Abstract:
A backlight unit driving apparatus is provided. The backlight unit driving apparatus includes a plurality of flash lamps at a backlight unit to supply light to a liquid crystal panel, supplies voltage necessary for discharge, and supplies a discharge initiating voltage so that the flash lamps can emit lights in a sequential order. Accordingly, motion picture characteristics improve, and good screen brightness is maintained.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. §119 of Korean Patent Application No. 10-2007-0042926, filed on May 3, 2007, in the Korean Intellectual Property Office (KIPO), the entire disclosure of which is hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a backlight unit driving apparatus and a method thereof More particularly, the present invention relates to a backlight unit driving apparatus and a method thereof, which divides an illuminating region of a backlight unit into a number of rows and illuminates the divided rows in sequences. 
         [0004]    2. Description of the Related Art 
         [0005]    A display apparatus such as a liquid crystal display (LCD) is employed in devices such as TVs, laptops, or desktops, to display images. Because displays such as LCD panels do not illuminate by themselves, these generally use a light from a separate light source to display images. Accordingly, a LCD employs a backlight unit at the backside of a LCD panel, and displays images, while adjusting transimisivity of light being irradiated from the backlight unit. 
         [0006]    In particular, in displaying the images, a LCD moves liquid crystal molecules to vary opening rate of unit cells for the duration of displaying one frame, and to maintain the varied opening rate until the next frame starts. A display apparatus employing this method suffers problems such as afterimage or motion blur in motion picture, due to different responsivity of liquid crystal molecules. 
         [0007]    In order to solve this problem, the backlight unit is illuminated by frame units, rather than being continuously illuminated.  FIGS. 1A to 1C  illustrate a conventional method for driving a backlight unit. 
         [0008]      FIGS. 1A and 1B  illustrate the structure of a conventional backlight unit.  FIG. 1A  illustrates a widely used cold cathode fluorescent lamp (CCFL), and  FIG. 1B  illustrates a light emitting diode (LED).  FIG. 1C  illustrates a driving timing for use in the driving of a conventional backlight unit. 
         [0009]    Referring to  FIGS. 1A and 1B , a backlight illuminating region is divided into five rows, and backlight of each row is controlled such that it is illuminated when in synchronization with a frame rate. This is frequently called as ‘backlight scanning’. In the backlight scanning, backlights of the respective rows are illuminated according to a driving timing as exemplified in  FIG. 1C . 
         [0010]    Accordingly, backlight of the first row is controlled to be illuminated for the duration T on1 , backlight of the second row is controlled to be illuminated for the duration T on2 , backlight of the third row is controlled to be illuminated for the duration T on3 , backlight of the fourth row is controlled to be illuminated for the duration T on4 , and backlight of the fifth row is controlled to be illuminated for the duration T on5 . 
         [0011]    However, screen darkens during backlight scanning, using a conventional CCFL or LED. Although CCFL or LED continuously illuminates, the illuminating time of backlights shortens in the backlight scanning, and therefore, the average luminosity decreases, degrading the brightness of screen. 
         [0012]    Increased power can be supplied to the backlights to compensate for the above problem, but this has a limit because light source efficiency deteriorates. Alternatively, the number of backlights may be increased, but this will cause increased cost. 
       SUMMARY OF THE INVENTION 
       [0013]    An aspect of exemplary embodiments of the present invention is to address at least the above problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of exemplary embodiments of the present invention is to provide a backlight unit driving apparatus and a method thereof, which performs backlight scanning, and prevents problems such as afterimage or motion blur of motion picture. 
         [0014]    Another aspect of exemplary embodiments of the present invention is to provide a backlight unit driving apparatus and a method thereof, which employs a flash lamp which instantly reaches a high level of luminous flux. 
         [0015]    The above objects of the present invention are substantially realized by providing a backlight unit driving apparatus, which includes a backlight unit comprising a plurality of flash lamps, a charging circuit unit to charge a voltage for use by the plurality of flash lamps to discharge, a discharge initiating unit to supply a discharge initiating voltage to the plurality of flash lamps to discharge lights, and a control unit to control the charging circuit unit and the discharge initiating unit so that the backlight unit is driven. 
