| 摘要 |
PROBLEM TO BE SOLVED: To provide a switching power supply circuit which can protect a switching element against a voltage surge of an AC power supply. SOLUTION: A surge voltage detector circuit 41a compares a drain voltage of an FET 34 supplied to an FET 34 of the switching element from a smoothing capacitor 10b with a specified value voltage VS and supplies a compared result to a switching control circuit 32. If the drain voltage of the FET 34 is higher than the specified voltage VS, the switching control circuit 32 inhibits an operation of the FET 34. As a result, the switching operation is not started, and hence the drain of the FET 34 does not become over a withstand voltage. COPYRIGHT: (C)2004,JPO
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