Patent ID: 7414869
Filing Date: 2008-08-19
Classification: H02M

Abstract:
1. A switching power supply unit, comprising: Two switching circuits each of which is of a full-bridge type including four switching elements, and produces input AC voltages based on an input DC voltage, a transformer having two primary windings and secondary windings, each of the two primary windings being provided correspondingly to each of the two switching circuits, and the number of windings of the two primary windings being equal to each other, the transformer transforming the input AC voltages to produce an output AC voltage, an output circuit provided at a secondary side of the transformer, and rectifying the output AC voltage to produce an output DC voltage, a drive circuit driving the two switching circuits in synchronization with each other, two inductors each provided correspondingly to each of the two switching circuits, and a connection changeover unit performing connection changeover such that when the input DC voltage is lower than a threshold voltage, a first current path passing one of the two switching circuits and one of the two primary windings of the transformer, and a second current path passing the other switching circuit and the other primary winding of the transformer are connected in parallel to each other, and on the other hand, when the input DC voltage is higher than the threshold voltage, the first and second current paths are connected in series to each other.