         [0016]    The plurality of flash lamps emit lights from upper to lower rows in a sequential order. 
         [0017]    A switch unit may further be provided, to switch the discharge initiating voltage being supplied from the discharge initiating unit, so that the plurality of flash lamps emit lights in the respective rows of the backlight unit in a sequential order. 
         [0018]    The charging circuit unit includes charging circuits corresponding to the number of rows of the backlight unit. 
         [0019]    A switch unit may further be provided, to switch a voltage being supplied from the charging circuit unit so that the plurality of flash lamps emit lights in the respective rows of the backlight unit. 
         [0020]    The plurality of flash lamps includes a linear or a dot-type arrangement. 
         [0021]    The flash lamps include one of zenon flash lamp, laser flash lamp, and arc discharge flash lamp. 
         [0022]    The backlight unit includes a plurality of dot-type flash lamps arranged in a vertical direction along one side of a screen, and lightguide plates to cause the lights from the plurality of dot-type flash lamps to pass against the front screen uniformly. 
         [0023]    The backlight unit further includes a plurality of dot-type flash lamps arranged in a vertical direction along the other side of the screen. 
         [0024]    The charging circuit unit includes a transformer in which the primary side has the opposite polarity to the secondary side, a transistor connected between the primary side and the ground of the transformer, to be turned on and off according to control of the control unit, a capacitor to store a voltage being supplied from the transformer, and a diode connected between the secondary side of the transformer and the capacitor, to supply a voltage induced at the secondary side of the transformer to the capacitor, if the transistor is in off state. 
         [0025]    At least one of the plurality of flash lamps is connected in parallel with the capacitor, to receive the voltage stored at the capacitor to use for discharging the plurality of flash lamps. 
         [0026]    The control unit controls the discharge initiating unit to supply the discharge initiating voltage to the plurality of flash lamps, if the flash lamps are charged with voltage necessary for discharge. 
         [0027]    The above objects of the present invention are substantially realized by providing a method of driving a backlight unit comprising a plurality of flash lamps, which includes charging a voltage for discharging the plurality of flash lamps, and supplying a discharge initiating voltage to the plurality of flash lamps to discharge lights. 
         [0028]    Switching the discharge initiating voltage so that the plurality of flash lamps emit lights from upper to lower rows in a sequential order, may further be provided. 
         [0029]    The charging includes charging the plurality of flash lamps in respective rows with voltage necessary for discharge, sequentially. 
         [0030]    Other objects, advantages and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings discloses exemplary embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    The above and other exemplary objects, features and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
           [0032]      FIGS. 1A and 1B  illustrate the structure of a conventional backlight unit; 
           [0033]      FIG. 1C  exemplifies a driving timing for a conventional backlight unit; 
           [0034]      FIGS. 2A and 2B  illustrate a backlight unit driving apparatus according to a first exemplary embodiment of the present invention; 
           [0035]      FIGS. 3A and 3B  illustrate a backlight unit driving apparatus according to a second exemplary embodiment of the present invention; 
           [0036]      FIG. 4A  illustrates the structure of a backlight unit according to a third exemplary embodiment of the present invention; 
           [0037]      FIG. 4B  illustrates the structure of a backlight unit according to a fourth exemplary embodiment of the present invention; 
           [0038]      FIG. 5  illustrates a backlight unit driving apparatus according to a fifth exemplary embodiment of the present invention; 
           [0039]      FIG. 6  illustrates a backlight unit driving apparatus according to a sixth exemplary embodiment of the present invention; 
           [0040]      FIG. 7  illustrates a backlight unit driving apparatus according to a seventh exemplary embodiment of the present invention; and 
           [0041]      FIGS. 8 to 10  illustrate a driving time for use in the first through seventh exemplary embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0042]    The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the embodiments of the invention. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness. 
