Protection Circuit And Motor Unit

The ivention provides a protection circuit and a motor unit. The protection circuit comprises a power smoothing capacitor, a current-limiting resistor, a surge current protection switch and a controlunit. The power smoothing capacitor is connected between a power supply line and a reference power supply line for supplying DC power for driving a load, the reference power supply line is applied with a reference potential lower than the potential of the power supply line. The current-limiting resistor is connected in series connection with the power source smoothing capacitor between the power source smoothing capacitor and the reference power source line. The surge current protection switch is connected in parallel connection with the current-limiting resistor between the power supply smoothing capacitor and the reference power supply line. The control circuit sets the surge current protection switch in a nonconductive state under the condition that the voltage on the side of the reference power supply line of