Patent Publication Number: US-10319328-B2

Title: Display device and method of driving the same

Description:
This application claims the benefit of priority from Korean Patent Application No. 10-2017-0048336, filed on Apr. 14, 2017, in the Korean intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present inventive concept relates to a display device and a method of driving the same. 
     Discussion of the Related Art 
     Display devices such as a liquid crystal display (LCD) and an organic light emitting diode display (OLED) have become popular and continue to be actively developed. 
     An LCD obtains a desired image by applying an electric field to a liquid crystal layer interposed between two display panels and adjusting the intensity of the electric field to control the transmittance of light passing through the liquid crystal layer. An OLED displays characters or images using electroluminescence of specific organic materials or polymers. 
     With regard to such display devices, an LCD includes an image display unit having pixels including switching elements and a pixel driving unit having various circuits and integrated circuits for generating signals used for driving each pixel included in the image display unit. 
     The pixel driving unit includes a scan driver which provides a scan signal to each pixel, a data driver which provides a data voltage to each pixel, a gamma voltage generator which provides a voltage to the data driver, and a signal controller which controls the scan driver, the data driver and the gamma voltage generator. 
     The data driver converts digital image data that is received from the signal controller in a digital format into an analog data signal in an analog format based on a gray voltage output from the gamma voltage generator, and provides the analog data signal to the image display unit. 
     The data driver is composed of a plurality of data driving chips. Each data driving chip is connected to a predetermined number of data lines to provide data signals to the data lines. Accordingly, as the number of data lines increases, the number of data driving chips that are used to provide data signals increases. 
     However, since the manufacturing cost of the data driver composed of data driving chips is relatively higher than the costs of manufacturing a scan driver, (even if the number of scan lines that receive scan signals from the scan driver increases), the number of data lines that receive data signals from the data driver is designed to be minimized. 
     However, as the number of pixels controlled by one data line increases, the frequency of change of data signals provided to the data lines also increases sharply, which may cause the data driving chips to overheat and be damaged. In other words, the data driver may overheat and be damaged. 
     Accordingly, there is a need in art to design a display device that can prevent overheating of the data driver while increasing the number of pixels controlled by one data line, and a method of driving the display device. 
     SUMMARY 
     The inventive concept provides a display device having a structure which can prevent overheating of a data driver. 
     The inventive concept also provides a method of driving a display device which can prevent overheating of a data driver. 
     However, the inventive concept is not limited to the embodiments shown and described herein. The inventive concept will become more apparent to one of ordinary skill in the art to which the inventive concept pertains by referencing the detailed description of the inventive concept given below. 
     According to the inventive concept, there is provided a display device. The display device comprises a detector which calculates (detects) the number of toggles in which the amount of change in gray values of successive pixels driven by the same data line in one frame is equal to or greater than a reference gray change amount, a comparator which compares the number of toggles detected by the detector with a reference number of toggles, and a lookup table selector which selects any one of a first lookup table and a second lookup table based on the comparison result of the comparator and provides the selected first lookup table or second lookup table to a data driver. 
     According to the inventive concept, there is provided a display device. The display device comprises a detector which detects the number of toggles in which the amount of change in gray values of successive pixels driven by the same data line in one frame is equal to or greater than a reference gray change amount, a comparator which compares the number of toggles detected by the detector with a reference number of toggles, and a driving voltage converter which controls a data driver to be driven using any one of a first driving voltage and a second driving voltage based on the comparison result of the comparator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The inventive concept will become better appreciated by a person of ordinary skill in the art from the following description of the embodiments, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a block diagram of a liquid crystal display (LCD) according to an embodiment of the inventive concept; 
         FIG. 2  is an equivalent circuit diagram of one pixel of the LCD according to the embodiment of  FIG. 1 ; 
         FIG. 3  is a block diagram of a signal controller according to an embodiment of the inventive concept; 
         FIG. 4  is a schematic diagram illustrating some pixels included in an image display unit of  FIG. 1  and signal lines connected to the pixels; 
         FIG. 5  is a waveform diagram of signals for driving the pixels of  FIG. 4  in an example where a first lookup table is used; 
         FIG. 6  illustrates the first lookup table; 
         FIG. 7  is a waveform diagram of the signals for driving the pixels of  FIG. 4  in an example where a second lookup table is used; 
         FIG. 8  illustrates the second lookup table; 
         FIG. 9  is a flowchart illustrating the operation of an overheat prevention circuit of the display device according to the embodiment of  FIG. 3 ; 
         FIG. 10  is a block diagram of a signal controller according to an embodiment of the inventive concept; 
         FIG. 11  is a waveform diagram of six pixels corresponding to the pixels of  FIG. 4  in a display device according to the embodiment of  FIG. 10 ; 
         FIG. 12  is a flowchart illustrating the operation of an overheat prevention circuit according to the embodiment of  FIG. 10 ; 
         FIG. 13  is a block diagram of a signal controller according to an embodiment of the inventive concept; 
         FIG. 14  is a waveform diagram of six pixels corresponding to the pixels of  FIG. 4  in a display device according to the embodiment of  FIG. 13 ; 
         FIG. 15  is a flowchart illustrating the operation of an overheat prevention circuit according to the embodiment of  FIG. 13 ; 
         FIG. 16  is a flowchart illustrating the operation of an overheat prevention circuit according to an embodiment of the inventive concept; and 
         FIG. 17  is a flowchart illustrating the operation of an overheat prevention circuit according to an embodiment of the inventive concept. 
     
    
    
     DETAILED DESCRIPTION 
     The present inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. The same reference numbers indicate the same components throughout the specification. In the attached figures, the thickness of layers and regions is exaggerated for clarity. 
     It will be understood by persons of ordinary skill in the art that, although the terms first, second, third, etc., may be used herein to describe various elements, these elements are not be limited by these terms. These terms are only used to distinguish one element from another element. Thus, a first element discussed below could be termed a second element without departing from the teachings of the inventive concept. 
     The terminology used herein is for the purpose of describing particular embodiments only and is the inventive concept is limited thereby. As used herein, the singular forms “a,”, “an” and “the” are intended to include the plural forms, including “at least one”, unless the content clearly indicates otherwise. “Or” means “and/or.” As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be further understood by persons of ordinary skill in the art that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof. 
     Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood by persons of ordinary skill in the art that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly. 
     In the present inventive concept, an electronic apparatus may be any apparatus provided with a display device. Examples of the electronic apparatus may include but are not limited to smart phones, mobile phones, navigators, game machines, TVs, car head units, notebook computers, laptop computers, tablet computers, personal media players (PMPs), and personal digital assistants (PDAs). The electronic apparatus may be embodied as a pocket-sized portable communication terminal having a wireless communication function. Further, the display device may be a flexible display device capable of changing its shape. 
     Hereinafter, embodiments of the present inventive concept will now be described with reference to the attached drawings. 
       FIG. 1  is a block diagram of an LCD according to an embodiment of the inventive concept. 
     Referring now to  FIG. 1 , the LCD according to the embodiment includes an image display unit PU and a pixel driving unit DU. 
     The image display unit PU includes a plurality of scan lines SL 1  through SLn, a plurality of data lines DL 1  through DLm, and a plurality of pixels PX. The pixels PX are connected to the scan lines SL 1  through SLu and the data lines DL 1  through DLm and are arranged in a substantially matrix form. The scan lines SL 1  through SLn extend substantially in a row direction so as to be substantially parallel to each other. The data lines DL 1  through DLm extend substantially in a column direction to be substantially parallel to each other. The data lines and the scan lines are substantially orthogonal to each other. 
     Although only the scan lines SL 1  through SLn and the data lines DL 1  through DLm are connected to the pixels PX in the drawing, various signal lines can be additionally connected to the pixels PX depending on the structure or driving method of the pixels PX. 
     The pixel driving unit DU comprises hardware including a signal controller  100 , a scan driver  200 , a data driver  300 , a gray voltage generator  400 , and a power supply unit  500 . Each component of the pixel driving unit DU may be connected, as an integrated circuit, to a display panel (not illustrated) having the image display unit PU by a tape carrier package (TCP). Alternatively, a circuit may be directly formed in an area of the display panel where the pixels PX are not formed. 
     The signal controller  100  receives input control signals including an image signal R, G, B, a data enable signal DE, a horizontal synchronization signal Hsync, a vertical synchronization signal Vsync, and a main clock signal MCLK. 
     The image signal R, G, B includes information about luminance levels of a plurality of pixels. For example, the luminance levels may correspond to a predetermined number of gray levels, for example, 1024 (=210), 256 (=28), or 64 (=26) gray levels, respectively. The image signal R, G, B may be converted by the signal controller  100  into an image data signal DATA including information about gray levels that should used by the pixels PX for display. 
     With continued reference to  FIG. 1 , the signal controller  100  generates a scan driver control signal CONT 1 , a data driver control signal CONT 2 , a gray voltage generator control signal CONT 3 , a power supply unit control signal CONT 4 , and the image data signal DATA in response to the image signal R, G, B, the data enable signal DE, the horizontal synchronization signal Hsync, the vertical synchronization signal Vsync and the main clock signal MCLK. 
     The signal controller  100  provides the image data signal DATA, the data driver control signal CONT 2 , and a lookup table selection signal LSS to the data driver  300 . The data driver control signal CONT 2  is a signal that controls the operation of the data driver  300  and may include a horizontal synchronization start signal (not illustrated) for notifying the start of transmission of the image data signal DATA, a load signal (not illustrated) for instructing the output of data signals D 1  through Dm to the data lines DL 1  through DLm, and a data clock signal (not illustrated). The data driver control signal CONT 2  may further include, for example, an inversion signal (not illustrated) for inverting the voltage polarity of the image data signal DATA with respect to a common voltage (not illustrated). 
     The lookup table selection signal LSS includes, for example, information about voltage levels of the data signals D 1  through Dm that the data driver  300  should provide to the image display unit PU based on gray values included in the image data signal DATA. This part of the inventive concept will be described in detail later. 
     The signal controller  100  provides the scan driver control signal CONT 1  to the scan driver  200 . The scan driver control signal CONT 1  may include, for example, one or more signals that may be commands, e.g. a scan start signal (not illustrated) for the scan driver  200 , and may include at least one clock signal for controlling the output of scan-on voltages which are on-state voltages of scan signals S 1  through Sn. The scan driver control signal CONT 1  may further include an output enable signal (not illustrated) that may limit a duration of the scan-on voltages to periods when the output enable signal is at a predetermined logic level, or for example, activates a latch. 
     The data driver  300  is connected to the data lines DL 1  through DLm disposed in the image display unit PU and receives the reference gray voltages VGMA from the gray voltage generator  400 . The data driver  300  processes the received reference gray voltages VGMA and provides the processed reference gray voltages VGMA to the data lines DL 1  through DLm as the data signals D 1  through Dm. To simplify construction, it is within the inventive concept that the gray voltage generator  400  may provide only a predetermined number of reference gray voltages VGMA instead of providing voltages for all gray levels. Here, the data driver  300  may divide the reference gray voltages VGMA into gray voltages for all gray levels and select the data signals D 1  through Dm from the gray voltages for all gray levels. 
     The scan driver  200  provides the scan lines SL 1  through SLn with the scan signals S 1  through Sn, each composed of a scan-on voltage for turning on switching elements Qpx (see  FIG. 2 ) connected to one of the scan lines SL 1  through SLn of the image display unit PU and a scan-off voltage for turning off the switching elements Qpx. 
     The power supply unit  500  receives a power supply voltage VDD from an external source and receives the power supply unit control signal CONT 4  from the signal controller  100 . The power supply unit  500  converts the power supply voltage VDD and provides the converted power supply voltage VDD to the scan driver  200  and the gray voltage generator  400 . The power supply unit  500  provides a scan-on voltage Von and a scan-off voltage Voff to the scan driver  200  and a driving voltage AVDD to the gray voltage generator  400 . 
     The gray voltage generator  400  receives the scan driver control signal CONT 3  from the signal controller  100  and receives the driving voltage AVDD from the power supply unit  500 . Then, the gray voltage generator  400  generates a plurality of reference gray voltages VGMA and provides the generated reference gray voltages VGMA to the data driver  300 . 
