Patent ID: 8207713

Claim:
A switching power supply circuit configured to produce a DC voltage output from an input AC power supply, the switching power supply circuit comprising: a full-wave rectifier configured to full-wave rectify the input AC power supply; a boost circuit configured to generate the DC voltage output with a predetermined voltage value from an output terminal voltage of the rectifier, the boost circuit including a boost inductance element having a first end connected to an output terminal of the rectifier, a switching device connected between a second end of the inductance element and a reference potential, a rectifying device, and a capacitor connected to the second end of the inductance element via the rectifying device; and a power factor controller configured to control an ON-period of the switching device based on an error signal obtained by amplifying a difference between feedback of the DC voltage output and a reference voltage; the power factor controller configured to compare the DC voltage output feedback with a first protection voltage as the reference voltage, for shortening the ON-period of the switching device by an amount of time corresponding to a difference between the DC voltage output feedback and the first protection voltage.