Patent ID: 6078143
Filing Date: 2000-06-20
Classification: H05B,Y10S

Abstract:
A ballast circuit for a gas discharge lamp, comprising:(a) a d.c.-to-a.c. converter circuit with means for coupling to a resonant load circuit, for inducing a.c. current therein, said converter circuit comprising:(i) a pair of switches serially connected between a bus conductor at a d.c. voltage and a reference conductor, the voltage between a reference node and a control node of each switch determining the conduction state of the associated switch;(ii) the respective reference nodes of said switches being connected together at a common node through which said a.c. current flows, and the respective control nodes of said switches being connected together;(b) a gate drive arrangement for regeneratively controlling said first and second switches, said arrangement comprising:(i) a feedback circuit for providing a feedback signal representing current in said load circuit;(ii) a coupling circuit including an inductor for coupling said feedback signal to said control nodes; and(iii) a first bidirectional voltage clamp connected between said common node and said control nodes; and(c) a second bidirectional voltage clamp coupled across said inductor in such manner as to limit the positive and negative voltage excursions across said inductor, and in such manner as to increase frequency of operation above a minimum frequency point and thereby limit the positive and negative voltage excursions across said lamp to the output voltage at said minimum frequency.