Patent ID: 8072785

Claim:
A switching power supply unit, comprising: an inverter switching a DC input voltage to generate an AC voltage, one or more transformers, each having a primary winding on a side of the inverter and secondary windings, and transforming the AC voltage and outputting an AC output voltage, a pair of rectifier circuits each connected to secondary sides of each of the transformers, each of the rectifier circuits rectifying the AC output voltage, and a smoothing circuit smoothing output voltages from the pair of rectifier circuits so as to generate a DC output voltage, the smoothing circuit including: a capacitance element, first and second magnetic cores, a common magnetic core disposed between the first and second magnetic cores, first and second windings, each winding being connected to one of the rectifier circuits at one end, and wound on the first magnetic core, third and fourth windings, each winding being connected to one of the rectifier circuits at one end, and wound on the second magnetic core, a first common winding connecting between one end of the capacitance element and a connection point of the other ends of the first and third windings, and wound on the common magnetic core, and a second common winding connecting between the other end of the capacitance element and a connection point of the other ends of the second and fourth windings, and wound on the common magnetic core, wherein a current through the first winding and a current through the second winding generate a first circular magnetic path passing through the inside of the first magnetic core and the common magnetic core, a current through the third winding and a current through the fourth winding, which are synchronized with the current through the first winding and the current through the second winding, generate a second circular magnetic path passing through the inside of the second magnetic core and the common magnetic core, and the common magnetic core is shared by a magnetic flux in the first circular magnetic path, a magnetic flux in the second circular magnetic path, a magnetic flux generated by the current through the first common winding, and a magnetic flux generated by the current through the second common winding.