Abstract:
A heat dissipation device for a computer case is positioned over a hole of the computer case. The heat dissipation device includes a fan, two motors, two plates, and a controller. The fan is fixed in the computer case, and covers the hole. The two motors are positioned at two opposite sides of the fan. Each motor has a motor shaft parallel to a fan shaft of the fan. The two plates are respectively fixed on the two motor shafts. A distance between the two plates along the direction parallel to the motor rotor is greater than or equal to the thickness of the board. A controller is electrically connected to the fan and the two motors. The controller controls the two motors rotate the two boards for exposing or blocking the hole as the fan is on or off.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to a heat dissipation device. 
         [0003]    2. Description of Related Art 
         [0004]    One common heat dissipation device for computers is a fan. The fan is fixed to a side wall of the computer case, in alignment with a hole defined in the side wall. However, when the fan stops, dust enters the fan through the hole, thereby adversely affecting the performance and working life of the fan. 
         [0005]    What is needed, therefore, is a heat dissipation device capable of overcoming the described limitations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. 
           [0007]      FIG. 1  is a schematic view of a heat dissipation device, together with a computer case according to an embodiment. 
           [0008]      FIG. 2  is a schematic view of a heat dissipation module of the heat dissipation device of  FIG. 1 . 
           [0009]      FIG. 3  is a schematic view of the heat dissipation device of  FIG. 1  in an open state. 
           [0010]      FIG. 4  is a schematic view of the heat dissipation device of  FIG. 1  in a closed state. 
           [0011]      FIG. 5  is a schematic view of a control module of the heat dissipation device of  FIG. 1 . 
           [0012]      FIG. 6  is a schematic view of a motor driving circuit of the control module of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Embodiments of the present disclosure are described in detail as follows, with reference to the accompanying drawings. 
         [0014]    Referring to  FIGS. 1 and 2 , a computer case  100  according to an embodiment is shown. The computer case  100  includes a case  10 , a heat dissipation device  20  fixed in the case  10 , and a circuit board  30  fixed in the case  10 . A side wall  110  of the case  10  defines a circular hole  120 . A filter is mounted in the hole  120 . 
         [0015]    The heat dissipation device  20  includes a control module  200  and a heat dissipation module  300 . The control module  200  is fixed on the circuit board  30 . The heat dissipation module  300  is fixed against the inner surface  111  of the side wall  110 , and faces the hole  120 . 
         [0016]    The heat dissipation module  300  includes a fan  310 , two plates  320 , and two motors  330 . The fan  310  is fixed on the inner surface  111  by a base  311  of the fan  310 . The base  311  defines a vent  312 , with a substantially rectangular hole configuration, to face the hole  120 . 
         [0017]    The two motors  330  are disposed at the two opposite sides of the fan  310 . The two motors  330  respectively drive the two plates  320  rotate simultaneously. In the present embodiment, both the two motors  330  are stepper motors. Each motor  330  includes a motor shaft  331  parallel to a fan shaft  313  of the fan  310 . The motor shafts  331  and the fan shaft  313  are substantially on the same plane. 
         [0018]    The two plates  320  are positioned between the base  311  and the side wall  110 . The two plates  320  are respectively fixed on the two motor shafts  331  parallel to each other. In the present embodiment, the plates  320  as mounted on the motor shaft  331  are not coplanar, the perpendicular distance between the two planes  320  being equal to or greater than the thickness of one of the plates  320 . The plate  320  includes a rotating portion  321  and a blocking portion  322 . The rotating portion  321  is fixed on the motor shaft  331 . The blocking portion  322  blocks approximately one half of the hole  120 . In the present embodiment, the blocking portion  322  is a semicircle. The diameter of the blocking portion  322  is at least equal to that of the hole  120 . The two blocking portions  322  effectively form a circle to block the hole  120  and prevent dust from entering the fan  310 . The blocking portion  322  includes a straight line portion  322   a  and an arc portion  322   b . The rotating portion  321  is integral with the arc portion  322   b . The rotating portion  321  is positioned on a perpendicular line from the middle of the straight line portion  322   a.    
         [0019]    Referring to  FIGS. 3 and 4 , when the two motors  330  rotate the two plates  320  away from each other, the vent  312  is exposed to the hole  120 . When the two motors  330  rotate the two plates  320  back towards each other until the two straight line portions  322   a  meet or coincide with each other, the vent  312  is blocked to prevent dust from entering the fan  310 . 
         [0020]    Referring to  FIG. 5 , the control module  200  includes a controller  210 , a crystal oscillator circuit  220 , two driving circuits  230 , and a reset circuit  240 . The crystal oscillator circuit  220 , the two driving circuits  230 , and the reset circuit  240  are all electrically connected to the controller  210 . 
         [0021]    In the present embodiment, the controller  210  is a type 89C2051 microcontroller. A VCC terminal of the controller  210  is electrically connected to a voltage source VCC. A P1.7 terminal of the controller  210  is electrically connected to the fan  310  to receive a power on signal or a power off signal of the fan  310 . A P1.1 terminal and a P1.0 terminal of the controller  210  are each electrically connected to a pull-up resistor (two pull-up resistors R 0 ). A GRD terminal of the controller  210  is grounded. 
         [0022]    An XTAL1 terminal and an XTAL2 terminal of the controller  210  are electrically connected to the crystal oscillator circuit  220 . The crystal oscillator circuit  220  includes two capacitors  221  and  222 , and a crystal oscillator  223 . The XTAL1 terminal of the controller  210  is electrically connected to an end of the capacitor  221  and an end of the crystal oscillator  223 . The XTAL2 terminal of the controller  210  is electrically connected to the opposite end of the capacitor  222  and the opposite end of the crystal oscillator  223 . The crystal oscillator  223  generates a clock frequency to the controller  210 . 
