Patent ID: 7365498

Claim:
An electrodeless discharge lamp lighting device, comprising: a DC/AC conversion circuit that converts DC power into high frequency power in response to a drive signal with a drive frequency, said high frequency power having an operating frequency corresponding to the drive frequency; a resonance circuit that has a resonance characteristic and receives said high frequency power to provide high frequency power varying in response to said operating frequency based on the resonance characteristic, said resonance characteristic being a characteristic in which a first resonance curve with a resonance peak at a prescribed resonance frequency in a start mode is shifted to a second resonance curve lower than the first resonance curve in a lighting mode, said start mode being a mode before an electrodeless discharge lamp lights, said lighting mode being a mode while the electrodeless discharge lamp is lighting; an induction coil that: generates high frequency electromagnetic field in response to the high frequency power provided through said resonance circuit; and induces high frequency power to said electrodeless discharge lamp by applying the high frequency electromagnetic field to said electrodeless discharge lamp; a voltage detection circuit that detects a voltage applied to said induction coil by the high frequency power from said resonance circuit and then provides a detection voltage; a drive circuit that provides said DC/AC conversion circuit with said drive signal having the drive frequency while adjusting the drive frequency in response to variable power; and a start circuit that, when said electrodeless discharge lamp is started, sweeps down or up said variable power so as to sweep said detection voltage while sweeping down said operating frequency from a prescribed start frequency higher than said resonance frequency to a prescribed end frequency lower than the start frequency; wherein said electrodeless discharge lamp lighting device further comprises: a current detection circuit that detects a current flowing through said resonance circuit to provide a detection current; a control circuit that increases or decreases said variable power so that said detection current comes to equal a prescribed current for shifting said operating frequency to a middle range frequency between said start frequency and said end frequency, said prescribed current being set so that said detection voltage in case of the middle range frequency becomes lower than that in case of the end frequency; and a suppression means that starts suppression of said control circuit's operation when said electrodeless discharge lamp is started, and then holds the suppression during at least said start mode.