Patent ID: 6737860
Filing Date: 2004-05-18
Classification: H05K

Abstract:
A system for controlling a rotational speed of a fan, according to a reference clock having a reference frequency, and the rotational speed corresponding to a fan rotational speed signal, the system comprising:a fan rotational speed controlling unit, for comparing the reference clock with the fan rotational speed signal, to output a speed control signal, the fan rotational speed controlling unit comprising: a reference rotational speed calculating unit for determining a reference rotational speed corresponding to the reference frequency; a fan rotational speed calculating unit for determining a fan rotational speed corresponding to the fan rotational speed signal; and a comparator, coupled to the reference rotational speed calculating unit and the fan rotational speed calculating unit, for producing the speed control signal according to a difference between the reference rotational speed and the fan rotational speed, the speed control signal being indicative of accelerating, decelerating, or maintaining the rotational speed of the fan; a voltage generating circuit, for generating a level signal corresponding to the speed control signal, the voltage generating circuit comprising a charge pump which generates the level signal according to the speed control signal; and a driving unit, for generating a driving signal to control the rotational speed of the fan according to the level signal.