Patent Publication Number: US-7911155-B2

Title: Backlight unit, display apparatus comprising the same and control method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Korean Patent Application No. 10-2007-0082942, filed on Aug. 17, 2007, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Apparatuses and methods consistent with the present invention relate to a backlight unit, a display apparatus comprising the same and a control method thereof, and more particularly, to a backlight unit which has a plurality light source modules driven independently, a display apparatus comprising the same and a control method thereof. 
     2. Description of the Related Art 
     In recent years, a flat panel display apparatus such as a liquid crystal display (LCD), a plasma display panel (PDP) and an organic light emitting diode (OLED) has replaced a related art cathode ray tube (CRT). 
     A liquid crystal panel of the LCD device does not emit light itself. Thus, a backlight unit is disposed behind the liquid crystal panel to emit light. Transmittance of light emitted by the backlight unit is adjusted by an arrangement of liquid crystals. The liquid crystal panel and the backlight unit are accommodated in a chassis. A light source of the backlight unit includes a linear light source such as a lamp or a point light source such as a light emitting diode (LED). The LED has drawn attention recently. 
     As the display device becomes large in size, the number of the point light sources and drivers driving the point light sources of the backlight unit has increased. As a technology such as local dimming has been developed to individually control the point light sources, the point light sources are generally driven in a unit of a plurality of light source modules. 
     In this case, an error detector should also be provided in every light source modules to detect the opening or short-circuit of the point light sources. Then, a configuration of the backlight unit becomes very complicated and production costs rise. 
     SUMMARY OF THE INVENTION 
     Exemplary embodiments of the present invention overcome the above disadvantages and other disadvantages not described above. Also, the present invention is not required to overcome the disadvantages described above, and an exemplary embodiment of the present invention may not overcome any of the problems described above. 
     Accordingly, it is an aspect of the present invention to provide a backlight unit which detects errors of a light source without difficulty, a display apparatus comprising the same and a control method thereof. 
     Also, it is another aspect of the present invention to provide a backlight unit which informs errors of a light source to a user without difficulty, a display apparatus comprising the same and a control method thereof. 
     Further, it is another aspect of the present invention to provide a backlight unit which has a simple configuration and reduces production costs, a display apparatus comprising the same and a control method thereof. 
     Additional aspects of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the present invention. 
     The foregoing and/or other aspects of the present invention are also achieved by providing a display apparatus, including: a display panel; a light source which includes a plurality of light source modules and supplies light to the display panel; a light source driver which drives the light source modules; a power source which supplies power to the light source driver; a current detector which detects a current of power supplied from the power source to the light source driver; and a controller which controls the light source driver to sequentially drive the plurality of light source modules and compares the sequentially-detected current with a preset acceptable range to detect errors from the respective light source modules. 
     The controller may include a comparator which compares a voltage corresponding to the current with a predetermined reference voltage. 
     The reference voltage may be set to be approximately 40% to 60% of a voltage corresponding to a normal current supplied from the power source to the light source driver if the errors do not occur in the light source modules, and the controller may determine that the errors occur in the light source modules if the voltage corresponding to the current is lower than the reference voltage. 
     The current detector may include a resistor which is connected between the power source and the light source driver. 
     The display apparatus may further include a switch which is provided between the power source and the light source driver and bypasses the resistor, wherein the controller turns off the switch so that power output from the power source is supplied to the light source driver through the resistor while detecting the errors. 
     The switch may include a first type transistor which is connected with the resistor in parallel, and a second type transistor which has an input terminal connected with a control terminal of the first type transistor and is differently structured from the first type transistor. 
     The current detector may include a hall sensor. 
     The display apparatus may further include an interface which transmits information on error occurrence or information on the light source modules having the errors if errors occur in the light source modules. 
     The display apparatus may further include an error informer which displays error occurrence if the errors occur in the light source modules. 
     The controller may cut off power supplied from the power source to the light source driver if the errors occur in the light source modules. 