         [0043]      FIGS. 2A and 2B  illustrate a backlight unit driving apparatus according to a first exemplary embodiment of the present invention. 
         [0044]    Referring to  FIG. 2A , a backlight unit driving apparatus includes a backlight unit  100 , a first to n-th charging circuits  110 - 1 ,  110 - 2 , . . . ,  110 - n,  a first switch unit  130 , a discharge initiating unit  150 , and a driving control unit  180 . 
         [0045]    The backlight unit  100  includes first to n-th flash lamps  100 - 1 ,  100 - 2 , . . . ,  100 - n.  The flash lamps  100 - 1 ,  100 - 2 , . . . ,  100 - n  are each driven by short-width high-current pulses, and has the ability to output strong light instantly. The flash lamps  100 - 1 ,  100 - 2 , . . . ,  100 - n  radiate light from several hundreds of us to several tens of ms, and has a relatively low radiation period ranging from several Hz to several hundreds of Hz. 
         [0046]    The flash lamps  100 - 1 ,  100 - 2 , . . . ,  100 - n  may be implemented as a zenon flash lamp which injects gases such as zenon or krypton into a glass tube, and causes electric discharge and subsequent radiation, by applying high voltage instantly. Alternatively, laser flash lamp using a laser light, or an arc flash lamp using an arc discharge, may be employed. 
         [0047]    The first to n-th charging circuits  110 - 1 ,  110 - 2 , . . . ,  110 - n  are connected to both sides of the first to n-th flash lamps  100 - 1 ,  100 - 2 , . . . ,  100 - n,  to supply voltage necessary to discharge the flash lamps  100 - 1 ,  100 - 2 , . . . ,  100 - n,  respectively. 
         [0048]    The discharge initiating unit  150  supplies discharge initiating voltage to the backlight unit  100 , so that the flash lamps  100 - 1 ,  100 - 2 , . . . ,  100 - n  to start discharge and radiating lights. 
         [0049]    The first switch unit  130  switches the discharge initiating voltage being supplied from the discharge initiating unit  150 , so that the flash lamps  100 - 1 ,  100 - 2 , . . . ,  100 - n  radiate lights in sequence. In particular, the discharge initiating voltage from the discharge initiating unit  150  is switched such that the flash lamps  100 - 1 ,  100 - 2 , . . . ,  100 - n  radiate light in sequence, each for the duration of time corresponding to one frame divided by n. 
         [0050]    The driving control unit  180  controls the first to n-th recharge circuits  110 - 1 ,  110 - 2 , . . . ,  110 - n,  the first switch unit  130 , and the discharge initiating unit  150  so that the backlight unit  100  is driven. In particular, the first to n-th charging circuits  110 - 1 ,  110 - 2 , . . . ,  110 - n  are driven in sequence by a control signal {circle around ( 1 )} being output from the driving control unit  180 , to supply voltage required for the first to n-th flash lamps  100 - 1 ,  100 - 2 , . . . ,  100 - n  to radiate lights. The driving control unit  180  also controls the first switch unit  130  so that a flash lamp to initiate discharge is selected in sequence from upper to lower rows, from among the first to n-th flash lamps  100 - 1 ,  100 - 2 , . . . ,  100 - n.  When a flash lamp to initiate discharge is selected, the discharge initiating unit  150  is controlled such that a discharge initiating voltage is supplied to the selected flash lamp. 
         [0051]      FIG. 2B  shows in detail the circuit structures of the first to n-th charging circuits  110 - 1 ,  110 - 2 , . . . ,  110 - n,  and the discharge initiating unit  150 . 
         [0052]    Referring to  FIG. 2B , the first charging circuit  110 - 1  employs a flyback circuit. The first charging circuit  110 - 1  includes a first transformer TF 1 , a first transistor TR 1 , a first diode D 1 , and a first capacitor C 1 . 
