A novel two-stage electronic ballast for metal-halide-type HID lamps

This paper presents a novel two-stage, high-power-factor electronic ballast for metal-halide (MH)-type high-intensity-discharge (HID) lamps. The ballast comprises of a boundary-conduction-mode (BCM)-operated buck boost-flyback converter to achieve input current shaping and a half-bridge-type inverter to supply the lamp with low-frequency square-wave sources. The features of the proposed ballast are high power factor (≫0.99), low total-harmonic-distortion (THD) of input ac-current, cost-effective and acoustic-resonance-free. Operational principles and experimental results of the proposed ballast for one 70-W NH-type HID lamp operating at 400 Hz switching frequency with 110V-rms input ac-voltage are presented.