| 摘要 |
A switching power supply includes a transformer having a primary winding connected to a pair of a.c. input terminals via a rectifier circuit, and a secondary winding connected to a pair of d.c. output terminals via a rectifying and smoothing circuit. Connected between the pair of outputs of the rectifier circuit via an inductor, reverse-blocking diode, and part or whole of the transformer primary, a primary switch is turned on and off at a repetition frequency higher than the frequency of the a.c. input voltage. A soft-switching circuit is provided which comprises a serial connection of a transformer tertiary, an ancillary diode and an ancillary switch. This serial circuit is connected in parallel with the serial connection of the transformer primary and primary switch for zero-voltage switching of the primary switch.
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