Cooling Fan Velocity Control Apparatus Using Timer and Temperature Sensor

Abstract

An apparatus and method for controlling a velocity of a cooling fan using a timer and a temperature sensor in a set-top box (STB) are provided. An apparatus for controlling a velocity of a cooling fan in an STB may include a temperature sensor unit to change a resistor to be in inverse proportion to an internal temperature, using a thermistor, a timer unit to generate a pulse signal using a capacitor and the resistor of the temperature sensor unit, a switching unit to turn on/off applied voltage, using the generated pulse signal, and a power source unit to apply the voltage to the switching unit.

What is claimed is: 
     
         1 . A cooling fan velocity control apparatus in a set-top box (STB), the cooling fan velocity control apparatus comprising:
 a temperature sensor unit to change a resistance value of a resistor to be in inverse proportion to an internal temperature, using a thermistor;   a timer unit to generate a pulse signal using a capacitor and the resistance value of a resistor of the temperature sensor unit;   a switching unit to turn on/off applied voltage, using the generated pulse signal; and   a power source unit to apply the voltage to the switching unit.   
     
     
         2 . The cooling fan velocity control apparatus of  claim 1 , wherein the timer unit adjusts, using an NE555 timer, a frequency of the generated pulse signal by changing a time constant value of the NE555 timer based on a change in the resistance value of a resistor of the temperature sensor unit, and
 wherein a frequency of a signal output from the timer unit is obtained by the following equation:   
       
         
           
             
               f 
               = 
               
                 1.49 
                 
                   
                     ( 
                     
                       
                         R 
                         A 
                       
                       + 
                       
                         2 
                          
                         
                           R 
                           B 
                         
                       
                     
                     ) 
                   
                    
                   
                     C 
                     A 
                   
                 
               
             
           
         
         where R A  denotes a resistance value of a resistor connected to the timer unit, R B  decodes a resistance value of a resistor of the temperature sensor unit, and C A  denotes a value of a capacitor connected to the timer unit. 
       
     
     
         3 . The cooling fan velocity control apparatus of  claim 2 , wherein, as the frequency of the generated pulse signal increases, an on/off switching speed of the switching unit increases, and
 wherein, as the frequency of the generated pulse signal decreases, the on/off switching speed of the switching unit decreases.   
     
     
         4 . The cooling fan velocity control apparatus of  claim 1 , wherein the switching unit comprises a transistor,
 wherein the switching unit switches a state of the generated pulse signal, and turns on/off the voltage applied by the power source unit,   wherein, when a high pulse signal is received, the switching unit allows the applied voltage, and   wherein, when a low pulse signal is received, the switching unit disallows the applied voltage.   
     
     
         5 . The cooling fan velocity control apparatus of  claim 4 , wherein the transistor comprises an NPN transistor and a positive-channel metal-oxide-semiconductor (PMOS) transistor, and
 wherein the transistor applies the generated pulse signal to a base terminal of the NPN transistor, and turns on/off voltage applied to a gate terminal of the PMOS transistor through a collector of the NPN transistor.