Abstract:
A backlight unit that minimizes damage to an optical sheet due to external impacts, and a liquid crystal display employing the backlight unit are disclosed. The backlight unit comprises a light source unit comprising a plurality of light sources; a bottom cover that receives the light source unit and comprises a first protrusion; support sides fastened to both opened shorter sides of the bottom cover to support the light source unit and comprising a second protrusion; and an optical sheet unit disposed on the light source unit and comprising a first long hole in which the first protrusion is inserted and a second long hole in which the second protrusion is inserted, wherein the first and second long holes have a dumbbell shape in which the diameter of a curved portion is larger than the width of a linear portion through which the first and second protrusions pass.

Description:
[0001]    This nonprovisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 10-2008-0014196 filed in Republic of Korea on Feb. 15, 2008 the entire contents of which are hereby incorporated by reference. 
       BACKGROUND 
       [0002]    1. Field 
         [0003]    This document relates to a backlight unit and, more particularly, to a backlight unit that minimizes damage to an optical sheet due to external impacts, and a liquid crystal display employing the same. 
         [0004]    2. Related Art 
         [0005]    In general, currently, an application coverage of a liquid crystal display (LCD) extends thanks to its characteristics that it is lighter, thinner, and driven at a low power consumption. Thus, the LCD is being commonly applied to office automation equipment, audio/video equipment, or the like. The LCD displays a desired image on its screen by controlling the amount of transmission of light beams according to a video signal applied to a plurality of control switches arranged in a matrix form. 
         [0006]    Because the LCD is not a self-emissive display device, it requires a light source such as a backlight. The backlight unit for the LCD is divided into a direct type backlight unit and an edge type backlight unit. The edge type backlight unit is configured such that a light source is disposed at an outer side of a flat panel and light from the light source is made incident to the entire surface of a liquid crystal panel by using a transparent light guide plate. The direct type backlight unit is configured such that a light source is disposed on a rear surface of the liquid crystal panel to directly illuminate the entire surface of the liquid crystal panel. Compared with the edge type backlight unit, the direct type backlight unit is advantageous in that it can use a plurality of light sources to enhance the luminance and widen a light emission surface. An LCD TV, for which a large-scale liquid crystal panel is required, commonly employs the direct type backlight unit. 
         [0007]    With reference to  FIGS. 1 and 2 , the direct type backlight unit comprises a light source unit  10  to emit light to the liquid crystal panel, a bottom cover  20  to receive the light source unit  10 , support sides  30  installed at both slope faces of the bottom cover  20  and supporting the light source unit  10 , and a diffuser  40  and optical sheets sequentially stacked on the light source unit  10 . 
         [0008]    The bottom cover  20  includes a bottom surface  20   a,  slope faces  20   b  extending from the bottom surface  20   a  in one direction and facing each other, and upper faces  20   c  extending from the slope faces  20   b  in one direction and allowing the diffuser  40  and the optical sheets  50  to be stacked thereon. First protrusions  22  are formed on the upper faces  20   c  of the bottom cover  20  to prevent wobbling of the diffuser  40  and the optical sheets  50  and guide them. Second protrusions  34  are formed on the upper faces  32  of the support sides  30  to also prevent wobbling of the diffuser  40  and the optical sheets  50  and guide them. 
         [0009]    The diffuser  40  diffuses light, which is made incident from the light source unit  10 , toward a front side of the liquid crystal panel to thereby make a distribution density of light emitted to the liquid crystal panel uniform. The diffuser  40  is guided by the first and second protrusions  22  and  34  so as to be disposed on the upper faces  20   c  of the bottom cover  20  and the upper faces  32  of the support sides  30 . 
         [0010]    The optical sheets  50  are to make light, which has been diffused by the diffuser  40 , proceed to be perpendicular to the liquid crystal panel to thus enhance light efficiency. The optical sheets  50  comprise one or more diffusion sheets and one or more prism sheets. Further, the optical sheets  50  comprise first ear portions  52  each with a long hole  52   a  and second ear portions  54  each with a long hole  54   a  so as to be fixed on the upper faces  20   c  of the bottom cover  20  and the upper faces  32  of the support sides  30 . The first long holes  52   a  of the first ear portions  52  are fastened with the first protrusions  22  formed on the upper faces  20   c  of the bottom cover  20 , while the second long holes  54   a  of the second ear portions  54  are fastened with the second protrusions  34  formed on the upper faces  32  of the support sides  30 . Here, the first and second long holes  52   a  and  54   a  contact with the first and second protrusions  22  and  34  in a point contact manner or with a quite narrow contact area. 
