Patent ID: 7511432

Claim:
A discharge lamp lighting device, comprising: a direct current power source; a chopper circuit capable of controlling an output power by performing DC-DC conversion with the direct current power source as a power source; a smoothing capacitor connected between output terminals of the chopper circuit; a polarity inversion circuit for performing DC-AC conversion with a voltage across the smoothing capacitor as a power source; a high pressure discharge lamp to which an alternating voltage is applied by the polarity inversion circuit; a control circuit for controlling an output of the polarity inversion circuit as well as an output power of the chopper circuit; and a voltage detecting circuit for detecting a voltage corresponding to a lamp voltage of a high pressure discharge lamp, wherein a switch voltage for defining a range of voltages detected by the voltage detecting circuit is set in the control circuit, and the control circuit has a function of controlling the polarity inversion circuit such that an inversion frequency, at which the polarity of the lamp current of the high pressure discharge lamp is inverted according to a magnitude relation between the detected voltage and the switch voltage, is changed in plural stages.