit von der reflektierten Lichtmenge geregelten Nutzblitzdauer

Publications (1)

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US3662213A true US3662213A (en) 1972-05-09

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US8271A Expired - Lifetime US3662213A (en) 1969-06-03 1970-02-03 Cascaded thyristor quenching arrangement for a pulsed flash device

Country Status (9)

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US (1) US3662213A (de)
JP (1) JPS493582B1 (de)
BE (1) BE751424A (de)
CH (1) CH537594A (de)
DE (1) DE1928157A1 (de)
FR (1) FR2045812A1 (de)
GB (1) GB1307244A (de)
NL (1) NL7007869A (de)
SE (1) SE359999B (de)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3737721A (en) * 1971-01-22 1973-06-05 Honeywell Inc Computer flash with remote sensor and two-wire control of flash firing and quench
US3787704A (en) * 1970-02-20 1974-01-22 Loewe Opta Gmbh Electronic flash unit with controlled light energy
US4029992A (en) * 1974-04-08 1977-06-14 Braun Aktiengesellschaft Flash apparatus with flash terminating switch controlled by photosensor
EP1191825A2 (de) * 2000-09-25 2002-03-27 Fuji Photo Film Co., Ltd. Flashgerät für eine Kamera

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE387497B (sv) * 1975-06-19 1976-09-06 Ericsson Telefon Ab L M Pulsgenerator
DE4029203C2 (de) * 1990-09-14 1995-04-20 Hella Kg Hueck & Co Einrichtung zur Lichtbogenlöschung bei Lichtblitzerzeugungseinrichtungen für Flugzeuge

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3293449A (en) * 1963-06-24 1966-12-20 Gen Electric Solid state thyratron replacement
US3509422A (en) * 1967-10-31 1970-04-28 Research Corp Automatic photographic fill-in flash circuit
US3541387A (en) * 1968-04-23 1970-11-17 Bosch Elektronik Gmbh Control system for terminating the discharge of a flash lamp

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3293449A (en) * 1963-06-24 1966-12-20 Gen Electric Solid state thyratron replacement
US3509422A (en) * 1967-10-31 1970-04-28 Research Corp Automatic photographic fill-in flash circuit
US3541387A (en) * 1968-04-23 1970-11-17 Bosch Elektronik Gmbh Control system for terminating the discharge of a flash lamp

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3787704A (en) * 1970-02-20 1974-01-22 Loewe Opta Gmbh Electronic flash unit with controlled light energy
US3737721A (en) * 1971-01-22 1973-06-05 Honeywell Inc Computer flash with remote sensor and two-wire control of flash firing and quench
US4029992A (en) * 1974-04-08 1977-06-14 Braun Aktiengesellschaft Flash apparatus with flash terminating switch controlled by photosensor
EP1191825A2 (de) * 2000-09-25 2002-03-27 Fuji Photo Film Co., Ltd. Flashgerät für eine Kamera
EP1191825A3 (de) * 2000-09-25 2004-12-29 Fuji Photo Film Co., Ltd. Flashgerät für eine Kamera

Also Published As

Publication number Publication date
JPS493582B1 (de) 1974-01-26
BE751424A (fr) 1970-12-03
GB1307244A (en) 1973-02-14
FR2045812A1 (de) 1971-03-05
DE1928157A1 (de) 1970-12-10
CH537594A (de) 1973-05-31
SE359999B (de) 1973-09-10
NL7007869A (de) 1970-12-07

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