Abstract:
A liquid crystal display device includes a liquid crystal display panel, a plurality of light sources for irradiating onto the liquid crystal display panel, at least two electrode boards at ends of each of the light sources for electrically connecting the light sources, an inverter board aligned parallel to the light sources for providing drive signals to the light sources through the electrode boards, and a first cover for accommodating the liquid crystal display panel, the light sources and the electrode boards on a first side thereof and for accommodating the inverter board on a second side thereof such that the inverter board is substantially on a same plane as a main portion of the cover.

Description:
This application claims the benefit of Korea Patent Application No. 10-2008-0017996 filed on Feb. 27, 2008 in Korea and Korea Patent Application No. 10-2008-0039048 filed on Apr. 25, 2008 in Korea, which are respectively incorporated herein by reference for all purposes as if fully set forth herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The embodiments of the invention relate to a liquid crystal display device, and more particularly, to a slim-sized liquid crystal display device and a liquid crystal display device that maintains balance of a driving signal supplied to lamps in an accompanying light source. 
     2. Discussion of the Related Art 
     Generally, liquid crystal display devices are widely used due to advantageous characteristics of light weight, thin profile, and low power consumption. As a result, liquid crystal display devices are widely used in office automation equipment and audio/video equipment. 
     A liquid crystal display device includes a plurality of control switches arranged in a matrix and controls the amount of light being transmitted in accordance with a signal applied to the control switches, thereby generating a desired image. Because the liquid crystal display device is not a self luminous display device, it requires a separate light source, such as a backlight unit. 
     A backlight unit may be generally classified as a direct type and an edge type in accordance with the location of a light source. The edge type backlight unit has a light source along one side of a liquid crystal display device, and irradiates light from the light source to a liquid crystal display panel through a light guide plate and a plurality of optical sheets. The direct type backlight unit has a plurality of light sources disposed directly under a liquid crystal display panel, and irradiates light from the light sources to the liquid crystal display panel through a diffusion plate and a plurality of optical sheets. Recently, the direct type backlight unit is more often used in LCD TVs because it has improved brightness, more consistent light uniformity and better color purity, as compared to the edge type backlight. 
     A cold cathode fluorescent lamp (hereinafter, referred to as “CCFL”) and an external electrode fluorescent lamp (hereinafter, referred to as “EEFL”) may be used for a light source in a backlight unit. To drive the lamps, a power transmission control device called an inverter is utilized. The inverter is electrically connected to the lamps of the backlight unit and serves to amplify a voltage and to control a current so that a high voltage and an appropriate current can be delivered to the lamps. 
       FIGS. 1   a  and  1   b  are views showing a two-board inverter according to the related art. As shown in  FIGS. 1   a  to  1   b , an inverter  12  is mechanically mounted to opposite sides of a back surface of a bottom cover  10 . The bottom cover  10  accommodates lamps  14  and supplies a driving power to the lamps  14  through a lamp wire  18 . A high-capacity transformer  16  and a plurality of passive devices (not shown) are mounted on a printed circuit board (hereinafter, referred to as “PCB”) of the inverter  12 . The transformer  16  is a means for raising/reducing an input voltage by the turn ratio of primary coil and secondary coil that are wound around an iron core, and occupies a relatively large volume compared to the other passive devices. In particular, the inverter  12  and the PCB are arranged perpendicularly to the lengthwise dimension of the lamps  14 . Also, the inverter  12  projects from the back surface of the bottom cover  10  to the mounting height of the transformer  16 , which acts as a limitation in realizing a slim liquid crystal display device. Further, because the inverter  12  is arranged at both sides of the back surface of the bottom cover  10  (two-board inverter), space for a mountable space of a system module, such as a digital board or power board, is restricted and reduced. 
