Abstract: 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.

Abstract: An overcurrent protection circuit of a switching power supply apparatus, wherein a rectangular wave voltage is formed from an input voltage by the ON/OFF operation switching means, and an output voltage is formed by smoothing the rectangular wave voltage by using an inductance device and a capacitor, restricts overcurrent by detecting the peak current of a current flowing through the switching means and by using an input voltage Vin, an output voltage Vout and a voltage proportional to the ON/OFF ratio D of the switching means.

Abstract: In an isolation type DC-DC converter for performing full-wave rectification in the secondary of a transformer, two switching sections 11 and 13 alternately switch ON and OFF, thereby reversing the current I3 flowing through a primary winding 3a of the transformer 3. A switching control circuit 7 outputs switching signals G1 and G3 to the switching sections 11 and 13, respectively, thereby controlling the switching of the switching sections. A load current sensing section 9 senses the amount of load current, then compares it with a predetermined threshold value. When the amount of load current sensed is smaller than the threshold value, a delay circuit 8 delays the switching signals G1 and G3 to the switching sections 11 and 13 for a predetermined delay time. The delay time is set to be substantially equal to ¼ of the resonance period determined by the self-inductance of the primary winding 3a of the transformer 3.

Abstract: 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.

Abstract: In an isolation type DC-DC converter for performing full-wave rectification in the secondary of a transformer, two switching sections 11 and 13 alternately switch ON and OFF, thereby reversing the current I3 flowing through a primary winding 3a of the transformer 3. A switching control circuit 7 outputs switching signals G1 and G3 to the switching sections 11 and 13, respectively, thereby controlling the switching of the switching sections. A load current sensing section 9 senses the amount of load current, then compares it with a predetermined threshold value. When the amount of load current sensed is smaller than the threshold value, a delay circuit 8 delays the switching signals G1 and G3 to the switching sections 11 and 13 for a predetermined delay time. The delay time is set to be substantially equal to ¼ of the resonance period determined by the self-inductance of the primary winding 3a of the transformer 3.