Patent ID: 8724348

Claim:
A power-supply unit, comprising: a transformer; a full bridge circuit consisting of four arm switches provided on a primary side of said transformer; a rectifier and smoothing circuit including two synchronous rectifier switches provided on a secondary side of said transformer, at least one choke coil, and a capacitor; an output terminal provided in said rectifier and smoothing circuit; a control circuit controlling ON/OFF of said four arm switches of said full bridge circuit and said two synchronous rectifier switches of said rectifier and smoothing circuit; a resonant inductor consisting of a leakage inductor component of said transformer and a parasitic inductor component of wirings on said primary side of said transformer; and a resonant capacitor consisting of a parasitic capacitor component of said arm switches of said full bridge circuit, wherein said control circuit comprises timing variable means which varies switching timings of said two synchronous rectifier switches of said rectifier and smoothing circuit based on an output current flowing in said output terminal provided in said rectifier and smoothing circuit, and said switching timings of said two synchronous rectifier switches are shifted by said timing variable means from a trailing edge to a leading edge of OFF periods of top and bottom arm switches on a lag phase side of said four arm switches of said full bridge circuit.