Patent Publication Number: US-2011051048-A1

Title: Backlight unit and display device using the same

Description:
The present application claims priority under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2009-0079030 filed on Aug. 26, 2009, which is hereby incorporated by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     An embodiment of the present invention relates to a backlight unit and a display device using the same. 
     2. Description of the Related Art 
     A liquid crystal display (LCD) which has been widely used in recent years has advantages of miniaturization, light weight, and low-power consumption. Therefore, the LCD has gradually received public attention as an alternative means capable of overcoming demerits of the existing cathode ray tube (CRT) and at present, it is mounted on and used in almost all information processing apparatuses requiring a display device. 
     Since the LCD is not a self-light emitting display device, the LCD needs an additional light source such as a back light unit (BLU). A lot of researches are in progress in order to provide a high-quality image by effectively utilizing light emitted from the BLU. 
     SUMMARY OF THE INVENTION 
     An embodiment provides a backlight unit having a new structure and a display device using the same. 
     An embodiment provides a backlight unit having a plurality of optical assemblies and a display device using the same. 
     An embodiment provides a backlight unit which can be manufactured by an easy manufacturing process and with low cost, and a display device using the same. 
     An embodiment may provide a backlight unit which can be applied to a large-size display panel and has a slim thickness and a display device using the same. 
     A backlight unit according to an embodiment includes: a plurality of light guide panels which incline at a first angle with a uniform thickness, and of which at least one is disposed in a first direction and which are partially overlapped with each other in a second direction perpendicular to the first direction; reflection members disposed under the light guide panels; and a light emitting module unit disposed under the reflection member and providing light to the side of each of the plurality of light guide panels. 
     A backlight unit according to another embodiment includes: a backlight unit including a plurality of light guide panels which incline at a first angle with a uniform thickness, and of which at least one is disposed in a first direction and which are partially overlapped with each other in a second direction perpendicular to the first direction, reflection members disposed under the light guide panels, and a light emitting module unit disposed under the reflection member and providing light to the side of each of the plurality of light guide panels; and a display panel disposed on the backlight unit and receiving light from the backlight unit to display an image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a display device according to an embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of a display module taken along line A-A of  FIG. 1 ; 
         FIG. 3  is a cross-sectional view of a backlight unit; 
         FIG. 4  is a perspective view of a backlight unit; 
         FIG. 5  is a plan view of the backlight unit; 
         FIG. 6  is a diagram showing light guide panels of a plurality of optical assemblies; and 
         FIGS. 7 and 8  are diagrams showing a diffusion plate. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In describing embodiments, it will be understood that when layers (films), regions, patterns, or structures are referred to as being “on” or “under” a substrate, layers (films), regions, pads, or patterns, “on” and “under” include “directly” or “indirectly”. Further, “on” or “under” will be described on the basis of the drawings. 
     In the drawings, thicknesses or sizes of layers are exaggerated, omitted, or schematically illustrated for convenience and clarity of description. Further, sizes and actual sizes of constituent members are not fully reflected. 
     A backlight unit and a display device using the same according to embodiments of the present invention will be described with reference to the accompanying drawings. 
       FIG. 1  is an exploded perspective view of a display device according to an embodiment of the present invention. 
     Referring to  FIG. 1 , the display device  1  according to the embodiment includes a display module  200 , a front cover  300  disposed on the front surface of the display module  200 , a back cover  400  disposed on the back surface of the display module  200 , and a fixation member  500  for fixing the display module  200  to the front cover  300  and/or the back cover  400 . 
     The fixation member  500  may be disposed between the front cover  300  and the display module  200  and enables the front cover  300  and the display module  200  to be coupled with each other. 
     Further, the fixation member  500  may be disposed between the back cover  400  and the display module  200  and enables the back cover  400  and the display module  200  to be coupled with each other. 
