A switching power supply apparatus includes a first commutation inductor which
is provided in a path of current flowing from a power supply input unit through
a first switching circuit and an inductor during an ON period of a first switching
circuit, and a second commutation inductor provided in a path of current flowing
through the inductor during an OFF period of the first switching circuit. The first
and second commutation inductors and the inductor are connected to a first junction
point. One end of a clamping series circuit, which includes a second switching
circuit and a series capacitor connected in series, is connected to a second junction
point, which connects the first commutation inductor and the first switching circuit,
and the other end thereof is connected so that the first and second commutation
inductors and the series capacitor constitute a resonance circuit. Accordingly,
first and second switching elements can be turned on at a zero voltage.
