SWITCHING-MODE POWER SUPPLY DEVICE, IMAGE FORMING APPARATUS, POWER SUPPLY DEVICE, AND ELECTRONIC DEVICE AND METHOD FOR SUPPLYING POWER TO THE ELECTRONIC DEVICE

摘要

PROBLEM TO BE SOLVED: To provide a switching-mode power supply device and a power supply device, which include each a surge protection circuit for preventing a malfunction due to a surge noise.

SOLUTION: A switching-mode power supply device includes: a feedback part for outputting a predetermined feedback voltage in a case where an output voltage value of the aforementioned device shifts outside a predetermined range; a protection pin; a pulse width modulation control part for shutting off power supply to the aforementioned device in a case where a voltage applied to the protection pin exceeds a predetermined threshold voltage; and a surge protection part connected to the protection pin. Further, a surge protection voltage for shutting off a surge voltage flowing from outside the surge protection part is set to be higher than the threshold voltage of the protection pin of the pulse width modulation control part to shut off an external surge voltage lower than the surge protection voltage, and in a case where an output voltage value of the aforementioned device shifts outside the predetermined range, a voltage obtained by subtracting a surge protection voltage of the surge protection part from the feedback voltage output from the feedback part is applied to the protection pin.

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