The DC-DC power convertor includes following parts: switch tube at primary side turned to on/off periodically is connected to the input power source of the convertor; transformer composed of winding at primary side and winding at subsidiary side is capable of bearing DC bias magnet; being composed of a clamping switch tube and clamping capacitor, a clamping network is connected to two ends of winding at subsidiary side in parallel; the winding at subsidiary side is connected to a full-wave rectifier; output from the full-wave rectifier is connected to low pass filter; phase relation of ducting time between the said clamping switch tube and switch tube at primary side is complemental. The disclosed switch tube can turn on/off at zero voltage to reduce loss. Comparing with prior art, the invention overcomes disadvantages not in favor of applications of large current output and multiple outputs in positive excited convertor, also prevents too large voltage stress from happening. |