Lighting circuit for vehicular discharge lamp

Abstract

Disclosed is a lighting circuit for a discharge lamp, which employs a rectangular-wave based lighting system and is designed to prevent lighting failure from frequently occurring in the discharge lamp immediately after the lighting of the discharge lamp starts or at the end of the lamp's life. In the lighting circuit, a battery voltage is boosted by a DC booster circuit and is then converted to a rectangular-wave voltage by a DC/AC converter. This rectangular-wave voltage is then applied via an inductor of an igniter circuit to a metal halide lamp. The DC booster circuit has a chopper type structure and has a smoothing capacitor at the output stage. A resonance controller comprising a diode and a resonance capacitor is located between the DC booster circuit and the DC/AC converter. The DC/AC converter has a bridge structure having field effect transistors (FETs). The two pairs of FETs are reciprocally switched from one pair to the other by a drive controller. The diode of the resonance controller serves to cut off the current path to block the coupling of the inductor to the smoothing capacitor of the DC booster circuit and couple the resonance capacitor to the inductor, when the polarity of the rectangular-wave voltage is inverted.

Dependencies are inferred from the claim text.