     The light source may module include a plurality of point light sources. 
     The light source driver may include a plurality of driving modules which individually drives the light source modules. 
     The foregoing and/or other aspects of the present invention are also achieved by providing a backlight unit, including: a light source which includes a plurality of light source modules; a light source driver which includes a plurality of driving modules to drive the light source modules; a power source which supplies power to the light source driver; an error detector which detects a current of power supplied from the power source to the light source driver, and compares the sequentially-detected current with a preset acceptable range to detect errors from the respective light source modules; and a controller which controls the light source driver to sequentially drive the plurality of light source modules, and cuts off power supplied from the power source to the light source driver if errors are detected from the light source modules. 
     The error detector may include a current detector which detects a current of power supplied from the power source to the light source driver, and a comparator which compares a voltage corresponding to the current with a predetermined reference voltage. 
     The current detector may include a resistor which is connected between the power source and the light source driver. 
     The error detector may further include a switch which is provided between the power source and the light source driver and bypasses the resistor, and the controller may turn off the switch so that power output from the power source is supplied to the light source driver through the resistor if the error detector detects whether the errors occur in the light source modules. 
     The current detector may include a hall sensor. 
     The backlight unit may further include an error informer which displays error occurrence if the errors occur in the light source modules. 
     The foregoing and/or other aspects of the present invention are also achieved by providing a control method of a display apparatus which has a display panel, a light source having a plurality of light source modules, a light source driver driving the light source modules and a power source supplying power to the light source driver, the control method including: sequentially driving the plurality of light source modules; sequentially detecting a current of power supplied from the power source to the light source driver; and detecting errors from the respective light source modules by comparing the detected current with a preset acceptable range. 
     The control method may further include cutting off power supplied from the power source to the light source driver if the errors occur in the light source modules. 
     The control method may further include informing error occurrence if the errors occur in the light source modules. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects of the present invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a control block diagram of a display apparatus according to a first exemplary embodiment of the present invention; 
         FIG. 2  is a schematic circuit diagram of a controller in  FIG. 1 ; 
         FIG. 3  is a schematic circuit diagram of a controller of a display apparatus according to a second exemplary embodiment of the present invention; 
         FIG. 4  is a control block diagram of a display apparatus according to a third exemplary embodiment of the present invention; 
         FIG. 5  is a control flowchart to describe a control method of the display apparatus according to an exemplary embodiment of the present invention; and 
         FIG. 6  is a control block diagram of a backlight unit of a display apparatus according to a fourth exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION 
     Hereinafter, exemplary embodiments of the present invention will be described with reference to accompanying drawings, wherein like numerals refer to like elements and repetitive descriptions will be avoided as necessary. 
       FIG. 1  is a control block diagram of a display apparatus according to a first exemplary embodiment of the present invention. 
     As shown therein, the display apparatus according to the present embodiment includes a display panel  100  and a backlight unit  200  which emits light behind or beside the display panel  100 . The display panel  100  includes a liquid crystal panel having a liquid crystal layer (not shown), but not limited thereto. Alternatively, the display panel  100  may include other display panels as long as it receives light from the backlight unit  200 . The backlight unit  200  includes a light source  210 , a light source driver  220  to drive the light source  210 , a power source  230  to supply power to the light source driver  220 , a current detector  240  and a controller  250  to control the foregoing elements. 
     The liquid crystal display panel  100  includes a first substrate (not shown) which has thin film transistors, a second substrate (not shown) which faces the first substrate and a liquid crystal layer (not shown) which is formed between the first and second substrates. A gate line  110 , a data line  120  and a plurality of pixels  130  are formed in the display panel  100 . The plurality of pixels  130  is defined by the gate line  110  and the data line  120  which are perpendicular to each other, has a thin film transistor (not shown) and is formed in a matrix pattern. 
