Patent ID: 7348733

Claim:
A lighting circuit for a discharge lamp comprising a DC-AC converter circuit to receive a DC input voltage and to convert the DC input voltage to an AC voltage and boost the AC voltage, a starter circuit for supplying the discharge lamp with a starting signal, and control means having an input voltage detector circuit for detecting the DC input voltage for controlling power output by said DC-AC converter circuit to perform a lighting control of the discharge lamp, wherein: said DC-AC converter circuit includes a transformer, a plurality of switching elements, and a resonance capacitor, said switching elements being driven by said control means, said DC-AC converter circuit utilizing a series resonance of said resonance capacitor with an inductance component of said transformer or an inductance element connected to said resonance capacitor, and when said input voltage detector circuit detects the DC input voltage equal to or lower than a predefined threshold, a driving frequency for said switching elements is shifted to a frequency lower than a frequency range when the discharge lamp is turned on to increase a voltage which can be output by said DC-AC converter circuit to maintain the lighting state of the discharge lamp.