Patent ID: 7282872

Claim:
A discharge lamp lighting circuit comprising: a DC-AC converter circuit comprising: an AC conversion transformer having primary and secondary sides; a plurality of switching elements; and a series resonant circuit coupled to the primary side of the AC conversion transformer and including a resonance capacitor and an inductance element being serially connected to said resonance capacitor; where said DC-AC converter circuit is operable to perform DC-AC conversion by controlling a driving frequency of said switching elements so as to supply a resonance voltage from said AC conversion transformer to a discharge lamp; voltage detecting means for detecting a voltage applied to a discharge lamp; current detecting means for detecting a current flowing through said discharge lamp where said current detection is performed by an auxiliary winding forming a transformer with said inductance element, and means for determining light on/off state of said discharge lamp based on values corresponding, respectively, to the voltage detected by said voltage detecting means and the current detected by said current detecting means, wherein said determination is performed with respect to such a condition that an absolute value of difference between the value corresponding to the voltage detected by the voltage detection means and the value corresponding to the current detected by the current detection means being detected during light-off state is larger than that of being detected during light-on state.