Multi-mode integrated regulating circuit for controlling fan

The invention relates to a multimode integrated regulating circuit able to control fan speed, comprising a voltage regulating circuit, an integrated regulating circuit and a fan motor drive circuit, where the voltage regulating circuit is used to receive an external voltage signal and regulates the external voltage signal into a proper working voltage range and generates a first output voltage, the integrated regulating circuit is connected with the voltage regulating circuit and used to receive a PWM signal with a duty cycle and generates a second output signal according to the product of the duty cycle and the first output voltage, and the fan motor drive circuit is used to receive the second output voltage and determines the speed of the fan motor according to the second output voltage. And it integrates voltage regulating mode and PWM mode into fan speed control by low-price circuit components.