Abstract:
A backlight module has a light guide plate, a back plate and light emitting assemblies. The light guide plate is substantially prism-like. The back plate has a shape corresponding to that of the light guide plate, and has an inclined first side plate and an inclined second side plate opposite to the first side plate. Each of the first and second side plates has at least one receiving recess, and the light emitting assemblies are received in the receiving recesses. In comparison with a side-light type backlight module, the present invention saves a heat-dissipation aluminum extrusion member. In comparison with a direct-light type backlight module, the present invention shortens the light mixing distance in a vertical direction, so as to reduce the module thickness.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a manufacture field of liquid crystal display (LCD), and more particularly to a backlight module. 
       BACKGROUND OF THE INVENTION 
       [0002]    In a traditional technology, a light guide plate (LGP) in a side-light type LED (light emitting diode) backlight module is generally rectangular.  FIG. 1A  and  FIG. 1B  are schematic views of a structure of a side-light type LED backlight module in a traditional technology, wherein  FIG. 1A  is a perspective view, and  FIG. 1B  is a cross-sectional view of  FIG. 1A  taken along a line A-A. The backlight module comprises a back plate  11 , two aluminum extrusion members  12 , two driver circuit boards  13 , a plurality of LEDs  14  and a light guide plate  15 . The light guide plate  15  is disposed on a central portion of the back plate  11 , and is a rectangular structure. The driver circuit board  13  is provided with the plurality of LEDs  14 , and commonly mounted on two sides of the light guide plate  15  with the LEDs  14 . The LEDs  14  generate light which is emitted into the light guide plate  15 , and then scattered to form uniform light used as a backlight source of a liquid crystal display (LCD). The aluminum extrusion member  12  is mounted between the driver circuit board  13  and the back plate  11  which is used to dissipate heat generated during the LEDs work into the ambient environment by the high thermal conductivity of aluminum material. In a large-size side-light type LED backlight module, the LEDs  14  generate and accumulate heat, so that it needs to use the aluminum extrusion member  12  to guide the heat toward the bottom of the back plate  11  for dissipating the heat outward. Because the volume of the light guide plate  15  and the aluminum extrusion member  12  is considerably large, the backlight module of an LED backlight type display is relatively heavy. Because it inevitably needs to transmit the heat to the back plate  11  through the aluminum extrusion member  12 , an area disposed with the aluminum extrusion member  12  will accumulate the heat, and thus the brightness and color generated by the light guide plate  15  may be uneven. 
         [0003]    If wanting to reduce the weight, the backlight of the LED backlight type display generally must use the direct-light type design, i.e. the LEDs must be mounted on the bottom of the back plate in the backlight module. However, it needs a longer light mixing distance, so that the direct-light type LED backlight module needs a greater thickness. 
         [0004]    As described above, the backlight design of the LED backlight modules in the traditional technology can not meet needs of light weight and compactness at the same time. 
       SUMMARY OF THE INVENTION 
       [0005]    To solve the foregoing technical problems, an object of the present invention is to provide a backlight module applied to a liquid crystal display (LCD) for meeting needs of light weight and compactness of an LED backlight module at the same time. 
         [0006]    To solve the above problems, the present invention provides a backlight module comprising a light guide plate, a back plate and a plurality of light emitting assemblies, wherein the light guide plate is substantially prism-like. The back plate has a shape corresponding to that of the light guide plate, and has an inclined first side plate and an inclined second side plate opposite to the first side plate, wherein each of the first and second side plates has at least one receiving recess, and the light emitting assemblies are received in the receiving recesses. 
         [0007]    As a possible technical solution, the back plate is provided with a buffering support pad thereon, and the light guide plate is abutted against on the buffering support pad. 
         [0008]    As a possible technical solution, the buffering support pad is mounted on a connection portion between the first side plate and the second side plate of the back plate. 
         [0009]    As a possible technical solution, the light guide plate has a first side surface and two second side surfaces inclined opposite to the first side surface and symmetrically arranged to each other, wherein a connection portion of the two second side surfaces is abutted against on the buffering support pad. 
