A control circuit for controlling a motor. The control circuit includes a control module, a current transformation module and a comparison module. The control module generates a control current and a comparison voltage according to a first current, a first voltage and an input voltage. The current transformation module, coupled to the control module, generates a first output voltage from a first output terminal and a second output voltage from a second output terminal. The comparison module, coupled to the control module and the current transformation module, compares a threshold voltage, the first output voltage, the second output voltage, and the comparison voltage and generates a plurality of control signals to control the motor.