Patent ID: 6927556

Claim:
A switching power supply apparatus comprising: a first switching circuit for supplying and interrupting power from a power supply input unit; an inductor for accumulating the power input through the first switching circuit and discharging the power to a power supply output unit; a rectifier diode for rectifying a current flowing to the output unit; and a smoothing capacitor for smoothing a voltage of the output unit; wherein a first commutation inductor is provided in a path of current flowing from the power supply input unit through the first switching circuit and the inductor during an ON period of the first switching circuit; a second commutation inductor is provided in a path of current flowing through the inductor during an OFF period of the first switching circuit; the inductor and the first and second commutation inductors are connected to a first junction point; a clamping series circuit including a second switching circuit and a series capacitor connected in series is provided, and one end of the clamping series circuit is connected to a second junction point, which connects the first commutation inductor and the first switching circuit, so that the first and second commutation inductors and the series capacitor constitute a resonance circuit; the first switching circuit includes a parallel circuit of a first switching element, a first diode, and a first capacitor; the second switching circuit includes a parallel circuit of a second switching element, a second diode, and a second capacitor; and a switching control circuit for alternately turning on/off the first and second switching elements in a period when both switching elements are off therebetween is provided.