Systems and methods of synchronous rectification in active clamp flyback power converters

A driver for a secondary-side synchronous rectifier, the driver comprising:

• a drain-sense terminal and a gate terminal;
• a controller configured to:
• sense a first slope of a voltage on the drain-sense terminal, the first slope indicative of a power converter entering a charge mode of a transformer arranged for flyback operation;
• change, responsive to entering the charge mode, an operational state of the driver from an original state to a modified state;
• assert the gate terminal during a discharge mode of the transformer;
• sense a second slope of the voltage at the drain-sense terminal, the second slope indicative of the power converter entering the discharge mode;
• and
• return, responsive to sensing the second slope, the operational state to the original state.

A power converter comprising:

• a primary side comprising:
• a primary winding of a transformer, the primary winding has a first lead coupled to an input voltage, and a second lead that defines a switch node;
• a primary field effect transistor (FET) coupled between the switch node and ground on the primary side;
• a clamp FET coupled between the switch node and a clamp capacitor;
• a secondary side comprising:
• a secondary winding of the transformer arranged for flyback operation;
• a secondary rectifier FET (SR FET) defining a drain, a source, and a gate, the drain coupled to the secondary winding;
• a driver for the SR FET, the driver defining a gate terminal coupled to the gate, and a drain-sense terminal coupled to the drain;
• wherein the driver is configured to:
• sense the power converter has entered a charge mode of the transformer;
• and then
• change an operational state of the driver from an original state to a modified state;
• make the SR FET conductive during a discharge mode of the transformer;
• sense the discharge mode has ended;
• and then
• return the operational state of the driver to the original state.