     The light source  210  includes light source modules  211  to  215  which include point light sources  210   a  and are divided into a plurality of domains. The light source  210  supplies light to the display panel  100 . The point light sources  210   a  according to the present embodiment include a light emitting diode (LED), and are uniformly formed across an LED circuit substrate (not shown) disposed behind the display panel  100 . The light source modules  211  to  215  include a plurality of point light source groups which has three or four LEDs. The point light source group which has three LEDs includes red, green and blue LEDs. The point light source group which has four LEDs may further include a white LED. The point light sources  210   a  which emit the same color are connected in series to form a point light source string. The point light sources  210   a  are not limited to the LED, and may include a laser diode or an oxygen nano tube. According to another exemplary embodiment, the light source  210  may include a surface light source. That is, the surface light source is plurally divided to be uniformly arranged behind the display panel  100 . 
     The light source driver  220  includes a circuit to output driving power to the light source  210 . The light source driver  220  includes a plurality of driving modules  221  to  225  corresponding to the number of the light source modules  211  to  215 . A single driving module is controlled to drive a single light source module. The driving modules  221  to  225  control driving power supplied to the light source modules  211  to  215  individually, and change the driving sequence of the light source modules  211  to  215  according to a control of the controller  250 . 
     According to another exemplary embodiment, the light source driver  220  may include a smaller number of driving modules than that of the light source modules  211  to  215 . In this case, a single driving module drives more than two light source modules. The light source modules  211  to  215  are sequentially driven at predetermined time intervals. 
     Using constant voltage power, the power source  230  supplies a predetermined-level voltage to the light source driver  220 . A current of the constant voltage power, which is output from the power source  230  to the light source driver  220 , varies depending on efficiency of the light source driver  220 , the number of the point light sources  210   a  of the light source  210  and errors of the point light sources  210   a . Vi is a voltage of power output from the power source  230  to the light source driver  220 , Ii is a current of power output from the power source  230  to the light source driver  220 , Vo and Io are respectively a voltage and a current of power output from the light source driver  220  to the light source  210  and K is efficiency of the light source driver  220 . Then, a formula is established as follows: Vo*Io=Vi*Ii/κ 
     The current detector  240  is provided between the power source  230  and the light source driver  220 , and detects a current of power supplied from the power source  230  to the light source driver  220 . As Vi is a constant as described above, Ii includes information on the light source  210 . For example, if the point light sources  210   a  are open or short-circuit, Ii changes smaller or larger than the normal current. The current detector  240  detects the current and outputs it to the controller  250 . The current detector  240  includes a resistor  241  and a current detection amplifier  242  as shown in  FIG. 2 . The current detection amplifier  242  amplifies a current detected from both ends of the resistor  241  to supply the current to a comparator  252  (to be described later). Preferably but not necessarily, the current detection amplifier  242  may include a differential amplifier. The current detector  240  further includes an RC filter  243  which is connected between the current detection amplifier  242  and the comparator  252  to reduce noises which may occur during the current detecting process. The RC filter  243  includes a resistor R 1  which is connected with the current detection amplifier  242  in series, and a capacitor C 1  which is connected with the resistor R 1  and a ground terminal. The capacitor C 1  may be connected with both ends of the comparator  252 . Alternatively, the RC filter  243  may be provided between the resistor  241  and the current detection amplifier  242 . The RC filter  243  may be replaced by various known filters to remove noises. 
     The controller  250  controls the light source driver  220  to sequentially drive the plurality of light source modules  211  to  215 , and detects errors of the respective light source modules  211  to  215  by comparing the current detected sequentially by the current detector  240  with a preset acceptable range. The controller  250  sequentially drives the light source driver  220 , but that does not mean to limit that it drives sequentially from the first driving module  221  to the fifth driving module  225 . Instead, the controller  250  does not drive more than two driving modules  211  to  225  repetitively, but drives one by one in a predetermined sequence. If the controller  250  does not detect errors, it controls the light source driver  220  according to a dimming signal input from the outside. 
