A control circuit includes a triangular wave generating circuit, a temperature sensing circuit, a first comparator, and a switching circuit. The triangular wave generating circuit outputs a triangular wave signal. The temperature sensing circuit senses a temperature surrounding a fan and outputs a temperature signal. A non-inverting terminal of the first comparator is connected to the triangular wave generating circuit. An inverting terminal of the first comparator is connected to the temperature sensing circuit. The first comparator compares the triangular wave signal with the temperature signal to output a control signal. The switching circuit is connected between a power supply and the fan. The switching circuit turns on or off according to the control signal.