     In the embodiment, the fixation member  500  having a bar shape is shown, but the fixation member  500  is not necessarily needed and the front cover  300 , the display module  200 , and the back cover  400  may be coupled with each other by a fastening member such as a screw. 
       FIG. 2  is a cross-sectional view of a display module taken along line A-A of  FIG. 1 . 
     Referring to  FIG. 2 , the display module  200  includes a display panel  210  on which an image is displayed, a backlight unit  100  providing light to the display panel  210 , a bottom plate  110  disposed under the display module  200 , a panel supporter  240  supporting the display panel  210  at the lower side, and a top plate  230  forming the outline of the display module  200  while supporting the display panel  210  at the upper side. 
     The bottom plate  110  may have a box shape of which a top surface is opened to receive the backlight unit  100 . The bottom surface of the bottom plate  110  may have an uneven structure like the back surface of the backlight unit  100  to correspond to the shape of the backlight unit  100 . In the embodiment, a plurality of slopes are included in the bottom surface of the bottom plate  110 . 
     However, the shape of the bottom plate  110  is not limited and for example, the bottom surface of the bottom plate  110  is flattened and an additional support for supporting the backlight unit  100  may be formed on the bottom plate  110 . 
     In addition, one portion of the bottom plate  110  may be fixed to one portion of the top plate  230 . For example, the fastening member such as the screw penetrates a part where the bottom plate  110  and the top plate  230  are overlapped with each other to allow the bottom plate  110  and the top plate  230  to be coupled with each other. However, it is not limited. 
     Although the display panel  210  is not shown in detail, the display panel  210  may include a first substrate  211  and a second substrate  222  that are bonded to each other to maintain a uniform cell gap while facing each other, and a liquid crystal layer interposed between the first and second substrates  211  and  212 . A plurality of gate lines and a plurality of data lines crossing the plurality of gate lines are formed on the first substrate  211  and a thin film transistor (TFT) may be formed at an intersection region of the gate line and the data line. Color filters may be formed on the second substrate  212 . However, the structure of the display panel  210  is not limited and the display panel  210  may have various structures. For example, the first substrate  211  may include the color filter in addition to the thin film transistor. Further, the display panel  210  may have various types of structures in accordance with a scheme driving the liquid crystal layer. 
     Although not shown, a gate driving printed circuit board (PCB) supplying a scan signal to the gate line and a data driving printed circuit board (PCB) supplying a data signal to the data line may be provided at the edge of the display panel  210 . A polarizing film (not shown) may be disposed at any one of an upper part and a lower part of the display panel  210 . 
     An optical sheet  220  may be disposed between the display panel  210  and the backlight unit  100  and the present invention is not limited thereto. 
     The optical sheet  220  may include a diffusion sheet and/or a prism sheet. 
     The diffusion sheet may evenly diffuse light emitted from a light guide panel and the diffused light may focus on the display panel by the prism sheet. The type or number of the optical sheets  220  may be added or deleted within the technical scope of the embodiment and the present invention is not limited thereto. 
     Meanwhile, the backlight unit  100  may include a plurality of optical assemblies  10  forming a plurality of divided driving regions. In addition, the optical assemblies  10  are driven with different luminances depending on a gray peak value of an image signal inputted into the display panel  210  or a color coordinate signal so as to control the luminance of an image displayed through the display panel  210 . 
     Hereinafter, a configuration of the backlight unit  100  will be described in detail. 
       FIG. 3  is a cross-sectional view of the backlight unit,  FIG. 4  is a perspective view of the backlight unit, and  FIG. 5  is a plan view of the backlight unit. 
     Referring to  FIGS. 3 to 5 , the backlight unit  100  includes the plurality of optical assemblies  10 . The plurality of optical assemblies  10  incline at a first angle θ to be disposed in a second direction b such that first regions M of the optical assemblies  10  are overlapped with each other. 
     The optical assembly  10  may include a light guide panel  15 , a light emitting module unit  13  disposed at one portion of the light guide panel  15 , and a side cover  20  fixing the light guide panel  15  and the light emitting module unit  13 . 
     The light emitting module unit  13  is disposed on the side of the light guide panel  15  and provides light to the light guide panel  15 . 