         [0010]    As a possible technical solution, the receiving recess of the first side plate and the receiving recess of the second side plate are symmetrically arranged to each other. 
         [0011]    As a possible technical solution, a connection between the light emitting assemblies and the receiving recess is selected from one of thermal conductive tape adhesion and screw connection. 
         [0012]    As a possible technical solution, an opening of the receiving recess is covered with a light diffusion/guide strip, and light emitted by the light emitting assemblies passes through the light diffusion/guide strip to enter the light guide plate. 
         [0013]    As a possible technical solution, a light output surface of the light diffusion/guide strip has a plurality of light diffusion particles, and at least one surface of the light diffusion/guide strip is frosted or coated with nano-material for enhancing the diffusion efficiency. 
         [0014]    As a possible technical solution, a light input surface of the light diffusion/guide strip has first recesses, and a light output surface of the light diffusion/guide strip has second recesses, wherein a first planar surface is defined between each two of the adjacent first recesses, a second planar surface is defined between each two of the adjacent second recesses, and the first recesses of the light input surface and the second recesses of the light output surface are staggered and opposite to each other. 
         [0015]    As a possible technical solution, the first recesses and the second recesses of the light diffusion/guide strip are V-shape or curved. 
         [0016]    As a possible technical solution, the light input surface and the light output surface of the light diffusion/guide strip are waved. 
         [0017]    As a possible technical solution, peaks and valleys of the light input surface are corresponding to valleys and peaks of the light output surface, respectively. 
         [0018]    The advantages of the present invention are that a cross section of a bottom of the light guide plate is designed to be a shape of isosceles triangle, and two sides of the shape of isosceles triangle are disposed with the light emitting assemblies. In comparison with a side-light type backlight module in a traditional technology, the light emitting assemblies are directly mounted on the back plate, so as to save a heat-dissipation aluminum extrusion member. Thus, the weight of the light guide plate can be reduced, while the brightness and color of the module become uniform. In comparison with a direct-light type backlight module, the two inclined sides of the shape of isosceles triangle are used to mix light based on the transverse width of the light guide plate, so as to shorten the light mixing distance in a vertical direction and thus reduce the module thickness. 
         [0019]    Furthermore, the surface of the light emitting assemblies can be covered with light diffusion/guide strips to further reduce the module thickness. The function of the light diffusion/guide strips is to diffuse the light emitted from the light emitting assemblies, and thus this function is similar to the function of the light guide plate. In comparison with the light guide plate, the light diffusion/guide strips are directly covered on the openings of the receiving recesses, to tightly cover on the surface of the light emitting assemblies, so that it is helpful to enhance the diffusion efficiency of the light, and thus has better effect than that of the light guide plate for further lowering the thickness of the light guide plate. The light emitting assemblies are installed in the receiving recesses of the back plate, so that it is possible to implement the technical solution of covering the light diffusion/guide strip on the light emitting assemblies. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0020]      FIGS. 1A and 1B  are schematic views of a structure of a side-light type LED backlight module in a traditional technology; 
           [0021]      FIG. 2A  is a cross-sectional view of a structure of a backlight module according to a preferred embodiment of the present invention; 
           [0022]      FIG. 2B  is a perspective view of a light guide plate of  FIG. 2A ; 
           [0023]      FIG. 3A  is a schematic view of a structure of a light emitting assembly according to the preferred embodiment of the present invention; 
           [0024]      FIG. 3B  is a schematic view of a structure of a light emitting assembly according to another preferred embodiment of the present invention; 
           [0025]      FIG. 4A  is a schematic view of a surface of a light diffusion/guide strip according to the preferred embodiment of the present invention; 
           [0026]      FIG. 4B  is a schematic view of a light pathway of the light diffusion/guide strip according to the preferred embodiment of the present invention; 
           [0027]      FIG. 4C  is a schematic view of a surface of a light diffusion/guide strip according to another preferred embodiment of the present invention; and 
           [0028]      FIG. 5  is a partially cross-sectional view of the structure of the backlight module of  FIGS. 2A and 2B  according to the preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    A backlight module according to a preferred embodiment of the present invention is described more detailed by referring to the following detailed description and the accompanying drawings. 