       FIGS. 2   a  and  2   b  are views showing a one-board inverter according to the related art. To increase the mountable space of the system module, a one-board inverter method has been proposed as shown in  FIGS. 2   a  and  2   b . In  FIGS. 2   a  and  2   b , an inverter  22  is mechanically mounted to a lateral side of the back surface of a bottom cover  20 . The bottom cover  20  accommodates lamps  24  and supplies a driving power to the lamps  24  through a lamp wire  28 . A high-capacity transformer  26  and a plurality of passive devices (not shown) are mounted on a printed circuit board (hereinafter, referred to as “PCB”) of the inverter  22 . In particular, the inverter  22  and the PCB are arranged perpendicular to the lengthwise dimension of the lamps  24 . The one-board inverter method has a fatal disadvantage in that because the inverter  22  is arranged further toward either one side from both electrodes of the lamps  24 , left and right balance of a driving current delivered to the lamps  24  is lacking. Further, this method has another limitation in realizing a slim liquid crystal display device because the inverter  22  still projects from the back surface of the bottom cover  20  to the mounting height of the transformer  26 . 
     Moreover, when the inverter according to the related art projects from the back surface of the bottom cover, the possibility that an electromagnetic interference may occur between the inverter and the system module increases. Furthermore, because the inverter according to the related art is arranged adjacent to the electrodes of the lamps, heat generation of the inverter is increased by the lamp heat, thereby decreasing inverter efficiency. 
     SUMMARY OF THE INVENTION 
     Accordingly, embodiments of the invention are directed to a liquid crystal display device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art. 
     An object of embodiments of the invention is to provide a liquid crystal display device that has slim profile by avoiding an increase in thickness due to an inverter. 
     Another object of embodiments of the invention is to provide liquid crystal display devices that preserves the mountable space for a system module and provides balance in driving signals. 
     Another object of embodiments of the invention is to provide liquid crystal display devices that reduce electromagnetic interferences between an inverter and a system module. 
     Another object of embodiments of the invention is to provide liquid crystal display devices that have improved inverter efficiency. 
     Additional features and advantages of embodiments of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of embodiments of the invention. The objectives and other advantages of the embodiments of the invention will 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 and other advantages and in accordance with the purpose of embodiments of the invention, as embodied and broadly described, a liquid crystal display device include a liquid crystal display panel, a plurality of light sources for irradiating onto the liquid crystal display panel, at least two electrode boards at ends of each of the light sources for electrically connecting the light sources, an inverter board aligned parallel to the light sources for providing drive signals to the light sources through the electrode boards, and a cover for accommodating the liquid crystal display panel, the light sources and the electrode boards on a first side thereof and for accommodating the inverter board on a second side thereof such that the inverter board is substantially on a same plane as a main portion of the cover. 
     In another aspect, a backlight device for a flat panel display includes a plurality of light sources generating light irradiated onto the flat panel display, at least two electrode boards at ends of each of the light sources for electrically connecting the light sources, an inverter board aligned parallel to the light sources for providing drive signals to the light sources through the electrode boards, and a first cover for accommodating the flat panel display, the light sources and the electrode boards on a first side thereof and for accommodating the inverter board on a second side thereof such that the inverter board is substantially on a same plane as a main portion of the cover. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of embodiments of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of embodiments 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 embodiments of the invention. In the drawings: 
         FIGS. 1   a  and  1   b  are views showing a two-board inverter according to the related art; 
         FIGS. 2   a  and  2   b  are views showing an one-board inverter according to the related art; 
         FIG. 3  is an exploded perspective view of a liquid crystal display device in accordance with an embodiment of the invention; 
         FIG. 4  is a view showing a lamp connection structure when an EEFL is implemented in accordance with an embodiment of the invention; 
         FIG. 5   a  is a view showing a lamp wire being covered with an insulation tube in accordance with an embodiment of the invention; 
         FIG. 5   b  is a view showing supports for supporting the lamp wire covered with the insulation tube in accordance with an embodiment of the invention; 