     The light emitting module unit  13  may include a substrate  12  and a plurality of light emitting devices  11  mounted on the substrate  12  while forming an array. 
     The substrate  12  may be a printed circuit board (PCB) and for example, may be formed by a metal core PCB, an FR-4 PCB, a general PCB, a flexible substrate, and the like. Further, the light emitting device  11  may be a light emitting diode (LED) and the light emitting diode may b for example, a red, green, blue, or white light emitting diode emitting red, green, blue, or white light, but the present invention is not limited thereto. 
     Meanwhile, although not shown, a light guide member (not shown) may be formed between the light emitting module unit  13  and the light guide panel  15 . The light guide member (not shown) may be made of the same material as the light guide panel  15  and the light guide member is formed in space between the light emitting module unit  13  and the light guide panel  15  to allow the light emitted from the light emitting module unit  13  to be effectively guided to the light guide panel  15 . 
     Further, although not shown, a phosphor luminescent film (PLF) may be formed between the light emitting module unit  13  and the light guide panel  15 . The phosphor luminescent film (PLF) is a film including a phosphor luminescent substance and the phosphor luminescent substance is excited by first light emitted from the light emitting module unit  13  to generate second light. 
     For example, the light emitted from the light emitting module unit  13  is blue and when the phosphor luminescent substance included in the PLF is a yellow phosphor luminescent substance which is excited by the blue light to generate yellow light, two kinds of lights are mixed, such that white light may be provided to the light guide panel  15 . However, the present invention is not limited thereto. 
     The light guide panel  15  makes a surface light source provided from the light emitting module unit  13  and provides the corresponding light to the display panel  210 . 
     The light guide panel  15  is made of a transparent material and for example, may include any one of acryl resin series such as polymethyl metaacrylate (PMMA), polyethylene terephthalate (PET), poly carbonate (PC), cycloolefin copolymer (COC), and polyethylene naphthalate (PEN) resin. 
     The light guide panel  15  may have a rectangular shape which elongates in a first direction a, but the present invention is not limited thereto. Further, the light guide panel  15  may have a substantially predetermined thickness with respect to the entire region. 
     A scattering pattern (not shown) may be formed on the top surface or bottom surface of the light guide panel  15 . The scattering pattern has a predetermined pattern to serve to improve the uniformity of light emitted through the light guide panel  15  by anti-reflecting incident light. 
     The light guide panel  15  may be manufactured by an extrusion molding method. Therefore, although the light guide panel  15  elongates with, for example, 1 meter or more in the first direction a, the light guide panel  15  may be easily manufactured and may be manufactured to have a predetermined thickness. Further, after the extrusion molding, the scattering pattern (not shown) may be formed on the top surface or bottom surface of the light guide panel  15 . 
     The light guide panel  15  may be manufactured by an injection molding method. However, when the light guide panel  15  is manufactured by the injection molding method, it is difficult to manufacturing the light guide panel  15  having a long length. 
     Further, the number of the light guide panels  15  arranged in the first direction a is smaller than the number of the light guide panels  15  arranged in a second direction b. For example, at least one light guide panel  15  may be disposed in the first direction a and a plurality of light guide panels  15  may be disposed in the second direction b which is perpendicular to the first direction a. Herein, the first direction a may be the same as a direction in which the plurality of light emitting devices  11  are linearly disposed. 
     In the embodiment, since the light guide panel  15  is manufactured by the extrusion molding method, the light guide panel  15  may be manufactured with a sufficiently long length and one light guide panel  15  may be disposed in the first direction a. 
     At least one light guide panel  15  is disposed in the first direction a and although two or more light guide panels  15  are disposed in the first direction a, the light guide panels  15  are not overlapped with each other. In addition, the plurality of light guide panels  15  are disposed in the second direction b and may be partially overlapped with each other in the second direction b. 
     A reflection member  17  may be formed on the bottom surface of the light guide panel  15 . Therefore, a part of the light inputted from the light emitting module unit  13  through the side of the light guide panel  15  is reflected by the reflection member  17  and thereafter, may be emitted to the top surface of the light guide panel  15 . 
