Abstract:
A backlight of a liquid crystal display device includes lamps and a conductive board. Each lamp has electrodes, one of which is contacted and retained by a contact terminal on the conductive board. The contact terminals are electrically connected by the conductive board. A bent part located in the conductive board is disposed between adjacent contact terminals such that when heat from the lamps absorbed by the conductive board expands the conductive board, the bent part is resiliently deformed to maintain the distance between the lamps.

Description:
This application claims the benefit of Korean Patent Application No. P2003-92700 filed in Korea on Dec. 17, 2003, which is hereby incorporated by reference. 
     BACKGROUND 
     1. Field 
     The present invention relates to a liquid crystal display device, and more particularly to a backlight of a liquid crystal display device that is adaptive for preventing picture quality deterioration. 
     2. Description of the Related Art 
     Generally, a liquid crystal display LCD controls the light transmissivity of liquid crystal cells in accordance with a video signal to display a picture corresponding to the video signal on a liquid crystal display panel where the liquid crystal cells are arranged in a matrix shape. 
     For this, the liquid crystal display device includes a liquid crystal display panel where liquid crystal cells are arranged in an active matrix shape; and a backlight unit in the rear surface or the side surface of the liquid crystal display panel to illuminate light onto the liquid crystal display panel. 
     The backlight is divided into an edge type and a direct lighting type in the way of arranging cylindrical fluorescent lamps. 
     Firstly, in the edge light type, the fluorescent lamps are installed at the outer area to disperse light to the whole surface by use of a light guide panel. The brightness of the edge light type is low because the fluorescent lamp is installed at the side surface and light passes through the light guide panel. Further, complicated optical design technology and process technology on the light guide panel is required for uniform distribution of light. 
     The direct light type is comparatively brighter and more uniform than the edge light type because multiple fluorescent lamps are arranged on a plane. 
     In the direct light type, the fluorescent lamp as a light source is mainly a cold cathode fluorescent lamp CCFL that has electrodes inside both the ends thereof. Recently, however, an external electrode fluorescent lamp (EEFL) has been developed. The EEFL has electrodes at the surface of both ends thereof. 
     The EEFL has no direct collision between electrodes and ions, thus heat generation in the electrode is restrained. In the EEFL, the generation of plasma joule heat is low because the EEFL is driven at high voltage and low current. In addition, self-discharge exists in the EEFL, thus it can be driven with high brightness and high efficiency. 
       FIGS. 1 and 2  are a perspective view and a plan view representing a prior art backlight unit of a liquid crystal display device using an external electrode fluorescent lamp. 
     A backlight using an external electrode fluorescent lamp shown in  FIGS. 1 and 2  includes a supporter having a first supporter  50  and a second supporter  52  where a lower contact terminal  56  holds both electrode parts  42   a ,  42   b  of the external electrode fluorescent lamp  40 . Herein, the supporter having the first supporter  50  and the second supporter  52  has a rectangular stick shape and is separated from each other with a designated distance therebetween. The supporter having the first supporter  50  and the second supporter  52  is formed of thermal plastic elastomer TPE and polybutylene terephthalates PBT. 
     A lower conductive board  54 , where a conductive nickel is coated over the original surface of phosphor bronze, beryllium copper, etc., is fixed by a screw  58  and the lower conductive board  54  is cut and bent to form a lower contact terminal  56  in the upper surface of the first supporter  50  and the second supporter  52 , wherein the lower contact terminal  56  can hold, and at the same time cover the electrode parts  42   a ,  42   b  of the fluorescent lamp  40 . 
     Herein, the first supporter  50 , the second supporter  52  and the lower conductive board  54  can be bonded together by glue, heat melt-adhesion, insert injection, etc. 
     And, there is a cover having a first cover  60  and a second cover  62  that covers the upper part of both the electrode parts  42   a ,  42   b  of the external electrode fluorescent lamp  40  with the upper contact terminal  66  on the supporter inclusive of the first supporter  50  and the second supporter  52 . 
     Herein, the first cover  60  and the second cover  62  have a rectangular stick shape and are separated from each other with a designated distance therebetween to correspond to the first supporter  50  and the second supporter  52 , respectively. 
