| 摘要 |
A transformer has a primary winding connected across a d.c. power supply via a parallel connection of a switch and a resonant capacitor, and a secondary winding connected across a load via a rectifying and smoothing circuit. In order for the switch to be turned on and off at zero voltage, there is provided, in parallel with the serial circuit of the transformer primary and the switch, a serial circuit of a tertiary and a quaternary winding of the transformer, a resonant inductor, a first diode, and a second switch. A second diode is connected in parallel with the serial connection of the transformer quaternary, resonant inductor, first diode, and second switch. A switch control circuit is connected between the rectifying and smoothing circuit and the first and second switches for on-off control of the latter according to the converter output voltage. The second switch is so controlled in relation to the first switch that the resonant capacitor is compulsorily caused to discharge, making the voltage across the first switch zero when it is turned on.
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