GB1331328A - Electronic flashlight units - Google Patents

Abstract

1331328 Electronic Flash Control MULTIBLITZ DR ING D A MANNESMANN GmbH & CO KG 22 April 1971 [5 May 1970 5 Aug 1970] 10830/71 Heading G2A [ Also in division H3] A flashlight unit comprises a flash tube 16 provided with an ignition electrode 24, a photo sensitive resistor 58 adapted to receive the light reflected from an object, a thyristor 22 connected in series with the tube, a capacitor 60 for integrating the reflected light flux and a quenching circuit for quenching the flash discharge when the integrated light flux reaches a pre-determined level. Closure of a switch 30 enables a capacitor 28 to discharge through the primary of a transformer 26 which supplies an ignition pulse to the electrode 24. Simultaneously, the increased voltage across a resistor 32 due to the closure of the switch, causes a diac 42 to condut and a capacitor 40 supplies a pulse to the gate electrode of the thyristor 22. A storage capacitor 14 therefore discharges through the tube 16 and a voltage appears across a resistor 20. The capacitor 60 charges up to a voltage dependent on the total light flux received by the photo sensitive resistor 58. At the pre-determined level a thyristor tetrode 64 becomes conductive enabling a capacitor 66 to discharge and supply a pulse to the gate electrode of a thyristor 50. A commutating capacitor 46 therefore supplies a positive potential to the cathode of the thyristor 22 which is thereby switched off to quench the tube discharge. In a modification the thyristors 22, 50 are each replaced by a pair of parallel connected thyristors, the diac 42 and the thyristors tetrode 64 also being replaced by thyristors.