     The first cover  60  and the second cover  62  are made of thermal plastic elastomer TPE and polybutylene terephthalates PBT. 
     And, an upper conductive board  64 , where a conductive nickel is coated over the original surface of phosphor bronze, beryllium copper, etc., is fixed by a screw  68  and the upper conductive board  64  is cut and bent to form an upper contact terminal  66  in the lower surface of the first cover  60  and the second cover  62 , wherein the upper contact terminal  66  can hold, and at the same time cover the electrode parts  42   a ,  42   b  of the fluorescent lamp  40  that is located at the lower contact terminal  56  of the supporter. 
     Herein, the first cover  60 , the second cover  62  and the upper conductive panel  64  can be bonded together by glue, heat melt-adhesion, insert injection, etc. 
     Accordingly, an operator holds the external electrode fluorescent lamp  40  to locate the electrode parts  42   a ,  42   b  of the external electrode fluorescent lamp  40  at the lower contact terminal  56  which is formed on the supporter having the first supporter  50  and the second supporter  52  that are separated from each other with a designated distance therebetween. 
     And then, the operator locates the cover having the first cover  60  and the second cover  62  on the supporter having the first supporter  50  and the second supporter  52  that hold the electrode parts  42   a ,  42   b  of the external electrode fluorescent lamp  40 , at the lower contact terminal  56 . 
     After then, the upper contact terminal  66  of the cover having the first cover  60  and the second cover  62  wraps to hold the upper part of the electrode parts  42   a ,  42   b  of the fluorescent lamp and covers the electrode parts  42   a ,  42   b  of the external electrode fluorescent lamp  40  that are held by the lower contact terminal  56 . 
     In the prior art backlight unit using the external electrode fluorescent lamp  40 , the upper and lower conductive boards  54 ,  64  are deformed by the heat conducted to the external electrode fluorescent lamp  40 . This generates defects in the backlight. 
     More specifically, if an AC power is supplied to the external electrode fluorescent lamp  40  through the upper and lower contact terminal  54 ,  64 , the external electrode fluorescent lamp  40  is driven. If the external electrode fluorescent lamp  40  is driven in this way, the heat conducted from the external electrode fluorescent lamp  40  causes the upper and lower conductive boards  54 ,  64 , where the conductive nickel is coated on the original surface of the phosphor bronze, beryllium copper, etc., to be extended by thermal expansion. Herein, the extended upper and lower conductive boards  54 ,  64 , as shown in  FIG. 3 , are separated from the supporter  50 ,  52  or the cover  60 ,  62 , or expanded in a parallel direction to the supporter  50 ,  52  or the cover  60 ,  62 , thereby causing the location of the lamp  40  to be changed. This causes the picture quality of the liquid crystal display panel to deteriorate due to the non-uniform light. Thus, the distance between the lamps  40  becomes non-uniform or the extended upper and lower conductive boards  54 ,  64  are separated from the supporter  50 ,  52  and the cover  60 ,  62 . 
     SUMMARY 
     By way of introduction only, a backlight according to an aspect of the present invention includes a plurality of lamps, a plurality of contact terminals, and a conductive board electrically connecting the contact terminals. Each lamp has an electrode. Each contact terminal contacts one of the electrodes. The conductive board has a resilient bent part disposed therein. 
     A backlight according to another aspect of the present invention includes a plurality of lamps, a plurality of contact terminals, and a conductive board electrically connecting the contact terminals. Each lamp has an electrode. Each contact terminal contacts one of the electrodes. At least one elastic buffer part absorbs heat expansion of the conductive board. 
     A backlight according to another aspect of the present invention includes a plurality of lamps, a plurality of contact terminals, a conductive board electrically connecting the contact terminals and means for maintaining a distance between adjacent lamps with increasing heat from the lamps absorbed by the conductive board. 
     A method according to another aspect of the present invention includes inserting a plurality of lamps into contact terminals electrically connected by a conductive board such that electrodes of the lamps contact the contact terminals; supplying power to the lamps to turn on the lamps and display an image on a screen of a portable display device; and maintaining a distance between adjacent lamps independent of heat from the lamps absorbed by the conductive board by deforming a non-planar region of the conductive board. 