         [0011]    As for the LCD having such a backlight unit, if an impact ST is applied from the exterior while the LCD is being transported, the impact ST causes a stress concentration at a point Pi where a linear portion A 1  and a curved portion A 2  of the first long hole or the second long hole  52   a  or  54   a  meet as shown in  FIG. 3   a.  The stress concentration results in a crack at the particular point P 1  of the optical sheets  50  as shown in  FIG. 3   b.  The crack generated at the long holes  52   a  and  54   a  of the optical sheets  50  hinders the optical sheets  50  from being properly fixed on the upper faces  20   c  of the bottom cover  20  and on the upper faces  32  of the support sides  30 , making them wobble, which results in that debris (particles) generated when the crack was made are introduced to the liquid crystal panel to degrade display quality. 
       SUMMARY 
       [0012]    One aspect of this document is to provide a backlight unit that minimizes damage to an optical sheet due to external impacts, and a liquid crystal display (LCD) employing the same. 
         [0013]    Another aspect of this document is to provide a backlight unit capable of preventing degradation of display quality possibly caused as an optical sheet is cracked, and an LCD employing the same. 
         [0014]    In an aspect, a backlight unit comprises a light source unit having a plurality of light sources; a bottom cover that receiving the light source unit and having a first protrusion; support sides fastened to both opened shorter sides of the bottom cover to support the light source unit and having a second protrusion; and an optical sheet unit disposed on the light source unit and having a first long hole in which the first protrusion is inserted and a second long hole in which the second protrusion is inserted, wherein the first and second long holes have a dumbbell shape in which the diameter of a curved portion is larger than the width of a linear portion through which the first and second protrusions pass. 
         [0015]    The first protrusion may be formed on an upper face of the bottom cover facing the optical sheet unit, the second protrusion may be formed on an upper face of the support side facing the optical sheet unit, and the first and second protrusions may have a cylindrical shape or a polygonal column shape. 
         [0016]    The first long hole may be formed at a first ear portion provided at a longer side of the optical sheet unit, and the second hole may be formed at a second ear portion provided at a short side of the optical sheet unit. 
         [0017]    The optical sheet unit may have such a structure that one or more diffusion sheets and one or more prism sheets are stacked, and the first and second ear portions are provided on each of the diffusion sheets and the prism sheets. 
         [0018]    The optical sheet unit may have such a structure that one or more diffusion sheets and one or more prism sheets are stacked, and the first and second ear portions are provided at the uppermost one of the stacked sheets. 
         [0019]    In another aspect, a liquid crystal display comprise: a backlight unit comprising a light source unit having a plurality of light sources, a bottom cover receiving the light source unit and having a first protrusion, support sides fastened to both opened shorter sides of the bottom cover to support the light source unit and having a second protrusion, and an optical sheet unit disposed on the light source unit and having a first long hole in which the first protrusion is inserted and a second long hole in which the second protrusion is inserted; and a liquid crystal panel to display an image by using light made incident from the backlight unit, wherein the first and second long holes have a dumbbell shape in which the diameter of a curved portion is larger than the width of a linear portion through which the first and second protrusions pass. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. 
           [0021]    In the drawings: 
           [0022]      FIG. 1  is an exploded perspective view of a direct type backlight unit according to the related art. 
           [0023]      FIG. 2  is a drawing illustrating a state that optical sheets are fixed on upper faces of a bottom cover and support sides according to the related art. 
           [0024]      FIG. 3   a  is a drawing illustrating a phenomenon that stress concentration is generated due to external impacts. 
           [0025]      FIG. 3   b  is a drawing illustrating a phenomenon that a particular portion of optical sheets are damaged (cracked) due to the stress concentration. 
           [0026]      FIG. 4  is an exploded perspective view of a liquid crystal display (LCD) according to an exemplary embodiment of the present invention. 
           [0027]      FIG. 5  is a sectional view of a portion of the LCD in  FIG. 4  in an assembled state. 
           [0028]      FIG. 6  is a drawing illustrating a state that optical sheets are fixed on upper faces of a bottom cover and support sides according to an exemplary embodiment of the present invention. 
           [0029]      FIG. 7   a  is a drawing illustrating one example of the configuration of first and second ear portions. 
           [0030]      FIG. 7   b  is a drawing illustrating another example of the configuration of the first and second ear portions. 
           [0031]      FIG. 8  is a drawing illustrating a reduction or removal of a stress concentration due to external impacts. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]    Hereinafter, exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. 
         [0033]      FIG. 4  is an exploded perspective view of a liquid crystal display (LCD) according to an exemplary embodiment of the present invention,  FIG. 5  is a sectional view of a portion of the LCD in  FIG. 4  in an assembled state, and  FIG. 6  is a drawing illustrating a state that optical sheets are fixed on upper faces of a bottom cover and support sides according to an exemplary embodiment of the present invention. 
