Gas discharge lamp ballast circuit with indicator of ballast operability.

摘要

The lamp ballast circuit includes circuitry for DC bus voltage supply on a bus conductor w.r.t. a ground. A resonant load circuit includes lamp terminals for connecting to a removable gas discharge lamp, and has a resonant inductor and a resonant capacitor which are selected to set a magnitude, and resonant frequency, of a bidirectional current in the lamp. Converter circuitry includes two serially connected switches coupled between the bus conductor and the ground, and supplying an alternating voltage to the load circuit at a node coupled between the switches. Circuitry generates two switch-control signals to alternately switch into conduction switches, including circuitry responsive to a feedback current signal from the resonant load circuit. Overload detection circuitry detects if any of the positive and negative excursions of voltage applied to the lamp terminals exceeds an overload level. Probable operability of the ballast circuit is indicated in response to a detected overload condition. The overload detection circuit includes a transformer winding coupled to detect current through the load circuit, with a second transformer winding mutually coupled to the first winding, and has an intermediate tap connected to ground, and a full-wave rectifier coupled across the second winding.