US Patent 7558092 Switching power supply unit

A switching power supply unit is provided, in which a convertible voltage range can be more widened. A transformer having four windings at a high-voltage side, the windings having the number of turns equal to one another, and four inductors are provided in correspondence with four switching circuits. Four current paths assume one of the states of a 4-parallel connection state, a 4-series connection state, or a 2-series/2-parallel connection state with one another depending on magnitude of an input voltage in forward operation, and a target voltage value of an output voltage in reverse operation.