         [0053]    First, the operation of the first charging circuit  110 - 1  is explained below. According to a control signal {circle around ( 1 )} output from the driving control unit  180 , the first transistor TR 1  is turned on, and accordingly, voltage in the opposite polarity to that of the primary side is induced at the secondary side of the first transformer TF 1 , thereby turning off the first diode D 1 . Accordingly, electric current flows the secondary side of the first transformer TF 1 , and stored. If the first transistor TR 1  is turned off according to the control signal {circle around ( 1 )}, voltage is induced at the secondary side of the first transformer TF 1 , in the polarity opposite to when the first transistor TR 1  is in on state, thereby turning on the first diode D 1 . As a result, voltage stored at the secondary side of the first transformer TF 1  is charged in the first capacitor C 1 . 
         [0054]    As the first transistor TR 1  repeats on and off according to control signal {circle around ( 1 )}, voltage for the first flash lamp  100 - 1  to discharge is charged in the first capacitor C 1 . Accordingly, voltage is supplied to the first flash lamp  100 - 1  in parallel connected with the first capacitor C 1 . The operation at the second to n-th charging circuits  110 - 2 , . . . ,  110 - n  are the same as that of the first charging circuit  110 - 1  explained above, and therefore, these will not be explained for the sake of brevity. In a desirable implementation, the first to n-th charging circuits  110 - 1 , . . . ,  110 - n  are driven in sequence to charge necessary radiation voltage, according to control signal {circle around ( 1 )}. 
         [0055]    The discharge initiating unit  150  includes a transformer TF and a transistor TR. When the transistor TR is turned on according to control signal {circle around ( 2 )} of the driving control unit  180 , voltage in the same polarity as that at the primary side is induced at a secondary side, and accordingly, discharge initiating voltage is supplied to the flash lamps  100 - 1 ,  100 - 2 , . . . ,  100 - n,  respectively. The first switch unit  130  performs switching to select a flash lamp to discharge, before the transistor TR is turned on according to control signal {circle around ( 2 )}. 
         [0056]      FIGS. 3A and 3B  illustrate a backlight unit driving apparatus according to a second exemplary embodiment of the present invention. 
         [0057]    Referring to  FIG. 3A , a backlight unit driving apparatus includes a backlight unit  200 , a shared charging circuit  220 , a second switch unit  240 , a first switch unit  260 , a discharge initiating unit  280 , and a driving control unit  285 . 
         [0058]    The backlight unit  200  as substantially the same structure and characteristics as the backlight unit  100  illustrated in  FIG. 2A . Likewise, the operations at the first switch unit  260  and the discharge initiating unit  280  are substantially the same as the operations at the first switch unit  130  and the discharge initiating unit  150  illustrated in  FIG. 2A . Therefore, detailed description on the overlapping elements or operations will be omitted for the sake of brevity. 
         [0059]    A backlight unit driving apparatus as the one illustrated in  FIG. 3A  generates a voltage for discharge from the shared charging circuit  220 , and supplies the generated voltage to the first to n-th flash lamps  200 - 1 ,  200 - 2 , . . . ,  200 - n.  The second switch unit  240  performs switching so that the voltage for discharge generated at the shared charging circuit  220  can e supplied to the first to n-th flash lamps  200 - 1 ,  200 - 2 , . . . ,  200 - n.    
         [0060]    The driving control unit  260  controls the shared charging circuit  220  to generate a voltage for discharge according to control signal {circle around ( 1 )}, and then controls the second switch unit  240  so that the voltage charged in the shared charging circuit  220  is supplied to the first to n-th flash lamps  200 - 1 ,  200 - 2 , . . . ,  200 - n,  in sequence. A flash lamp to discharge is then selected by controlling the first switch unit  260 , and the discharge initiating unit  280  is controlled to supply discharge initiating voltage to the selected flash lamp. 
         [0061]    Referring to  FIG. 3B , the shared charging circuit  220  is implemented as a flyback circuit. The shared charging circuit  220  includes a transformer TF, a transistor TR, a diode D, and a capacitor C. 
