Abstract:
A back light unit includes a plurality of lamps arranged at predetermined distances from each other, each lamp having a lamp tube provided with electrodes at both ends thereof. Common electrodes communicate with both ends of said plurality of lamps and contain a plurality of gripping members for accomodating each of said plurality of lamps. A plurality of releasable connectors fix the common electrodes to first and second lower structures formed below both ends of the plurality of lamps. Electrical connecting elements connect the common electrodes to an inverter.

Description:
This application claims the benefit of the Patent Korean Application No. P2004-89250, filed on Nov. 4, 2004, which is hereby incorporated by reference as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a back light unit, and more particularly, to a back light unit which has common electrodes capable of applying electrical power to light-emitting lamps without soldering. 
     2. Discussion of the Related Art 
     Generally, a CRT (Cathode Ray Tube) is employed for a monitor of a TV, of a measuring instrument and of an information terminal. A CRT is not capable of meeting the demands of miniaturization and lightweight due to its own weight and size. 
     A CRT is expected to be replaced by a LCD (Liquid Crystal Display), a PDP (Plasma Display Panel) and an ELD (Electro Luminescence Device) due to the limit of weight and size. The LCD uses the field optical effect, a PDP uses a discharging gas and an ELD uses the field luminous effect. Studies involving the LCD are presently ongoing. 
     To replace the CRT, a LCD apparatus is currently under development and has shown to provide many advantages, such as small size, lightweight and low electrical power consumption. Such a LCD apparatus has been applied as a monitor of a lap top computer, a monitor of a desk top computer and a large information display apparatus. 
     Since a LCD apparatus displays a picture by adjusting the amount of light from the outside, a back light unit is needed as another source of light to irradiate light to a LCD panel. 
     Generally, a back light unit is classified into an edge type and a direct type according to the disposition of cylinder-shaped luminous lamps. 
     In the edge type, a lamp unit is installed in the side of a light guide element. The lamp unit includes a lamp emitting light, a lamp holder interposed between both ends of the lamp to protect the lamp, and a lamp reflection sheet for reflecting light emitted from the lamp to the light guide element. 
     The edge type in which the lamp unit is installed on the side of the light guide element is applied to a small-sized LCD apparatus like a monitor of a lap top computer and a monitor of a desk top computer and has the advantages in producing a flat LCD apparatus with equalized irradiation of light and endurance. 
     The direct type back light unit has been developed since the size of the LCD apparatus has started to increase to be larger than 20 inches. The direct type back light unit directly irradiates light to the front of the LCD panel by disposing a plurality of lamps on the downstream side of a diffusion sheet. 
     Such a direct type back light unit is applied to a large screen LCD apparatus demanding high brightness due to a higher light utilization efficiency when compared with an edge type back light. 
     However, the LCD apparatus employing the direct type back light may cause malfunction of lamps or introduce a short lamp life in the case that a large monitor and a large television employing the direct type back light is operated for a long period. Compared with the edge type unit, there are more possibilities where a LCD apparatus employing the direct type back light may have a lamp not operate due to a malfunction of the lamp and the existence of a short lamp life. 
     Also, in the case where a lamp does not operate in the edge type, only the brightness of the screen may deteriorate. Since the plurality of the lamps is installed at the down side of the screen in the direct type, the portion in which the lamp does not operate is noticeably darker than the other portions 
     Thus the lamps must be replaced repeatedly, requiring the LCD apparatus with the direct unit to have a structure of assembly and disassembly without difficulty. 
     The direct type back light unit according to the conventional systems is described in the following accompanying drawings. 
       FIG. 1  is a perspective view of a direct type back light unit according to conventional systems.  FIG. 2  is a partial view of a direct type back light unit according to the conventional systems.  FIG. 3  is a perspective view of a direct type back light unit according to another conventional system.  FIG. 4  is a partial view of a direct type back light unit applying electrical power to a lamp according to another conventional system. 
     As illustrated in  FIG. 1 , a conventional back light unit comprises a plurality of lamps  1  with electrodes  2  in both ends of the lamps, a lower structure  3  disposed at both ends of the lamps  1  at a predetermined distance and of which the first side forms grooves to accommodate both ends of the plurality of the lamps  1 , a reflection sheet  4  mounted on the lower structure  3 , a plurality of lamp holders  5  combined in both ends of a pair of the lamps to fix and support the lamps  1  with the lower structure  3 , and an upper structure  6  formed along edges of both ends of the lamps  1  to fix the lamp holders  5 . 
