Patent ID: 7535736

Claim:
A switching power supply comprising: a switching device connected via a primary winding of a transformer to DC input voltage; a rectification smoothing circuit for rectifying voltage which is induced at a secondary winding of the transformer, and outputting an output signal; and a control circuit which controls on/off states of the switching device and includes: a current signal detection circuit for detecting a current signal generated based on a forward voltage which is generated at a drive winding of the transformer while the switching device is on; an input correction circuit for generating an input correction signal using the current signal which is generated based on the forward voltage, wherein the level of the input correction signal varies in accordance with the level of the DC input voltage; a switching device current detection circuit for detecting a signal of current which flows through the switching device; and an overcurrent detection circuit for comparing the input correction signal with the signal of the current flowing through the switching device, and limiting the maximum value of the current flowing through the switching device in accordance with the DC input voltage.