         [0062]    When the transistor TR is turned on according to the control signal {circle around ( 1 )} being output from the driving control unit  285 , voltage in the opposite polarity to that at the primary side is induced at the secondary side of the transformer TF, thereby turning off the diode D. Accordingly, electric current flows the secondary side of the transformer TF, and stored. When the transistor TR is turned off according to the control signal {circle around ( 1 )}, voltage is induced at the secondary side of the transformer TR, in the polarity opposite to voltage when the transistor TR is in on state, thereby turning on the diode D. As a result, voltage stored in the secondary side of the transformer TF is charged in the capacitor C. 
         [0063]    The driving control unit  285  controls the second switch unit  240  according to the control signal {circle around ( 1 )}, so that a flash lamp to discharge is selected before the voltage for discharge is charged in the capacitor C. When the flash lamp receives the supply of voltage from the shared charging circuit  220  and thus is ready to discharge, the driving control unit  285  controls the first switch unit  260  to select this flash lamp. As the final step, the driving control unit  285  controls the discharge initiating unit  280  to supply discharge initiating voltage to the flash lamp, which is ready to discharge, according to the control signal {circle around ( 2 )}. 
         [0064]    By using a single shared charging circuit  220 , which has a fast operation cycle, the number of charging circuits can be reduced. The flash lamps  200 - 1 ,  200 - 2 , . . . ,  200 - n  may be implemented in a linear arrangement as illustrated in  FIGS. 2A and 3A . Alternatively, the flash lamps  200 - 1 ,  200 - 2 , . . . ,  200 - n  may be implemented in a U-type arrangement, or dot arrangement as generally employed in LEDs. 
         [0065]      FIG. 4A  illustrates the structure of a backlight unit according to a third exemplary embodiment of the present invention. 
         [0066]    Referring to  FIG. 4A , the backlight unit  300  according to the third exemplary embodiment of the present invention includes a plurality of dot-type flash lamps  300 - 1 ,  300 - 2 ,  . . .  300 - n  in a linear arrangement along one side, and a plurality of lightguide plates  320 - 1 ,  320 - 2 , . . . ,  320 - n  to cause the lights from the dot-type flash lamps  300 - 1 ,  300 - 2 , . . . ,  300 - n  to pass against the front panel uniformly, and to control inter-row light spreading. 
         [0067]    The circuit structure to drive the backlight unit  300  illustrated in  FIG. 4A  is substantially the same as those illustrated in  FIGS. 2A and 3A , and therefore, detailed explanation will be omitted for the sake of brevity. 
         [0068]      FIG. 4B  illustrates the structure of a backlight unit according to a fourth exemplary embodiment of the present invention. 
         [0069]    Referring to  FIG. 4B , the backlight unit  350  according to the fourth exemplary embodiment of the present invention includes a plurality of lightguide plates  355 - 1 ,  355 - 2 , . . . ,  355 - n,  and a plurality of dot-type flash lamps  351 - 1 ,  351 - 2 ,  351 - n  and  353 - 1 ,  353 - 2 , . . . ,  353 - n  in linear arrangements along both sides of the lightguide plates  355 - 1 ,  355 - 2 , . . . ,  355 - n.    
         [0070]    Circuit structure for driving the backlight unit  350  illustrated in  FIG. 4B  will be explained in detail below, with reference to  FIGS. 5 and 6 . 
         [0071]      FIG. 5  illustrates a backlight unit driving apparatus according to a fifth exemplary embodiment of the present invention.  FIGS. 5 to 7  illustrate a backlight unit structure as illustrated in  FIG. 1B , in which M number of dot-type flash lamps are arranged in a single row. 
         [0072]    Referring to  FIG. 5 , a backlight unit driving apparatus according to the fifth exemplary embodiment of the present invention includes a first to n-th flash lamp units  400 - 1 ,  400 - 2 , . . . ,  400 - n,  a first to n-th charging circuits  410 - 1 ,  410 - 2 , . . . ,  410 - n,  a first switch unit  430 , a discharge initiating unit  450  and a driving control unit (not shown). 
