| 摘要 |
A switching power supply includes a rectifier circuit (4 or 4a), a transformer (5, 5a, 5b or 5c), a rectifying and smoothing circuit (6), a smoothing capacitor (C1), an inductor (L1), a primary switch (Q1), and a soft-switching capacitor (Cq1) connected in parallel with the primary switch. For improvements in power factor and input waveform, a soft-switching circuit (7) is provided which comprises an ancillary switch (Q2) connected in parallel with the smoothing capacitor (C1)) for supplying to a transformer tertiary (N3) a current of sufficient magnitude to cause a transformer primary (N1) to develop a voltage that enables the soft-switching capacitor (Cq1) to discharge. A switch control circuit (8) initiates conduction through the ancillary switch earlier than the beginning of each conducting period of the primary switch and terminates conduction through the ancillary switch not later than the end of each conducting period of the primary switch. <IMAGE> |