       FIG. 2  is a schematic circuit diagram of the controller  250  according to the present embodiment. As shown therein, the controller  250  includes a relay switch  251 , the comparator  252  and a storage unit  257 . 
     A related art display apparatus having a plurality of light source modules includes an error detecting circuit in end parts of respective driving modules or light source modules to detect errors of point light sources. As the size of the display panel increases, the number of the light source modules and driving modules increases, too. Also, the number of error detecting circuits increases, which enlarges the size and thickness of the backlight unit and raises production costs. The display apparatus according to the present embodiment does not have an error detecting circuit individually connected to the driving modules or to the light source modules, but sequentially drives the light sources modules  211  to  215  and detects a current between the power source  230  and the light source driver  220 . If the current between the power source  230  and the light source driver  220  is out of the acceptable range, the controller  250  determines that the errors occur in the light source modules  211  to  215  driven when the current is detected. That is, the controller  250  may determine whether errors occur in the respective light source modules  211  to  215  according a simpler configuration than the related art configuration. 
     The controller  250  detects the errors only if a particular event occurs, thereby reducing power consumption due to the resistor  241 . If the point light sources  210   a  supply light to the display panel  100  continuously while an image is displayed, a current applied from the power source  230  to the light source driver  220  has a much larger value than one of the light source modules  211  to  215  is driven. Thus, the controller  250  may detect errors at particular timing when a particular event occurs, e.g. when the display apparatus is power-on initially, when an image is not displayed on the display panel  100  in a standby mode or when power is not supplied to the display panel  100 . Thus, power consumption is reduced, and the controller  250  may detect the errors while not affecting a user to view an image. The controller  250  applies a control signal {circle around (a)} corresponding to the particular event to the relay switch  251 . The relay switch  251  which is provided between the power source  230  and the light source driver  220  is turned on or off according to the control signal {circle around (a)}. If the controller  250  detects the errors, the relay switch  251  is turned off so that power is output from the power source  230  to the light source driver  220  through the resistor  241 . If an image is displayed normally, the relay switch  251  is turned on, and power output from the power source  230  to the light source driver  220  bypasses the resistor  241 . 
     In some cases, the light source modules  211  to  215  are sequentially driven by the driving modules  221  to  225  at predetermined intervals. Then, the controller  250  may detect the errors when a particular event occurs as described above, or may detect the errors while supplying light normally to the display panel  100 . 
     The comparator  252  compares a voltage corresponding to the detected current with a predetermined reference voltage, and outputs a control signal corresponding to the individual error information of the light source modules  211  to  215 . If the light source modules  211  to  215  are in a normal state as the point light sources  210   a  are not open or short-circuit, the current flowing between the power source  230  and the light source driver  220  is Ii=Vo*Io/Vi*κ. If the point light sources  210   a  of the light source modules  211  to  215  are all open, a closed circuit is not formed to allow the current to flow. Thus, the current is not detected between the power source  230  and the light source driver  220 . If a part of the point light sources  210   a  is open, a current larger than the normal current Ii may flow between the power source  230  and the light source driver  220 . If the point light sources  210   a  are completely short-circuit, they act as a large capacity resistor, thereby flowing a current close to zero between the power source  230  and the light source driver  220 . If the point light sources  210   a  are partly short-circuit, a current smaller than the normal current Ii flows therebetween. 
     The comparator  252  determines whether the voltage corresponding to the detected current is out of the preset acceptable range, based on the reference voltage. The reference voltage is set to be approximately 40% to 60%. For example, the reference voltage may be set to 50% of the voltage corresponding to the normal current Ii supplied to the power source  230  and the light source driver  220 . The reference voltage is set as described above so that misjudgment on the noises is minimized when the errors are detected in consideration of the noises occurring during the current detecting process. If the voltage corresponding to the detected current is present between the reference voltage and a voltage corresponding to the normal current Ii, the light source modules  211  to  215  are in the normal state. If the voltage corresponding to the detected current exceeds the foregoing range or does not reach the range, it may be determined that the errors occur in the light source modules  211  to  215 . The voltage comparison method of the comparator  252  may vary. For example, the reference voltage may be set corresponding to the normal current Ii or a plurality of reference voltages may be set to determine the extent of the errors. 
