Fan control circuit and system

Abstract

A fan control circuit for controlling a two-wire or three wire fan in a fan control system includes: a rotational speed detecting module, for detecting a rotational speed of the fan, in order to generate a rotational speed signal; a rotational speed converting module, coupled to the rotational speed detecting module, for converting the rotational speed signal into a first voltage signal; and a feedback control module, coupled to the rotational speed converting module, for generating a fan control signal to control the fan according to the first voltage signal.

What is claimed is: 
     
         1 . A fan control circuit for controlling a two-wire or three wire fan in a fan control system, the fan control circuit comprising:
 a rotational speed detecting module, for detecting a rotational speed of the fan, in order to generate a rotational speed signal;   a rotational speed converting module, coupled to the rotational speed detecting module, for converting the rotational speed signal into a first voltage signal; and   a feedback control module, coupled to the rotational speed converting module, for generating a fan control signal to control the fan according to the first voltage signal.   
     
     
         2 . The fan control circuit of  claim 1 , further comprising a DC-DC converter, for converting the fan control signal to output a signal corresponding to a voltage specification of the fan. 
     
     
         3 . The fan control circuit of  claim 1 , wherein the rotational speed signal is in a voltage form or a current form. 
     
     
         4 . The fan control circuit of  claim 1 , wherein the fan control system further comprises a temperature sensor, for detecting an ambient temperature of the fan, in order to generate a temperature parametric signal. 
     
     
         5 . The fan control circuit of  claim 4 , wherein the feedback control module is further coupled to the temperature sensor, in order to generate the fan control signal according to the temperature parametric signal. 
     
     
         6 . The fan control circuit of  claim 1 , wherein the fan control system further comprises an external control module, for generating an external control signal to control the fan control circuit. 
     
     
         7 . The fan control circuit of  claim 6 , wherein the external control signal is a pulse width modulation signal, and the fan control circuit further comprises a modulation converting module for converting the pulse width modulation signal into a second voltage signal. 
     
     
         8 . The fan control circuit of  claim 7 , wherein the feedback control module is further coupled to the modulation converting module, in order to generate the fan control signal according to the second voltage signal. 
     
     
         9 . The fan control circuit of claim.  8 , wherein the fan control system further comprises a temperature sensor, for detecting an ambient temperature of the fan, in order to generate a temperature parametric signal. 
     
     
         10 . The fan control circuit of  claim 9 , wherein the feedback control module is further coupled to the temperature sensor, in order to generate the fan control signal according to the temperature parametric signal. 
     
     
         11 . The fan control circuit of  claim 10 , wherein the feedback control module comprises:
 a signal integrating device, for integrating the first voltage signal and the second voltage signal to generate a third voltage signal; and   a selection device, for selecting one of the temperature parametric signal and the third voltage signal according to which has a greater voltage as a fourth voltage signal, and generating the fan control signal via the fourth voltage signal.   
     
     
         12 . The fan control circuit of  claim 11 , wherein the signal integrating device comprises an operational amplifier, which comprises:
 a first input terminal, coupled to the rotational speed converting module, for receiving the first voltage signal;   a second input terminal, coupled to the modulation converting module, for receiving the second voltage signal; and   an output terminal, coupled to the selection device, for outputting the third voltage signal.   
     
     
         13 . The fan control circuit of  claim 7 , wherein the modulation converting module adjusts a correspondence between the pulse width modulation signal and the second voltage signal according to a correspondence between the first voltage signal and the second voltage signal. 
     
     
         14 . The fan control circuit of  claim 1 , wherein the fan control circuit further comprises a minimum rotational speed setting module, for limiting a minimum rotational speed of the fan. 
     
     
         15 . A fan control system, comprising:
 a two-wire or three-wire fan; and   a fan control circuit, for controlling the fan, the fan control circuit comprising:
 a rotational speed detecting module, for detecting a rotational speed of the fan, in order to generate a rotational speed signal; 
 a rotational speed converting module, coupled to the rotational speed detecting module, for converting the rotational speed signal into a first voltage signal; and 
 a feedback control module, coupled to the rotational speed converting module, for generating a fan control signal to control the fan according to the first voltage signal. 
   
     
     
         16 . The fan control system of  claim 15 , further comprising a DC-DC converter, for converting the fan control signal to output a signal corresponding to a voltage specification of the fan. 
     
     
         17 . The fan control system of  claim 16 , wherein the rotational speed signal is in a voltage form or a current form. 
     
     
         18 . The fan control system of  claim 15 , further comprising a temperature sensor, for detecting an ambient temperature of the fan, in order to generate a temperature parametric signal. 
     
     
         19 . The fan control system of  claim 18 , wherein the feedback control module is further coupled to the temperature sensor, in order to generate the fan control signal according to the temperature parametric signal. 
     
     
         20 . The fan control system of  claim 15 , further comprising an external control module, for generating an external control signal to control the fan control circuit. 
     
     
         21 . The fan control system of  claim 20 , wherein the external control signal is a pulse width modulation signal, and the fan control circuit further comprises a modulation converting module for converting the pulse width modulation signal into a second voltage signal. 
     
     
         22 . The fan control system of  claim 21 , wherein the feedback control module is further coupled to the modulation converting module, in order to generate the fan control signal according to the second voltage signal. 
     
     
         23 . The fan control system of  claim 22 , further comprising a temperature sensor, for detecting an ambient temperature of the fan, in order to generate a temperature parametric signal. 
     
     
         24 . The fan control system of  claim 23 , wherein the feedback control module is further coupled to the temperature sensor, in order to generate the fan control signal according to the temperature parametric signal. 
     
     
         25 . The fan control system of  claim 24 , wherein the feedback control module comprises:
 a signal integrating device, for integrating the first voltage signal and the second voltage signal to generate a third voltage signal; and   a selection device, for selecting one of the temperature parametric signal and the third voltage signal according to which has a greater voltage as a fourth voltage signal, and generating the fan control signal via the fourth voltage signal.   
     
     
         26 . The fan control system of  claim 25 , wherein the signal integrating device comprises an operational amplifier, which comprises:
 a first input terminal, coupled to the rotational speed converting module, for receiving the first voltage signal;   a second input terminal, coupled to the modulation converting module, for receiving the second voltage signal; and   an output terminal, coupled to the selection device, for outputting the third voltage signal.   
     
     
         27 . The fan control system of  claim 21 , wherein the modulation converting module adjusts a correspondence between the pulse width modulation signal and the second voltage signal according to a correspondence between the first voltage signal and the second voltage signal. 
     
     
         28 . The fan control system of  claim 15 , wherein the fan control circuit further comprises a minimum rotational speed setting module, for limiting a minimum rotational speed of the fan.