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This paper presents a digital controller using a novel complex modulation method for the metal halide lamp ballast. The proposed controller has an ability to prevent acoustic resonance more effectively than the conventional modulation controller. Furthermore, the proposed controller includes some useful functions such as soft starting, lamp fault protection, power control for dimming, overload protection, real-time acoustic resonance detection, and so on. To accommodate future application-specific integrated circuits (ASICs), the proposed controller has been designed with erasable programmable logic devices (EPLDs). In this paper, detailed complex modulation algorithms and digital control schemes are described, and experimental results of the prototype 150-W metal halide lamp ballast with the proposed digital controller are finally discussed.
Date of Publication: Jan 2003