Patent ID: 8803464

Claim:
A fan speed control circuit to control the rotation speed of at least one fan, each of the at least one fan corresponding to one load and being to dissipate heat of the corresponding load, an inductance being connected between a processing chip and one load, each of the at least one processing chip converting the inputted voltage to the PWM signal containing an unique duty cycle and outputting the converted PWM signal, each of the at least one inductance converting the PWM signal outputted by the corresponding processing chip to the direct current voltage and outputting the direct current voltage to the corresponding load, the duty cycle of the PWM signal outputted by each processing chip increasing as the corresponding load consuming more electrical power, the fan speed control circuit comprising: at least one counter corresponding to the at least one processing chip, each of the at least one counter counting the number of PWM signals outputted by the corresponding processing chip; and a control chip connected between each of the at least one processing chip and the corresponding inductance, and being connected to the at least one counter; the control chip being configured to store a relationship table recording a plurality of duty cycle intervals and a plurality of rotational speeds of the fan; each of the duty cycle intervals corresponding to one of the rotational speeds of the fan; and the control chip being further configured to control each of the at least one counter to add one upon obtaining one pulse outputting by the corresponding processing chip, obtain a preset number of PWM signals outputted by each of the at least one processing chip when the counting of the counter reaches the preset number, determine each average value according to the duty cycle of the obtained preset number of PWM signals outputted by each of the at least one processing chip, determine which duty cycle interval each average value is in, according to the relationship table, determine each rotational speed of the fan corresponding to the determined duty cycle interval according to the relationship table, and control each fan to rotate according to the determined corresponding rotational speed of the fan.