         [0073]    The first to n-th flash lamps  400 - 1 ,  400 - 2 , . . . ,  400 - n  are provided in structure in which M number of dot-type flash lamps are connected with each other in parallel. The M number of dot-type flash lamps are driven by a short-width high-current pulse, and are able to output strong lights instantly. The flash lamps radiate light from several hundreds of us to several tens of ms, and have a relatively low radiation period ranging from several Hz to several hundreds of Hz. Alternatively, zenon flash lamps, laser flash lamps, or arc flash lamps may be employed. 
         [0074]    The operation of the first charging circuit  410 - 1  will be explained below. When the first transistor TR 1  is turned on according to control signal {circle around ( 1 )} being output from the driving control unit, voltage is induced in the secondary side of the first transformer TF 1 , in the polarity opposite to that at the primary side, thereby turning off the first diode D 1 . Accordingly, electric current flows the secondary side of the first transformer TF 1 , and stored. When the first transistor TR 1  is turned off according to the control signal {circle around ( 1 )}, voltage is induced at the secondary side of the first transformer TF 1  in the polarity opposite to when the first transistor TR 1  is in on state, thereby turning on the first diode D 1 . As a result, voltage stored in the secondary side of the first transformer TF 1  is charged in the first capacitor C 1 . 
         [0075]    As the first transistor TR 1  repeats on and off according to control signal {circle around ( 1 )}, a sufficient amount of voltage is charged for the discharge of M number of flash lamps of the first flash lamp unit  400 - 1 , and supplied to the first flash lamp unit  400 - 1  connected in parallel with the first capacitor C 1 . The above operations are carried out at the second to n-th charging circuits  410 - 2 , . . . ,  410 - n  in the same manner, and therefore, further explanation will be omitted for the sake of brevity. It is desirable that the first to n-th charging circuits  410 - 1 ,  410 - 2 , . . . ,  410 - n  are driven in sequence according to control signal {circle around ( 1 )}, to store a necessary amount of voltage. 
         [0076]    The discharge initiating unit  450  includes a transformer TF and a transistor TR. When the transistor TR is turned on according to control signal {circle around ( 2 )} of the driving control unit, voltage is induced at the secondary side of the transformer TF, in the same polarity as that of the primary side, and supplied to the flash lamp units  400 - 1 ,  400 - 2 , . . . ,  400 - n  as a discharge initiating voltage. A flash lamp to discharge is selected by the switching of the first switch unit  430 , before the transistor TR is turned on according to control signal {circle around ( 2 )}. Accordingly, the first switch unit  430  switches the discharge initiating voltage being supplied from the discharge initiating unit  450 , so that the first to n-th flash lamp units  400 - 1 ,  400 - 2 , . . . ,  400 - n  radiate lights in sequence, each for the duration corresponding to one frame divided by n. 
         [0077]    If each of the first to n-th flash lamp units  400 - 1 ,  400 - 2 , . . . ,  400 - n  include two flash lamps, respectively, these can be used as a driving circuit of the backlight unit  350  illustrated in  FIG. 4B . 
         [0078]      FIG. 6  illustrates a backlight unit driving apparatus according to a sixth exemplary embodiment of the present invention. 
         [0079]    The first to n-th flash lamp units  500 - 1 ,  500 - 2 , . . . ,  500 - n  have the substantially same structure and characteristics as those of the first to n-th flash lamp units  400 - 1 ,  400 - 2 ,  . . . ,  400 - n.  Operations at the first switch unit  560  and the discharge initiating unit  580  are also substantially the same as those of the first switch unit  430  and the discharge initiating unit  450  illustrated in  FIG. 5 . Therefore, detailed explanation will be omitted for the sake of brevity. 
         [0080]    The backlight unit driving apparatus illustrated in  FIG. 6  generates discharge voltage at a shared charging circuit  520 , and supplies the generated voltage to the first to n-th flash lamp units  500 - 1 ,  500 - 2 , . . . ,  500 - n.  The second switch unit  540  switches so that the discharge voltage generated at the shared charging circuit  520  is supplied to the first to n-th flash lamp units  500 - 1 ,  500 - 2 , . . . ,  500 - n.    
