A control circuit including a motor drive unit and a processing control unit is provided. The motor drive unit includes a drive current for a motor according to a modulation signal, and the motor is powered by a storage battery. The processing control unit obtains an actual speed of the motor, calculate the modulation signal by comparing the actual speed and a target speed, and transmit the modulation signal to the motor drive unit. Also, the modulation signal is used to control rotation of the motor by modulating the drive current, so that the actual speed tends to be equal to the target speed.