Patent ID: 8860351

Claim:
A fan speed control circuit applied in an electronic device to control the rotation speed of a fan of the electronic device, the fan speed control circuit comprising: a sensor to sense a temperature of an electronic component which heat is dissipated by the fan and generate a corresponding temperature signal; an AD converter to convert the temperature signal into a digital signal; a control chip connected between the AD converter and the electronic component, the control chip outputting a PWM signal containing a unique duty cycle corresponding to the digital signal to the fan to control the rotation speed of the fan; a first integrated circuit connected to the control chip, the first integrated circuit obtaining the PWM signal output by the control chip, and integrating and smoothing the obtained PWM signal output by the control chip to generate a first equivalent voltage; an integrated operational amplifier connected to the first integrated circuit, the integrated operational amplifier amplifying the first equivalent voltage to generate an upper limit voltage and reducing the first equivalent voltage to generate a lower limit voltage; a second integrated circuit connected to the fan, the second integrated circuit obtaining the PWM signal output by the fan, integrating and smoothing the obtained PWM signal output by the fan to generate a second equivalent voltage; and a feedback comparator connected to the integrated operational amplifier and the second integrated circuit, the feedback comparator comparing the second equivalent voltage with the upper limit voltage and the lower limit voltage to generate a comparison value to the control chip; wherein the control chip adjusts the duty cycle of the PWM signal corresponding to the digital signal according to the comparison value, and outputs the adjusted PWM signal to the fan to regulate the rotation speed of the fan.