Energy extraction and utilization from the parasitic elements in power converters

A switching power conversion apparatus, for converting power from an input voltage source to an output load, comprising:

• the input voltage source;
• the output load;
• a first switch connected to a switching node;
• a second switch connected to the switching node, wherein the second switch is turned on after the first switch turns off;
• a transformer a primary winding, at least a secondary winding, and first and second auxiliary windings;
• the primary winding is connected to the switching node, the primary winding is connected to deliver energy via the first and second switches from the input voltage source to the output load during a succession of power conversion cycles;
• a current injection circuit containing a current injection switch, a current injection diode, and a current injection voltage source are connected across the first auxiliary winding, wherein the current injection switch is turned on prior to the first switch turning on and is turned off after the first switch is turned on;
• a current injection capacitor connected between (a) a termination of the current injection switch which is not connected to the first auxiliary winding and (b) a cathode of the current injection diode;
• a capacitance connected to the switching node, wherein the capacitance is configured to resonate with the primary winding during a portion of the power conversion cycles to cause a parasitic oscillation unrelated to the power conversion cycles;
• a first clamp subcircuit placed across the second auxiliary winding containing a unidirectional auxiliary switch in series with a storage capacitor to trap energy from the transformer and prevent the parasitic oscillation and store the energy in a storage capacitor;
• wherein the auxiliary switch is complementary to the first switch, and the storage capacitor is in series with the current injection voltage source;
• a second clamp subcircuit placed across the second auxiliary winding containing a unidirectional auxiliary switch in series with a controlled voltage source;
• and
• the controlled voltage source to inject energy in the secondary auxiliary winding to control amplitude of a magnetizing current of the transformer at a determined level, when the unidirectional auxiliary switch turns off to discharge the parasitic capacitance to a given voltage by using the trapped energy in the transformer in addition to the injected energy from the controlled voltage source.