| 摘要 |
A switching power supply 10 includes snubber capacitors 8Cb and 8Cc connected in parallel with rectifying devices 4b and 4c, respectively, on the secondary side of a transformer 3. A switching control circuit 7 controls the switching of four switching sections 1H, 1L, 2H, and 2L. In particular, the primary current It of the transformer 3 is cut off while the secondary current flowing through a smoothing inductor 5 decreases. Furthermore, when the primary current It of the transformer 3 is cut off, one of the high-side switching section 1H/2H and the low-side switching section 1L/2L that are ON is turned OFF a delay time later than the other. Then, resonance occurs between the equivalent capacitance of the snubber capacitor 8Cb/8Cc and the leak inductance on the secondary side of the transformer 3 with the primary winding 3a short-circuited, and thereby, commutation on the secondary side is quickly achieved. In other words, the equivalent primary current of the transformer 3 is quickly and sufficiently cancelled. Thus, the primary current It is quickly reduced, immediately before the cut-off. |