         [0034]    With reference to  FIGS. 4 and 5 , a liquid crystal display (LCD) according to an exemplary embodiment of the present invention comprises a support main  100 , a backlight unit  200  and a liquid crystal panel  170  stacked in the support main  100 , and a top case  180  to cover the edges of the liquid crystal panel  170  and slope faces of the support main  100 . 
         [0035]    The top case  180  is fabricated to have a rectangular band shape with a slope face portion and a plane portion bent at a right angle. The top case  180  is configured to cover the edges of the liquid crystal panel  170  and a panel guide  160 . 
         [0036]    The support main  100 , a mold product, comprises an internal side wall face molded as a step face, on which the backlight unit  200  and the liquid crystal panel  170  are stacked. 
         [0037]    The liquid crystal panel  170  comprises a color filter array substrate  170   a  and a thin film transistor (TFT) array substrate  170   b.  Liquid crystal cells are arranged in an active matrix form between the color filter array substrate  170   a  and the TFT array substrate  170   b,  and TFTs are installed in each liquid crystal to switch video signals. As the refractive index of each liquid crystal cell varies according to video signals, an image corresponding to the video signals is displayed on the liquid crystal panel  170 . A gate tape carrier package  172 , on which a gate IC (Integrated Circuit) is mounted to generate gate signals, and a data tape carrier package  174 , on which a data IC is mounted to generate data signals, are attached on the TFT array substrate  170   b  of the liquid crystal panel  170 . 
         [0038]    The panel guide  160  comprises a rectangular frame covering a slope face of the liquid crystal panel and a mounting portion extending with a certain length from an inner wall of the rectangular frame to allow the liquid crystal panel  170  to be mounted thereon. The panel guide  160  is stacked on the support main  100  to support the liquid crystal panel  170 . 
         [0039]    The backlight unit  200  comprises a plurality of lamps  110  to emit light to the liquid crystal panel  170 , a plurality of lamp holders  114  connected with both ends of the respective lamps  110 , a bottom cover  120  disposed on a rear surface of the plurality of lamps  110  and receiving the plurality of lamps  110  and the plurality of lamp holders  114 , support sides  130  installed at both open sides of the bottom cover  120  to support the plurality of lamps  110 , a diffuser  140  positioned on the plurality of lamps, and optical sheets  150  placed on the diffuser  140 . 
         [0040]    As the lamps  110 , a CCFL (Cold Cathode Fluorescent Lamp) or an external electrode type fluorescent lamp may be used. Each lamp  110  comprises a glass tube, inert gases present within the glass tub, and a cathode and an anode installed at both end portions of the glass tube. The glass tube is filled with inert gases, and phosphor is coated on the inner wall of the glass tube. The lamps  110  are fixed by lamp guides (not shown) so as to be disposed on the bottom cover  120 . Meanwhile, besides the lamps  110 , an LED (Light Emitting Diode) array or a hybrid array comprising both an LED and a lamp may be also used as the backlight. The plurality of lamp holders  114  are connected with the edges of the plurality of lamps to fix and support the lamps  110 . 
         [0041]    The diffuser  140  diffuses light, which is made incident from the lamps  110 , toward the front side of the liquid crystal panel, to thereby make a distribution density of light emitted to the liquid crystal panel uniform. The diffuser  140  is guided by first and second protrusions  122  and  134  and disposed on upper faces  120   c  of the bottom cover  120  and on upper faces  132  of the support sides  130 . The diffuser  140  may be made of PMMA (Polymethylmeth Acrylate) or glass so as to be prevented from being deformed by heat generated from the lamps  110 . 
         [0042]    The optical sheets  150  serve to make light, which has been diffused by the diffuser  140 , proceed to be perpendicular to the liquid crystal panel to thus increase light efficiency. The optical sheets  150  may comprise two diffusion sheets and two prism sheets. The optical sheets  150  comprise first ear portions  152  each with a first long hole  152   a  in a dumbbell shape and second ear portions  154  each with a second long hole  154   a  in a dumbbell shape, so as to be fixed on the upper faces  120   c  of the bottom cover  120  and the upper faces  132  of the support sides  130 . The first ear portions  152  are provided at the longer side of the optical sheets  150 , while the second ear portions  154  are provided at the shorter side of the optical sheets  150 . As shown in FIG. C, the first long holes  152   a  in the dumbbell shape formed on the first ear portions  152  are fastened with the first protrusions  122  formed on the upper faces  120   c  of the bottom cover  120 , and the second long holes  154   a  in the dumbbell shape formed on the second ear portions  154  are fastened with the second protrusions  134  formed on the upper faces  132  of the support sides  130 . Here, the reason for forming the first and second long holes  152   a  and  154   a  in the dumbbell shape is to reduce or remove a stress concentration possibly caused by external impacts. This will be described in detail with reference to  FIG. 8 . The optical sheets  150  are made of a PET (PolyethyleneTerephthalate) material. The first and second ear portions  152  and  154  may be formed at each of the optical sheets as shown in  FIG. 7   a,  or may be formed only at an uppermost optical sheet disposed to be closest to the liquid crystal panel as shown in  FIG. 7   b.  If the first and second ear portions  152  and  154  are formed at each of the optical sheets  150  as shown in  FIG. 7   a,  the optical sheets  150  may be more firmly fixed relatively, while the fabrication and assembling process of the optical sheets are disadvantageously complicated. If the first and second ear portions  152  and  154  are formed only at the uppermost optical sheet as shown in  FIG. 7   b,  the fabrication and assembling process of the optical sheets can be simplified, but the optical sheets cannot be firmly fixed relatively. 
