Patent ID: 6304041
Filing Date: 2001-10-16
Classification: H05B,Y02B,Y10S

Abstract:
A dimmable ballast circuit for a gas discharge lamp, comprising:a resonant load circuit including a resonant inductance and a resonant capacitance for coupling a.c. current to a gas discharge lamp;a self-oscillating complementary converter circuit for inducing a.c. current in the resonant load circuit, the converter circuit including a pair of switches serially connected between a d.c. bus and a reference bus, respective reference nodes of the switches being connected at a common node through which the a.c. current flows, and respective control nodes of the switches being substantially directly interconnected;a gate drive circuit for controlling the switches, including a drive winding connected between the common node and the control nodes, and mutually coupled to the resonant inductance for coupling voltage therefrom; anda clamping circuit including an inductor serially connected between the drive winding and the common node, and active circuitry directly coupled to terminals of the inductor for controlling a maximum voltage amplitude across the inductor in response to an error signal representing a difference between a user-selectable set point signal and a feedback signal representing a time-averaged value of a lamp operating parameter.