       FIG. 2  is an equivalent circuit diagram of one pixel of the LCD such as shown in the embodiment of  FIG. 1 . 
     Referring now to  FIG. 2 , a pixel PX includes a first substrate  210  on which a switching element Qpx and a pixel electrode PE are formed, a second substrate  220  on which a color filter CF and a common electrode CE are formed, and liquid crystal molecules LC interposed between the first substrate  210  and the second substrate  220 . The color filter CF faces the pixel electrode PE of the first substrate  210 . In the current embodiment, the color filter CF is formed on the second substrate  220 . However, the color filter CF may be formed on the first substrate  210 . 
     A pixel PXij connected to an i th  scan line SLi (where i is one of 1 through n) and a j th  data line DLj (where j is one of 1 through m) includes a switching element Qpx connected to the i th  scan line SLi and the j th  data line DLj and a liquid crystal capacitor Clc and a storage capacitor Cst connected to the switching element Qpx. The storage capacitor Cst can be omitted. The construction may employ thin-film technology, for example, the switching element Qpx may be a thin-film transistor. 
       FIG. 3  is a block diagram of a signal controller  100  according to an embodiment of the inventive concept.  FIG. 4  is a schematic diagram illustrating some pixels included in the image display unit of  FIG. 1  and signal lines connected to the pixels.  FIG. 5  is a waveform diagram of signals for driving the pixels of  FIG. 4  in a case where a first lookup table LUT 1  is used.  FIG. 6  illustrates the first lookup table LUT 1 .  FIG. 7  is a waveform diagram of the signals for driving the pixels of  FIG. 4  in a case where a second lookup table LUT 2  is used.  FIG. 8  illustrates the second lookup table LUT 2 . 
     Referring now to  FIG. 3 , the signal controller  100  may include an image signal conversion unit  110  and an overheat prevention unit  120  (hereinafter overheat prevention circuit  120 ). In  FIG. 3 , signals related to particularly the overheat prevention circuit  120  of the signal controller  100  are mainly illustrated, and other components are omitted. 
     The image signal conversion unit  110  may convert the image signal R, G, B received from an external source into the image data signal DATA including information about gray levels that the pixels PX should actually display and provide the image data signal DATA to the data driver  300 . In addition, the image signal conversion unit  110  may provide the image data signal DATA to the overheat prevention circuit  120 . 
     The overheat prevention circuit  120  receives the image data signal DATA from the image signal conversion unit  110  and analyzes the image data signal DATA to perform compensation for preventing the overheating of the data driver  300 . If the image data signal DATA includes a pattern or an image that will cause the data driver  300  to overheat, the overheat prevention circuit  120  detects the pattern or the image and changes a lookup table used for driving the data driver  300 , thereby preventing the data driver  300  from overheating. 
     More specifically, the overheat prevention unit  120  may include a detector  121 , a comparator  122 , and a lookup table selector  123 . 
     With continued reference to  FIG. 3 , the detector  121  receives the image data signal DATA from the image signal conversion unit  110 , analyzes an image displayed in each frame, and detects the number of toggles. A person of ordinary skill the art should understand that a toggle is defined as a case where the amount of change (e.g. Δ gray levels) in gray levels of successive pixels controlled by the same data line (one of DL 1  through DLm) is equal to or greater than a reference gray change amount. The reference gray change amount may be defined as a gray change amount (e.g. Δ gray levels) by which the gray levels of successive pixels PX are changed to 90% or more of a maximum gray level. As the number of toggles detected while one frame is displayed increases, the amount of change in the gray levels of successive pixels PX may often be large, and may be relatively larger than a case where the number of toggles while one frame is displayed decreases or remains about the same. In addition, as the amount of change in the gray levels of the successive pixels PX becomes larger, a data signal (one of D 1  through Dm) provided to a corresponding data line (one of DL 1  through DLm) may be changed significantly and frequently. Therefore, the data driver  300  can become overloaded and may overheat, adversely affecting the operation of the data driver and may cause damage to the data driver. In this regard, the number of toggles occurring in one frame may be detected in advance using the image data signal DATA to predict whether the data driver  300  will overheat. When there is, for example, an increased likelihood that overheating of the data driver may occur, some preemptive operations may prevent or delay the driver from overheating. 
     According to the inventive concept, the toggles will now be described in more detail with reference to  FIGS. 4 and 5 . 
       FIG. 4  illustrates a group of six pixels PX 1  through PX 6  whose gray levels are controlled by the first data line DL 1 . The six pixels PX 1  through PX 6  will be named as a first pixel PX 1 , a second pixel PX 2 , a third pixel PX 3 , a fourth pixel PX 4 , a fifth pixel PX 5  and a sixth pixel PX 6  and may be controlled by the first through sixth scan lines SL 1  through SL 6 , respectively. In this example, the first through sixth pixels PX 1  through PX 6  may correspond to pixels PX arranged in a first row and a first column through a sixth row and the first column among the pixels PX arranged in the image display unit PU according to the embodiment of  FIG 1 . 
     As can be seen in  FIG. 4 , long axes of the first through sixth pixels PX 1  through PX 6  may be parallel to a direction in which the first through sixth scan lines SL 1  through SL 6  extend, and short axes of the first through sixth pixels PX 1  through PX 6  may be parallel to a direction in which the first data line DL 1  extends. Accordingly, from the viewpoint of  FIG. 4 , the first through sixth pixels PX 1  through PX 6  may be relatively longer in a horizontal direction than in a vertical direction, and three pixels PX successively arranged in the vertical direction may form a shape close to a square. Three pixels PX arranged in the vertical direction may form one upper pixel UPX 1  or UPX 2  defined as a minimum unit whose color can be controlled. A group of the first through third pixels PX 1  through PX may be defined as a first upper pixel UPX 1 , and a group of the fourth through sixth pixels PX 4  through PX 6  may be defined as a second upper pixel UPX 2 . 
