Patent ID: 7920391

Claim:
Apparatus for converting power from an input source at an input voltage for delivery to a load at an output voltage, the apparatus comprising, a transformer having a primary winding and a secondary winding, secondary circuit elements connected to the secondary winding adapted to deliver power to the load at the output voltage, a first switch connected between a first terminal of the input source and a first terminal of the primary winding, a second switch connected between a second terminal of the input source and the first terminal of the primary winding, a clamp circuit including a clamp capacitor connected in series with a clamp switch to provide a current path between a first terminal and a second terminal through the clamp capacitor when the clamp switch is closed and to open the current path through the clamp capacitor when the clamp switch is open; a fixed connection between the first terminal of the clamp circuit and a second terminal of the primary winding; a fixed connection between the second terminal of the clamp circuit and the input source; a fourth switch connected between the second terminal of the input source and the second terminal of the primary winding, and a switch controller adapted to operate the switches in a series of converter operating cycles, each converter operating cycle comprising (a) an energy-storage phase during which: the primary winding is connected to the input source by conduction of the first and fourth switches, energy is transferred from the input source to the transformer, and current in the secondary winding is essentially zero.