         FIG. 6  is a view showing a lamp connection structure when parallel type CCFLs using balance capacitors are implemented in accordance with an embodiment of the invention; 
         FIG. 7  is a view showing a lamp connection structure when parallel type CCFLs using balance transformers are implemented in accordance with an embodiment of the invention; 
         FIG. 8  is a perspective view showing an EI type transformer in accordance with an embodiment of the invention; 
         FIG. 9  is a perspective view showing a CI type transformer in accordance with an embodiment of the invention; 
         FIGS. 10   a  and  10   b  are perspective views showing a U-shaped transformer in accordance with an embodiment of the invention; 
         FIG. 11  is a schematic equivalent circuit diagram of an inverter having two transformers connected to each other in series in accordance with an embodiment of the invention; 
         FIG. 12  is a schematic equivalent circuit diagram of an inverter having two transformers connected to each other in parallel in accordance with an embodiment of the invention; 
         FIG. 13  is a plane view showing a coupling state between an inverter having two transformers and a bottom cover in accordance with an embodiment of the invention; 
         FIG. 14  is a cross-sectional view showing a coupling state between an inverter having two transformers and a bottom cover in accordance with an embodiment of the invention; 
         FIG. 15  is another cross-sectional view showing a coupling state between an inverter having two transformers and a bottom cover in accordance with an embodiment of the invention; 
         FIG. 16  is a schematic equivalent circuit diagram of an inverter having one transformer in accordance with an embodiment of the invention; and 
         FIG. 17  is a plane view showing a coupling state between an inverter having one transformer and a bottom cover in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to embodiments which are illustrated in the accompanying drawings. Wherever possible, similar reference numbers will be used to refer to the same or similar parts. 
       FIG. 3  is an exploded perspective view of a liquid crystal display device in accordance with an embodiment of the invention, and  FIG. 4  is a view showing a lamp connection structure when an EEFL is implemented in accordance with an embodiment of the invention. Referring to  FIGS. 3 and 4 , a liquid crystal display device in accordance with an embodiment of the invention includes a top case  102 , a liquid crystal display panel  106 , a backlight unit, and an inverter  130 . 
     The top case  102  covers the edges of the liquid crystal display panel  106 . The liquid crystal display panel  106  includes an upper substrate  105  and a lower substrate  103 . Liquid crystal materials (not shown) are formed between the upper substrate  103  and the lower substrate  105 . The liquid crystal display panel  106  is provided with a spacer (not shown) for maintaining a constant gap between the upper substrate  103  and the lower substrate  105 . The upper substrate  103  is provided with a color filter, a common electrode and a black matrix (not shown). The common electrode may be formed on the lower substrate  105  according to an electric field driving method. Signal lines, such as a data line and a gate line (not shown), are formed on the lower substrate  105 . A thin film transistor (hereinafter, referred to as “TFT”) is formed at a crossing of the data line and the gate line. The TFT switches a data signal to be transmitted from the data line to the liquid crystal cell in response to a scanning signal (i.e., a gate pulse) from the gate line. A pixel electrode is formed at a pixel area between the data line and the gate line. 
     One side of the liquid crystal display panel  106  is provided with data and gate pad areas connected to the data and gate lines, respectively. A plurality of tape carrier packages (hereinafter, referred to as “TCPs”)  104  and  108  are attached to the data and gate pad areas. These TCPs  104  and  108  are divided into data TCPs  108 , which are attached to a source PCB  128  supplying video signals to the data lines of the liquid crystal display panel  106  and to data pads on the lower substrate  105  and have data driving integrated circuits  110  mounted thereon for supplying video signals to the data lines in response to a control signal from the source PCB  128 , and gate TCPs  104  which are attached to gate pads on the lower substrate  105  and have gate driving integrated circuits  112  mounted thereon for supplying gate signals to the gate lines in response to a control signal from the source PCB  128 . 
     The backlight unit includes a plurality of lamps  120  arranged side by side, for irradiating light to the liquid crystal display panel  106 , a guide support  121  for inserting the lamps  120  therein and covering the edges of the lamps  120 , a bottom cover  114  arranged at the back surface of the lamps  120 , for accommodating the lamps  120 , a diffusion plate  116  arranged to cover the bottom cover  114 , for diffusing the light generated from the lamps  120  and irradiating the light to the liquid crystal display panel  106 , and a plurality of optical sheets  118  for vertically raising the traveling path of the light accumulated and incident on the diffusion plate  116  toward the liquid crystal display panel  106 . 
