Analysis and Implementation of an HPF Electronic Ballast for HID Lamps With LFSW Voltage

In this paper, a novel high power-factor electronic ballast for metal-halide (MH) lamps based on integration of a buck-boost converter, a buck converter, and a full-bridge inverter is proposed. The buck-boost converter that serves as a power-factor corrector (PFC) is designed to operate at discontinuous conduction mode to achieve a high power factor at the input line. A bidirectional buck converter formed by a full-bridge inverter, an inductor, and a capacitor drives an MH lamp with a low-frequency square-wave voltage to prevent the lamp from acoustic resonance. The lamp power is controlled by adjusting the duty ratio of the active switches of the PFC. The circuit operation is analyzed in detail to derive the design equations. Circuit parameters are designed based on design considerations in practical applications. Finally, a prototype electronic ballast for a 70-W MH lamp is built and tested. Satisfactory performances are obtained from the experimental results.