     The storage unit  257  stores information output by the comparator  252 . The storage unit  257  stores information on the errors occurring in the light source modules, types of the errors and the particular light source modules  211  to  215  having the errors. 
     The controller  250  according to another exemplary embodiment may include an A/D (analog-to-digital) converter and a digital processor, instead of the comparator  252 . That is, the configuration of the controller  250  is not limited to the foregoing configuration to detect the errors, and may include known hardware or software. 
       FIG. 3  is a schematic circuit diagram of a controller of a display apparatus according to a second exemplary embodiment of the present invention. As shown therein, the controller  250  includes a plurality of transistors  253  and  254  and resistors R 2  and R 3 , instead of the relay switch  251 . The first transistor  253  includes a P type transistor while the second transistor  254  includes an N type transistor differently structured from the first transistor  253 . An input terminal of the second transistor  254  is connected with a control terminal of the first transistor  253 . A pull-up resistor R 2  is connected between the power source  230  and the control terminal of the first transistor  253  while a pull-down resistor R 3  is connected between the control terminal of the first transistor  253  and the input terminal of the second transistor  254 . 
     If a high signal is applied to the control terminal of the second transistor  254  to turn on the N type transistor, a low signal is applied to the control terminal of the first transistor  253  by the pull-down resistor R 3 . Then, the first transistor  253  is turned on, too, and power applied from the power source  230  to the light source driver  220  bypasses the resistor  241 . Conversely, if a low signal is applied to the control terminal of the second transistor  254  to turn off the N type transistor, a high signal is applied to the control terminal of the first transistor  253  by the pull-up resistor R 2 . Then, the first transistor  253  is turned off, too, and power applied from the power source  230  to the light source driver  220  passes through the resistor  241 . As a result, the high signal applied to the second transistor  254  corresponds to a control signal applied when normal power is supplied to the light source driver  230 , and the low signal applied to the second transistor  254  corresponds to a control signal applied when the controller  250  detects errors. 
     The channel types of the first and second transistors  253  and  254  are not limited to the foregoing channels. If the channel types are changed with each other, the current flowing therebetween may be reverse according to the control signal. 
       FIG. 4  is a control block diagram of a display apparatus according to a third exemplary embodiment of the present invention. As shown therein, the display apparatus according to the present embodiment further includes an error informer  260  and an interface  270 . 
     If point light sources  210   a  are open or short-circuit to generate errors, the error informer  260  displays the error occurrence so that a user recognizes the errors of the light source  210 . The error informer  260  may include a light emitting diode (LED) which flickers when the errors occur, or a sound output unit which outputs siren or particular sound when the errors occur. The error informer  260  may include a UI (user interface) generator to display UI information on the errors of the backlight unit, on the display panel  100 . The UI information includes the error occurrence, the types of the errors and the light source modules  211  to  215  having the errors. The information on the light source modules  211  to  215  refer to information on a physical position of the light source modules  211  to  215  so that a user recognizes the specific light source module having the errors, among the plurality of light source modules  211  to  215 . 
     If the errors occur in the light source modules  211  to  215 , the interface  270  may transmit information of the error occurrence or the light source modules  211  to  215  having the errors. The information is stored in the storage unit  257 , and may be transmitted to the outside through the interface  270  automatically or by user&#39;s selecting. The interface  270  may include a wired/wireless LAN unit for wired/wireless communication, a wireless communication unit such as Bluetooth, or a storage medium connector such as a memory card slot and a USB port. Through the interface  270 , a use may inform the errors occurring in the backlight unit  200  to a service center, etc. 
