System and method for synchronous rectifier

An integrated three-pin rectifier for a power converter, comprising:

• an input pin for coupling to a transformer of the power converter;
• an output pin for coupling to an output terminal of the power converter;
• a ground pin for coupling to a ground terminal of the power converter;
• a power switch coupled to the input pin and the output pin of the power converter, wherein the power switch comprises a four-terminal MOSFET having a source, a drain, a gate, and a body, and wherein a body diode is formed by a junction between the body and the drain or by a junction between the body and the source, the body diode being coupled in parallel to the source and drain of the power transistor;
• a control circuit powered by the output pin and the ground pin, the control circuit being configured to provide a control signal for controlling an on/off state of the power switch in response to a voltage condition of two terminals of the power switch;
• wherein:
• when the body diode makes a transition from reverse bias to forward bias, the control circuit causes the MOSFET to turn on, and when the forward bias voltage drops below a reference voltage, the control circuit causes the MOSFET to turn off;
• and
• when the body diode makes a transition from forward bias to reverse bias, the control circuit causes the MOSFET to turn off.

A power converter having a synchronous rectifier, the power converter comprising:

• a transformer with a primary winding for receiving a DC input voltage and a secondary winding for providing an output voltage through an output capacitor;
• a synchronous rectifier coupled to the secondary winding of the transformer and the output capacitor, the synchronous rectifier including:
• a power switch for coupling to a secondary winding of a transformer of the power supply and an output capacitor of the power supply, wherein the power switch comprises a four-terminal MOSFET having a source, a drain, a gate, and a body, and wherein a body diode is formed by a junction between the body and the drain or by a junction between the body and the source, the body diode being coupled in parallel to the source and drain of the power transistor;
• and a control circuit configured to provide a control signal for controlling an on/off state of the power switch in response to a voltage condition of two terminals of the power switch, wherein:
• when the body diode makes a transition from reverse bias to forward bias, the control circuit causes the MOSFET to turn on, and when the forward bias voltage drops below a reference voltage, the control circuit causes the MOSFET to turn off;
• and
• when the body diode makes a transition from forward bias to reverse bias, the control circuit causes the MOSFET to turn off.