As shown on this slide, an overvoltage protection circuit uses filter capacitors, ZND and fuses. The illustrations on this slide present an examples of applying an overvoltage or reverse voltage transiently or instantaneously to a power line of devices. The left side shows a case where a positive transient overvoltage (positive surge voltage) comes into a power line. The surge voltage is clamped at the clamp voltage Vc of the Zener diode to protect the load from overvoltage. The right side shows a case where a negative transient reverse voltage (negative surge voltage) comes into a power line. A surge voltage is clamped at the forward clamp voltage Vc of the Zener diode to protect the load from reverse voltage. For a transient or instantaneous over or reverse voltage, even a Zener diode capable of 200 mW can be sufficiently used since such a voltage exists only for a very short time and has a low electric energy.