Patent ID: 8542501

Claim:
A switching power-supply apparatus comprising: a first transformer including a primary winding, a secondary winding and an auxiliary winding; a second transformer including a primary winding and a secondary winding; a first converter in which a first switching element and a second switching element are connected to both ends of a direct-current power-supply in series, and a first capacitor and the primary winding of the first transformer are connected to both ends of the first switching element or the second switching element in series, wherein the first converter includes a first rectifying circuit that rectifies a voltage generated in the secondary winding of the first transformer; a second converter in which a third switching element and a fourth switching element are connected to both ends of the direct-current power-supply in series, and a second capacitor and the primary winding of the second transformer are connected to both ends of the third switching element or the fourth switching element in series, wherein the second converter includes a second rectifying circuit that rectifies a voltage generated in the secondary winding of the second transformer; a smoothing circuit that smoothes currents output from the first rectifying circuit and the second rectifying circuit; a series resonance circuit that includes a resonance reactor and a resonance capacitor and is connected to the auxiliary winding of the first transformer in series; and a control circuit that turns on/off the third switching element and the fourth switching element according to a polarity of a current flowing in the series resonance circuit, wherein a phase of the current is delayed by 90 degrees with respect to a phase of a voltage generated in the auxiliary winding of the first transformer, wherein the second converter is operated out of phase with the first converter by 90 degrees.