A control circuit includes a current sensing circuit, an analog digital converter (ADC), an amplifying circuit, a processor, and a switching circuit. The current sensing circuit senses current supplied to an electronic device by a power supply and outputs a first voltage signal. The amplifying circuit amplifies the first voltage signal output from the current sensing circuit to a second voltage signal. The ADC converts the second voltage signal to a digital signal. The processor outputs pulse width modulation (PWM) signals according to the digital signal. The switching circuit receives the PWM signals to control a fan of the electronic device according to the PWM signals.