         [0030]    The objects, features and advantages of the present invention can be best understood by referring to the following detailed description of the preferred embodiments and the accompanying drawings. The specification of the present invention provides different embodiments to describe technical features of different implementation solutions, wherein arrangement of various elements in the embodiments is used to clearly describe the content of the present invention, but the present invention is not limited thereto. Meanwhile, numerals of drawings are partially repeated between different embodiments for simplifying the description, but not for building the relationship between the different embodiments. 
         [0031]      FIG. 2A  is a cross-sectional view of a structure of a backlight module according to a preferred embodiment of the present invention, wherein the backlight module comprises optical films  20 , a light guide plate  21 , a reflective sheet  22 , a back plate  23  and light emitting assemblies  25 . An upper surface of the back plate  23  is stacked with the light guide plate  21  and the optical films  20  in turn. The reflective sheet  22  is further disposed between the back plate  23  and the light guide plate  21 , wherein the reflective sheet  22  are tightly attached to an inner surface of the back plate  23 , and used to reflect light reflected from the light guide plate  21 . The backlight module of  FIG. 2A  further comprises a buffering support pad  24  between the light guide plate  21  and the back plate  23 , wherein the buffering support pad  24  provides a buffering function of supporting the light guide plate  21 , so as to prevent a bottom of the light guide plate  21  from being directly in contact with the back plate  23 . 
         [0032]      FIG. 2B  is a perspective view of the light guide plate  21  of  FIG. 2A . Referring to  FIG. 2B , the light guide plate  21  is substantially prism-like, wherein a cross section of the light guide plate  21  is substantially a shape of isosceles triangle. The light guide plate  21  has a first side surface  211  and two second side surfaces  212  inclined opposite to the first side surface  211  and symmetrically arranged to each other, wherein the optical films  20  are covered on the first side surface  211 . 
         [0033]    Referring still to  FIG. 2A , the back plate  23  has a shape corresponding to that of the two second side surfaces  212  of the light guide plate  21 , and has an inclined first side plate  231  and an inclined second side plate  232  which is connected and opposite to the first side plate  231 , wherein the first side plate  231  and the second side plate  232  have at least one first receiving recess  233  and at least one second receiving recess  234 , respectively. Two of the light emitting assemblies  25  are received in the first receiving recess  233  and the second receiving recess  234 , respectively. Preferably, the first receiving recess  233  and the second receiving recess  234  are symmetrically arranged to each other. In addition, the number of the first receiving recess  233  and the second receiving recess  234  can be one or more, respectively. For example, each of the number of the first receiving recess  233  and the second receiving recess  234  is exemplified by one in present invention. 
         [0034]    Preferably, the buffering support pad  24  is mounted on a connection portion between the first side plate  231  and the second side plate  232 . The two second side surfaces  212  of the light guide plate  21  are arranged adjacent to the first side plate  231  and the second side plate  232  of the back plate  23 . A connection portion of the two second side surfaces  212  of the light guide plate  21  is abutted against on the buffering support pad  24 . 
         [0035]      FIG. 3A  is a cross-sectional view of the light emitting assembly  25  according to the preferred embodiment of the present invention. In the preferred embodiment, the light emitting assembly  25  is LED (light emitting diode) type light emitting assembly, which comprises a plurality of LEDs  31 , a driver circuit board  32 , a light diffusion/guide strip  34  and a thermal conductive tape  33 . The LEDs  31  are mounted on the driver circuit board  32  along a linear direction thereof, wherein the driver circuit board  32  is a strip-like circuit board. The driver circuit board  32  mounted with the LEDs  31  constructs a light bar which is installed on a bottom of the first receiving recess  233 . In the embodiment, the driver circuit board  32  is attached to the first receiving recess  233  of the back plate  23  through the thermal conductive tape  33 . The corresponding second receiving recess  234  has the same structure, and thus the description and drawing thereof are omitted herein. In other embodiments, the type of the light emitting assembly  25  is not limited to use the LEDs as components of light source, and also can be various common types of light source including CCFL (cold cathode fluorescent lamp) and etc. 
