Patent ID: 8278896

Claim:
A switching power supply device, comprising: an inverter circuit for a main oscillation element, which is serially connected to an input power source, to turn on/off to generate an intermittent voltage; a synchronized rectifying element which turns on/off complementarily with the main oscillation element; a rectifying circuit which rectifies the intermittent voltage; a smoothing circuit, which smooths the voltage rectified by the rectifying circuit, to supply output power to a load; an additional diode, which is connected to each end of the synchronized rectifying element, and is connected in an orientation allowing a current to be supplied to the smoothing circuit in a duration in which the main oscillation element turns off; a control circuit, which turns on the main oscillation element with a predetermined delay time, after the synchronized rectifying element has turned off; and an auxiliary rectification circuit including a serial circuit of an auxiliary switch element and an auxiliary capacitor which are connected in parallel to both ends of the additional diode and which are driven by the control circuit; and wherein the control circuit causes the auxiliary switch element to turn on in conjunction with turning-off of the synchronized rectifying element within the delay time, and thereafter, causes the main oscillation element to turn on to generate a control pulse causing the auxiliary switch element to turn off before the main oscillation element turns off, and then, drive the auxiliary switch element.