Abstract: A rectification device rectifies an input voltage from an AC power source. First and second switching devices are arranged between a pair of output terminals of the rectification device and alternately turned on/off. A series circuit of a first capacitor and an inductor is arranged between the two terminals of one of the first and second switching devices so as to perform a smoothing operation with respect to the frequency of an output from the rectification device. A second capacitor serves to form a resonance circuit in cooperation with the inductor in accordance with the ON/OFF operations of the first and second switching devices. The capacitance of the second capacitor is smaller than that of the first capacitor.

Abstract: A power supply apparatus has a rectifier for outputting a non-smoothed DC. A switching circuit alternately shut off output of the rectifier at a high frequency, which includes first and second switches. A first capacitor couples to the first and second switches for smoothing output of the rectifier. A series resonance circuit includes a second capacitor and an inductor so that the voltage across the first capacitor becomes lower by the resonance voltage than that of the output of the rectifier. The switches are coupled to a feedback circuit including a saturatable current transformer having a primary winding and secondary winding. A control means varies the saturation time of the saturatable current transformer.