Patent ID: 7778048

Claim:
A switching power supply apparatus comprising: a first switching circuit including a parallel connection circuit that includes a first switching element, a first diode, and a first capacitor; a second switching circuit including a parallel connection circuit that includes a second switching element, a second diode, and a second capacitor; a first control circuit configured to operate using a direct current and control ON and OFF of the first switching element; a second control circuit configured to control ON and OFF of the second switching element, the second control circuit including a turn-off circuit; and a transformer including a primary winding, a secondary winding, a first driving winding, and a second driving winding, the secondary winding being connected to a first rectifying and smoothing circuit, the first and second driving windings each generating a voltage substantially proportional to a voltage of the primary winding, the first driving winding being connected to the first control circuit via a second rectifying and smoothing circuit, the second driving winding being connected to the second control circuit; wherein a power input portion, an inductor, the primary winding of the transformer, at least one capacitor, and the first switching circuit define a series circuit, and a series circuit including the inductor, the primary winding of the transformer, and the at least one capacitor is connected in parallel to the second switching circuit; or the power input portion, the inductor, the primary winding of the transformer, and the first switching circuit define a series circuit, and a series circuit including the inductor and the primary winding of the transformer is connected in parallel to a series circuit including the second switching circuit and at least one capacitor; or the power input portion, the inductor, the primary winding of the transformer, and the first switching circuit define a series circuit, and a series circuit including the second switching circuit and at least one capacitor is connected in parallel to the first switching circuit; and an output voltage is controlled by controlling an ON period of the first switching element, and the second switching element is forcefully turned off after a predetermined time set by the turn-off circuit has elapsed since the second control circuit, operated using an alternating voltage generated by the second driving winding, turned the second switching element on.