         [0036]      FIG. 3B  is a cross-sectional view of a light emitting assembly  25  according to another preferred embodiment of the present invention. The light emitting assembly  25  comprises a plurality of LEDs  31 ′, a driver circuit board  32 ′, screws  33 ′ and a light diffusion/guide strip  34 ′. The difference between the embodiment and the foregoing embodiment of  FIG. 3A  is that: the embodiment uses the screws  33 ′ to connect the driver circuit board  32 ′ to the back plate  23 . For the strip-like driver circuit board  32 ′, the screws  33 ′ are spaced a predetermined distance and equidistantly arranged on the driver circuit board  32 ′ along a direction vertical to the plane of the drawing. Generally, the adhesion of using the thermal conductive tape  33  has a better heat dissipation effect than that of the connection of using the screws  33 ′. But, if the driver circuit board  32 ′ is a metal-based printed circuit board and the flatness of the metal-based printed circuit board and the back plate is good, the heat dissipation effect of mounting the LED type light emitting assembly  25  on the back plate  23  through the screws  33 ′ will be better than the heat dissipation effect of mounting the LED type light emitting assembly  25  on the back plate  23  through the thermal conductive tape  33 . 
         [0037]    Referring still to  FIG. 3A , the light diffusion/guide strip  34  is covered on an opening of the first receiving recess  233 , wherein the light emitted from the LED type light emitting assembly  25  passes through the light diffusion/guide strip  34  and enter the light guide plate  21 . The function of the light diffusion/guide strip  34  is to diffuse the light emitted from the LEDs  31  and then guide the diffused light into the light guide plate  21 . The light diffusion/guide strip  34  is close to the surface of the LEDs  31 , so that the light diffusion efficiency thereof is very high and thus the thickness of the light guide plate  21  can be further reduced. The second receiving recess  234  is also mounted with the same light diffusion/guide strip  34 , so that the description and drawing thereof are omitted herein. 
         [0038]      FIG. 4A  is a cross-sectional view of the light diffusion/guide strip  34  according to the preferred embodiment of the present invention, wherein a light input surface  41  of the light diffusion/guide strip  34  has V-shape first recesses  411 , and a light output surface  42  thereof has V-shape second recesses  421 . A first planar surface  412  is defined between each two of the adjacent first recesses  411 , while a second planar surface  422  is defined between each two of the adjacent second recesses  421 . Furthermore, the first recesses  411  of the light input surface  41  and the second recesses  421  of the light output surface  42  are staggered and opposite to each other. In other words, the first recesses  411  of the light input surface  41  and the second planar surfaces  422  of the light output surface  42  are corresponding to each other in a vertical direction, while the first planar surfaces  412  of the light input surface  41  and the second recesses  421  of the light output surface  42  are corresponding to each other. 
         [0039]      FIG. 4B  is a schematic view of a light pathway of the light diffusion/guide strip  34  according to the preferred embodiment of the present invention during guiding the light. As shown in the view of the light pathway, an included angle θ of the recess on the light output surface of the light diffusion/guide strip must satisfy the following condition: 
         [0000]      θ&gt;[90−arcsin( n 1/ n 2)]×2
 
         [0040]    To prevent the light from generating the total reflection on the light output surface of the light diffusion/guide strip to loss the light due to the increase of the light pathway, 
         [0000]        i &lt;arcsin( n 1/ n 2)θ/2+ i= 90°→θ&gt;[90−arcsin( n 1/ n 2)]*2   (I)
 
         [0041]    wherein n 1  is the refractive index of air, and the value thereof is 1; if the light diffusion/guide strip is made of polymethyl methacrylate (PMMA), the value of n 2  is 1.49. 
         [0042]    The calculated result is θ&gt;95.68° 
         [0043]    If the light diffusion/guide strip is made of polycarbonate (PC), the value of n 2  is 1.59. The calculated result is θ&gt;101.82° 
         [0044]    Moreover, other material, including methylmetahacrylate styrene (MS) and polystyrene (PS) and etc., also can be used. 
