| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply that can realize its small body and low cost. SOLUTION: The switching power supply includes a switching element 40, to which DC voltage is fed via a primary winding 20; an output voltage detecting circuit 180 for detecting the rectified and smoothed voltage of secondary winding 30 and generating an error signal between the detected voltage and a reference voltage; a regulator 80 for generating a prescribed voltage, based on the voltage generated at a connection point of the switching element and the primary winding; a photocoupler 110, in which a feed-back current signal is caused to flow corresponding to the error signal, connected in parallel with a capacitor 100 that is connected to a power supply terminal and stabilizing the output voltage of the regulator; a feed-back current detecting circuit 140 for detecting the feed-back current signal; a feed-back voltage forming circuit 150 for generating a feed-back voltage, corresponding to the current generated from the feed-back current detecting circuit and holding the feed-back voltage generated during on-time or during off-time; and a control circuit 60 for controlling the on/off duty, according to the increase or the decrease in the feed-back voltage. COPYRIGHT: (C)2006,JPO&NCIPI
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