GB1265944A - - Google Patents

Abstract

1,265,944. Supply circuits for discharge lamps. INTERNATIONAL STANDARD ELECTRIC CORP. 5 May, 1970 [12 May, 1969], No. 21492/70. Heading H2H. A starting and operating circuit for a highpressure arc lamp 15 such as a xenon or mercury arc lamp comprises a first circuit 45, 57-59, 64 for supplying a high starting voltage, a second circuit 18-20 for supplying a first relatively low direct current voltage for operating the lamp, and a number of circuits 34-36 for supplying a corresponding number of direct current voltages respectively progressively higher than the first voltage. The circuits 34- 36 include diodes 40, 42, 43 and are connected to taps of the secondary winding 26 of a transformer 23, the primary winding 24 of which is supplied with alternating current at 400 c/s. via an inverter 25 and a battery 18. To start the lamp a switch 55 is momentarily closed so that the first circuit which includes a spark gap 58 applies a high voltage across the lamp electrodes. On initial ionisation of the lamp and opening switch 55 lamp current flows in the diodes 43 and a resistor 39, the diodes 40, 42 being back biased so that current does not flow in the circuits 34, 35. As the current in the lamp increases, the back bias on the diodes 42 and then on the diodes 40 is removed so that the lamp is supplied by the low voltage of the circuit 35 and then by the relatively lower voltage of the circuit 34. As the lamp current approaches its operating value, the back bias on a diode 20 is removed so that the lamp current is supplied by the source 18 thus causing the coil 62 of a relay 60 to actuate a contact 63 thereby de-energizing the transformer 23.