Patent ID: 7405955

Claim:
A switching power supply unit comprising: a first bridge circuit of a full bridge type including four first switching elements and generating a first AC voltage on the basis of a DC input voltage that is input to the switching power supply unit; first capacitative elements each of which is connected in parallel with each of the first switching elements; a first inductor connected to the first bridge circuit so as to form an H bridge and configuring a first resonance circuit in cooperation with the first capacitative elements; a first transformer for transforming the first AC voltage to generate a second AC voltage; a rectifier circuit provided on a secondary side of the first transformer, including a plurality of first rectifier elements, and rectifying the second AC voltage by the plurality of first rectifier elements, thereby generating a DC output voltage that is output from the switching power supply unit; a pair of second capacitative elements connected in series, the pair of second capacitative elements connected in parallel with the first bridge circuit and configuring a second bridge circuit in cooperation with two switching elements connected in series, the two switching elements included in the four first switching elements; a second inductor connected to the second bridge circuit so as to form an H bridge and configuring a second resonance circuit in cooperation with the second capacitative elements; a second transformer for transforming an input voltage from the second bridge circuit to generate an output voltage and supplying the output voltage to the rectifier circuit; and a driving circuit for driving the first and second bridge circuits.