     Each of the lamps  120  includes a glass tube and electrodes mounted on both end portions of the glass tube. The glass tube is filled with the inert gases, and a fluorescent substance is coated on the inner wall of the glass tube. The lamps  120  may include EEFLs having external electrodes  120   a  projecting at both opposite ends or CCFLs. 
     The bottom cover  114  includes a first surface  114   a  for mounting the lamps  120  and a common electrode board  123  thereon, a second surface  114   b  diagonally bent and extended from the first surface  114   a , a third surface  114   c  bent and extended from the second surface  114   b  to be made parallel with the first surface  114   a , a fourth surface  114   d  vertically bent and extended from the third surface  114   a , and a fifth surface  114   e  vertically bent from the fourth surface  114   d  and extended between the first and third surfaces  114   a  and  114   c  to be made parallel with these surfaces  114   a  and  114   c.    
     The second to fifth surfaces  114   b ,  114   c ,  114   d , and  114   e  are formed at both long sides of the bottom cover  114  parallel to the lamps  120 , and both short sides of the bottom cover  114  perpendicular to the lamps  120  are opened. The second to fifth surfaces  114   b ,  114   c ,  114   d , and  114   e  form a recess  115  at the long sides of the upper and lower ends of the bottom cover  114 . A side support  121  is mounted to the left and right short sides of the bottom cover  114 . The side support  121  is provided with depressed and raised portions for inserting the lamps  121  therein, and supports the lamps  120  from both short sides of the bottom cover  114 . 
     The diffusion plate  116  diffuses the light incident from the lamps  120 , thereby making uniform the distribution density of the light irradiated on the liquid crystal display panel  106 . The plurality of optical sheets  118  stacked on the diffusion plate  110  converts the light incident from the diffusion plate  116  to be perpendicular to the liquid crystal display panel  106 , thereby improving light efficiency. The optical sheets  118  are typically comprised of two prism sheets and two diffusion sheets. 
     The inverter  130  includes an inverter PCB  132 , a transformer  134  mounted on the inverter PCB  132 , and a plurality of passive devices (not shown). The transformer  134  may be implemented in any one of an EI type transformer, a CI type transformer, and a U-shaped transformer. 
       FIG. 6  is a view showing a lamp connection structure when parallel type CCFLs using balance capacitors are implemented in accordance with an embodiment of the invention, and  FIG. 7  is a view showing a lamp connection structure when parallel type CCFLs using balance transformers are implemented in accordance with an embodiment of the invention. As shown in  FIGS. 6 and 7 , the lamps  120  may include parallel type CCFLs. In a CCFL, electrodes are formed inside a glass tube and parallel type CCFLs are implemented to apply a lamp driving power commonly to the lamps  120 . In  FIG. 6 , parallel type CCFLs are implemented by a plurality of balance capacitors  225  connected to both end portions of the lamps  120 , respectively, through a connector (not shown), and a balance board  223  for mounting the balance capacitors  225  thereon. The balance capacitors  225  serve as external electrodes, and they are commonly connected by being conducted to each other on the balance board  223 . Therefore, the lamps  120  are able to commonly receive a lamp driving power from the inverter  130 . 
     Furthermore, as shown in  FIG. 7 , the parallel type CCFLs are implemented by a plurality of balance transformers  325  connected to both end portions of the lamps  120 , respectively. The balance transformers  325  serve as external electrodes, and primary coils  325   a  thereof are connected to each other in series to form a closed circuit, and secondary coils  325   b  thereof are connected to the end portions of the lamps  120 . Therefore, a tube current flowing in the lamps  120  is controlled equally by the current flowing in the primary coils  325   a  through the closed circuit, thereby allowing the lamps  120  to commonly receive a lamp driving power from the inverter  130 . These balance transformers  325  can be mounted on a balance board (not shown) like the balance capacitors  225  of  FIG. 6 . 
     Hereinafter, embodiments will be described under the assumption that lamps  120  are EEFLs for the convenience of explanation. 
