Patent ID: 7605546

Claim:
A discharge lamp lighting apparatus for converting a direct current into an alternating current of positive-negative symmetry and supplying power to a discharge lamp, comprising: a first resonant circuit including a first transformer, a first capacitor connected to at least one of primary and secondary windings of the first transformer, and an output end connected to a first end of the discharge lamp; first and second switching elements connected to ends of a DC power source and configured to pass a current through the primary winding of the first transformer and the first capacitor; a second resonant circuit including a second transformer, a second capacitor connected to at least one of primary and secondary windings of the second transformer, and an output end connected to a second end of the discharge lamp, the second resonant circuit being configured to output an alternating current whose phase is opposite to the phase of an alternating current provided by the first resonant circuit; third and fourth switching elements connected to the ends of the DC power source and configured to pass a current through the primary winding of the second transformer and the second capacitor; an oscillator configured to generate a triangular signal; a first control part configured to generate a first PWM control signal according to the triangular signal from the oscillator and an error voltage between a first reference voltage and a voltage corresponding to a first current passed through the secondary winding of the first transformer, the first PWM control signal being used to turn on/off the first and second switching elements with a phase difference of about 180 degrees and a pulse width corresponding to the first current; and a second control part configured to turn on/off the third and fourth switching elements in synchronization with the first PWM control signal and according to the triangular signal from the oscillator and an error voltage between a second reference voltage and a voltage corresponding to a second current passed through the secondary winding of the second transformer, with a phase difference of about 180 degrees and a pulse width corresponding to the second current, wherein PWM control operations are individually carried out to generate alternating currents of opposite phases that are applied to the ends of the discharge lamp.