Patent ID: 8055124
Filing Date: 2011-11-08
Classification: F04D,Y02B

Abstract:
1. A system for controlling a rotary speed of a computer fan connected to a fan header, the system comprising: a basic input and output system (BIOS); a first and a second power supplies; a control circuit connected to the second power supply and the fan header; an adjusting circuit connected to the first power supply and the control circuit; a control chip connected to the adjusting circuit, the BIOS, and the fan header; and a switch circuit connected between the control chip and the control circuit; wherein the BIOS controls the control chip to output a first control signal to turn on the switch circuit, the first power supply provides a first voltage to the adjusting circuit, the adjusting circuit rectifies a first pulse-width modulation (PWM) signal output from the control chip as a first analog voltage signal to the control circuit, the control circuit controls the second power supply to output a constant driving voltage according to the first analog voltage signal, and provides the constant driving voltage to a power terminal of the fan header, the BIOS controls the control chip to output second and third PWM signals with different duty factors to a control terminal of the fan header, the BIOS also measures second and third rotary speeds of the fan under the second and third PWM signals, wherein the fan is a 4-pin fan in response to a ratio of the second rotary speed to the third rotary speed being substantially equal to a ratio of a duty factor of the second PWM signal to a duty factor of the third PWM signal, wherein the fan is a 3-pin fan in response to the ratio of the second rotary speed to the third rotary speed being not substantially equal to the ratio of the duty factor of the second PWM signal to the duty factor of the third PWM signal; and wherein the BIOS controls the control chip to output a second control signal to turn off the switch circuit in response to the fan being a 3-pin fan, the control chip outputs the PWM signal whose duty factor changes with temperature to make the first power supply provide a second voltage to the adjusting circuit, the adjusting circuit rectifies the PWM signal output from the control chip as analog voltage signals to the control circuit, and the control circuit controls the second power supply to output a changeable driving voltage to the power terminal of the fan header to control the rotary speed of the fan.