     Further, the reflection member  17  may serve to prevent interference by light generated in other optical assemblies  10  which are overlapped with each other. 
     Referring to  FIGS. 3 and 4 , since the light guide panel  15  may have an uniform thickness, a lot of light may be emitted to a side  19  disposed in an opposite direction to a side facing the light emitting device  11 . Since a part where the side  19  of the light guide panel  15  is disposed is brighter than other parts when viewed from the upper side of the light guide panel  15 , the bright line may be observed in the part of the side  19 . 
     Therefore, the side  19  of the light guide panel  15  is surface-treated to prevent the bright line from being generated, thereby providing light having uniform luminance. 
     The surface treatment may include, for example, painting using photo solder resist (PSR) ink having at least one color of black, white, and gray colors. However, it is not limited thereto. 
     Meanwhile, in order to prevent a bright line from being generated, the diffusion plate may be disposed on the backlight unit  100 . This will be described below. 
     The side cover  20  may be coupled with one portion of the light guide panel  15  and may receive the light emitting module unit  13  therein. Therefore, the side cover  20  may fix the light guide panel  15  and the light emitting module unit  13  and may couple the backlight unit  100  to the bottom plate  110  by using a fastening screw  51  such as a screw, and the like. 
     The side cover  20  may be made of a plastic or metallic material. However, it is not limited to the shape and material of the side cover  20  and the side cover may be modified in accordance with the design of the backlight unit  100 . 
     The optical assemblies  10  include a partial region of the light guide panel  15 , a first region M including the light emitting module unit  13  and the side cover  20 , and a second region N emitting light provided from the first region M to the front side. 
     That is, the optical assembly  10  may include a first region M disposed under an adjacent optical assembly  10  and a second region N other than the first region M. Herein, the second region N may include a region disposed on an adjacent optical assembly  10  and a region which is not disposed on or under the adjacent optical assembly  10 . 
     The plurality of optical assemblies  10  may be disposed in the second direction b such that the first region M is disposed under a second region N of the adjacent optical assembly  10 . 
     Accordingly, the first regions M of the optical assemblies  10  may not be observed when viewed from an upper direction of the optical assembly  10 . However, since a first region M of an optical assembly  10  which is disposed at the leftmost side in  FIG. 4  among the optical assemblies  10  is not overlapped, the first region M may be observed when viewed from the upper direction. 
     The optical assemblies  10  may have a rectangular shape which elongates in the first direction a as shown in  FIGS. 4 and 5  and is not limited thereto. Since the optical assemblies  10  have such a shape, the plurality of optical assemblies  10  are disposed in the second direction b to configure the backlight unit  100 . For example, the backlight unit  100  may be formed by disposing the plurality of optical assemblies  10  in an array of 1×n. 
     Each of the optical assemblies  10  may be manufactured as an independent assembly and the optical assemblies  10  are disposed close to each other to form a module-type backlight unit. The module-type backlight unit may provide light to the display panel  210  as a backlight means. 
     The backlight unit  100  according to the embodiment may be driven in a full driving scheme or a partial driving scheme such as a local dimming scheme, an impulsive scheme, or the like. 
     When the backlight unit  100  is driven in, for example, the local dimming scheme, each of the optical assemblies  10  may be driven in accordance with a gray-level peak value of an image signal or a color coordinate signal applied to the display panel  210 . 
     That is, when the backlight unit  100  operates in the local dimming scheme, a black part of an image decreases the luminance of the backlight unit  100  in link with the luminance of the image signal and a bright part of the image increases the luminance of the backlight unit  100  to improve a contrast ratio and definition and save cost by reducing power consumption. 
       FIG. 6  is a diagram showing light guide panels of a plurality of optical assemblies. 
     Referring to  FIGS. 3 and 6 , since the plurality of optical assemblies  10  incline at the first angle θ to be disposed in the second direction b, a thickness L occupied by the light guide panel  15  may be determined depending on the first angle θ and the width A and the thickness B of the light guide panel  15  in the backlight unit  100  as shown in Equation 1. 
         L=A  cos θ+ B  sin θ  [Equation 1]
 
