Patent ID: 7116561

Claim:
A resonant power source apparatus comprising: a first series circuit of first and second switching elements being connected to ends of one of a DC power source and an input circuit for rectifying an AC voltage of an AC power source; a second series circuit of a resonant capacitor, a resonant reactor, and a primary winding of a transformer, being connected to ends of one of the first and second switching elements; a rectifying/smoothing circuit configured to rectify and smooth a voltage of a secondary winding of the transformer; a controller configured to alternately turn on/off the first and second switching elements according to an output voltage from the rectifying/smoothing circuit; and a resonant period detector configured to detect a period during which energy is transmitted from the primary side to the secondary side of the transformer, wherein the controller determines an ON period of the first switching element according to a signal from the resonant period detector and an ON period of the second switching element according to a signal from the rectifying/smoothing circuit.