     In the non-limiting example shown in  FIG. 4 , the first pixel PX 1  and the fourth pixel PX 4  may display blue, the second pixel PX 2  and the fifth pixel PX 5  may display green, and the third pixel PX 3  and the sixth pixel PX 6  may display red. However, the inventive concept is broader than as shown in  FIG. 4 , and the colors displayed by the first through sixth pixels PX 1  through PX 6  may be changed. In addition, one upper pixel is not necessarily composed of three pixels PX but may also be composed of a quantity of pixels PX other than three. 
       FIG. 5  illustrates waveforms of the first through sixth scan signals S 1  through S 6  illustrated in  FIG. 4  provided to the first through sixth scan lines SL 1  through SL 6 . The first data signal D 1  is provided to the first data line DL 1  in a case where the two upper pixels UPX 1  and UPX 2  illustrated in  FIG. 4  display cyan. Cyan is a color that is displayed when blue and green are mixed. Therefore, it is assumed that the cyan color illustrated in  FIG. 5  is displayed when the first pixel PX 1  and the fourth pixel PX 4 , which are blue, emit light at a maximum gray level, the second pixel PX 2  and the fifth pixel PX 5 , which are green, emit light at the maximum gray level, and the third pixel PX 3  and the sixth pixel PX 6 , which are red, emit light at a minimum gray level. 
     In addition, it is assumed that the first through sixth pixels PX 1  through PX 6  shown in  FIG. 4  are driven sequentially, and elements of row inversion driving, column inversion driving, and dot inversion driving will be excluded from the following description. Although the elements of the row inversion driving, the column inversion driving and the dot inversion driving are omitted, the concept of such inversion driving can be applied to determine the waveform of each of the data signals D 1  through Dm and the waveform of each of the scan signals S 1  through Sn. However, even if the concept of the inversion driving is applied, the same effect of suppressing heat generation according to the inventive concept can be brought about. 
     First, assuming that a reference voltage of the first data signal D 1  transmitted to the first data line DL 1  is 0 [V], when the first pixel PX 1  displays blue of the maximum gray level, the first data signal D 1  is changed by Vm 2  [V] from 0 [V] to Vm 2  [V]. In addition, when the second pixel PX 2  displays green of the maximum gray level, the first data signal D 1  is changed by Vm 1 -Vm 2  [V] from Vm 2  [V] to Vm 1  [V] (the reason why a voltage level of the first data signal D 1  which corresponds to the maximum gray level of blue is different from a voltage level of the first data signal D 1  which corresponds to the maximum gray level of green will be described later). Also, when the third pixel PX 3  displays red of the minimum gray level, the first data signal D 1  is changed by Vm 1  [V] from Vm 1  [V] to 0 [V]. 
     For example, when the first upper pixel UPX 1  emits cyan light of the maximum gray level, the first pixel PX 1 , the second pixel PX 2  and the third pixel PX 3  constituting the first upper pixel UPX 1  emit red light of the maximum gray level, green light of the maximum gray level, and red light of the minimum gray level, respectively. Therefore, one toggle occurs in the process in which the first pixel PX 1  displays the blue of the maximum gray level, and one toggle occurs in the process in which the third pixel PX 3  displays the red of the minimum gray level. In the process in which the second pixel PX 2  displays the green of the maximum gray level, the amount of change in the voltage level of the first data signal D 1  is not large because the first pixel PX 1  which is a previous pixel is already displaying the blue of the maximum gray level. Therefore, no toggle may occur. Consequently, when the first upper pixel UPX 1  emits the cyan light of the maximum gray level, two toggles occur. 
     Similarly, when the second upper pixel UPX 2  emits the cyan light of the maximum gray level, two toggles occur while the fourth pixel PX 4 , the fifth pixel PX 5 , and the sixth pixel PX 6  are driven. 
     For example, when x pixels PX (where x is a natural number which is a multiple of 3) display the cyan color of the maximum gray level, a total of x*⅔) toggles may occur. 
     The same concept may be applied not only to a case where cyan is displayed, but also to a case where magenta or yellow is displayed, or to cases where red, blue and green monochromatic colors are displayed. For example, when any one of cyan, magenta, yellow, and red, blue and green monochromatic colors is displayed, a total of (x*⅔) toggles may occur per x pixels PX even if the timing of a toggle is different. 
     The comparator  122  ( FIG. 3 ) receives information about the number of toggles included in each frame from the detector  121 , determines whether the number of toggles included in each frame is equal to or greater than a reference number of toggles, and provides information about the comparison result to the lookup table selector  123 . 
     Here, the reference number of toggles is defined as the number of toggles included in one frame that may cause the data driver  300  to overheat. The reference number of toggles may be initially set at the time of production of a display device, and its value may be modified by changing settings even after production of the display device. For example, a value (e.g., a total number of the pixels PX) obtained by multiplying the number of the data lines DL 1  through DLm connected to the data driver  300  by the number of the scan lines SL 1  through SLn connected to the scan driver  200 , may be multiplied by ⅔, which is a ratio of the number of toggles occurring when a monochromatic color is displayed to the total number of the pixels PX, and may be additionally multiplied by 0.7, which is the proportion of an area occupied by the monochromatic color in the entire image. Then, the multiplication result may be determined as the reference number of toggles. The criterion for determining the proportion as 0.7 will be described later. For example, when the number of toggles included in one frame is (m*n*⅔*0.7) or more, the data driver  300  can overheat. According to the inventive concept, the data driving may be performed in a way that prevents overheating. A person of ordinary skill in the art should appreciate that in the inventive concept, the reference number of toggles is not limited to the above example and can be changed to other values. More specifically, when the data driver  300  is manufactured, for example, using a plurality of data driving chips, the reference number of toggles may be determined in consideration of the number of data lines (some of DL 1  through DLm) connected to one driving chip, so that heat generation can be managed on a data driving chip-by-data driving chip basis. In addition, the number of the scan lines SL 1  through SLn, the ratio of the number of toggles to the total number of the pixels PX, and the proportion of the area occupied by the monochromatic color in the entire image can all be changed. This concept will be subsequently described herein in more detail. 
