Patent ID: 7005808

Claim:
A discharge lamp illumination circuit comprising: a DC-AC conversion circuit which effects AC conversion and boosting upon receipt of a DC input; and a starter circuit for supplying a start-up signal to a discharge lamp, the discharge lamp illumination circuit being used for illumination control using control means for controlling a power output from the DC-AC conversion circuit, wherein the DC-AC conversion circuit comprises: an AC conversion transformer; a plurality of switching elements; and a resonance capacitor, wherein the switching elements are activated by the control means, thereby causing serial resonance between the resonance capacitor and an inductance component of the AC conversion transformer, or between the resonance capacitor and an inductance component connected to the resonance capacitor; wherein the operating frequency of the switching elements is controlled so that a resonance voltage generated at a primary side of the AC conversion transformer is boosted to supply electric power to the discharge lamp from a secondary side of the AC conversion transformer; and wherein when a resonance frequency of the discharge lamp during an extinction period is denoted as fi and a resonance frequency of the discharge lamp during an illumination period is denoted as f 2 , switching of a no-load voltage applied on the discharge lamp before the discharge lamp is illuminated is controlled in so that the operating frequency is regulated at a frequency that initially differs from f 1 and then gradually approaches f 1 .