| 摘要 |
PURPOSE:To prevent an electric shock accident surely by discharging a smoothing capacitor in a power loss and an output loss of auxiliary winding. CONSTITUTION:In a switching power source, an AC power source 11 is rectified by a rectifier circuit 12 and a switching element 15 is ON-OFF controlled by switching control circuits 18-20 via a smoothing capacitor 13. Then, power is supplied from an output winding of switching transformer 14 to a load 17 via a rectifying and smoothing circuit 16. In this case, there are provided dis charging circuits 30-35. Then, rectifying diodes 30, 31 are connected with a connecting line from the AC power supply 11 to the rectifier circuit 12, a switch circuit 34 taking as inputs a detection output of said rectifying diodes of supply voltage and an output of the auxiliary winding 14A of said transformer 14 converts both inputs into an OR signal to ON-OFF control a transistor 35, and an initial charging resistance 21 is connected in parallel with the smoothing capacitor 11. Thus, said smoothing capacitor 13 is discharged quickly when an apparatus stops and so on.
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