     External electrodes  120   a  of the lamps  120  are commonly connected to each other on a common electrode board  123 , and are supplied with a lamp driving power commonly through the common electrode board  123 . For this, the common electrode board  123  is provided with metal clips  125  for pressing the external electrodes  120   a  of the lamps  120  by an elastic force to fit the lamps  120  thereto. These metal clips  125  may be mounted by a surface mount technology (“SMT”) and soldered to be electrically connected to a power transmission line (not shown) formed on the common electrode board  123 . The power transmission line formed on the common electrode board  123  supplies a lamp driving power from the inverter  130  to the lamps  120  through a connector  127  and a lamp wire  129 . 
       FIG. 5   a  is a view showing a lamp wire being covered with an insulation tube in accordance with an embodiment of the invention. As shown in  FIG. 5   a , the lamp wire  129  is covered with an insulation tube  129   a  to minimize the amount of signal leaked upon transmission of a lamp driving power. The insulation tube  129   a  may be formed of a rubber material or an electrical insulator material, and serves to reduce the amount of leakage capacitance by increasing the distance between the lamp wire  129  and the metal surface of the bottom cover  114  (shown in  FIG. 3 ). 
       FIG. 5   b  is a view showing supports for supporting the lamp wire covered with the insulation tube in accordance with an embodiment of the invention. As shown in  FIG. 5   b , to further increase the distance between the lamp wire  129  and the metal surface of the bottom cover  114  (shown in  FIG. 3 ), the liquid crystal display device includes a plurality of supports  129   b  formed on the back surface of the bottom cover  114  corresponding to the lamp wire  129 , and the lamp wire  129  covered with the insulation tube  129   a  may be supported by these supports  129   b.    
       FIG. 8  is a perspective view showing an EI type transformer in accordance with an embodiment of the invention,  FIG. 9  is a perspective view showing a CI type transformer in accordance with an embodiment of the invention, and  FIGS. 10   a  and  10   b  are perspective views showing a U-shaped transformer in accordance with an embodiment of the invention. In  FIG. 8 , an EI type transformer  1341  includes an outer core leg  1341   a  having an “E”-like shape, a central core leg  1341   b  having an “I”-like shape, coils  1341   c  wound around first and second sides of the central core leg  1341   b , a frame member  1341   d  for covering one side of the outer leg core  1341   a , and electrodes  1341   e  connected through the frame member  1341   d.    
     In  FIG. 9 , an CI type transformer  1342  includes an outer core leg  1342   a  having an “C”-like shape, a central core leg  1342   b  having an “I”-like shape, coils  1342   c  wound around first and second sides of the central core leg  1342   b , a frame member  1342   d  for covering one side of the outer leg core  1342   a , and electrodes  1342   e  connected through the frame member  1342   d . In EI type and CI type transformers, a magnetic line of force Φ is generated only in a vertical direction (on the x-y-z space) of the upper and lower sides of the central core leg  1341   b  or  1342   b . Therefore, unlike the conventional EE type transformer having one central core leg coupled between two “E”-shaped outer core legs, these transformers can resolve the problems of power loss or heat generation caused by a horizontal magnetic field by removing a magnetic line of force generated in a horizontal direction on the x-y surface. 
     Generally, it is known that a horizontal magnetic line of force has a large probability of increasing the amount of power consumption and causing heat generation by generating an unnecessary induction current. Further, the EI type or CI type transformer can have a higher interlink magnetic flux as compared to the conventional EE type transformer (unshielded) having the same number of coils, because the back surface of the outer core leg  1341   a  or  1342   a  is shielded as shown in the drawing. Therefore, when the EL type or CI type transformers are used, it is possible to obtain the same interlink magnetic flux as an unshielded transformer even with a smaller number of coils. Hence, thicker coils compared to those of the unshielded transformer can be used, resultantly acquiring the effects, such as reduction of winding resistance and reduction of heat generation. 
     As shown in  FIGS. 10   a  and  10   b , an U-shaped transformer  1343  includes a pair of “U”-like shaped outer core legs  1343   a , coils  1343   b  wound around first and second sides of the pair of outer core legs  1343   a , a frame member (not shown), and electrodes (not shown). The U-shaped transformer has the advantage that the manufacturing cost is less than that of the EI type or CI type transformer. 