       FIG. 5  is a control flowchart to describe a control method of the display apparatus according to an exemplary embodiment of the present invention. The control method of the display apparatus will be described with reference to  FIG. 5 . 
     First, the controller  250  turns off the switch to detect the errors (S 10 ). The switch may include the relay switch  251 , and the transistors  253  and  254 . If the switch is turned off, power is supplied through the resistor  241  connected between the power source  230  and the light source driver  220 . 
     The controller  250  controls the light source driver  220  to sequentially drive the light source modules  211  to  215  and detects the errors, and power is sequentially supplied to the driving modules  221  to  225 , starting from an “i” th driving module (S 20 ). 
     The current detector  240  detects the current of power supplied to the “i” th driving module by the power source  230  (S 30 ), and the controller  250  determines whether the voltage corresponding to the detected current is within the preset acceptable range (S 40 ). 
     If the voltage corresponding to the detected current is not within the acceptable range, i.e., if an over current flows, a current lower than the reference voltage flows or if the current is not detected, the controller  250  determines that the errors occur in the “i” th light source module and stores the error occurrence in the storage unit  257  (S 50 ). Then, the controller  250  determines whether the “i” corresponds to N, the number of the light source modules (S 60 ). 
     If the voltage corresponding to the detected current is within the acceptable range, the controller  250  also determines whether “i” corresponds to N, the number of the light source modules (S 60 ). 
     If “i” is not N, the controller  250  controls to supply power to a subsequent driving module, i.e., an “i+1” th driving module (S 70 ) and repeats the operation after the current detection. 
     If “i” corresponds to N, the controller  250  determines whether all the light source modules  211  to  215  are in the normal state (S 80 ). If errors are found even in a single light source module, power supplied to the light source driver  220  is cut off (S 90 ). According to another control method, if errors are found in the predetermined number or more of the light source modules, instead of in a single light source module, power supplied to the light source driver  220  may be cut off. 
     If errors occur in the light source modules  211  to  215 , the present invention may further include an operation of informing the error occurrence to a user and transmitting the error occurrence to the outside. 
       FIG. 6  is a control block diagram of a backlight unit of a display apparatus according to a fourth exemplary embodiment of the present invention. As shown therein, the backlight unit includes a light source  210 , a light source driver  220 , a power source  230 , an error detector  280  and a controller  290  which controls the foregoing elements. Description of the light source  210 , the light source driver  220  and the power source  230  are omitted since it is repetitive. 
     The error detector  280  detects a current flowing between the power source  230  and the light source driver  220 , and individually detects errors of the light source modules  211  to  215 . The error detector  280  includes a hall sensor  281  corresponding to the current detector  240 , and a comparator  282 . If the error detector  280  includes the hall sensor  281 , it does not include the resistor. Thus, the error detector  280  may accurately detect the current while not affecting the flow of the current. If the hall sensor  281  is used, the error detector  280  does not need to include switching elements  251 ,  253  and  254  to change the supply path of power. The error detector  280  may include a single chip, or a chip integrated with the controller  290 . 
     If the error detector  280  detects the errors of the light source modules  211  to  215 , the controller  290  stores error occurrence information, and the information on the types of the errors and the light source modules  211  to  215  having the errors in the storage unit  257 , and cuts off power supplied to the light source driver  220  from the power source  230 . 
     As described above, an exemplary embodiment of the present invention provides a backlight unit which detects errors of a light source without difficulty, a display apparatus comprising the same and a control method thereof. 
     Also, an exemplary embodiment of the present invention provides a backlight unit which informs errors of a light source to a user without difficulty, a display apparatus comprising the same and a control method thereof. 
     Further, an exemplary embodiment of the present invention provides a backlight unit which has a simple configuration and reduces production costs, a display apparatus comprising the same and a control method thereof. 
     Although a few exemplary embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these exemplary embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.