ES355174A1 - Starter circuits for discharge lamps - Google Patents

Abstract

A control system for a discharge lamp, such as a high pressure sodium or mercury vapour lamp, comprises means whereby the restarting of a hot lamp is enhanced. A discharge lamp 12 is connected to an A.C. supply OP by way of an inductor having a tapping 11, the lamp being shunted by a circuit connected to the tapping 11 and comprising a thyristor 18 and a condenser 16. The control electrode 20 of the thyristor is connected to a point in a circuit connected across the major part 10 of the inductor, the circuit including a resistor 22 and a contact 28 operated by a relay winding 26 which is energized by the minor part 13 of the inductor by way of a full-wave rectifier 24. When the system is initially switched on by a switch 14 the inductor carries little current, the relay winding 26 is thus not energized and the contact 28 remains open. A periodic signal is thus devised by way of the resistor 22 and applied to the control electrode 20 so making the thyristor conductive during alternate half-cycles of the supply OP. A pulsating current flows via the part 13 of the inductor to charge the capacitor 16. A high voltage is then induced across the whole inductor which causes the lamp 12 to ignite after one or, at the most, a few half-cycles of the supply. After the lamp has ignited the portion 13 of the inductor provides a voltage sufficient to energize the relay winding 26 to close the contact 28. The thyristor is thus rendered non-conductive during normal running of the lamp 12. Should the lamp be switched on when hot following a short interruption in the running thereof, the thyristor will continue to provide starting pulses for the lamp until it has cooled sufficiently to enable it to be re-ignited.