Energy extraction from the parasitic elements in power converters

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

• 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;
• an inductive element connected to the switching node, wherein the inductive element is connected to deliver energy via the first and second switches from the input voltage to the load during a succession of power conversion cycles;
• the switching node is a primary winding of a transformer, the transformer having at least a secondary winding and at least an auxiliary winding;
• a current injection circuit containing a current injection switch, a current injection diode, and a current injection voltage source connected across an 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 termination of the current injection switch which is not connected to the auxiliary winding and a cathode of the current injection diode;
• a capacitance connected to the switching node, wherein the capacitance is configured to resonate with the inductive element during a portion of the power conversion cycles to cause a parasitic oscillation unrelated to the power conversion cycles;
• a clamp subcircuit placed across the primary winding containing an auxiliary switch to trap energy in the inductive element and prevent the parasitic oscillation, wherein the auxiliary switch is complementary to the first switch;
• and
• a controlled voltage source to inject energy in the inductive element to control amplitude of a magnetizing current of the inductive element at a determined level, when the auxiliary switch turns off to discharge the parasitic capacitance to a given voltage by using trapped energy in the inductive element in addition to injected energy from the controlled voltage source.

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

• 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;
• an inductive element connected to the switching node, wherein the inductive element is connected to deliver energy via the first and second switches from the input voltage to the load during a succession of power conversion cycles;
• the switching node is a primary winding of a transformer, the transformer having at least a secondary winding, and having first and second auxiliary windings;
• a current injection circuit containing a current injection switch, a current injection diode, and a current injection voltage source 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 termination of the current injection switch which is not connected to the first auxiliary winding and a cathode of the current injection diode;
• a capacitance connected to the switching node, wherein the capacitance is configured to resonate with the inductive element during a portion of the power conversion cycles to cause a parasitic oscillation unrelated to the power conversion cycles, and
• a clamp subcircuit placed across the second auxiliary winding containing an auxiliary switch to trap energy in the inductive element and prevent the parasitic oscillation;
• wherein the auxiliary switch is complementary to the first switch;
• and
• a controlled voltage source to inject energy in the inductive element to control amplitude of a magnetizing current of the inductive element at a determined level, when the auxiliary switch turns off to discharge the parasitic capacitance to a given voltage by using trapped energy in the inductive element in addition to injected energy from said controlled voltage source.