GAS DISCHARGE LAMP BALLAST CIRCUIT WITH INDICATOR OF BALLAST OPERABILITY

A gas discharge lamp ballast with an indicator of operability of the ballast is disclosed. The ballast circuit comprises circuitry for providing a d.c. bus voltage on a bus conductor with respect to a ground, and a resonant load circuit. The resonant load circuit includes lamp terminals for connecting to a removable gas discharge lamp, a resonant inductor, and a resonant capacitor. The resonant inductor and resonant capacitor are selected to set a magnitude, and resonant frequency, of a bidirectional current in the lamp. Further included is a converter circuitry, including first and second serially connected switches coupled between the bus conductor and the ground, and providing to the resonant load circuit, at a node coupled between the first and second switches, a voltage that alternates between first and second voltage levels. Circuitry for generating first and second switch control signals for alternately switching into conduction the first and second switches, including circuitry responsive to a feedback signal representing a current in the resonant load circuit, are further included. The ballast circuit, moreover, includes overload detection circuitry for detecting if voltage applied to the lamp terminals exceeds an overload level; and circuitry for indicating, in response to such an overload condition being detected by the overload detection circuitry, probable operability of the ballast circuit.