Abstract: A lossless clamping circuit for use in a synchronous rectifier DC-DC converter in which at least one transistor switch (MOSFET) periodically connects two terminals of an output transformer winding across a main output and return terminal to provide a DC current at a selected voltage for a load connected between the output and reference terminals. A diode and an auxiliary capacitor are connected in series across the MOSFET's drain source so that the capacitor accumulates a charge in accordance with the reverse recovery current in the winding leakage inductance when the MOSFET is turned off and an auxiliary DC-DC converter is connected to the auxiliary capacitor for converting the accumulated charge across the capacitor to a DC current at a selected output voltage. Preferably the output of the auxiliary DC-DC converter is connected to the main output terminal to supplement the output power.

Abstract: An improvement in a power factor correction circuit with ZVS provides low resonance current. The basic circuit includes a positive input and ground terminal and an output capacitor connected between a positive output terminal and ground. A power factor indicator (Lin) and an output diode (D2) are connected between the positive input and output terminals. A main transistor switch (Q1) periodically connects a node between Lin and D2 to ground to store energy in Lin which is transferred to the output when Q1 is turned off. A resonant indicator (Lr) and an auxiliary transistor switch, connected across Q1, discharges Q1's source drain capacitance prior to turning Q1 on to provide ZVS. The improvement comprises an additional inductor (L2) connected in series between Lin and D2 to isolate D2's reverse recovery current from the resonant current in Lr.