Abstract:
A cooling apparatus for an integrated circuit. The cooling apparatus comprises cooling fan means, a control circuit and heat pipe means. The control circuit determines a spinning speed of the cooling fan and an operation performance mode of the integrated circuit according to the load and the temperature of the integrated circuit, the ambient temperature and a reference temperature. Within a tolerable range of the output of adder means, the heating pipe means continues dispelling heat of the integrated circuit without turning on the cooling fan. While the output of the adder means exceed the tolerable range, the fan is turned on to enforce the heat dissipation.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of Invention 
   The present invention relates to a cooling device and a control circuit thereof. More particularly, the present invention relates to a device and a control circuit for cooling an integrated circuit (IC) in the application of a microprocessor in a computer system. 
   2. Description of Related Art 
     FIG. 1  is a circuit diagram showing a conventional cooling fan control circuit for cooling an integrated circuit. The integrated circuit  11  is connected to a voltage stabilizer  12  which supplies an operation voltage to the integrated circuit  11 . The input terminal of the stabilizer  12  is connected to one terminal of a sense resistor  15  as well as the negative (−) input terminal of an operation amplifier  13 . The other terminal of the sense resistor  15  is connected to a power source Vcc and the positive (+) terminal of the operation amplifier  13 . The output terminal of the operation amplifier  13  is connected to a cooling fan  14 . Using the above circuit connections, the current flowing through the sense resistor  15  will change according to the actual loading in the integrated circuit  11 . That is, a higher current will pass through the sense resistor  15  when the loading in the integrated circuit  11  is increased. Since there is a voltage drop whenever a current flow through the sense resistor, the resulting voltage drop across the sense resistor  15  is fed into the input terminal of the operation amplifier  13  to be amplified. According to the amplified voltage drop of the loading, the spinning speed of the cooling fan can be determined as required to control the operation mode of the cooling fan. 
   With the system as shown in  FIG. 1 , while the computer system is turned off, the central processing unit (CPU, the integrated circuit) is still at a high temperature. After the computer is restarted, the cooling fan does not operate since the loading of the CPU is not large enough. The CPU is thus easily to burn out due to the high temperature. 
   Moreover, an output signal for the operation amplifier is continuously supplied to the cooling fan  14 , thus, it causes an additional power consumption, especially in the application of notebook computer because a portable computer requires an additional battery to supply voltage to the CPU and the peripheries. The design of the conventional fan cooling apparatus will increase power consumption and reduce the lifetime of the battery. Furthermore, in case that the cooling fan is burned out, it can not be detected from the circuit design of the conventional system, and thus, the CPU easily burns out consequently. 
   As the portable electronic equipment has a great demand in smaller dimension and configuration, the heat dissipation design and function are very much restricted. For example, active heat dissipation devices for portable computers can only adapt those small and thin fans. Hence, the performance and efficiency of heat dissipation may be severely affected. To prevent possible mal-functioning or damages to the hardware caused by a poor heat dissipating effect, some portable computers are designed with a thermal sensor to detect internal temperature variation. As soon as the thermal sensor detects an abnormally high temperature, the system automatically lowers the system performance such as lowering the operating frequency and voltage, so that the system is under a state with a lower thermal energy and temperature. In contrast, when the system has a good heat dissipating (for example, when the system is in an air-conditioned room or in a ventilated environment), the detected temperature is within a normal operating range. The operation performance can be enhanced to a high efficiency operation mode with a high clock of an operating frequency. However, as the temperature variation reflects a result of heat dissipation mechanism, using the thermal sensor to switch the operation clock speed is inevitably slow responsive. Thus, when the system is over heated, the thermal sensor may not perform an appropriate execution speed and good performance in time. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention provides a cooling apparatus which can control the speed of a fan so that an integrated circuit is sufficiently cooled as requried. The fan is made rotated at a speed according to the temperature of the integrated circuit, the ambient temperature and a reference temperature. 
