Synchronous rectifier continuous conduction mode detection apparatus and control method

A method comprising:

• detecting a voltage across a synchronous rectifier switch;
• determining whether the synchronous rectifier switch operates in a continuous conduction mode based on a rising slope of the voltage across the synchronous rectifier switch;
• and
• after finding that the synchronous rectifier switch operates in the continuous conduction mode, measuring a conduction time of the synchronous rectifier switch in a current cycle, and turning off the synchronous rectifier switch after the conduction time of the synchronous rectifier switch in the current cycle is substantially equal to the conduction time measured in an immediately previous cycle.

A system comprising:

• a secondary winding magnetically coupled to a primary winding;
• a synchronous rectifier switch having a first drain/source terminal connected to the secondary winding and a second drain/source terminal connected to a common voltage node;
• a controller configured to generate a gate drive signal applied to a gate of the synchronous rectifier switch, wherein the controller comprises:
• a continuous conduction mode detection circuit configured to receive a voltage across the synchronous rectifier switch and determine whether the synchronous rectifier switch operates in a continuous conduction mode based on a rising slope of the voltage across the synchronous rectifier switch;
• and
• a turn-off timer control circuit configured to measure a conduction time of the synchronous rectifier switch in a current cycle, and turn off the synchronous rectifier switch after the conduction time of the synchronous rectifier switch in the current cycle is substantially equal to the conduction time measured in an immediately previous cycle.