BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to backlight modules and, more particularly, to a direct type backlight module with light emitting diodes (LEDs) light sources, typically used in a liquid crystal display (LCD) device. 
         [0003]    2. Discussion of the Related Art 
         [0004]    Most liquid crystal display (LCD) devices are passive devices in which images are displayed by controlling an amount of light rays input from an outside light source. Thus, a separate light source (for example, a backlight module) is generally employed for illuminating an LCD panel that includes the LCD device. 
         [0005]    Generally, backlight modules can be classified into edge type backlight modules and direct type backlight modules, based upon the arrangement of lamps within the backlight module. The edge type backlight module has a lamp arranged at a side portion of a light guiding plate for guiding light. An edge type backlight module is commonly employed in small-sized LCDs due to it being compact and lightweight, and having low power consumption. However, in general the edge type backlight module is not suitable for large-sized LCDs (20 inches or more). The direct type backlight module has a plurality of lamps arranged in a regular array to directly illuminate an entire main input surface of an LCD panel. The direct type backlight module has a higher efficiency of utilization of light energy and a longer operational service life than the edge type backlight module. The direct type backlight module is particularly suitable for large-sized LCDs. 
         [0006]    The lamps of the direct type backlight module can be selected from the group consisting of cold cathode fluorescent lamps (CCFLs) and light emitting diodes (LEDs). LEDs have purer color and a lower operation voltage than CCFLs, and are also lightweight. Thus LEDs are more commonly used in direct type backlight modules. However, LEDs generate much heat energy when emitting light. For example, in LEDs with substrate materials of GaN (gallium nitride), 10% of electric energy is converted to light energy and 90% of electric energy is converted to heat energy. Thus heat dispersion is very important with LEDs, particularly LEDs employed in direct type backlight modules. 
         [0007]    Referring to  FIG. 9 , a typical direct type backlight module  10  is shown. The backlight module  10  includes a housing  11 , a plurality of LEDs  12  acting as light sources, a circuit board  13 , a reflective sheet  14 , two heat sink modules  15 , a light diffusion plate  16 , a light diffusion plate  17 , and a prism sheet  18 . The housing  11  includes a bottom board  111 , and four sidewalls  112  perpendicular to the bottom board  111 . The bottom board  111  and the sidewalls  112  cooperatively define a receiving space  113 . The circuit board  13  is received in the receiving space  113  on the bottom board  111 . The LEDs  12  are arranged on the circuit board  13 . The reflective sheet  14  is disposed above and is spaced from the circuit board  13 . The heat sink modules  15  are mounted at an outer surface of the bottom board  111  by a plurality of bolts (not shown). A heat transferring layer  19  is provided between the bottom board  111  and each of the heat sink modules  15 . The light diffusion plate  16 , the light diffusion plate  17 , and the prism sheet  18  are arranged on top of the housing  11  in that order. 
         [0008]    In the above-described backlight module  10 , the heat sink modules  15  are mounted to the housing  11  by the bolts. Thus, assembly of the backlight module  10  is relatively complicated. Furthermore, the heat transferring layers  19  are needed in addition to the heat sink modules  15 , which makes the cost of the direct type backlight module  10  unduly high. 
         [0009]    Therefore, a new backlight module is desired in order to overcome the above-described shortcomings. 
       SUMMARY 
       [0010]    An exemplary backlight module includes a housing includes a one-piece housing, at least one circuit board, and a plurality of light emitting diodes. The one-piece housing includes a base plate, at least three sidewalls, and a plurality of fins. The at least three sidewalls are extended from a first main side of the base plate. The base plate and the sidewalls cooperatively defines a cavity. The fins are extended from a second main side of the base plate for dissipating heat from the housing. The at least one circuit board are disposed in the cavity of the housing. The light emitting diodes are disposed on the at least one circuit board. 
         [0011]    Other advantages and novel features will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present backlight module. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views, and all the views are schematic. 
           [0013]      FIG. 1  is an exploded, isometric view of a backlight module in accordance with a first embodiment of the present invention. 
           [0014]      FIG. 2  is a cross-sectional view of the backlight module of  FIG. 1  when assembled, corresponding to line II-II thereof. 
           [0015]      FIG. 3  is a side cross-sectional view of a backlight module in accordance with a second embodiment of the present invention. 
           [0016]      FIG. 4  is a side cross-sectional view of a backlight module in accordance with a third embodiment of the present invention. 
           [0017]      FIG. 5  is a side cross-sectional view of a backlight module in accordance with a fourth embodiment of the present invention. 
           [0018]      FIG. 6  is a side cross-sectional view of a backlight module in accordance with a fifth embodiment of the present invention. 