     As illustrated in  FIG. 2 , the lamp  1  is a CCFL (Cold Cathode Fluorescent Lamp) and comprises electrodes  2  provided in both ends inside a lamp tube, an inner lead line  7  for applying electrical power to the electrodes  2 , and an out lead line (not shown) connected to the inner line for applying electrical power outside. 
     The inner lead line  7  and the outer lead line are connected by soldering  9 . 
     The outer lead line is fixed and connected by a contraction tube  11  and a wire  10  connected to an inverter provided in rear of the lower structure  3 . 
     However the conventional back light unit with the above configuration connects by soldering  9  the inner lead line  7  and the outer lead line to apply a driven voltage to the lamps  1 . In the process of modulation the soldered portion between the inner lead line and the outer lead line may experience the most stress when a bending force is introduced like, e.g., the interposition of the contraction tube  11 , transportation, and the operator&#39;s handling. 
     The above stress may dislodge the soldered portion  9 , whereby the inner lead line and the outer lead line becomes disconnected. 
     The disconnection of the inner lead line and the outer lead line may cause problems such as lighting malfunction, spark generation, and the like. 
     Consequently, the conventional systems in which the inner lead line  7  and the outer lead line are soldered together has its drawbacks. 
     As illustrated in  FIG. 3  and  FIG. 4 , another conventional back light unit utilizes a plurality of lamps  31 , an outer case  33  fixing and supporting the lamps  31 , light scattering means  35   a ,  35   b ,  35   c  disposed between the lamps  31  and a liquid crystal panel (not shown). 
     The light scattering means  35   a ,  35   b ,  35   c  are employed to prevent appearance of the lamps from becoming visible on a display surface of the liquid crystal panel and to supply a source of light with uniform luminosity distribution. Diffusion sheets and diffusion plates are disposed between the liquid crystal panel and the lamps  31  to enhance the light scattering efficiency. 
     A reflection sheet  37  is disposed inside of the outer case  33  in order that light generated from the lamps  31  may be irradiated to the LCD panel, resulting in maximizing the light utilization efficiency. 
     The lamp  31  is CCFL. Electrodes  32  are disposed in both ends of the lamp tube. When electrical power is applied to the electrodes  32 , the lamps  31  emit light. Both ends of the lamps  31  are inserted in holes formed on both sides of the outer case  33 . 
     For transmitting electrical power for driving the lamp, leading wires  39 ,  39   a  are connected to both electrodes  32  of the lamps  31 . Also, the leading wires  39 ,  39   a  are connected to a drive circuit through additional connectors, wherein the additional connectors are needed for each lamp. 
     That is, a leading wire  39  connected to one electrode  32  of each lamp  31  and a leading wire  39   a  connected to the other electrode  32  of each lamp  31  are connected to one connector and one of the wires  39 ,  39   a  bent into a lower part of the outer case  33  is connected to an additional connector. 
     The wires  39 ,  39   a  passing though a hole of an outer case  33  is fixed in an outer case  33  by soldering  40 . The outer case  33  may apply an electrical signal to the lamps  31  by soldering  40  as a printed-circuit board. 
     However, the conventional back light unit has the difficulty of preventing the soldered portion from falling apart, since the wires  39 ,  39   a  are fixed in the outer case  33  by soldering  40 . 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a back light unit that substantially obviates one or more problems due to limitations and disadvantages of the related art. 
     An object of the present invention is to provide a back light unit for fixing lamps without soldering, thereby cutting expenses and enhancing work efficiency. 
