Patent ID: 7123490

Claim:
A synchronous rectification switching power supply circuit comprising: a transformer comprising a primary winding and a secondary winding; a main switching device serially connected to the primary winding of the transformer between terminals of a direct current input power supply; a synchronous rectification device serially connected to the secondary winding of the transformer on a secondary side of the transformer between output terminals; a power supply apparatus comprising an output capacitor charged with a voltage which appears across the secondary winding of the transformer as the main switching device turns on and off; a control section that sends a control signal to a control input terminal of the synchronous rectification device, the control section being provided in an electronic instrument to which the power supply apparatus is connected so as to supply electric power thereto; and an auxiliary winding, the auxiliary winding being coupled in parallel with an output capacitor, with a resistive circuit, and between a first control terminal of the control section and one of the output terminals; wherein when the synchronous rectification device is turned on, the output capacitor is charged and the direct current input power supply recovers electric power from the output capacitor through the transformer, thereby supplying output electric power which is set by the control section to the electronic instrument, and wherein the synchronous rectification device is further coupled to the resistive circuit, such that a voltage may be produced across the auxiliary winding for charging a gate capacitance of the synchronous rectification device when the electronic instrument is disconnected from the power supply apparatus.