     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description of the embodiments of the present invention refer to the accompanying drawings, in which: 
         FIG. 1  is a plan view representing a prior art backlight unit using an external electrode fluorescent lamp; 
         FIG. 2  is a sectional view representing the backlight unit using the external electrode fluorescent lamp of  FIG. 1 ; 
         FIG. 3  is a diagram representing deformation of a conductive board that supplies power to an external electrode fluorescent lamp of  FIGS. 1 and 2 ; 
         FIG. 4  is a plan view representing a backlight unit using an external electrode fluorescent lamp according to an embodiment of the present invention; 
         FIG. 5  is a sectional view representing the backlight unit using the external electrode fluorescent lamp of  FIG. 4 ; and 
         FIGS. 6A and 6B  are diagrams explaining the buffing and absorbing of heat expansion of a bended part shown in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     Hereinafter, embodiments of the present invention will be described in detail with reference to  FIGS. 4 to 6 . 
     A liquid crystal display device according to one embodiment of the present invention includes a liquid crystal display panel where liquid crystal cells are arranged in an active matrix shape; and a backlight unit to illuminate light onto the liquid crystal display panel. 
     The liquid crystal display panel includes an upper array substrate where a black matrix, a color filter and so on are sequentially formed on an upper substrate; a lower array substrate where a TFT, a pixel electrode and so on are formed on a lower substrate; and a liquid crystal injected into an inner space between the upper array substrate and the lower array substrate. 
     The backlight is an external electrode fluorescent lamp EEFL having electrodes on the surface of both ends in the direct lighting type backlight where a plurality of lamps are arranged in the rear surface of the liquid crystal display panel. 
       FIGS. 4 and 5  are a perspective view and a sectional view representing a backlight of a liquid crystal display device using an external electrode fluorescent lamp according to an embodiment of the present invention. 
     A backlight using an external electrode fluorescent lamp shown in  FIGS. 4 and 5  includes a supporter having a first supporter  150  and a second supporter  152  that hold both electrode parts  142   a ,  142   b  of the external electrode fluorescent lamp to a lower contact terminal  156 . Herein, the supporter having the first supporter  150  and the second supporter  152  have a rectangular stick shape and are separated from each other with a designated distance therebetween. The supporter having the first supporter  150  and the second supporter  152  is formed of a material of thermal plastic elastomer TPE, polybutylene terephthalates PBT, etc. 
     A lower conductive board  154 , where a conductive nickel is coated over the original surface of phosphor bronze, beryllium copper, etc., is fixed by a screw  158  and the lower conductive board  154  is cut and bent to form a lower contact terminal  156  in the upper surface of the first supporter  150  and the second supporter  152 , wherein the lower contact terminal  156  can hold, and at the same time cover the electrode parts  142   a ,  142   b  of the fluorescent lamp  140 . 
     Further, the lower conductive board  154  includes a lower bent part  170  projected from the lower conductive board  154  as well as being located between the lower contact terminals  156 , more specifically, between the lower contact terminal  166  and the screw  168 . The lower bent part  170  is resilient, and thus able to absorb and relax expansion of the lower due to heat conducted from the fluorescent lamp  140 . This permits the lower bent part  170  to lessen the deformity of the conductive board  154 . 
     The first supporter  150 , the second supporter  152  and the lower conductive board  154  can be bonded together by glue, heat melt-adhesion, insert injection or other means. 
     A cover having a first cover  160  and a second cover  162  covers the upper part of both the electrode parts  142   a ,  142   b  of the external electrode fluorescent lamp  140  with the upper contact terminal  166  on the supporter inclusive of the first supporter  150  and the second supporter  152 . 
     The first cover  160  and the second cover  162  have a rectangular stick shape and are separated from each other with a designated distance therebetween to correspond to the first supporter  150  and the second supporter  152 , respectively. The first cover  160  and the second cover  162  are made of thermal plastic elastomer TPE and polybutylene terephthalates PBT. 