           [0019]      FIG. 7  is a side cross-sectional view of a backlight module in accordance with a sixth embodiment of the present invention. 
           [0020]      FIG. 8  is a side cross-sectional view of a backlight module in accordance with a seventh embodiment of the present invention. 
           [0021]      FIG. 9  is a side cross-sectional view of a conventional backlight module. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0022]    Referring now to the drawings in detail,  FIG. 1  and  FIG. 2  show a direct type backlight module  20  according to a first preferred embodiment. The backlight module  20  includes a housing  21 , a plurality of LEDs  22  acting as light sources, and a circuit board  23 . Alternatively, the LEDs  22  may also be other kinds of light sources such as CCFLs. 
         [0023]    The housing  21  includes a base plate  211 , and four sidewalls  212  perpendicularly extending from a periphery of the base plate  211 . The base plate  211  and the sidewalls  212  cooperatively define a cavity  213 . A plurality of fins  24  is formed in a predetermined pattern beneath the base plate  211 . The fins  24  are arranged in two groups, at two opposite ends of the housing  21  underneath the cavity  213 . The fins  24  and the housing  21  are integrally formed by high pressure diecasting technology or compression molding technology. The fins  24  are made of material with high thermal conductivity, such as aluminum alloy, magnesium alloy, or aluminum-magnesium alloy. The circuit board  23  is disposed in the cavity  213  of the housing  21  in contact with the base plate  211 . The LEDs  22  are disposed on the circuit board  23  in a predetermined array. In alternative embodiments, the housing  21  may include only three sidewalls, or more than four sidewalls. 
         [0024]    In the backlight module  20 , because the fins  24  and the housing  21  are integrally formed, heat can be transferred from the housing  21  to the fins  24 . In addition, unlike in the above-described conventional backlight module  10 , no heat transferring layer is required. Furthermore, unlike in the above-described conventional backlight module  10 , there is no need for a procedure of attaching the fins  24  to the housing  21  by bolts. Therefore, assembly of the backlight module  20  is simple. 
         [0025]    Further, referring to  FIG. 2 , each of inner surfaces of the sidewalls  212  of the housing  21  can be coated with a high reflectivity film  214  for reflecting light rays emitted from the LEDs  22 . 
         [0026]    The backlight module  20  also includes a reflective sheet  25 . The reflective sheet  25  defines a plurality of through holes  251 . The reflective sheet  25  is received in the cavity  213  of the housing  21 . Each of the LEDs  22  includes a light output portion (not labeled) at a top thereof. The light output portions of the LEDs  22  are exposed above the through holes  251  of the reflective sheet  25  respectively. Thus the reflective sheet  25  is positioned above the circuit board  23  while still providing full reflection capability. 
         [0027]    The backlight module  20  further includes at least one optical sheet. That is, the backlight module  20  may employ more than one optical sheet. For example, a combination of optical sheets may include at least one light diffusion plate, at least one prism sheet, and at least one brightness enhancement layer. In this embodiment, the backlight module  20  includes a first diffusion plate  26 , a second diffusion plate  27 , and a prism sheet  28  disposed on top of the housing  21  in that order. The first diffusion plate  26  is configured to diffuse light rays emitted from the LEDs  22  so as to enhance a uniformity of the light rays. The second diffusion plate  27  is configured to further diffuse light rays emitted from the first diffusion plate  26 . The prism sheet  28  is configured to collect the light rays from the second diffusion plate  27 , so that a spread angle of light rays emitted from the backlight module  20  is approximately 70 degrees. Therefore, a brightness of the backlight module  20  is enhanced. 
         [0028]    Referring to  FIG. 3 , a backlight module  30  according to a second embodiment is shown. The backlight module  30  is substantially the same as the backlight module  20  of the first embodiment, except that a plurality of fins  34  is formed throughout an entire expanse of a base plate  311  of a housing  31 . 
         [0029]    Referring to  FIG. 4 , a backlight module  40  according to a third embodiment is shown. The backlight module  40  is substantially the same as the backlight module  20  of the first embodiment. However, the backlight module  40  includes a housing  41 . The housing  41  includes a base plate  411 , and four sidewalls  412  perpendicularly extending from a periphery of the base plate  411 . A plurality of fins  44  is formed in a predetermined pattern beneath the base plate  411 , and on an outer surface of each sidewall  412 . The fins  44  formed on the base plate  411  are disposed at two opposite sides of the base plate  411 . 