         [0045]    The included angle φ of the recesses on the light input surface of the light diffusion/guide strip must satisfy: 
         [0000]      φ/2+arcsin[cos(φ/2)* n 1/ n 2]&gt;180°−arcsin( n 1/ n 2)
 
         [0000]        k= 90°−φ/2
 
         [0000]      sin  k*n 1=sin  r*n 2→ r =arcsin[sin(90°−φ/2)* n 1/ n 2]
 
         [0000]      φ/2+ r+t= 180° t= 180°−φ/2−arcsin[cos(φ/2)* n 1/ n 2]
 
         [0046]    To prevent from generating the total reflection on the light output surface of the light diffusion/guide strip, having: 
         [0000]        t &lt;arcsin( n 1/ n 2) 
         [0047]    then, having: 
         [0000]      180°−φ/2−arcsin[cos(φ/2)* n 1/ n 2]&lt;arcsin( n 1/ n 2)
 
         [0048]    The calculated result is: 
         [0000]      φ/2+arcsin[cos(φ/2) n 1/ n 2]&gt;180°−arcsin( n 1/ n 2)   (II)
 
         [0049]    The foregoing two equations (I) and (II) are only rough calculation of θ and φ and when the distance between the LEDs and the light diffusion/guide strip is considerably greater than sizes (h, p, a, and etc.) in  FIG. 4B   
         [0050]    To optimize the diffusion effect of emitting light through the light diffusion/guide strip, it needs to use a light tracking simulation software for simulating to ensure the values in the drawing (θ, φ, h, p, a, d and etc.). 
         [0051]      FIG. 4C  is a schematic view of a surface of another light diffusion/guide strip  34  further optimized based on the structure of  FIG. 4A . The planar surface  422  of the light output surface  42  is further covered with a plurality of light diffusion particles  423  for further diffusing/scattering the emitted light. 
         [0052]    Moreover, in other embodiments, the surface of the light diffusion/guide strip  34  also can be frosted, or the light diffusion/guide strip  34  can be coated with nano-material, in order to enhance the diffusion efficiency. The light input surface  41  and the light output surface  42  of the light diffusion/guide strip  43  also can be waved. Peaks and valleys of the light input surface  41  are corresponding to valleys and peaks of the light output surface  42 , respectively. In addition, the first recesses  411  and the second recesses  421  of the light diffusion/guide strip  43  are not limited to V-shape, but also can be curved. 
         [0053]      FIG. 5  is a partially cross-sectional view of the structure of the backlight module having the light guide plate of  FIGS. 2A and 2B  according to the preferred embodiment of the present invention, wherein the backlight module comprises optical films  50 , a light guide plate  51 , a reflective sheet  52 , a back plate  53  and a housing  59 , wherein the housing  59  encloses edges of the back plate  53 . For clear description,  FIG. 5  only illustrates a schematic view of the installation structure of one end of the back plate  53  and the housing  59 , wherein the other end of the back plate  53  is symmetric to this end. Relationships of other components of the light guide plate can be referring to  FIG. 2A ,  FIG. 2B , other drawings and descriptions thereof, and thus the description thereof will be omitted herein. 
         [0054]    The installation of  FIG. 5  shows an outer engagement type installation of the housing  59 , i.e. a side wall of the housing  59  is located outside a side wall of the back plate  53 , and the side wall of the back plate  53  is engaged in the side wall of the housing  59 . The other installation is an inner engagement type installation, wherein the side wall of the housing  59  is located inside the side wall of the back plate  53 , and the side wall of the back plate  53  is engaged outside the side wall of the housing  59 . The two installations have no apparent difference, and thus drawings of the inner engagement type installation are omitted herein. 
         [0055]    The foregoing descriptions are only the preferred embodiment of the present invention, and it is understood that many changes and modifications to the described embodiment made by the man skilled in the art can be carried out without departing from the scope and the spirit of the invention that is intended to be limited only by the appended claims.