     Another object of the present invention is to provide a back light unit capable of contributing to the development of environmentally friendly products by not using soldering. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a back light unit utilizes a plurality of lamps arranged in at a predetermined distance, each lamp having a lamp tube and electrodes on both outer ends of the lamp tube; common electrodes formed in a gripping member to fix both ends of the lamps; first and second lower structures formed in one direction below both ends of the plurality of lamps; a plurality of releasable/fixing members, e.g., screws, to fix the common electrodes to the first and second lower structure respectively; and connectors, e.g., wires connecting the common electrodes to an outer inverter. The common electrodes contain a plurality of gripping members spaced apart from each other to fasten the electrodes of each lamp to each common electrode, first and second common electrode lines formed on both sides of the gripping members for connecting the gripping members, a plurality of the stoppers formed in the second common electrode line corresponding to each of the plurality of gripping members to prevent the lamp from being inclined to the left or the right when assembling the lamps, and a plurality of holes formed in the first and second common electrodes for attachment to the first and second lower structures, e.g., by screws. 
     The gripping members wrap around the lamps. 
     In the gripping members, more than 2 such members are formed at a predetermined distance from each other and each gripping member has a first elastic member having a different length from a second elastic member, with the first and second elastic members facing each other. 
     The at least two gripping members include a first gripping member and a second gripping member, the first gripping member including a first elastic member having length shorter than the second elastic member, the second grip including the first elastic member having a length longer than the second elastic member. 
     The stoppers extend in a vertical direction at the end of the second common electrode line. 
     The second common electrode line is located adjacent to the first common electrode line. 
     On the upper side of the lamp, a diffusion sheet and a diffusion plate are further disposed for scattering light emitted from the lamp. 
     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 accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings: 
         FIG. 1  is a perspective view of a direct type back light unit according to conventional art; 
         FIG. 2  is a partial view of a configuration of a direct type back light unit according to conventional art; 
         FIG. 3  is a perspective view of a direct type back light unit according to another conventional system; 
         FIG. 4  is a partial view of a configuration of a direct type back light unit applying electrical power to a lamp according to another conventional system; 
         FIG. 5  is a perspective view of a back light unit according to a first embodiment of the present invention; 
         FIGS. 6A and 6B  are exploded perspective views of areas A and B of  FIG. 5 ; 
         FIG. 7  is a perspective view illustrating a common electrode of the back light unit according to the first embodiment of the present invention; 
         FIG. 8  is a partial perspective view illustrating a common electrode of the back light unit according to a second embodiment of the present invention; and 
         FIG. 9  is a plane view illustrating a common electrode of a back light unit according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
       FIG. 5  is a perspective view of a back light unit according to the first embodiment of the present invention.  FIGS. 6A and 6B  are exploded perspective views of A and B of  FIG. 5 .  FIG. 7  is a perspective view illustrating a common electrode of a back light unit according to the first embodiment of the present invention. 
     As shown in  FIGS. 5 through 7 , a back light unit according to the first embodiment of the present invention utilizes a plurality of lamps  51 , two common electrodes  53 , first and second lower structures  54   a  and  54   b , a plurality of screws  55 , and two wires  56 . 
     The plurality of lamps  51  is arranged at a predetermined distance, each lamp  51  having a lamp tube and two electrodes  50   a ,  50   b  on both outer ends of the lamp tube. The common electrodes  53  are formed in a gripper type to fix both ends of each lamp  51 . The first and second lower structures  54   a  and  54   b  are formed below both ends of the lamps  51  in one direction to seat the common electrodes  53 . 
     A plurality of fixing members, e.g., screws  55 , clamps, etc., fix the common electrodes  53  to the first and second lower structures  54   a  and  54   b , respectively. The wires  56  connect the common electrodes  53  with an inverter (not shown). 
     As shown in  FIG. 7 , each common electrode  53  comprises a plurality of fastening parts  58 , first and second common electrode lines  59   a  and  59   b , a plurality of stoppers  60 , a plurality of holes  61 , and a circular electrode  57 . 
     The plurality of fastening parts  58  are formed spaced apart with a plurality of gripping members to fasten the electrodes  50   a    50   b  of each lamp  51 . The first and second common electrode lines  59   a  and  59   b  are formed at both sides of the plurality of fastening parts  58  to connect the fastening parts  58 . The at least two gripping members include a first gripping member and a second gripping member, the first gripping member including a first elastic member  58   a  having a length shorter than the second elastic member  58   b , the second gripping member including the first elastic member  58   a  having a length longer than the second elastic member  58   b.    