         [0081]    Referring to  FIG. 6 , the shared charging circuit  520  is implemented as a flyback circuit. The shared charging circuit  520  includes a transformer TF, a transistor TR, a diode D, and a capacitor C. 
         [0082]    When the transistor TR is turned on according to control signal {circle around ( 1 )} being output from a driving control unit (not shown), voltage is induced at the secondary side of the transformer TF, in the polarity opposite to that of the primary side, thereby turning off the diode D. Accordingly, electric current flows the secondary side of the transformer TF, and stored. When the transistor TR is turned off according to control signal {circle around ( 1 )}, voltage is induced at the secondary side of the transformer TF, in the polarity opposite to when the transistor TR is in on state, thereby turning on the diode D. As a result, voltage stored at the secondary side of the transformer TF is charged in the capacitor. 
         [0083]    The second switch unit  540  is controlled to select a flash lamp unit to discharge according to control signal {circle around ( 1 )}, before voltage for discharge is charged in the capacitor C. If voltage generated at the shared charging circuit  520  is supplied to the selected flash lamp unit, the driving control unit controls the first switch unit  560  to select this flash lamp unit. The driving control unit then controls the discharge initiating unit  580  so that the flash lamp unit, which is readied to discharge, receives a discharge initiating voltage. 
         [0084]    If each of the flash lamp units  500 - 1 ,  500 - 2 , . . . ,  500 - n  employs two flash lamps, the backlight unit driving apparatus illustrated in  FIG. 6  can be used to drive the backlight unit  350  illustrated in  FIG. 4B . 
         [0085]      FIG. 7  illustrates a backlight unit driving apparatus according to a sixth exemplary embodiment of the present invention. 
         [0086]    A backlight unit illustrated in  FIG. 7  is connected with M number of charging circuits  610 - 1 ,  610 - 2 , . . . ,  610 - n  in each row. Specifically, a flash lamp unit  600 - 1  in one row includes a M number of dot-type flash lamps, each being connected with the charging circuits  610 - 1 ,  610 - 2 , . . . ,  610 - n.  The operations of the charging circuits  610 - 1 ,  610 - 2 , . . . ,  610 - n  are same as those of the charging circuits  610 - 1 ,  610 - 2 , . . . ,  610 - n  illustrated in  FIGS. 2A to 6 . The other rows have the same structures, and detailed explanation thereof will be omitted for the sake of brevity. 
         [0087]      FIGS. 8 to 10  illustrate driving timings used in the exemplary embodiments of the present invention explained above. 
         [0088]    The driving timings illustrated in  FIGS. 8 to 10  are specifically applicable for a backlight unit having five rows. The driving timings are supplied to the backlight unit by the first switch unit  130 ,  260 ,  430 ,  560 ,  630 . 
         [0089]      FIG. 8  specifically illustrates a driving timing to perform backlight scanning, in which the backlights are illuminated from upper to lower rows in sequence, and in which each row is illuminated once in the equally divided intervals of one frame. 
         [0090]      FIG. 9  specifically illustrates a driving timing to perform backlight scanning, in which the backlights are illuminated from upper to lower rows in sequence, and in which each row is illuminated twice in the equally divided intervals of one frame. Although  FIG. 9  illustrates an example where the backlights are illuminated twice, the backlights can be illuminated more than twice. 
         [0091]      FIG. 10  illustrates a driving timing in which the backlights are illuminated from upper to lower rows almost simultaneously, at the last interval of one frame. 
         [0092]    As explained above, illuminating area of a backlight unit is divided into a plurality of sub-areas, and the sub-areas are scanned in a sequential order. Accordingly, afterimage or motion blur is avoided in a motion picture. Additionally, by using a flash lamp which emits strong luminosity instantly, brightness degrading can be avoided. 
         [0093]    While the present invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the sprit and scope of the invention as defined by the appended claims and their equivalents.