Gas discharge lamp ballast circuit with reduced parts-count starting

Abstract

Disclosed is an electronic ballast circuit for a high pressure gas discharge lamp with a reduced parts-count starting circuit. The circuit comprises an arrangement for supplying d.c. voltage from a d.c. source, and a main inductor for receiving energy from the d.c. source and supplying the energy to the lamp. The main inductor has a plurality of windings. A first winding of the inductor is coupled to receive energy from the d.c. source. Further included is a current-switching arrangement conductive during periodic first part cycles for transferring energy from the d.c. source to the main inductor, and non-conductive during periodic second part cycles. A first part cycle is followed by a second part cycle in successive periods of switching operation of the current-switching arrangement. The first winding of the main inductor has impressed across it substantially the d.c. source voltage during the first part cycles, and reflects substantially the lamp voltage during the second part cycles. The circuit further includes a starting circuit for providing a pulse in excess of 15,000 volts across the lamp to facilitate starting the lamp. The starting circuit comprises a spark gap device, a pulse transformer, and a voltage-generating circuit. The voltage-generating circuit comprises a starting capacitor for storing energy and impressing across a spark gap an increasing voltage, which reaches the breakdown voltage of the spark gap during a lamp start-up period, and also a circuit for charging the starting capacitor with energy from the main inductor during the second part cycles.