   In another aspect, the invention provides a cooling apparatus for cooling an integrated circuit such that the operating speed of the integrated circuit can be adjusted according to the temperature of the integrated circuit and overall efficiency of the cooling apparatus. 
   To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a cooling apparatus for cooling an integrated circuit. The cooling apparatus controls the speed of a cooling fan of the integrated circuit according to the loading of the integrated circuit, the ambient temperature, the temperature of the integrated circuit and a reference temperature. The cooling apparatus comprises at least one adder means, control means and cooling fan means. 
   The adder means receive a first, a second and a third voltage signals to generate a corresponding control signal. The first voltage signal corresponds to a specific loading of the integrated circuit. The second voltage signal corresponds to the difference between the temperature of the integrated circuit and the ambient temperature. The third voltage signal corresponds to the difference between the ambient air temperature and the reference temperature. The control means are connected to the adder means. Switch means are controlled by the control means according to the control signal of the adder means and the speed of the cooling fan. The cooling fan means are connected to the control means and attached to the integrated circuit. When the switch means of the cooling fan are turned on, the cooling fan starts spinning. Hence, the integrated circuit is cooled down by forced convention. 
   If the integrated circuit is operating within a tolerable temperature range, the cooling fan is not activated, or the operation of the integrated circuit is adjusted at a higher clock speed. Alternatively, if the ambient temperature is low, the integrated circuit can be switched to a high-speed mode or the cooling fan is turned off. However, should the temperature in the integrated circuit exceed the tolerable range such as V max  value, the control means forward a signal to the switch means to turn on the cooling fan again. 
   In a second embodiment of this invention, a cooling apparatus for cooling an integrated circuit is provided. The cooling apparatus is particularly applicable for cooling the integrated circuit in a portable electronic equipment. The cooling apparatus of the integrated circuit contains at least cooling fan means, heat pipe means, and a driving circuit. The cooling fan means are coupled to the integrated circuit to enforce dissipation of the heat generated by the integrated circuit. The cooling fan means further include a cooling fan and a heat sink. The heat pipe means are attached to the heat sink. The heat pipe means further include a first heat pipe and a second heat pipe. Both the first and the second heat pipes are used for radiating the accumulated heat in the integrated circuit away. The first and second heat pipes are in contact with the housing of the main body. Furthermore, the second heat pipe is also attached to a metallic rope. The driving circuit is used to control the speed of the cooling fan in the cooling assembly. The speed of the cooling fan is determined by the driving circuit according to the loading condition in the integrated circuit, the ambient temperature, body temperature of the integrated circuit and a reference temperature. 
   It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings, 
       FIG. 1  is a circuit diagram showing a control circuit of a conventional cooling fan of an integrated circuit; 
       FIG. 2  is a circuit diagram showing a control circuit of a cooling fan for cooling an integrated circuit according to a first embodiment of this invention; 
       FIG. 3  is a diagram illustrating one operable circuit of the weighted summer as shown in  FIG. 2 ; 
       FIG. 4  circuit diagram illustrating the connection between the control means and the cooling fan means as shown in  FIG. 2 ; 
       FIG. 5  shows a cooling apparatus in a portable computer according to a second embodiment of this invention; 
       FIG. 6  is an exploded view showing relations between components in the cooling apparatus shown in  FIG. 5 ; and 
       FIG. 7  is a schematic diagram showing the profiles of a metal cord and a metal sheath; and 
       FIG. 8  is a cross-sectional view of the metal cord and the metal sheath as shown in FIG.  7 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     FIG. 2  is a circuit diagram showing a control circuit of a cooling apparatus of an integrated circuit  100  according to a first embodiment of this invention. The cooling apparatus controls the speed of the cooling fan  144  according to the loading of the integrated circuit  100 , the ambient temperature T air , the temperature T IC  of the integrated circuit  100  and a reference temperature T REF . The cooling apparatus contains at least an adder  120 , a control means  130  and a cooling fan  140 . 
