Patent ID: 8749154

Claim:
A switching power supply comprising: a transformer including a first winding, a second winding, and a third winding; a resonant capacitor connected to both ends of the first winding; a pair of switching elements being normally-on type elements and alternately turned off according to a voltage induced in the third winding, each of the switching elements including a first main terminal, a second main terminal, and a control terminal, the first main terminal of one of the switching elements being connected to the first main terminal of one other of the switching elements, the second main terminal of the one of the switching elements being connected to one end of the first winding, the second main terminal of the one other of the switching elements being connected to one other end of the first winding, the control terminal of the one of the switching elements being connected to one end of the third winding, the control terminal of the one other of the switching elements being connected to one other end of the third winding; an inductor configured to supply a direct-current power supply voltage between a middle point of the first winding and the each first main terminal of the switching elements; and rectifying element configured to rectify a voltage induced in the second winding.