Patent ID: 8976547
Filing Date: 2015-03-10
Classification: H02M,Y02B

Abstract:
1. A synchronous rectifying control circuit for a switching mode power supply, the switching mode power supply having an output configured to provide an output signal, wherein the switching mode power supply comprises a transformer having a primary winding and a secondary winding, and a secondary switch coupled to the secondary winding, and wherein the synchronous rectifying control circuit comprises: an integrating circuit having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is coupled to a first terminal of the secondary winding, wherein the second input terminal is coupled to a second terminal of the secondary winding, and wherein the integrating circuit integrates the voltage across the secondary winding and generates an integrating signal at the output terminal; a first comparison circuit having a first input terminal, a second input terminal and an output terminal, wherein the first input terminal is coupled to the output terminal of the integrating circuit to receive the integrating signal, wherein the second input terminal is configured to receive a first threshold signal, and wherein the first comparison circuit compares the integrating signal with the first threshold signal and generates a first comparing signal at the output terminal; and a logic circuit having a first input terminal and an output terminal, wherein the first input terminal is coupled to the output terminal of the first comparison circuit to receive the first comparing signal, the output terminal is coupled to a control terminal of the secondary switch, and wherein based on the first comparing signal, the logic circuit generates a control signal at the output terminal; and wherein the secondary switch is turned OFF when the integrating signal is less than the first threshold signal.