         [0030]    Referring to  FIG. 5 , a backlight module  50  according to a fourth embodiment is shown. The backlight module  50  is substantially the same as the backlight module  20  of the first embodiment. However, the backlight module  50  includes a housing  51 . The housing  51  includes a base plate  511 , and four sidewalls  512  perpendicularly extending from a periphery of the base plate  511 . A plurality of fins  54  is formed throughout an entire expanse of the base plate  511 , and on an outer surface of each of the sidewalls  512 . 
         [0031]    Referring to  FIG. 6 , a backlight module  60  according to a fifth embodiment is shown. The backlight module  60  is substantially the same as the backlight module  20  of the first embodiment, except that a plurality of electric fans  69  are provided corresponding to two groups of fins  64 . The fans  69  are configured to accelerate a flow of air so that heat can be dispersed more efficiently from the fins  64 . In the illustrated embodiment, the fans  69  are provided in receptacles defined in the groups of fins  64 , respectively. 
         [0032]    Referring to  FIG. 7 , a backlight module  70  according to a sixth embodiment is shown. The backlight module  70  is substantially the same as the backlight module  20  of the first embodiment, except that the backlight module  70  includes a housing  71 . The housing  71  comprises a first unit  711  and a second unit  712 , which are complementary to each other. The first unit  711  includes a first base plate  7111  having four edges. Three sidewalls  7112  perpendicularly extend from three of the edges of the first base plate  7111 , respectively. A plurality of fins  7113  is formed beneath the first base plate  7111 . The fins  7113  are disposed at one end of the first base plate  7111  distal from the second unit  712 . The edge of the first base plate  7111  without a sidewall  7112  extending therefrom forms a bending portion  7114 . The second unit  712  includes a second base plate  7121  having four edges. Three sidewalls  7122  perpendicularly extend from three of the edges of the second base plate  7121 , respectively. A plurality of fins  7123  is formed beneath the second base plate  7121 . The fins  7123  are disposed at one end of the second base plate  7111  distal from the first unit  711 . The edge of the second base plate  7121  without a sidewall  7122  extending therefrom forms a protruding portion  7124 . At least one bolt  79  is provided to connect the first unit  711  and the second unit  712 . That is, the at least one bolt  79  is threadingly engaged in the bending portion  7114  and the protruding portion  7124 , whereby the first and second units  711 ,  712  are attached together. Thereby, the housing  71  with a composite base plate and four sidewalls (including two composite sidewalls) is formed. The first unit  711  and the fins  7113  are integrally formed, and the second unit  712  and the fins  7123  are integrally formed. In alternative embodiments, the first unit  711  and the second unit  712  may be connected together by riveting or welding. In another alternative embodiment, the housing  71  may be constituted by three or more units connected together. Large-sized backlight modules can employ the housing  71  with more than one unit because large-sized housings are difficult to be manufactured. 
         [0033]    Referring to  FIG. 8 , a backlight module  80  according to a seventh embodiment is shown. The backlight module  60  is substantially the same as the backlight module  20  of the first embodiment. However, in the backlight module  80 , a plurality of partitions  89  are formed on a base plate  811  of a housing  81 . Correspondingly, the backlight module  80  includes a plurality of circuit boards  83 . The partitions  89  are disposed inside the housing  81 . The partitions  89  are evenly spaced apart from one another, and are perpendicular to the base plate  811 . The circuit boards  83  are separated from one another by the partitions  89 . A plurality of LEDs  82  are disposed in a cavity (not labeled) of the housing  81 . The LEDs  82  can be colored LEDs  82  having selected colors. The LEDs  82  are partitioned into a plurality of light-mixing units by the clipboards  89 . Each light-mixing unit is mounted on one corresponding circuit board  83 . With this configuration, the LEDs  82  of each light-mixing unit can be controlled by the corresponding circuit board  83 , either independently of the other light-mixing units or in coordination with selected one or more of the other light-mixing units. Thereby, the LEDs  82  of the light-mixing units can have different colors and levels of brightness as desired. Further, a reflective layer is coated on all exposed portions of each of the partitions  89 . 
         [0034]    It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.
An exemplary direct type backlight module ( 20) includes a one-piece housing ( 21), at least one circuit board ( 23), and a plurality of light emitting diodes ( 22). The housing includes a plurality of fins ( 24), a base plate ( 211) and at least three sidewalls ( 212) extending out from a first main side of the base plate. The base plate and the sidewalls cooperatively defines a cavity ( 213). The fins are extended from a second main side of the housing. The fins are configured for dissipating heat from the housing. The fins and the housing are integrally formed. The at least one circuit board is disposed in the cavity of the housing. The light emitting diodes are disposed on the at least one circuit board. The backlight module is easy to be assembled and has low cost.