Two-Stage High Power Factor Electronic Ballast for Metal-Halide Lamps

This paper presents a novel two-stage high power factor electronic ballast for metal-halide (MH) lamps. The front stage is a single-switch two-output integrated converter, which is a combination of two buck-boost converters. The functions of power factor correction (PFC) and lamp power control are achieved by the integrated converter. The post stage is a low frequency half-bridge inverter, which is used to drive the MH lamp with a low-frequency square-wave current for avoiding acoustic resonance. The analyses of input current, the constant lamp power control, DC-bus voltage, and boundary conditions are discussed. A 70 W laboratory prototype is implemented to verify the performance. The measured results illustrate that the harmonic distortion of AC input current satisfies the requirements of the IEC 61000-3-2 Class C standard, and the lamp power is maintained at a constant level within plusmn 1.1 %.