| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply apparatus, capable of continuing a protective operation against an overcurrent at the secondary side, even after an output voltage drops to 0 [V]. SOLUTION: The switching power supply apparatus 1 includes a negative-voltage generating circuit 3, which generates a given negative voltage V<SB>N</SB>from an AC voltage induced at a secondary coil T<SB>2</SB>, and an overcurrent detecting circuit 5 which has a detecting resistance R<SB>3</SB>, causing a voltage drop corresponding to an output current I<SB>OUT</SB>and detects an overcurrent state of the output current I<SB>OUT</SB>based on the voltage drop. A current is made to flow, from a cathode of a photodiode PC<SB>1</SB>of a photocoupler to a negative voltage line LN to forcibly cause the photodiode PC<SB>1</SB>to emit a light, thereby the output voltage V<SB>OUT</SB>to limit the output current I<SB>OUT</SB>is lowered. COPYRIGHT: (C)2010,JPO&INPIT
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