Patent ID: 7239091

Claim:
A discharge lamp lighting apparatus for lighting a plurality of discharge lamps, the apparatus comprising: a DC power supply; a control circuit to output signals; a step-up transformer defining a primary side and a secondary side; switching elements connected to the DC power supply, the switching elements driving the primary side of the step-up transformer based on the signals from the control circuit so as to light the plurality of discharge lamps which include one reference discharge lamp and at least one controllable discharge lamp, and which are connected to the secondary side of the step-up transformer; a first variable inductance element provided between one terminal of the secondary side of the step-up transformer and one terminal of the reference discharge lamp, a first lamp current detecting unit connected to the other terminal of the reference discharge lamp; a first lamp current controlling circuit connected to the first variable inductance element; a first series resonant circuit constituted by a leakage inductance of the step-up transformer, an inductance of the first variable inductance element, and a composite capacitance of a capacitance element with a stray capacitance provided between the first variable inductance element and the reference discharge lamp; at least one second variable inductance element provided between the one terminal of the secondary side of the step-up transformer and one terminal of the controllable discharge lamp; at least one second current detecting unit connected to the other terminal of the controllable discharge lamp; at least one second lamp current controlling circuit connected to the second variable inductance element; and at least one second series resonant circuit constituted by the leakage inductance of the step-up transformer, an inductance of the second variable inductance element, and a composite capacitance of a capacitance element with a stray capacitance provided between the second variable inductance element and the controllable discharge lamp, wherein an output signal from the first lamp current detecting unit connected to the reference discharge lamp and also an output signal from the second lamp current detecting unit connected to the controllable discharge lamp are connected to the second lamp current controlling circuit for the controllable discharge lamp, and wherein an output signal from the second lamp current controlling circuit for the controllable discharge lamp is connected to the second variable inductance element for the controllable discharge lamp so as to vary the inductance of the second variable inductance element for the controllable discharge lamp thereby controlling a lamp current of the controllable discharge lamp.