Patent ID: 7136294

Claim:
In a DC-DC converter having first and second input terminals to which an input DC voltage is coupled and two output terminals where the output DC power is provided, a bridge having a first and second switching leg, each leg comprising two controlled switches connected in series, each switch having a switch capacitance and a control input, each switching leg connected between the input terminals and having a junction point between its series-connected switches; a transformer having a primary winding and a secondary winding each having a first and second end, said first end of said primary winding is connected to said junction point of said first switching leg; a rectifier and output filter circuit coupled between said secondary winding and said output terminals, a circuit comprising: a first capacitive voltage divider formed by a first and a second capacitor and connected between said input terminals; a second capacitive voltage divider formed by a third and a fourth capacitor and connected between said input terminals; a first and second diode each connected in parallel with a respective capacitor of said first capacitive voltage divider; a third and fourth diode each connected in parallel with a respective capacitor of said second capacitive voltage divider; a first inductor connected in series between said junction point of said first switching leg and a junction of said first and second capacitor; a second inductor connected in series between said junction point of said second switching leg and a junction of said third and fourth capacitor; and wherein each of said capacitors in said first and second capacitive dividers is selected such that each of said capacitors is capable of storing only enough energy required to enable substantially zero voltage switching of the respective switch to which said capacitor is coupled across.