         [0043]    The bottom cover  120  are disposed on the rear surface of the plurality of lamps  110  to receive and support the plurality of lamps  110  and the plurality of lamp holders  114 . The bottom cover  120  comprises a bottom surface  120   a,  slope faces  120   b  extending from the bottom surface  120   a  in one direction and facing each other, and upper faces  120   c  extending from the slope faces  120   b  in one direction to allow the diffuser  140  and the optical sheets  150  to be stacked and fixed thereon. The slope faces  120   b  and the upper faces  120   c  are formed only at both longer sides of the bottom cover  120 , and are not formed at both shorter sides of the bottom cover  120 . Both shorter sides of the bottom cover  120  are open. The first protrusions  122  are formed on the upper faces  120   c  of the bottom cover  120  to prevent the diffuser  140  and the optical sheets  150  from wobbling and guide the diffuser  140  and the optical sheets  150 . The first protrusions  122  may be formed to have a cylindrical shape or a polygonal column shape such as a triangular column shape or a square column shape. A reflection sheet  115  is attached on the bottom surface  120   a  and the slope faces  120   b  of the bottom cover  120 . The reflection sheet  115  is made of a material that reflects light, and attached to the bottom surface  120   a  and the slope faces  120   b  of the bottom cover  120  by means of a double-sided adhesive tape. The reflection sheet  115  reflects light, which proceeds to the bottom cover  120  from the plurality of lamps  110 , toward the liquid crystal panel  170  to thus improve the efficiency of light emitted to the liquid crystal panel  170 . 
         [0044]    The support sides  130  comprise a concavo-convex portion (a depressed and protruded pattern) in which the plurality of lamp holders  114  are inserted, and is combined with both shorter sides of the bottom cover  120 . The second guide protrusions  134  are formed on the upper faces  132  of the support sides  130  in order to prevent the diffuser  140  and the optical sheets  150  from wobbling and guide the diffuser  140  and the optical sheets  150 . The second protrusions  134  may have a cylindrical shape or a polygonal column shape such as a triangular column shape or a square column shape. The support sides  130  support the plurality of lamps  110  the diffuser  140 , and the optical sheets  150 , and reflect light, which proceeds to the both shorter sides of the bottom cover  120  from the plurality of lamps  110 , toward the liquid crystal panel  170  to thus enhance the efficiency of light emitted to the liquid crystal panel  170 . 
         [0045]      FIG. 8  is a drawing illustrating a reduction or removal of a stress concentration due to external impacts. 
         [0046]    With reference to  FIG. 8 , the long holes  152   a  and  154   a  in the dumbbell shape are formed on the ear portions  152  and  154  of the optical sheets  150  such that the diameter D 1  of curved portions A 2  is larger than the width D 2  of the linear portion A 1  according to the exemplary embodiment of the present invention. Accordingly, even if an impact ST is applied from the exterior while being transported, a stress concentration that may be possibly formed at a point P 2  where the linear portion A 1  and the curved portion A 2  of the long holes  152   a  and  154   a  meet can be considerably reduced. This is because the stress concentration point generated by the external impact ST is distributed to the entire points of the curved portion A 2  of the long holes  152   a  and  154   a  from the point P 2  where the linear portion A 1  an the curved portion A 2  meet. The curved portion A 2  of the long holes  152   a  and  154   a  has the diameter larger than that of the related art, thus increasing the effect of distributing the concentration point of the stress. Thus, the optical sheets  150  according to the exemplary embodiment of the present invention cannot be easily damaged (cracked) by external impacts, owing to such effect of distributing the concentration point of the stress. 
         [0047]    As described above, the backlight unit and the LCD employing the same according to the exemplary embodiments of the present invention have the advantages that because the optical sheets have the long holes in the dumbbell shape in which the diameter of the curved portion is larger than the width of the linear potion, the stress concentration point with respect to an external force can be distributed, whereby damage to the optical sheets possibly caused by external impacts during transportation can be drastically reduced. Therefore, the backlight unit and the LCD employing the same according to the exemplary embodiment of the present invention can prevent degradation of display quality caused by the cracking phenomenon of the optical sheets. 
         [0048]    While the invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.