Patent attributes
A circuit for controlling rotational speed of a fan includes a sensor, a first chipset, and a second chipset. The sensor detects an ambient temperature and generates a corresponding temperature signal. The first chipset provides a pulse-width modulation signal to the fan for driving the fan, and receives a rotational speed signal from the fan. The second chipset defines a controlling relationship between the rotational speed of the fan and the temperature. The controlling relationship is that the temperature is partitioned into a plurality of temperature ranges and each of the temperature ranges corresponds to a rotational speed range. The temperature signal is transmitted from the sensor to the second chipset via the first chipset. The second chipset determines a rotational speed range according to the controlling relationship, and controls the first chipset to adjust the pulse-width modulation signal until the actual rotational speed of the fan is in the rotational speed range.
