| 摘要 |
PURPOSE:To prevent an electric shock accident surely by providing discharging circuits connecting a discharging resistance in parallel with a smoothing capaci tor when detecting a power loss and an output loss of auxiliary winding. CONSTITUTION:In a switching power source, an AC power source is rectified by a rectifier circuit 12 and a switching element 15 of switching circuit is ON- OFF controlled by switching control circuits 18-20 via a smoothing capacitor 13. Then, AC power is obtained by an output winding of switching transformer 14 and supplied to a load 17 via a rectifying and smoothing circuit 16. In this case, there are provided discharging circuits 30-39. Then, rectifying diodes 30, 31 are connected, an output of detection of AC supply voltage and an output of auxiliary winding 14A are taken in by an OR circuit 35 via diodes 33-34, and if a transistor 38 driven by a switch circuit 36 is turned ON, a discharging resistance 39 is connected in parallel with the smoothing capacitor 13. In this manner, a quick discharge is performed when an apparatus stops or any abnor mality occurs.
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