Acoustic-Resonance-Free High-Frequency Electronic Ballast for Metal Halide Lamps

To avoid the acoustic resonance on operating metal halide lamps, an autofrequency-searching method is implemented on the high-frequency electronic ballast. The proposed method allows the use of a high-frequency electronic ballast, making the ballast able to adjust the operating frequency automatically as soon as the acoustic resonance is detected and, consequently, to locate it at a stable frequency. The electronic ballast achieves a high efficiency and a high power density through the employment of a high-frequency resonant inverter with an embedded buck-boost converter for power-factor correction and lamp power regulation. The control strategy is realized by a microprocessor along with the acoustic-resonance detection circuit. The operation of autofrequency searching is illustrated by the experiments on an electronic ballast designed for 70-W metal halide lamps.