A unity power factor electronic ballast for metal halide lamps

This paper proposes a unity power factor high-frequency electronic ballast for high-intensity discharge lamps. The ballast consists of an integrated, single stage power factor corrected rectifier, and a half-bridge high-frequency resonant inverter to interface the lamp with the DC bus. PWM control of the single stage rectifier produces sinusoidal input current at unity input power factor. The lamp is referenced to the supply neutral, without ohmic isolation, which is an important safety feature. To prevent acoustic resonance, a commonly encountered problem in high-frequency operation, the inverter is driven by a frequency modulated PWM strategy. The choices of the carrier frequency, the frequency modulation range, and the modulation sweep frequency are functions of selected lamp type. The proposed ballast is analyzed, simulated and experimentally verified with a 250 W metal halide lamp