     Referring to  FIGS. 3 and 5 , the transformer  134  may include one of the EI type, the CI type and the U-shaped transformer shown in  FIGS. 8 ,  9 ,  10   a  and  10   b . The transformer  134  include a pair of first and second transformers  134 A and  134 B of the same type, and mounted on the inverter PCB  132 . More specifically, the first and second transformers  134 A and  134 B may be located end portions of the inverter PCB  132 . The first transformer  134 A may induce a lamp driving signal in a first phase, and the second transformer  134 B may induce a lamp driving signal in a second phase opposite to the first phase. Moreover, the first transformer  134 A and  134 B may have coils wound in directions opposite to each other. The lamp driving signal of the first phase is supplied to one electrode of the lamps  120  via a connector  133  and a lamp wire  129 , and the lamp driving signal of the second phase is supplied to the other electrodes of the lamps  120  via the connector  133  and the lamp wire  129 . Preferably, to adjust the left and right balance of a driving current supplied to the lamps  120 , the distance between the first transformer  134 A and one end portions of the lamps  120  and the distance between the second transformer  134 B and the other end portions of the lamps  120  should be equal to each other. 
       FIG. 11  is a schematic equivalent circuit diagram of an inverter having two transformers connected to each other in series in accordance with an embodiment of the invention, and  FIG. 12  is a schematic equivalent circuit diagram of an inverter having two transformers connected to each other in parallel in accordance with an embodiment of the invention. The first and second transformers  134 A and  134 B of this type can be serially connected to each other by a serial connection of the primary coils as shown in  FIG. 11 , or can be connected to each other in parallel by a parallel connection of the primary coils. In  FIGS. 11 and 12 , a control unit  136  may generate a switching control signal SWC by using a burst dimming signal generated from a dimming circuit (not shown). A switching unit  138  is provided with a plurality of field effect transistors, and is switched according to a switching control signal SWC and serves to convert a direct current signal VDD supplied from the outside into an alternating current signal and supply it to the first and second transformers  134 A and  134 B. Because the first and second transformers  134 A and  134 B are wound in directions opposite to each other, signals outputted through these transformers are in reverse phase to each other. 
     The inverter  130  may be provided with a plurality of screw holes  135  formed on the inverter PCB  132 , for securing to the back surface of the bottom cover  114 . The screw holes  135  are formed at ear portions (not shown) projecting from the second surface  114   b  of the bottom cover  114  toward the recess  115  and at positions corresponding to the fifth surface  114   e  of the bottom cover  114 . 
       FIG. 13  is a plane view showing a coupling state between an inverter having two transformers and a bottom cover in accordance with an embodiment of the invention, and  FIG. 14  is a cross-sectional view showing a coupling state between an inverter having two transformers and a bottom cover in accordance with an embodiment of the invention. Referring to  FIGS. 13 and 14 , the inverter  130  is mounted to the back surface of the bottom cover  114  by screws  137  penetrating through the screw holes  135  of the inverter PCB  132 . To secure the screws  137 , at least two ear portions  114   f  projecting toward the recess  115  while maintaining the same height as the fifth surface  114   e  are formed on the second surface  114   b  of the bottom cover  114 . As described above, the recessed  115  is formed at the long sides of the upper and lower ends of the back surface of the bottom cover  114 . These ear portions  114  project into the recess  115  formed at the lower end among the recess  115 . Thus, the inverter  130  is mounted to correspond to the recess  115  formed at the lower end. Especially, the inverter  130  is mounted so that circuit parts mounted on the inverter PCB  132  and the corresponding recess  115  can face each other. Preferably, the inverter PCB  132  and the back surface of the bottom cover  114  have the same height. 
