Patent ID: 8395343

Claim:
A rotation speed control circuit for controlling a rotation speed of a fan, comprising: a rotation speed detector, for generating a rotation speed voltage according to a rotation speed signal corresponding to the rotation speed; a sample and hold unit, coupled to the rotation speed detector, for sampling and storing the rotation speed voltage; an error amplifier, coupled to the sample and hold unit, for controlling a voltage across a filter capacitor according to the rotation speed voltage and a reference voltage, to adjust an error voltage; and a pulse width modulation (PWM) signal generator, coupled to the filter capacitor, for generating a PWM signal according to the error voltage and a triangle wave; wherein the error amplifier discharges the filter capacitor if the rotation speed voltage is greater than the reference voltage, to decrease the error voltage, and the error amplifier charges the filter capacitor if the rotation speed voltage is less than the reference voltage, to increase the error voltage.