| 摘要 |
PURPOSE: A switching mode power supplier and an image forming apparatus including a surge protecting circuit are provided to prevent the malfunction due to noise. CONSTITUTION: A feedback unit(70) outputs the predetermined feedback voltage when the output voltage of a switching mode power supplier deviates from the predetermined range. A pulse width modulation controller comprises a guard pin. If the voltage applied in the guard pin exceeds the predetermined threshold voltage, the pulse width modulation controller blocks the power supply of the switching mode power supplier. A surge protection unit(80) is connected to the guard pin. The surge protection capacity is set higher than the threshold voltage of the guard pin and blocks the external voltage which is lower than the surge protection capacity. If the output voltage exceeds the predetermined range, the voltage, in which the surge protection capacity of the surge protection unit is subtracted from the feedback voltage outputted from the feed pack unit, is applied to the guard pin.
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