     With reference to  FIG. 3 , the lookup table selector  123  receives from the comparator  122  information about whether the number of toggles included in each frame is equal to or greater than the reference number of toggles, selects any one of a plurality of lookup tables LUT 1  and LUT 2  based on the received information, and provides the selected lookup table LUT 1  or LUT 2  to the data driver  300 . The information about the selected lookup table LUT 1  or LUT 2  provided to the data driver  300  may be the lookup table selection signal LSS. 
     The lookup table selector  123  may store information about the first lookup table LUT 1  and the second lookup table LUT 2 . Here, each of the first lookup table LUT 1  and the second lookup table LUT 2  includes information about values of voltage levels that the data driver  300  should actually output to the data lines DL 1  through DLm as the data signals D 1  through Dm based on gray values included in the image data signal DATA received from the signal controller  100 . The first lookup table LUT 1  and the second lookup table LUT 2  may not necessarily be stored in the lookup table selector  123 , and a separate memory (not illustrated) can be provided outside the signal controller  100  and connected to the lookup table selector  123 , so that the information about the first lookup table LUT 1  and the second lookup table LUT 2  can be retrieved from the external memory. The information about the first lookup table LUT 1  and the second lookup table LUT 2  may be descriptive, or cumulative, in the event that the actual lookup tables are not stored in the lookup table selector  123 . In addition, while lookup tables are used because in general there is faster access, a person of ordinary skill in the art should understand and appreciate that according to the inventive concept that there are other ways that the values may be stored in addition to or instead of a lookup table. 
     The first and second lookup tables LUT 1  and LUT 2  will now be described with reference to  FIGS. 6 through 8 . 
     Referring to  FIG. 6 , in the first lookup table LUT 1 , the data signals D 1  through Dm having the same voltage level are set to be output for all of blue, green and red for gray levels of 0 to 243. However, for gray levels of 245 and above, the data signals D 1  through Dm having relatively lower voltage levels are set to be output for blue than for green and red. In an example, for a maximum gray level of 255, the data signals D 1  through Dm having a voltage level corresponding to 245 are output for blue, but the data signals D 1  through Dm having a voltage level corresponding to 255 are output for green and red, 
     On the other hand, referring now to  FIG. 8 , in the second lookup table LUT 2 , the data signals D 1  through Dm having the same voltage level are set to be output for blue, green and red for all gray levels of 0 to 255. 
     Therefore when the data driver  300  is driven using the first lookup table LUT 1 , the data signals D 1  through Dm having a relatively lower voltage level may be output when pixels PX displaying blue have a maximum gray value than when pixels PX displaying green and red have the maximum gray value. On the other hand, when the data driver  300  is driven using the second lookup table LUT 2 , the data signals D 1  through Dm having the same voltage level may be output when the pixels PX displaying blue, green and red have the maximum gray value. 
     For example, when the first lookup table LUT 1  is used, the data signals D 1  through Dm for the pixels PX displaying blue of the maximum gray value may be adjusted to have a relatively lower voltage level than that of the data signals D 1  through Dm for the pixels PX displaying red and green of the maximum gray value. On the other hand, when the second lookup table LUT 2  is used, such adjustment may not be performed. The adjustment is a correction made because the pixels PX displaying blue look relatively bright compared with pixels display other colors even if they receive the data signals D 1  through Dm having the same voltage level as that of the data signals D 1  through Dm transmitted to the pixels PX displaying green and red. Specifically, when the second lookup table LUT 2  is used, the voltage level of the data signals D 1  through Dm corresponding to the gray value of the image data signal DATA for the pixels PX displaying blue may be lowered (corrected) to be in a normal color gamut range to correct a phenomenon in which blue is viewed out of the normal gamut range as the gray value becomes closer to the maximum gray value. 
     Therefore, when the data driver  300  is driven using the first lookup table LUT 1 , even if two successive pixels PX are driven to have the maximum gray value, a data signal (one of D 1  through Dm) may be changed if any one of the two pixels displays blue. This change in the data signal may be one of the factors that cause the data driver  300  to generate heat. Therefore, when the data driver  300  is driven using the second lookup table LUT 2 , heat generation can be reduced compared with when the data driver  300  is driven using the first lookup table LUT 1 . 
     Hence, when the lookup table selector  123  receives from the comparator  122  information indicating that the number of toggles included in each frame is equal to or greater than the reference number of toggles, there can be a selection for the data driver  300  to be driven based on the first lookup table LUT 1  to be driven based on the second lookup table LUT 2 . Accordingly, the beat generation of the data driver  300  can be reduced. 
     The values shown in the first lookup table LUT 1  and the second lookup table LUT 2  of  FIGS. 6 and 8  are exemplary values, and actual values can be changed depending on a degree of correction. For example, an output gray value converted from each gray value corresponding to 90% or more of the maximum gray value of blue included in the first lookup table LUT 1  may be smaller than an output gray value converted from each gray value corresponding to 90% or more of the maximum gray value of red and green included in the first lookup table LUT 1 . 
     Controlling heat generation by selecting the first lookup table LUT 1  or the second lookup table LUT 2  can be more clearly understood by comparing  FIG. 5  with  FIG. 7 . 
     As described above,  FIG. 5  is a waveform diagram of signals for driving the pixels such as shown in  FIG. 4  in a case where the first lookup table LUT 1  is used, and  FIG. 7  is a waveform diagram of the signals for driving the pixels of  FIG. 4  in a case where the second lookup table LUT  2  is used. 
     Similarly to  FIG. 5 ,  FIG. 7  illustrates waveforms of the first through sixth scan signals S 1  through S 6  provided to the first through sixth scan lines SL 1  through SL 6  and the first data signal D 1  provided to the first data line DL 1  in a case where the two upper pixels UPX 1  and UPX 2  illustrated in  FIG. 4  display cyan. Cyan is a color displayed when blue and green are mixed. Therefore, it is assumed that the waveforms illustrated in  FIG. 7  correspond to when the color cyan is displayed. For example, when the first pixel PX 1  and the fourth pixel PX 4 , which are blue, emit light at the maximum gray level, the second pixel PX 2  and the fifth pixel PX 5 , which are green, emit light at the maximum gray level, and the third pixel PX 3  and the sixth pixel PX 6 , which are red, emit light at the minimum gray level. 
