Patent ID: 7209370
Filing Date: 2007-04-24
Classification: H02M,Y02B

Abstract:
1. In a DC-DC converter for providing substantially zero voltage switching (ZVS) 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, and a rectifier and output filter circuit coupled between said secondary winding and said output terminals, a circuit for reducing power losses at light loads and enabling very high frequency operation comprising: a first inductor connected between said junction points for charging and discharging each of said switch capacitances wherein control signals are provided to said control inputs of said switches in said first switching leg so that said first switching leg switches conduct alternately with dead times therebetween; and wherein control signals are provided to said control inputs of said switches in said second switching leg so that said second switching leg switches conduct alternately with dead times therebetween; and wherein each switch capacitance is discharged by said first inductor during its respective switch's dead time; and a second inductor having an end connected to said junction point of said first switching leg and another end connected to said first end of said primary winding, said second end of said primary winding is connected to said junction point of said second switching leg, wherein said second inductor is for providing high impedance to a sudden reversal of current for preventing the current of said first inductor from circulating in said primary winding until after the dead time generated in a corresponding switching leg, such that energy in said first inductor is available for said substantially zero voltage switching and current flowing through said first inductor is smaller than the reflected load current so as to substantially reduce power loss at light loads.