Patent ID: 7492615

Claim:
A switching power supply, comprising: a transformer having a primary winding, a secondary winding, and an auxiliary winding, a switching element for switching a DC voltage supplied to the primary winding and generating a pulse voltage on the secondary winding and the auxiliary winding, an output voltage generation circuit for supplying an output voltage to a load, the output voltage being generated by rectifying and smoothing the pulse voltage generated on the secondary winding, a rectifying/smoothing circuit for generating a feedback voltage by rectifying and smoothing the pulse voltage generated on the auxiliary winding, and a control circuit for controlling driving of the switching element, wherein the control circuit includes: a feedback circuit for comparing a voltage value of the feedback voltage with a reference voltage value to generate an error signal, a load detection circuit for generating a load detection signal having a signal level corresponding to a magnitude of the load based on the pulse voltage generated on the auxiliary winding, a reference voltage variable circuit for controlling the reference voltage value of the feedback circuit based on the load detection signal, and a switching control circuit for controlling on/off of the switching element by means of the error signal.