Patent ID: 7035120

Claim:
A driving circuit employing a synchronous rectifier circuit comprising: a transformer including a primary winding and a secondary winding which are insulated from each other; a main switch provided at a primary side of the circuit, which includes the primary winding of the transformer; a rectifying FET provided at a secondary side of the circuit, which includes the secondary winding of the transformer; a commutating FET provided at the secondary side of the circuit; a first auxiliary FET provided between a gate and a source of the rectifying FET, wherein the first auxiliary FET has a threshold voltage lower than a threshold voltage of the commutating FET and a gate of the first auxiliary FET is connected to a gate of the commutating FET; and a capacitor including a first electrode connected to the gate of the rectifying FET and a drain of the first auxiliary FET and a second electrode connected to the secondary winding of the transformer, wherein a short circuit is produced between the gate and the source of the rectifying FET while the commutating FET is in an on-state.