   The adder  120  can be a weighted summer used to receive a first voltage signal V D1 , a second voltage signal V D2  and a third voltage signal V D3  to generate a control signal V WS . The first voltage signal V D1  reflects the loading of the integrated circuit  100 . The second voltage signal V D2  reflects the difference between the temperature T IC  of the integrated circuit  100  and the ambient temperature T air . The third voltage signal V D3  reflects the difference between the ambient temperature T air  and a reference temperature T REF . The first voltage signal V D1  is generated by a load detecting circuit. The load detecting circuit contains a sense resistor R and an operation amplifier  104 . The voltage drop across the sense resistor R is fed into the operation amplifier  104  as an input for generating the first voltage signal V D1 . The temperature T IC  of the integrated circuit  100 , the ambient temperature T air , and the reference temperature T REF  are detected by the sensors  110 ,  112  and  114  to generate corresponding voltage signal V IC , V air , and V REF , respectively. A differential amplifier  116  receives the voltage signals V IC  and V air  to generate a second voltage signal V D2 , while a differential amplifier  118  receives the voltage signal V air  and V REF  to generate the third voltage signal V D3 . 
   In this embodiment, a weighted summer is used and described as an example of the adder  120 .  FIG. 3  shows a circuit diagram of a weighted summer  120 . The weighted summer  120  receives the first, the second and the third voltage signals V D1 ,V D2  and V D3  to generate a control signal V WS . 
   Referring to both FIG.  2  and  FIG. 3 , the control means  130  comprises a control circuit  132  and a switch device  134 . The control means  130  is electrically coupled to the adder  120 . The switch means  134  can be switched on or off according to the control signal V WS  provided by the adder  120  and the speed of the cooling fan  144 . The cooling apparatus  140  comprises a driving circuit  142 , the fan  144  and a fan speed inspection circuit  146 . The cooling apparatus  140  is coupled to the control means  130  and the integrated circuit  100 . Whenever the switch means  134  is on, the fan  144  of the cooling apparatus is activated. 
     FIG. 4  is a diagram illustrating a connection between the control means  130  and the cooling fan  144  as shown in FIG.  2 . As shown in  FIG. 4 , the control circuit  132  receives a reference voltage V max , the control signal V WS  output from the adder  120  and the speed FAN 13 SENS of the cooling fan  144  to determine whether the cooling fan  144  is to be activated. The reference voltage V max  corresponds to an allowed maximum weighted sum of the operation temperature difference for the integrated circuit  100  and the loading of the integrated circuit  100 . At a weighted sum V WS  below the allowed maximum value V max , heat generated by the integrated circuit  100  can be dissipated by other means, for example, heat pipes without activating the cooling fan  144 . However, if the voltage V WS  exceeds this allowed maximum value V max , the control means  130  switches on the switch means  134  to activate the cooling apparatus  140 . At the same time, the speed of the cooling fan  144  is monitored by the fan speed inspection circuit  146  to generate a sense signal FAN 13 SENS fed back to the control circuit  132 . Such fan-control circuit is particularly applicable for portable electronic equipment (for example, a portable computer), because the portable computer does not have a continuous lasting power source. Continuous operation of the cooling fan shortens the operation life of the battery. When the portable computer is working under a low operation performance mode, or in an air-conditioned room, the central processing unit does not generate too much heat or the heat generated can be dissipated and carried by the low ambient temperature. The heat can be dissipated without the aid of the driving cooling fan. 
   Additionally, the control circuit  132  may also receive a performance mode (PFM) signal for controlling the speed of the cooling fan  144 . Table 1 and Table 2 are lists of truth values corresponding to the output signal V OUT  of the circuit shown in FIG.  4 . Table 1 presents the condition when the cooling fan is operating normally and the signal FAN 13 SENS is HIGH, while Table 2 presents the condition when cooling fan is operating abnormally and the signal FAN 13 SENS is LOW. 
   Referring to  FIG. 4 , assuming that the V max  is 4 volts, the comparator  132   a  receives the voltage signals V max  and V WS  to generate a comparison result V WSO . When the voltage signal V WS  is larger than the voltage signal V max , provided that the performance mode of the system is normal, the voltage signal V WSO  is a high level signal, that is, the signal PFM is HIGH. Under the circumstance that the cooling fan is operating normally, the signal FAN 13 SENS is also HIGH. Therefore, the output of a logic gate  132   d  is HIGH. Meanwhile, the truth value is true (T) in Table 1, so that the cooling fan  146  is switched on. The operation theory of the control circuit  132  can be referred to Table 1 and Table 2 for various conditions. 
   
