Flyback converter with improved light load efficiency

A method of operating a plurality of switching devices of a flyback converter, the method being performed by control circuitry of the flyback converter and comprising:

• operating a main switch at a fixed frequency to alternately store energy in a flyback transformer when the main switch is turned on and deliver energy from the flyback transformer to an output when the main switch is turned off;
• operating a voltage clamp switch complementarily to the main switch to clamp a voltage across a primary winding of the flyback transformer while the flyback converter is delivering energy to the output;
• and
• operating a reverse current switch to recover leakage energy in the flyback converter by turning on the reverse current switch while the voltage clamp switch is turned on and after energy stored in the flyback transformer is delivered to the output and turning off the reverse current switch with turning off with the voltage clamp switch.

A flyback converter comprising:

• flyback converter circuitry including a flyback transformer and a main switch;
• a voltage clamp circuit coupled to the flyback transformer and including a voltage clamp switch that operates complementarily to the main switch;
• a reverse current circuit coupled to the flyback transformer, the reverse current circuit including at least one snubber capacitor and a reverse current control switch, wherein the reverse current control switch operates in conjunction with the voltage clamp switch to recover leakage energy from the flyback converter circuitry;
• and
• control circuitry that provides drive signals to the main switch, voltage clamp switch, and reverse current control switch so as to:
• operate the main switch to alternately store energy in the flyback transformer when the main switch is turned on and deliver energy from the flyback transformer to an output when the main switch is turned off;
• operate the voltage clamp switch complementarily to the main switch to clamp a voltage across a primary winding of the flyback transformer while the flyback converter is delivering energy to the output;
• and
• operate the reverse current control switch to recover leakage energy in the flyback converter by turning on the reverse current control switch while the voltage clamp switch is turned on and after energy stored in the flyback transformer is delivered to the output and turning off the reverse current control switch with turning off with the voltage clamp switch.