High-frequency electronic ballast with auto-tracking control for metal halide lamps

Abstract

An auto-tracking control strategy is proposed for high-frequency electronic ballasts to operate the metal halide lamp at a frequency free of acoustic resonance. In case the acoustic resonance should happen, the variation in the lamp voltage is detected and then the operating frequency is changed step by step until a frequency with stable operation is located. In cooperating with the detection circuit, the control strategy is implemented on an electronic ballast with the half-bridge class-D load-resonant inverter. A prototype designed for 70 W metal halide lamps is used to illustrate the operations of the auto-tracking control.