Patent ID: 7558092

Claim:
A switching power supply unit, which includes a first terminal pair and a second terminal pair, and performs voltage conversion between a first DC voltage at the first terminal pair side and a second DC voltage at the second terminal pair side, the unit comprising; a transformer having a plurality of first windings disposed at the first terminal pair side, and a second winding disposed at the second terminal pair side, the first windings having the number of turns equal to one another, a plurality of first circuits of a full-bridge type provided at the first terminal pair side in correspondence with the plurality of first windings respectively, each of the first circuits having four switching elements, and a connection changeover unit performing connection changeover such that a plurality of current paths are in parallel connection, series connection, or mixed connection of series and parallel with one another, each of the current paths including one of the plurality of first circuits and a corresponding first winding, the connection changeover unit automatically performing connection changeover based on a magnitude of the first DC voltage inputted from the first terminal pair or a magnitude of the second DC voltage inputted from the second terminal pair.