         [0023]    One driving circuit  230  is electrically connected to a P3.0 terminal and a P3.1 terminal of the controller  210 . The other driving circuit  230  is electrically and reversely connected to the P3.0 terminal and the P3.1 terminal of the controller  210 . The two driving circuits  230  are connected in parallel with each other. The controller  210  sends a control signal to the two driving circuits  230  simultaneously through the P3.0 terminal and the P3.1 terminal. 
         [0024]    An RET terminal of the controller  210  is electrically connected to the reset circuit  240 . The reset circuit  240  includes a capacitor  241 , a switch  242  and a resistor  243 . The RET terminal of controller  210  is electrically connected to an end of the capacitor  241 , an end of the switch  242 , and an end of the resistor  243 . The opposite end of the capacitor  241  and the opposite end of the switch  242  is electrically connected to a voltage source VCC. The opposite end of the resistor  243  is grounded. When the switch  242  is closed, the controller  210  is reset. At the same time, both the P3.0 terminal and the P3.1 terminal of the controller  210  output a high level signal to the two driving circuits  230 . 
         [0025]    Referring  FIG. 6 , the two driving circuits  230  drive the two motors  330  simultaneously. The driving circuit  230  includes a first input terminal  231 , a second input terminal  232 , a first controlling branch circuit  233  and a second controlling branch circuit  234 . 
         [0026]    The first input terminal  231  is electrically connected to the P3.0 terminal of the controller  210 . The first controlling branch circuit  233  includes a first resistor R 3 , a first transistor V 1 , a second resistor R 4 , a second transistor V 2 , a first relay J 1  and a first diode D 1  connected to the P3.0 terminal in order from the P3.0 to a voltage V DD . The first resistor R 3  is connected in series between the P3.0 terminal of the controller  210  and the base of the first transistor V 1 . The emitter of the first transistor V 1  is electrically connected to the voltage source VCC. The collector of the first transistor V 1  is electrically connected to an end of the second resistor R 4 . The other end of the second resistor R 4  is electrically connected to the collector of the second transistor V 2 . The emitter of the second transistor V 2  is grounded. The collector of the second transistor V 2  is connected to the first relay J 1 . The relay J 1  is connected to the second diode D 1  in parallel. The first relay J 1  is connected between a power supply  90  and the motor  330 . In the present embodiment, the motor  330  includes a first binding post  330   a , a second binding post  330   b  and a third binding post  330   c . The first relay J 1  is connected between an anode of the power supply  90  and the first binding post  330   a  of the motor  330 . A cathode of the power supply  90  is connected to the second binding post  330   b  of the motor  330 . A capacitor  332  is connected between the first binding post  330   a  and the third binding post  330   c . The first relay J 1  controls the connection of the first binding post  330   a  to the power supply  90  or the disconnection from the power supply  90  by a control signal from the first input terminal  231 . 
         [0027]    The second input terminal  232  is electrically connected to the P3.1 terminal of the controller  210 . The second controlling branch circuit  234  includes a third resistor R 5 , a third transistor V 3 , a fourth resistor R 6 , a fourth transistor V 4 , a second relay J 2  and a second diode D 2  connected to the P3.1 terminal in order from the P3.1 terminal to a voltage V DD . The connection method of the second controlling branch circuit  234  is similar to that method of the first controlling branch circuit  233 . But the second relay J 2  is connected between the anode of the power supply  90  and the third binding post  330   c  of the motor  330 . The second relay J 2  controls the third binding post  330   c  connect to the power supply  90  or disconnect from the power supply  90  by the control signal from the second input terminal  232 . 
         [0028]    The controller  210  pre-sets a number of revolutions. In the present embodiment, the number of revolutions is ½ of one revolution. In other embodiments, the number of revolutions can be ¼or ¾ of one revolution. When the P1.7 terminal of the controller  210  receives a power on signal from the fan  310 , the controller  210  outputs a first signal by the P3.0 terminal. In the present embodiment, the first signal is a low level signal. When the first controlling branch circuit  233  receives the first signal, the first relay J 1  makes the first binding post  330   a  of the two motor  330  connect to the power supply  90 . The two motors  330  rotate the two plates  320  away from each other until the two motors  330  have rotated ½ of one revolution, the vent  312  is then completely exposed to the hole  120 . When the P1.7 terminal of the controller  210  receives a power off signal of the fan  310 , the controller  210  outputs a second signal via the P3.1 terminal In the present embodiment, the second signal is a low level signal same as the first signal. When the second controlling branch circuit  234  receives the second signal, the second relay J 2  makes the third binding post  330   c  of the two motor  330  connect to the power supply  90 . The two motors  330  rotate the two plates  320  towards each other until the two motors  330  have rotated ½ of one revolution and the two straight line portion  322   a  coincide with each other so the vent  312  is blocked by the two blocking portions  322 . When the switch  242  is closed by a user, the P3.0 terminal and the P3.1 terminal both outputs the high level signal to stop the two motors  330 . 
         [0029]    While certain embodiments have been described and exemplified above, various other embodiments will be apparent to those skilled in the art from the foregoing disclosure. The present disclosure is not limited to the particular embodiments described and exemplified, and the embodiments are capable of considerable variation and modification without departure from the scope of the appended claims.