A converter topology that eliminates reverse recovery losses in its output rectifying
semiconductor devices employs an AC injection voltage source in series with a power
transformer primary winding. Input semiconductor switches in the converter's primary
circuit are controlled to provide in the power transformer secondary a voltage
across the winding or windings in a first direction forward biasing one of the
output rectifying devices followed by a lower level reverse biasing voltage produced
by the injection voltage. This lower level voltage across the secondary turns off
the previously conducting rectifier device and drives carriers out of its semiconductor
junction or junctions to eliminate reverse recovery losses occurring when the secondary
applies a higher level reverse bias across the non-conducting rectifier device.
The injection voltage source can be a transformer in addition to the power transformer
having a primary winding in series with the primary winding of the power transformer
and a secondary winding connected to ground through a capacitor. In addition to
preventing reverse recovery losses in the rectifying devices in the secondary,
the injection voltage transformer also injects an AC triangular waveform current
into the current in the converter primary input circuit to the junction of the
semiconductor switches where they are connected in a bridge circuit supplying the
power transformer primary. By this, the injection voltage source assures zero voltage
switching of the semiconductor switches even at light loads.