Abstract:
A fan controller includes an input module and an output module. The input module is used for receiving a power supply signal from a power supply which is used for providing power to a fan, and outputting a trigger signal when the power supply signal when the power supply turns off. The output module is used for providing power for the fan when the power supply turns off. The output module includes a timer circuit and an integrator circuit. The timer circuit is coupled to the input module, and is used for receiving the trigger signal, and providing the power for the fan according to the trigger signal for a predetermined amount of time. The integrator circuit is used for providing a threshold voltage for the timer circuit, the threshold voltage tripping termination of the power provided by the timer circuit.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a fan controller. 
         [0003]    2. Description of Related Art 
         [0004]    Various electronic devices, such as personal computers and media players, generate heat during use. Accordingly, the electronic devices must be cooled to prevent overheating. Fans are often incorporated as heat dissipating means. Commonly, the fans are powered by the electronic devices, when the electronic devices are turned off, so are the fans. Thus, any heat remaining will not be readily dissipated. Accordingly, components in the electronic devices may become overheated after the electronic devices are powered off; this shortens life of the components. 
         [0005]    Therefore, a need exists in the industry to provide a fan controller for powering a fan after an electronic device has been powered down. 
       SUMMARY 
       [0006]    In one embodiment, a fan controller includes an input module and an output module. The input module is used for receiving a power supply signal from a power supply which is used for providing power to a fan, and outputting a trigger signal when the power supply signal when the power supply turns off. The output module is used for providing power for the fan when the power supply turns off. The output module includes a timer circuit and an integrator circuit. The timer circuit is coupled to the input module, and is used for receiving the trigger signal, and providing the power for the fan according to the trigger signal for a predetermined amount of time. The integrator circuit is used for providing a threshold voltage for the timer circuit, the threshold voltage tripping termination of the power provided by the timer circuit. 
         [0007]    Other advantages and novel features of the present fan controller will become more apparent from the following detailed description of preferred embodiment when taken in conjunction with the accompanying drawings, in which: 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a block diagram of an electronic device incorporating a fan controller in accordance with an exemplary embodiment; and 
           [0009]      FIG. 2  is a schematic circuit diagram of the fan controller of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    Referring to  FIG. 1 , an electronic device includes a fan  10 , a power supply  20 , and a fan controller  30 . 
         [0011]    The fan  10  acts as a heat dissipating means for the electronic device, for dissipating heat generated by components of the electronic device, such as CPUs and chipsets. 
         [0012]    The power supply  20  is coupled to the fan  10 , for providing power to the fan  10  when the electronic device is turned on. When the electronic device is turned off, the power supply  20  is also turned off. 
         [0013]    The fan controller  30  is also coupled to the fan  10 , and provides power to the fan  10  when the power supply  20  is turned off. 
         [0014]    Referring also to  FIG. 2 , a schematic circuit diagram of the fan controller  30  of  FIG. 1  is illustrated. The fan controller  30  includes an input module  310 , an output module  320 , and a power module  330 . 
         [0015]    The input module  310  includes four resistors R 1 , R 2 , R 3 , R 4 , and two switch units T 1  and T 2 . 
         [0016]    The resistors R 1  and R 2  are connected in series between the power supply  20  and ground. 
         [0017]    In the embodiment, the two switch units T 1  and T 2  are bipolar junction transistors (BJT), each having a base, a collector, and an emitter. 
         [0018]    The base of the switch unit T 1  is connected to a node between the two resistors R 1  and R 2 . The collector of the switch unit T 1  is connected to the power module  330  through the resistor R 3 . The emitter of the switch unit T 1  is connected to ground. 
         [0019]    The base of the switch unit T 2  is connected to the collector of the switch unit T 1 . The collector of the switch unit T 2  is connected to the power module  330  through the resistor R 4 . The emitter of the switch unit T 2  is connected to ground. 
         [0020]    The output module  320  includes a timer circuit  322  and an integrator circuit  324 . The timer circuit  322  includes a timer chip  402 , two resistors R 5 , R 6 , two capacitors C 1 , C 2 , and two diodes D 1 , D 2 . 
         [0021]    In the embodiment, the timer chip  402  is an NE555 chip, with 8 pins having functions listed below: 
         [0000]    
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Pin No. 
                 Function 
               
               
                   
               
             
             
               
                 1 
                 GND 
               
               
                 2 
                 Trigger 
               
               
                 3 
                 Output 
               
               
                 4 
                 Reset 
               
               
                 5 
                 Control 
               
               
                   
                 Voltage 
               
               
                 6 
                 Threshold 
               
               
                 7 
                 Discharge 
               
               
                 8 
                 V CC   
               
               
                   
               
             
          
         
       
     
