| 摘要 |
PROBLEM TO BE SOLVED: To decide on an input excess voltage more accurately and at a high speed, based on a secondary winding side voltage using a simple configuration. SOLUTION: A switching power supply includes a differentiating circuit of a blanking circuit 18A which differentiates a secondary winding side voltage, when a secondary winding side voltage is induced in the secondary winding 13B of a transformer 13 and which outputs a differentiated voltage of a voltage, after this differentiation. When the differentiated voltage output from the differentiating circuit is reduced as a time is elapsed and the potential difference between one end a and the other end b of a capacitor 18AC becomes a predetermined value (for example, 0.5V-0.7V) or higher, the base current flows to a transistor 18AT, and the collector current flows. Thus, a voltage value of a secondary winding side voltage is input to a comparator 18C, and a voltage value of the secondary winding side voltage can be detected, based on a region except a rising region of a pulse which receives influence of ringing. COPYRIGHT: (C)2005,JPO&NCIPI
|