     For example, assuming that the reference voltage of the first data signal D 1  transmitted to the first data line DL 1  is 0 [V], when the first pixel PX 1  displays blue of the maximum gray level, the first data signal D 1  is changed by Vm 1  [V] from 0 [V] to Vm 1  [V]. In addition, when the second pixel PX 2  displays green of the maximum gray level, the first data signal D 1  is not changed but is maintained at Vm 1  [V], which is different from the waveform diagram of  FIG. 5 . Also, when the third pixel PX 3  displays red of the minimum gray level, the first data signal D 1  is changed by Vm 1  [V] from Vm 1  [V] to 0 [V]. 
     As described above, according to the inventive concept, when cyan is displayed, if the data driver  300  is driven using the second lookup table LUT 2 , the pixels PX displaying blue at the maximum gray value are not corrected. Thus, heat generation can be reduced. Specifically, when cyan is displayed based on the second lookup table LUT 2 , two toggles occur per one upper pixel UPX 1  or UPX 2  as when based on the first lookup table LUT 1 . However, since the data signals D 1  through Dm are not changed at the time of conversion from the maximum gray level of blue to the maximum gray level of green, the load on the data driver  300  is reduced, thereby reducing heat generation. 
     In addition, the reason why a value obtained by multiplying the number of toggles by 0.7, which is the proportion of the area occupied by a monochromatic color in the entire image, is determined as the reference number of toggles will now be described with reference to Table 1 below. 
     Table 1 below shows values obtained by measuring the temperature of the data driver  300  according to the proportion of the area occupied by a monochromatic color in the image display unit PU when the data driver  300  is driven using the first lookup table LUT 1 . The data driver  300  is composed of a total of four data driving chips which will be referred to as a first data driver DDI 1 , a second data driver DDI 2 , a third data driver DDI 3 , and a fourth data driver DDI 4 , respectively. Each of the first through fourth data drivers DDI 1  through DDI 4  may correspond to a separate data driving chip. 
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 0% 
                 50% 
                 60% 
                 65% 
                 70% 
                 80% 
                 90% 
                 100% 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 DDI 1 
                 89.65 
                 121.7 
                 134.6 
                 138.1 
                 140.2 
                 144.4 
                 161.3 
                 168.1 
               
               
                 DDI 2 
                 88.1 
                 130 
                 135.1 
                 141.3 
                 142.3 
                 152.6 
                 165.8 
                 176 
               
               
                 DDI 3 
                 90.1 
                 130 
                 136.8 
                 142.5 
                 143.8 
                 153.2 
                 169.1 
                 173.5 
               
               
                 DDI 4 
                 88.2 
                 121.7 
                 135.2 
                 139.8 
                 141.9 
                 145.9 
                 163.2 
                 165.6 
               
               
                   
               
            
           
         
       
     
     First, when the proportion of the area occupied by the monochromatic color in the image display unit PU is 0%, all of the first through fourth data drivers DDI 1  through DDI 4  maintain a temperature of 100 degrees or below. In addition, the temperatures of the first through fourth data drivers DDI 1  through DDI 4  tend to increase as the proportion of the area occupied by the monochromatic color in the image display unit PU increases. 
     However, when the temperatures of the first through fourth data drivers DDI 1  through DDI 4  are 500 degrees or above, significant damage can be done to a display device. Therefore, the first through fourth data drivers DDI 1  through DDI 4  should be maintained at a temperature of 150 degrees or below. In this case, if the proportion of the area occupied by the monochromatic color in the image display unit PU is 80% or more, the temperatures of the second data drive driver DDI 2  and the third data drive driver DDI 4  exceed 150 degrees. Therefore, when the proportion of the area occupied by the monochromatic color in the image display unit PU is 70% or more, the data driver  300  may be controlled to be driven using the second lookup table LUT 2 , so that the heat generation of the data driver  300  can be minimized. 
     However, the proportion of the area occupied by the monochromatic color in the image display unit PU is not limited to 70% or more and can be changed to any rate when the maximum allowable temperature of the data driver  300  is set to a temperature other than 150 degrees or when the specifications of the data driving chips constituting the data driver  300  are changed. 
       FIG. 9  is a flowchart illustrating the operation of the overheat prevention circuit  120  of the display device according to the embodiment including the signal controller of  FIG. 3 . 
     Referring to  FIG. 9 , at operation (S 101 ), the detector  121  counts the number of toggles included in each frame by using the input image data signal DATA. 
     Next, at operation (S 102 ), the comparator  122  receives information about the number of toggles included in each frame from the detector  121  and determines whether the number of toggles included in each frame is equal to or greater than a reference number of toggles. 
     When it is determined at operation (S 102 ) that the number of toggles included in each frame is equal to or greater than the reference number of toggles then at operation (S 103 ) the lookup table selector  123  controls the data driver  300  to be operated using the value(s) of the second lookup table LUT 2 . On the contrary, when it is determined at operation (S 102 ) that the number of toggles included in each frame is not equal to or greater than the reference number of toggles, then at operation (S 1004 ) the lookup table selector  123  controls the data driver  300  to be operated using value(s) of the first lookup table LUT 1 . 
       FIG. 10  is a block diagram of a signal controller  100   a  according to an embodiment of the inventive concept. 
     The lookup table selector  123  included in the overheat prevention circuit  120  of  FIG. 3  is replaced by a driving voltage converter  124   a  in  FIG. 10 . Therefore, the differences of  FIG. 10  as compared with the embodiment of  FIG. 3  will hereinafter be mainly described, and a description of identical components will be omitted. 
     Referring now to  FIG. 10 , the signal controller  100   a  according to the current embodiment includes an image signal conversion unit  110  and an overheat prevention circuit  120   a.    
     The image signal conversion unit  110  is substantially the same or similar to that described above in the embodiment of  FIG. 3  and thus will not be described here. 
     The overheat prevention circuit  120   a  includes a detector  121 , a comparator  122 , and the driving voltage converter  124   a.    
     The detector  121  and the comparator  122  are substantially the same or similar to those described above in the embodiment of  FIG. 3  and thus will not be described here. 
