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 buckboost converters. The functions of power factor correction and lamp-power control are achieved by the integrated converter in discontinuous conduction mode. The poststage 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 ± 1.1%.