Control of series-parallel mode (SPM) clamped flyback converter

A method for operating a power conversion apparatus, comprising:

• receiving an input voltage at a primary coil;
• providing an output voltage at a secondary coil, the secondary coil electromagnetically coupled to the primary coil;
• controlling a flow of current through the primary coil by using a first switch;
• and
• controlling a flow of current through an active clamp circuit by using a second switch, the active clamp circuit coupled in parallel with the primary coil and configured to absorb a leakage energy from a leakage inductance associated with the primary coil and the secondary coil, the active clamp circuit comprising a first capacitor and a secondary capacitor,
• wherein the first switch and second switch are controlled by a controller, the controller configured to:
• turn the first switch on, so as to store energy in the primary coil;
• turn the first switch off, so as to charge the first and the second capacitors in series;
• turn the second switch on when a voltage across the first switch approaches a peak value, so as to discharge the first and the second capacitors in parallel;
• and
• turn the second switch off when at least one of:
• a voltage across the first capacitor and a voltage across the second capacitor, falls to a predetermined voltage level.

A power converter, comprising:

• a primary coil coupled in series with a first switch, the primary coil configured to receive an input voltage;
• a secondary coil electromagnetically coupled to the primary coil, the secondary configured to provide an output voltage;
• an active clamp circuit coupled in parallel to the primary coil, the active clamp circuit comprising a second switch coupled in series with a first capacitor and a second capacitor;
• and
• a controller coupled to the first switch and the second switch, the controller configured to:
• turn the first switch on, so as to store energy in the primary coil;
• turn the first switch off, so as to charge the first and the second capacitors in series;
• turn the second switch on when a voltage across the first switch approaches a peak value, so as to discharge the first and the second capacitors in parallel;
• and
• turn the second switch off when at least one of:
• a voltage across the first capacitor and a voltage across the second capacitor, falls to a predetermined voltage level.