         [0022]    Pin  1  of the timer chip  402  is connected to ground. Pin  5  of the timer chip  402  is coupled to ground through the capacitor C 2 . Pin  2  of the timer chip  402  is coupled to the collector of the switch unit T 2  through the capacitor C 1 . Pins  4  and  8  of the timer chip  402  are connected to the power module  330 . Pins  6  and  7  of the timer chip  402  are connected to the integrator circuit  324 . Pin  3  of the timer chip  402  is connected to a power supply terminal of the fan  10  through the diode D 1 . 
         [0023]    The integrator circuit  324  includes an operational amplifier  404 , four resistors R 7 , R 8 , R 9 , R 10 , and a capacitor C 3 . 
         [0024]    The resistors R 7  and R 8  are connected in series between the power module  330  and node between the resistors R 7  and R 8 . An inverting input terminal of the operational amplifier  404  is connected to ground through the two resistors R 9  and R 10  that are connected in series. An output terminal of the operational amplifier  404  is connected to the pins  6  and  7  of the timer chip  402 . The output of the operational amplifier  404  is also fed back to a node between the resistors R 9  and R 10  through the capacitor C 3 . As an embodiment, the operational amplifier is an LMC6464. 
         [0025]    A working principle of the fan controller is described below. In the embodiment, the resistors R 1  and R 2  respectively have resistances of about 7K Ohms and 5K Ohms. If the electronic device is turned on, the power supply  20  provides voltage to the input module  310  of the fan controller  30 , e.g. 12V. The switch unit T 1  is conductive due to the node between the resistors R 1  and R 2  having a voltage level of 5V. Therefore, the switch unit T 2  is not conductive, because the base of the switch unit T 2  has a low voltage level from the collector of the switch unit T 1 . The input module  310  thus outputs a high voltage signal to the output module  320  through the collector of the switch unit T 2 . 
         [0026]    The high voltage level of the output end of the input module  310  charges the capacitor C 1 , therefore the pin  2  of the timer chip  402  is shifted to a high level. The pin  3  of the timer chip  402  thus outputs a low voltage through the diode D 2 . At this point, the power module  330  does not provide power to the fan  10 . The pin  7  of the timer chip  402  also has a high voltage, thus the timer circuit  322  provides a high voltage to the integrator circuit  324 , and the integrator circuit  324  is made inactive. 
         [0027]    If the electronic device is turned off, the power supply  20  no longer provides power to the fan  10 , and the input module  310  does not receive a power voltage from the power supply  20 . The switch unit T 1  does not conduct, so the collector of the switch unit T 1 , which is connected to the base of the switch unit T 2 , has a high voltage. Accordingly, the switch unit T 2  is conductive, and its collector, which is connected to the timer circuit  322  of the output module  320 , has a low voltage level. 
         [0028]    The low voltage level at the collector of the switch unit T 2  allows the capacitor C 1  to discharge, which makes the voltage on the pin  2  of the timer chip  402  go low. The falling edge of the voltage signal on the pin  2  of the timer chip  402  triggers the pin  3  of the timer chip  402  to output a high voltage, which powers the fan  10 . At this point, the power module  330  provides power to the fan  10 . 
         [0029]    The pin  7  of the timer chip  402  has a low voltage according to the low voltage on the pin  2 , which activates the integrator circuit  324 . In the embodiment, the two resistors R 7 , R 8  respectively have resistances of about 100K Ohms and 680 Ohms, the power module  330  provides a voltage of 6V. The non-inverting input terminal of the operational amplifier  404  has a voltage of about 0.04V, which is calculated by: 
         [0000]    
       
         
           
             
               
                 
                   0.68 
                    
                   
                       
                   
                    
                   K 
                 
                 
                   
                     100 
                      
                     
                         
                     
                      
                     K 
                   
                   + 
                   
                     0.68 
                      
                     
                         
                     
                      
                     K 
                   
                 
               
               × 
               6 
                
               
                   
               
                
               
                 V 
               
             
             ≈ 
             
               0.04 
                
               
                   
               
                
               
                 V 
                 . 
               
             
           
         
       
     
         [0000]    In the timer chip  402 , the pin  6  has a threshold voltage, which is 4V, ⅔ of the voltage provided by the power module  310 . Therefore, an integration cycle of the integrator circuit  324  is calculated by: 
         [0000]    
       
         
           
             
               
                 
                   
                     4 
                      
                     
                         
                     
                      
                     
                       V 
                     
                   
                   
                     0.04 
                      
                     
                         
                     
                      
                     
                       V 
                     
                   
                 
                 × 
                 R 
                 × 
                 C 
               
               = 
               
                 100 
                  
                 
                     
                 
                  
                 RC 
               
             
             , 
           
         
       
     
         [0000]    wherein R refers to a resistance of the resistor R 10 , which is 10K Ohms in the embodiment, and C refers to a capacitance of the capacitor C 3 , which is 100 μF in the embodiment. Thus the integration cycle of the integrator circuit  324  is set at 100 seconds. 
         [0030]    When the pin  3  of the timer chip  402  has output a high voltage to the fan  10  for 100 seconds, the output terminal of the operational amplifier  404 , which is connected to the pin  6  of the timer chip  402 , reaches the threshold voltage of 4V. The timer chip  402  is reset accordingly, and the pin  3  of the timer chip  402  no longer outputs a high voltage, which means that the fan controller  30  no longer provides power to the fan  10 . 
         [0031]    Obviously, in other embodiments, the integration cycle of the integrator circuit  324  can be set to other values by selectively coupling resistors and/or capacitors with different resistances and/or capacitances. The switch units T 1 , T 2  may be replaced by other components with switch functions, such as Field Effect Transistors (FET), or Insulated Gate Bipolar Transistors (IGBT). 
         [0032]    The electronic device utilizes the fan controller to provide power to the fan for a predetermined amount of time after the electronic device is turned off, so that the fan can dissipate any remaining excess heat. Therefore, overheating of the components in the electronic device is avoided, and life of the components and the electronic device is prolonged. 
         [0033]    The foregoing description of the exemplary embodiments of the invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. 
         [0034]    The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to enable others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.