Patent ID: 7161783

Claim:
An overcurrent protection circuit for a switching power supply, comprising: a transformer having a primary side comprising a primary winding and a secondary side comprising multiple secondary windings, the primary winding being provided with a DC current; a power switching element to switch on and off the DC current in the primary winding for inducing multiple currents in the multiple secondary windings, respectively, the currents being rectified and smoothed to provide multiple DC voltages, respectively, at the secondary side, thereby forming multiple voltage supply sections to output the multiple DC voltages, respectively, at the secondary side; a current detection resistor for detecting a current flowing in the secondary side; a switching element to be turned on when a voltage between both ends of the current detection resistor exceeds a given voltage value, the switching element comprising a transistor having an emitter connected to a winding side end of the current detection resistor; a photocoupler to be turned on and off depending on state of the switching element; and a switching control circuit to control on-duty of the power switching element in response to turning on and off of the photocoupler, wherein the current detection resistor is provided at least in a line of one of the multiple secondary windings which, among the multiple voltage supply sections, belongs to a lower output voltage supply section.