     
       
             
             
           
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
               TABLE 1 
             
           
           
             
                 
                 
             
             
                 
               Performance Mode (PFM) 
             
           
        
         
             
                 
               FAN_SENS is HIGH 
               High Level 
               Low Level 
             
             
                 
                 
             
           
        
         
             
                 
               V WSO   
               High Level 
               T 
               T 
             
             
                 
               V WSO   
               Low Level 
               T 
               F 
             
             
                 
                 
             
           
        
       
     
   
   
     
       
             
             
           
             
             
             
             
           
             
             
             
             
             
           
         
             
                 
                 
             
             
                 
               Performance Mode (PFM) 
             
           
        
         
             
                 
               FAN_SENS is HIGH 
               High Level 
               Low Level 
             
             
                 
                 
             
           
        
         
             
                 
               V WSO   
               High Level 
               F 
               F 
             
             
                 
               V WSO   
               Low Level 
               F 
               F 
             
             
                 
                 
             
           
        
       
     
   
   In a second embodiment of this invention, a specific application of the cooling apparatus described in the first embodiment to portable electronic equipment, for example, a portable computer, is introduced. 
   Referring to both FIG.  5  and  FIG. 6 , a portable computer comprises an integrated circuit  210  which may be used as a central processing unit. This portable electronic equipment comprises a main body  200   a  used as an enclosure to assemble a mother board, a display  200   b  used to as an enclosure to assemble a screen  200   c . The screen  200   c  may be a liquid crystal display (LCD) display. The portable computer further comprises cooling fan means, heat pipe means, and a driving circuit. 
   The cooling fan means are coupled the integrated circuit  210  for dissipating the heat generated by the integrated circuit  210 . The cooling fan means further comprises a fan  220  and a heat sink  222 . The heat pipe comprises at least a first heat pipe  224  and a second heat pipe  226 . Both the first and the second heat pipes  224  and  226  are coupled to the heat sink  222  and the main body enclosure  200   a . The main body enclosure  200   a  may be made of material such as metal, for example, aluminum alloy, aluminum-magnesium-copper alloy, aluminum-magnesium alloy, or other material, so that the heat generated by the integrated circuit  210  may be continuously directed to the heat pipes  224  and  226  via the heat sink  222  more effectively. 
   The driving circuit is used to control the speed of the cooling fan  220  according to the loading in the integrated circuit  210 , the ambient temperature, the temperature of the integrated circuit  210  and a reference temperature. Since the overall design is the same as that in the first embodiment, detailed description is omitted here. 
   Furthermore, the operating mode of the portable computer can be changed accordingly by several means. Firstly, a special Hi/Lo pin can be assigned to the CPU, so that by sending a signal to the Hi/Lo pin of the CPU, the CPU can work in a high operating speed or a low operating speed. Secondly, as shown in  FIG. 2 , a system managing (SM) bus can be used to change the clocking frequency from a clocking chip  152  to the CPU  100 . Hence, the performance of execution can be slowed down or fastened up depending on demand. However, the particular brand of CPU must be able to satisfy the phase lock loop requirement when the clocking frequency is changed. Thirdly, as shown in  FIG. 2 , when the STP clock pin of the CPU is at a low potential, the clock signal inside the CPU will stop. On the other hand, when the STP clock pin is at a high potential, the clock pulse signal inside the CPU will become normal again. Therefore, a logic gate connecting between the CPU and a chipset  150  such that a high potential or a low potential having a definite high/low timing ratio can be established. Hence, duty cycle of the CPU can be adjusted to achieve whatever rate of execution demanded. 
   Referring to both FIG.  7  and  FIG. 8 , schematic drawings of the heat pipe  226  connecting to a metal cord  230  are shown. The heat pipe  226  has one end connected to the metal cord  230  which is further covered by a metal sheath  228 . A grease  232  is spread between the metal cord  230  and the metal sheath  228  to enhance the efficiency of heat dissipation. A metal cord  234  can further installed under the screen  200   c . Using the metal cord, the heat can be dispelled via the metal enclosure more effectively. 
   The material of the heat sink comprises conductive metal. The heat sink may be formed with or without fins thereon. The types of fins comprise a pin type fin or plate type fin for increasing heat spreading area. 
   In the invention, the heat pipe further comprises an evaporation section, an adiabatic section and a condensation section. The water contained in the heat pipe absorbs heat to be vaporized into gas which flows through the adiabatic section into the condensation section to be cooled down to water. The condensed water then re-flows to the evaporation section using a wick structure. The wick structure can be a wire wick, a grooved wick, a mesh wick or a sintered power. The heat pipe may be in contact with the heat sink with or without a grease applied between each other. The heat pipe may be formed with a circle cross section, a rectangle cross section, or an ellipse cross section. The fan may be an axial-flow fan or a blower. 
   Thus, the invention adjusts the speed of cooling fan according to the loading of the integrated circuit, the temperature of the chip, the ambient temperature and a reference temperature. Therefore, the integrated circuit can work at a temperature within a tolerance without consuming too much power. 
   The cooling apparatus of this invention complies with the operating mode of the processor. 
   Furthermore, the cooling operation to the central processing unit of an integrated circuit is performed by a heat dissipating while the temperature of the integrated circuit is within a temperature tolerance. When the temperature of the integrated circuit is over a temperature limit, the fan is activated. 
   It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.