A digital controlled electronic ballast using high frequency modulation method for the metal halide lamp

This paper presents a digital controlled electronic ballast for the metal halide lamp. The proposed ballast operates with the modulated driving frequency range of 20 kHz to 100 kHz in order to avoid the acoustic resonance phenomenon. It can start up the lamp by using the LC resonant circuit without external igniter and its digital controller includes some functions for soft starting, lamp fault protection, power control for dimming, overload protection and frequency modulation. In this paper, detailed digital control algorithms are described and a novel real time detection method of the acoustic resonance and the tracking algorithm for its avoidance are proposed. And the experimental results on the proto-type 150W metal halide electronic ballast with the proposed digital controller, which has been designed using erasable programmable logic devices (EPLDs), are discussed.