| 摘要 |
PROBLEM TO BE SOLVED: To prevent a rush-in current from flowing through an overvoltage protecting circuit. SOLUTION: The overvoltage protecting circuit includes an external input terminal and an external output terminal, and when an input voltage supplied to the external input terminal exceeds a predetermined threshold voltage, turns off switch transistors of the external input terminal and the external output terminal. A charge pump circuit 10 boosts an input voltage Vdc, and outputs it to the gate of the switch transistor. A soft start resistor R20 is provided on a route that runs from a second input terminal Pi2 to an output capacitor Co, taking a detour around flying capacitors Cf1 and Cf2. A bypass switch SW20 is provided parallel to the soft start resistor R20. Prior to start of boosting operation, it turns on switches SW1, SW4, and SW7 for a predetermined period, and turns off the bypass switch SW20. Then, it turns on the bypass switch SW20 to start operation of a charge pump. COPYRIGHT: (C)2010,JPO&INPIT
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