GB1265401A - - Google Patents

Abstract

1,265,401. Control circuits for discharge lamps. ADDRESSOGRAPH-MULTIGRAPH CORP. 25 Feb., 1969 [5 March, 1968], No. 10089/69. Heading H2H. A discharge lamp is connected in series with an A.C. source and a controlled conduction device. A trigger circuit operates to place the device in a conductive state for a predetermined interval, and also energizes a starter electrode on the lamp. In the embodiment shown, a circuit for flashing a high-intensity radiation source such as a xenon lamp 12 provided with a trigger electrode 18 includes an A.C. input transformer. 20 and a thyristor 24 connected in series with the lamp. In the inoperative condition shown, capacitors 28 and 48 are fully charged and a further capacitor 38 is uncharged. To operate the lamp, a switch 36 is moved to position 36B so that during the next negative half-cycle current will flow into the capacitor 38 thus biasing the cathode and gate electrode of thyristor 24 into a conductive condition. A holding current through the thyristor is now provided by the discharge of capacitor 28, maintaining the thyristor conductive into the succeeding positive half-cycle. At the same time, the capacitor 48 also discharges through the primary winding 56A of a pulse transformer 56, which applies a high voltage pulse to the trigger electrode 18 enabling current from the input transformer 20 to energize the lamp for the duration of the positive half-cycle. The circuit will then return to its inoperative condition even if the switch 36 is held in position 36B. Return of the switch to position 36A discharges the capacitor 38 in readiness for subsequent operation.