     Further, an overlapping distance x in which the light guide panels  15  are overlapped with each other may also be determined depending on the first angle θ and the width A and the thickness B of the light guide panel  15  in the backlight unit  100  as shown in Equation 2. 
     
       
         
           
             
               
                 
                   x 
                   = 
                   
                     A 
                     - 
                     
                       B 
                       
                         tan 
                          
                         
                             
                         
                          
                         θ 
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
     Since the plurality of light guide panels  15  incline at the first angle θ to be disposed in the second direction b, it is possible to reduce thicknesses L occupied by the light guide panels  15 . 
     The first angle θ may be larger than 0° and less than 90° and may preferably be 0.1° to 30°, but is not limited thereto. 
     The optical assemblies  10  may individually provide light to each of the light guide panels  15  because the light emitting device  11  provides light on the side of the light guide panel  15  and is provided with the plurality of light guide panels  15 . 
     Therefore, since the light emitting device  11  is disposed under the reflection member  17 , a problem in which light emitted from the light emitting device  11  is observed as a hot spot may be solved and since the number of the optical sheets can be decreased, it is possible to reduce the thickness L of the backlight unit  100 . 
     Referring to  FIG. 2 , the optical sheet  220  may be disposed on the backlight unit  100 . At this time, the optical sheet  220  may line-contact the plurality of optical assemblies  10 . 
     Since the plurality of optical assemblies  10  incline at the first angle θ to be disposed in the second direction b and the light guide panel  15  has a rectangular shape which extends in the first direction a with a predetermined thickness, the top surface of the backlight unit  100  is constituted by a plurality of lines. Therefore, the optical sheet  220  may be supported on the backlight unit  100  by line contact. 
     However, the optical sheet  220  is not limited thereto and the optical sheets  220  may be arranged on the backlight unit  100  at a regular interval. 
     Further, since the plurality of optical assemblies incline at the first angle θ to be disposed in the second direction b, the plurality of optical assemblies  10  incline to have the first angle θ with respect to the display panel  210 . 
     In the backlight unit  100  according to the embodiment, a process of manufacturing the backlight unit  100  by assembling the optical assemblies  10  is simple and it is possible to improve productivity by minimizing loss which may be generated while the assembling process. Further, since the generation of a failure by a scratch of the light guide panel which may be generated during the assembling process of the backlight unit  100  is decreased and the generation of optical mura may be reduced, it is possible to improve process reliability and improve quality. 
     Since the optical assembly  10  can be manufactured by extrusion molding, a manufacturing process is simple and mass production is easy, and the backlight unit  100  according to the embodiment may be applied to backlight units having various sizes. 
     When a failure occurs in any one of the optical assemblies  10  of the backlight unit  100  according to the embodiment, only the optical assembly having the failure is replaced without replacing all the backlight units  100 . Therefore, a replacing work is easy and part replacing cost is saved. 
     The optical assembly  10  and the backlight unit  100  with the same according to the embodiment are robust and highly durable with respect to a shock from the outside or an environmental change. 
     In the optical assemblies  10  of the backlight unit  100  according to the embodiment, since the adjacent optical assemblies  10  are partially overlapped with each other and surface treatment of the side  19  of the optical assembly  10  is performed, the generation of the bright line or black line on the boundaries of the optical assemblies  10  is reduced and the uniformity of light can be ensured. 
     The backlight unit  100  according to the embodiment is easily applied to a large-size display panel. Further, the embodiment is advantageous in slimming the backlight unit and the display device. 
       FIGS. 7 and 8  are diagrams showing a diffusion plate. 
     Referring to  FIGS. 7 and 8 , the diffusion plate  30  is disposed between the backlight unit  100  and the optical sheet  220  to prevent the bright line from being generated in the backlight unit  100 . 
     A diffusion pattern  31  may be formed on the diffusion plate  30 . The diffusion pattern  31  may be formed in a part corresponding to the side  19  of the backlight unit  100 . That is, the diffusion pattern  31  may be partially formed in only an upper part of the side  19 . 
     The diffusion pattern  31  may be, for example, a hemispheric pattern  31  of  FIG. 7  or an uneven pattern  31   a  of  FIG. 8 , but is not limited thereto. 
     The diffusion plate  30  may be formed by, for example, extrusion molding, but is not limited thereto. The diffusion pattern  31  may be formed while extruding the diffusion plate  30  by using a roller during the extrusion molding. 
     The diffusion plate  30  may be made of, for example, any one of acryl resin series such as polymethyl metaacrylate (PMMA), polyethylene terephthalate (PET), poly carbonate (PC), cycloolefin copolymer (COC), and polyethylene naphthalate (PEN) resin. 
     When the diffusion plate  30  is disposed between the backlight unit  100  and the optical sheet  220 , the diffusion plate  30  may line-contact the backlight unit  100 . However, the diffusion plate  30  may not be formed. 
     An embodiment may provide a backlight unit having a new structure and a display device using the same. 
     An embodiment may provide a backlight unit having a plurality of optical assemblies and a display device using the same. 
     An embodiment may provide a backlight unit which can be manufactured by an easy manufacturing process and with low cost and a display device using the same. 
     An embodiment may provide a backlight unit which can be applied to a large-size display panel and has a slim thickness and a display device using the same. 
     Any reference in this specification to “one embodiment,” “an embodiment,” “example embodiment,” etc., means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with any embodiment, it is submitted that it is within the purview of one skilled in the art to effect such feature, structure, or characteristic in connection with other ones of the embodiments. 
     Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the disclosure, the drawings and the appended claims. In addition to variations and modifications in the component parts and/or arrangements, alternative uses will also be apparent to those skilled in the art.