Patent ID: 7012821

Claim:
A flyback converter with a synchronous rectifier, comprising: a flyback switching controller for switching a main switch in a critical conduction mode on the basis of a feedback voltage to convert an input voltage into a high-frequency pulse; a transformer having a primary coil for receiving the high-frequency pulse, and secondary main and auxiliary coils; a synchronous switch including a MOSFET having a source and drain connected to any one of first and second output lines connected respectively to both ends of the secondary main coil; a feedback controller for detecting an output voltage between the first output line and the second output line and outputting the detected voltage as the feedback voltage to the flyback switching controller; a voltage detector for detecting a voltage across the secondary auxiliary coil; a turn-on switch for switching a connection between an output terminal of the voltage detector and a gate of the synchronous switch according to a voltage at a common control terminal connected to the output terminal of the voltage detector through a common resistor; a turn-off switch for switching a connection between the gate and source of the synchronous switch according to the voltage at the common control terminal connected to the output terminal of the voltage detector through the common resistor; a current detector having primary and secondary coils for current detection, the current detector detecting load current flowing in any one of the first and second output lines according to a turn ratio between the primary and secondary current detection coils thereof; a current/voltage converter for converting the load current detected by the current detector into a voltage; and a ground switch for switching a connection between the common control terminal and the source of the synchronous switch according to the voltage converted by the current/voltage converter.