Patent ID: 7425777

Claim:
A lighting circuit which lights a vehicle discharge tube, the lighting circuit comprising: a DC/DC converting circuit which boosts an input DC voltage so as to produce boosted DC power; a detecting circuit coupled to said DC/DC converting circuit, which produces a detection signal in response to an output voltage of said DC/DC converting circuit; a DC/AC converting circuit which receives said boosted DC power and produces AC power to be supplied to said discharge tube; a starting circuit coupled to said DC/AC converting circuit, which starts up said discharge tube; and a control circuit coupled to said DC/DC converting circuit, which receives said detection signal from said detecting circuit, wherein said control circuit includes: a difference signal producing unit which produces a difference signal indicative of a difference between said detection signal and an initial value of said detection signal; a charging unit which receives said difference signal and supplies an electric charge in a case where said difference is greater than or equal to a predetermined threshold value; a capacitance element coupled to an output of said charging unit via a resistive circuit; a first discharging unit which is coupled to the output of said charging unit and to said capacitance element via said resistive circuit; a second discharging unit coupled to said capacitance element, which provides a discharging path for said capacitance element in response to a turning-OFF of said input DC voltage; and a signal producing unit which produces a control signal used to adjust the output of said DC/DC converting circuit in response to a terminal voltage of said capacitance element.