     An upper conductive board  164 , where a conductive nickel is coated over the original surface of phosphor bronze, beryllium copper, etc., is fixed by a screw  168  and the upper conductive board  164  is cut and bent to form an upper contact terminal  166  in the lower surface of the first cover  160  and the second cover  162 , wherein the upper contact terminal  166  can hold, and at the same time cover the electrode parts  142   a ,  142   b  of the fluorescent lamp  140  that is located at the lower contact terminal  156  of the supporter. The first cover  160  and the second cover  162  can be bonded by a guide alternatively or in addition to the screw  158 ,  168 . 
     Further, the upper conductive board  164  includes an upper bent part  180  projected from the upper conductive board  164  as well as being located between the upper contact terminals  166 , more specifically, between the upper contact terminal  166  and the screw  168 . The upper bent part  180  is resilient, and thus able to absorb and relax expansion of the lower due to heat conducted from the fluorescent lamp  140 . This permits the upper bent part  180  to lessen the deformity of the conductive board  164 . 
     The first supporter  160 , the second supporter  162  and the upper conductive board  164  can be bonded together by glue, heat melt-adhesion, insert injection, etc. 
     Accordingly, an operator holds the external electrode fluorescent lamp  140  to locate the electrode parts  142   a ,  142   b  of the external electrode fluorescent lamp  140  at the lower contact terminal  156  which is formed on the supporter having the first supporter  150  and the second supporter  152  that are separated from each other with a designated distance therebetween. 
     And then, the operator locates the cover having the first cover  160  and the second cover  162  on the supporter having the first supporter  150  and the second supporter  152  that hold the electrode parts  142   a ,  142   b  of the external electrode fluorescent lamp  140 , at the lower contact terminal  156 . 
     Subsequently, the upper contact terminal  166  of the cover having the first cover  160  and the second cover  162  wraps to hold the upper part of the electrode parts  142   a ,  142   b  of the fluorescent lamp and covers the electrode parts  142   a ,  142   b  of the external electrode fluorescent lamp  140  that are held by the lower contact terminal  156 . 
     In this way, the backlight unit of the liquid crystal display device according to one embodiment of the present invention includes resilient upper and lower bent parts  180 ,  170  located between the upper and lower contact terminals  166 ,  156  and projecting from the upper and lower conductive boards  154 ,  164 . The bent parts  180 ,  170  prevent the conductive panels  154 ,  164  from being deformed by the heat applied to the conductive boards  154 ,  164 . 
     More specifically, the backlight unit using the external electrode fluorescent lamp  140  has the upper and lower conductive panels  154 ,  164  that expand due to the heat conducted to the external electrode fluorescent lamp  140  upon driving the backlight. The expansion by the heat of the conductive boards  154 ,  164  is transmitted to the bent parts  180 ,  170 . In other words, as shown in  FIG. 6A , two bent areas (A) of each of the bent parts  170 ,  180  before the backlight is driven maintain a designated distance W 1  from each other. When the backlight is driven, as shown in  FIG. 6B , the two bent areas (A) of the bent part  170 ,  180 , to which the heat expansion is transmitted from the conductive boards  154 ,  160 , compress to have a relatively narrower distance W 2  than the distance W 1  thereof before driving the backlight, thereby absorbing and relaxing the expansion of the conductive boards  154 ,  164 . Accordingly, the distance between the lamps  140  is maintained (d1=d2). When the driving of the backlight is stopped, as shown in  FIG. 6A , the distance between the bent areas (A) of the bent parts  170 ,  180  returns to the unexpanded distance. Thus, the distance between the lamps  140  remains uniform and no separation occurs from the supporter and cover by the conductive boards  154 ,  164 , thereby permitting light to be incident uniformly on the liquid crystal display panel and improve the picture quality. 
     As described above, the backlight of the liquid crystal display device according to one embodiment of the present invention includes resilient upper and lower bent parts that are projected from the upper and lower conductive boards and located between the upper and the lower contact terminals. Accordingly, the bent part absorbs and relaxes the heat expansion of the conductive board, thereby preventing the backlight defect caused by the deformity of the conductive board, thus the picture quality of the liquid crystal display device is improved. 
     Although the present invention has been explained by the embodiments shown in the drawings described above, it should be understood to the ordinary skilled person in the art that the invention is not limited to the embodiments, but rather that various changes or modifications thereof are possible without departing from the spirit of the invention. Accordingly, the scope of the invention shall be determined only by the appended claims and their equivalents.