     The plurality of the stoppers  60  is formed at the end of the second common electrode line  59   b  corresponding to each fastening part  58  to prevent the lamps  51  from being inclined to the left or the right when assembling the lamps  51 . The plurality of holes  61  is formed in the first and second common electrode lines  59   a  and  59   b . The circular electrode  57  is extended from the first common electrode line  59   a  to connect the wire  56  with the common electrode  53  using the screw  55 . 
     Each of the gripping members has two semicircular elastic members  58   a  and  58   b  facing each other. 
     The plurality of gripping members wrap around the electrodes  50   a  and  50   b  of lamps  51 . Since at least two gripping members are formed in the fastening parts  58 , the fastening parts  58  reduce loose contact with the lamps  51  caused by process tolerance and maximize contact space, thereby enhancing electrical endurance and electric conductivity. 
     The fastening parts  58  are formed with gripper type, spring biased elastic members provided in the common electrodes  53 . Since the lamps  51  are inserted and fixed in the fastening parts  58 , the lamps  51  and the common electrodes  53  are electrically connected without soldering. 
     Since the common electrodes  53  are connected to wires  56  through the circular electrode  57  by the screws  55 , the wires  56  are connected to the common electrodes  53  and the inverter without soldering. 
     The second common electrode line  59   b  is disposed spaced apart from the first common electrode line  59   a.    
     As not shown in the drawings, a diffusion sheet and a diffusion plate provided on the upper side of the lamp  51  are further utilized which scatter light emitted from the lamp  51  in order to uniformly distribute the source of light to a display surface of a liquid crystal panel. 
     A back light unit according to the second embodiment of the present invention has a different common electrode shape, compared with the first embodiment. 
     For development of a high resolution and high brightness model, EEFLs are added to a back light unit of the same size, so that the lamp interval should be narrower. In the above case, the entire gripping length should be reduced when the semicircular elastic member structure is applied. 
     However, when the entire semicircular elastic member length is reduced, a problem may arise since the gripping members and the lamps are not in effective contact, thereby causing a deterioration in the reliability of the goods. 
     Consequently, the back light unit of the second embodiment of the present invention alternately disposes semicircular elastic members having different lengths at predetermined intervals, whereby the gripping members and the lamps are in effective contact, thereby enhancing the reliability of the goods. 
     As shown in  FIG. 8 , each common electrode  53  contains a plurality of fastening parts  58 , each of the fastening parts  58  having a plurality of gripping members. 
     Each of the plurality of gripping members has a first semicircular elastic member  58   a  and a second semicircular elastic member  58   b , the first semicircular elastic member  58   a  having different length from the second semicircular elastic member  58   b . In the plurality of gripping members, a first gripping member has the first semicircular elastic member  58   a  having a length shorter than the second semicircular elastic member  58   b , and a second gripping member has the first semicircular elastic member  58   a  having a length longer than the second semicircular elastic member  58   b.    
     The first and second gripping members are alternately disposed at a predetermined distance. 
     The stoppers  60  are vertically positioned at the end of the second common electrode line  59   b  corresponding to each of the fastening parts  58  to prevent the lamps  51  from being inclined to the right or the left. 
     As shown in  FIG. 8 , in the fastening parts  58  according to the second embodiment of the present invention, more than 2 grips are alternately disposed at a predetermined interval and at least two gripping members include a first gripping member and a second gripping member, the first gripping member including the first elastic member  58   a  having a length shorter than the second elastic member  58   b , and the second gripping member including the first elastic member  58   a  having a length longer than the second elastic member  58   b.    
     Thus gripping members with different lengths may effectively wrap the electrodes of the lamp  51 , thereby maintaining good contact between the lamp  51  and the common electrode  53 . 
     Additional lamps may be provided for a model with high resolution and high brightness while maintaining effective contact between the electrodes of the lamps and the common electrodes by alternately disposing the gripping members having a first gripping member and a second gripping member, the first gripping member including the first elastic member having a length shorter than the second elastic member, and the second gripping member including the first elastic member having a length longer than the second elastic member in the common electrode  53 . 
     As can be readily appreciated, the opposing elastic members of each gripping member can have the same length or different lengths, and each of the gripping members can have the same or different lengths from other gripping members. Also, although having at least two gripping members for supporting the electrodes at each end thereof is particularly effective, a single gripping member provided at each electrode end of a lamp tube can be used. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.