     The driving voltage converter  124   a  receives from the comparator  122  information about whether the number of toggles included in each frame is equal to or greater than a reference number of toggles, generates a driving voltage conversion signal VCS, which determines the voltage level of a driving voltage applied by a power supply unit  500   a  to a gray voltage generator  400 , based on the received information, and provides the generated driving voltage conversion signal VCS to the power supply unit  500   a.    
     More specifically, the power supply unit  500   a  may provide any one of a first driving voltage AVDD 1  and a second driving voltage AVDD 2  to the gray voltage generator  400 . The first driving voltage AVDD 1  is generated when the number of toggles included in each frame is less than the reference number of toggles. On the other hand, the second driving voltage AVDD 2  is generated when the number of toggles included in each frame is equal to or greater than the reference number of toggles. For example, the first driving voltage AVDD 1  may be provided to the gray voltage generator  400  when the data driver  300  is not likely to overheat, and the second driving voltage AVDD 2  is provided to the gray voltage generator  400  when the data driver  300  is likely to overheat. 
     Here, an average voltage level of the second driving voltage AVDD 2  may be relatively lower than that of the first driving voltage AVDD 1 . The gray voltage generator  400  provides reference gray voltages VGMA (see  FIG. 1 ) to a data driver  300  based on the first driving voltage AVDD 1  or the second driving voltage AVDD 2 , and the data driver  300  generates data signals D 1  through Dm (see  FIG. 1 ) by using the reference gray voltages VGMA (see  FIG. 1 ). Therefore, voltage levels of the data signals D 1  through Dm (see  FIG. 1 ) may be relatively lower when the second driving voltage AVDD 2  is used than when the first driving voltage AVDD 1  is used. Accordingly, when the power supply unit  500   a  generates and outputs the second driving voltage AVDD 2 , the voltage levels of the data signals D 1  through Dm (see  FIG. 1 ) output from the data driver  300  may be lower than when the power supply unit  500   a  generates and outputs the first driving voltage AVDD 1 . 
     Moreover,  FIG. 11  is a waveform diagram of six pixels corresponding to the pixels of  FIG. 4  in a display device according to the embodiment of  FIG. 10 . 
     In  FIG. 11 , a voltage level represented by a first line L 1  is the voltage level of a first data signal D 1  in a case where the first driving voltage AVDD 1  is used, and a voltage level represented by a second line L 2  is the voltage level of the first data signal D 1  in a case where the driving voltage AVDD 2  is used. As in the embodiment of  FIG. 5 , it is assumed in  FIG. 11  that each of first through sixth pixels PX 1  through PX 6  displays cyan. 
     Referring to  FIG. 11 , when the first driving voltage AVDD 1  is used, a toggle occurs at a time when a first scan signal S 1  is turned on, resulting in a voltage change of Vm 2  [V], and a toggle occurs at a time when a third scan signal S 3  is turned on, resulting in a voltage change of Vm 1  [V]. Further, a toggle occurs at a time when a fourth scan signal S 4  is turned on, resulting in a voltage change of Vm 2  [V], and a toggle occurs at a time when a sixth scan signal S 6  is turned on, resulting in a voltage change of Vm 1  [V]. 
     On the other hand, when the second driving voltage AVDD 2  is used, a toggle occurs at the time when the first scan signal S 1  is turned on, resulting in a voltage change of Vm 4  [V], and a toggle occurs at the time when the third scan signal S 3  is turned on, resulting in a voltage change of Vm 3  [V]. Further, a toggle occurs at the time when the fourth scan signal S 4  is turned on, resulting in a voltage change of Vm 4  [V], and a toggle occurs at the time when the sixth scan signal S 6  is turned on, resulting in a voltage change of Vm 3  [V]. 
     Here, Vm 3  has a voltage value smaller than that of Vm 1 , and Vm 4  has a voltage value smaller than that of Vm 2 . Therefore, the amount of change in the first data signal D 1  may be smaller when the second driving voltage AVDD 2  is used, Accordingly, the heat generated from the data driver  300  can be reduced. 
       FIG. 12  is a flowchart illustrating the operation of the overheat prevention circuit  120   a  according to the embodiment of  FIG. 10 . 
     Referring to  FIG. 12 , at operation (S 201 ), the detector  121  counts the number of toggles included in each frame by using input image data signal DATA. 
     At operation (S 202 ), the comparator  122  receives information about the number of toggles included in each frame from the detector  121  and determines whether the number of toggles included in each frame is equal to or greater than a reference number of toggles. 
     When it is determined that the number of toggles included in each frame is equal to or greater than the reference number of toggles, at operation (S 203 ), the driving voltage converter  124   a  controls the power supply unit  500   a  to generate the second driving voltage AVDD 2 . 
     On the contrary, when it is determined that the number of toggles included in each frame is not equal to or greater than the reference number of toggles, at operation (S 204 ) the driving voltage converter  124   a  controls the power supply unit  500   a  to generate the first driving voltage AVDD 1 . 
       FIG. 13  is a block diagram of a signal controller  100   b  according to an embodiment of the inventive concept. 
     Referring now to  FIG. 13 , an overheat prevention circuit  120   b  according to the current embodiment includes both the lookup table selector  123  (see  FIG. 3 ) included in the overheat prevention circuit  120  (see  FIG. 3 ) according to the embodiment of  FIG. 3  and the driving voltage converter  124   a  (see  FIG. 10 ) included in the overheat prevention circuit  120   a  (see  FIG. 10 ) according to the embodiment of  FIG. 10 . For simplicity, a redundant description will be omitted. 
     Referring to  FIG. 13 , the signal controller  100   b  according to the current embodiment includes an image signal conversion unit  110  and the overheat prevention circuit  120   b.    
     The image signal conversion unit  110  is substantially the same or similar to that described above in the embodiment of  FIG. 3  and thus will not be described here. 
     The overheat prevention circuit  120   b  includes a detector  121 , a comparator  122 , the lookup table selector  123 , and the driving voltage converter  124   a.    
     The detector  121  and the comparator  122  are substantially the same or similar to those described above in the embodiment of  FIG. 3  and thus will not be described here. 