     Consequently, the transformer  134  occupying a large portion of the thickness of the inverter  130  is located within the recess  115 , thus effectively preventing the problems of decrease in thinning and electromagnetic interference with a system module that have occurred due to the projection of the transformer  134 . Here, to prevent the problem of electromagnetic interference with a system module more effectively, an insulation sheet  144  is attached to the inner wall surface of the bottom cover forming the recess  115 . Further, since the inverter  130  is mounted to the underside of the back surface of the bottom cover  114  in a straight line, the mountable space of the system module greatly increases. Moreover, because the inverter  130  and the electrodes of the lamps  120  are not overlapped with each other, this prevents heat generation of the inverter  130 . from being increased by lamp heat, thereby preventing a decrease inverter efficiency. 
       FIG. 15  is another cross-sectional view showing a coupling state between an inverter having two transformers and a bottom cover in accordance with an embodiment of the invention. As shown in  FIG. 15 , it may also be possible to mount the transformer  134  at one surface of the inverter PCB  132 , mount other passive devices  150  on the other surface of the inverter PCB  132 , and then locate only the transformer  134  within the recess  115  and make the passive devices  150  project toward the back surface of the bottom cover  114 . In this case, a cover shield  170  may be further provided to protect the passive devices  150  projecting toward the back surface of the bottom cover  114 . Even if the passive devices  150  project toward the back surface of the bottom cover  114  as described above, similar effects as those in  FIGS. 13 and 14  can be obtained because the passive devices  150  do not occupy a large portion of the thickness of the inverter  130 . 
       FIG. 16  is a schematic equivalent circuit diagram of an inverter having one transformer in accordance with an embodiment of the invention, and  FIG. 17  is a plane view showing a coupling state between an inverter having one transformer and a bottom cover in accordance with an embodiment of the invention. On the other hand, in the liquid crystal display device in accordance with the invention, an inverter  230  having one transformer  234  as shown in  FIGS. 16 and 17  can be used in place of the inverter having two transformers as noted above. This transformer  234  is implemented in a two-in-one transformer having a primary coil and two secondary coils wound in directions opposite to each other. This transformer  234  is mounted on the inverter PCB  232 , and then located within the recess  115  at the lower end of the back surface of the bottom cover  114  by securing the inverter  230  and the bottom cover  114  by screws  237 . 
     A lamp driving signal of a first phase is induced in the first secondary coil of the transformer  234 , and a lamp driving signal of a second phase opposite to the first phase is induced in the second secondary coil of the transformer  234 . The lamp driving signal of the first phase is supplied to one electrode of the lamps  120  via a connector  233  and a lamp wire  229 , and the lamp driving signal of the second phase is supplied to the other electrodes of the lamps  120  via the connector  233  and the lamp wire  229 . Here, to adjust the left and right balance of a driving current supplied to the lamps  120 , the distance between the transformer  234  and one end portions of the lamps  120  and the distance between the transformer  234  and the other end portions of the lamps  120  should be equal to each other. A control unit  236  and switching unit  238  of  FIG. 16  perform substantially the same functions as the control unit  136  and switching unit  138  as shown in  FIGS. 11 and 12 , so detailed descriptions thereof will be omitted. 
     As described above, the liquid crystal display device in accordance with an embodiment of the invention can significantly reduce the entire thickness of the product and greatly improve the left and right balance of a driving current supplied to the lamps by securing the inverter in a manner that the transformer having a relatively large volume can be located at an equal distance from the left and right end portions of the lamps in the recess of the back surface of the bottom cover. Furthermore, the liquid crystal display device in accordance with an embodiment of the invention can greatly enlarge the mountable space of a system module by securing the inverter to correspond to the recess formed along the long side of the lower end of the back surface of the bottom cover, and minimize electromagnetic interference between the system module and the inverter through an insulation sheet attached to the inner wall surface of the bottom cover forming the recess. Moreover, the liquid crystal display device in accordance with an embodiment of the invention can greatly increase inverter efficiency by preventing heat generation of the inverter from being increased by lamp heat by securing the inverter to the back surface of the bottom cover not to be overlapped with the electrodes of the lamps. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in a liquid crystal display device shown in the above embodiments of the invention without departing from the spirit or scope of the invention. Thus, it is intended that the invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.