Patent ID: 8339808

Claim:
A switching power supply unit converting a DC input voltage inputted from an input terminal pair into a DC output voltage, and outputting the generated DC output voltage from an output terminal pair, the switching power supply unit comprising: a transformer including: a primary winding arranged on the input terminal pair side and a first and a second secondary windings arranged on the output terminal pair side, the first and a second secondary windings being connected in series to each other; a magnetic core including two base-plates facing each other and four legs provided between the two base-plates to couple the two base-plates together, the four legs including a first pair of legs on a first diagonal line and a second pair of legs on a second diagonal line, the first and second diagonal lines intersecting each other in a plane along facing surfaces of the two base-plates; a first conductive member having through-holes allowing the four respective legs to pass therethrough, and configuring the primary winding which is wound around the legs; and a second conductive member having through-holes allowing the four respective legs to pass therethrough, and configuring the first and second secondary windings which are wound around the legs; an inverter circuit arranged between the input terminal pair and the primary winding, and including switching elements; and a rectifying-smoothing circuit arranged between the output terminal pair and the first and second secondary windings, and including first and second rectifying elements, first to third choke coils, and a capacitive element arranged between the output terminal pair; wherein the first rectifying element is arranged between a first junction and one end of the capacitive element, the first junction being defined as a junction of one end of the first secondary winding and one end of the second choke coil; the second rectifying element is arranged between a second junction and the one end of the capacitive element, the second junction being defined as a junction of one end of the second secondary winding and one end of the third choke coil; a third junction is connected to the one end of the first choke coil, the third junction being defined as a junction of the other end of the first secondary winding and the other end of second secondary winding; and a fourth junction is connected to the other end of the capacitive element, the fourth junction being defined as a junction of the other end of the first choke coil, the other end of the second choke coil and the other end of the third choke coil.