     The lookup table selector  123  receives from the comparator  122  information about whether the number of toggles included in each frame is equal to or greater than a reference number of toggles, selects any one of a plurality of lookup tables LU 1  and LUT 2  based on the received information, and provides the selected lookup table LUT 1  or LUT 2  to a data driver  300 . The information about the selected lookup table LUT 1  or LUT 2  provided to the data driver  300  may be a lookup table selection signal LSS. Since other details of the lookup table selector  123  have been described above in the embodiment of  FIG. 3 , they will not be described here. 
     The driving voltage converter  124   a  receives from the comparator  122  the information about whether the number of toggles included in each frame is equal to or greater than the reference number of toggles, generates a driving voltage conversion signal VCS, which determines the voltage level of a driving voltage applied by a power supply unit  500   a  to a gray voltage generator  400 , based on the received information, and provides the driving voltage conversion signal VCS to the power supply unit  500   a.  Since other details of the driving voltage converter  124   a  have been described above in the embodiment of  FIG. 10 , they will not be described here. 
     As described above, when the overheat prevention circuit  120   b  includes both the lookup table selector  123  and the driving voltage converter  124   a,  the overheat prevention effect can be maximized. This issue will be described in more detail by additionally referring to  FIG. 14 . 
       FIG. 14  is a waveform diagram of six pixels corresponding to the pixels of  FIG. 4  in a display device according to the embodiment such as shown in  FIG. 13 . 
     In  FIG. 14 , a voltage level represented by a third line L 3  is the voltage level of a first data signal D 1  in a case where a first driving voltage AVDD 1  and value(s) from the first lookup table LUT 1  are used, and a voltage level represented by a fourth line L 4  is the voltage level of the first data signal D 1  in a case where a second driving voltage AVDD 2  and value(s) from the second lookup table LUT 2  are used. As in the embodiment of  FIG. 5 , it is assumed in  FIG. 14  that each of first through sixth pixels PX 1  through PX 6  displays cyan. 
     Referring now to  FIG. 14 , the first data signal D 1  represented by the third line L 3  undergoes a voltage change of Vm 2  [V] at a time when a first scan signal S 1  is turned on, undergoes a voltage change of Vm 1 -Vm 2  [V] at a time when a second scan signal S 2  is turned on, and undergoes a voltage change of Vm 1  [V] at a time when a third scan signal S 3  is turned on. Further, the first data signal D 1  represented by the third line L 3  undergoes a voltage change of Vm 2  [V] at a time when a fourth scan signal S 4  is turned on, undergoes a voltage change of Vm 1 -Vm 2  [V] at a time when a fifth scan signal S 5  is turned on, and undergoes a voltage change of Vm 1  [V] at a time when a sixth scan signal S 6  is turned on. 
     On the other hand, it is also shown that the first data signal D 1  represented by the fourth line L 4  undergoes a voltage change of Vm 3  [V] at the time when the first scan signal S 1  is turned on, undergoes no voltage change at the time when the second scan signal S 2  is turned on, and undergoes a voltage change of Vm 3  [V] at the time when the third scan signal S 3  is turned on. Further, the first data signal D 2  represented by the fourth line L 4  undergoes a voltage change of Vm 3  [V] at the time when the fourth scan signal S 4  is turned on, undergoes no voltage change at the time when the fifth scan signal S 5  is turned on, and undergoes a voltage change of Vm 3  [V] at the time when the sixth scan signal S 6  is turned on. Here, Vm 3  [V] has a value smaller than that of Vm 1  [V]. 
     Therefore, since the frequency and magnitude of change in the voltage level of the first data signal D 1  represented by the fourth line L 4  are all reduced, it can be seen that the heat generated by the data driver  300  is relatively reduced as compared with when the first data signal D 1  represented by the third line L 3  is transmitted. 
       FIG. 15  is a flowchart illustrating the operation of the overheat prevention circuit  120   b  according to the embodiment of the inventive concept shown in  FIG. 13 . 
     Referring to  FIG. 15 , at operation (S 301 ) the detector  121  counts the number of toggles included in each frame by using input image data signal DATA. 
     At operation (S 302 ), the comparator  122  receives information about the number of toggles included in each frame from the detector  121  and determines whether the number of toggles included in each frame is equal to or greater than a reference number of toggles. 
     When it is determined at operation (S 302 ) that the number of toggles included in each frame is equal to or greater than the reference number of toggles, at operation (S 303 ) the lookup table selector  123  controls the data driver  300  to generate data signals based on the second lookup table LUT 2 , and at operation (S 304 ) the driving voltage converter  124   a  controls the power supply unit  500   a  to generate the second driving voltage AVDD 2 . 
     On the contrary, when it is determined at operation (S 302 ) that the number of toggles included in each frame is not equal to or greater than the reference number of toggles, at operation (S 305 ) the lookup table selector  123  controls the data driver  300  to generate data signals based on the first lookup table LUT 1 , and at operation (S 306 ) the driving voltage converter  124   a  controls the power supply unit  500   a  to generate the first driving voltage AVDD 1 . 
       FIG. 16  is a flowchart illustrating the operation of an overheat prevention circuit according to an embodiment of the inventive concept. 
     At operation (S 401 ) a detector  121  ( FIG. 10 ) counts the number of toggles included in each frame by using input image data signal DATA. 
     At operation (S 402 ), a comparator  122  receives information about the number of toggles included in each frame from the detector  121  and determines whether the number of toggles included in each frame is equal to or greater than a reference number of toggles. 
     When it is determined at operation (S 402 ) that the number of toggles included in each frame is equal to or greater than the reference number of toggles, it is additionally determined at operation (S 403 ) whether a data driver  300  is currently being driven by a first lookup table LUT 1 . 
     If it is determined at operations (S 402 ) and (S 403 ), respectively, that the number of toggles included in each frame is equal to or greater than the reference number of toggles and that the data driver  300  is currently being driven by the first lookup table LUT 1 , it is determined at operation (S 404 ) whether to control the data driver  300  being driven by the first lookup table LUT 1  to be driven by the second lookup table LUT 2  according to how many frames in an entry size (e.g. set the entry size). The number of frames corresponding to the entry size may be a predetermined number of frames. However, the number of frames corresponding to the entry size is not limited to the predetermined number of frames and can be variably determined according to the number of toggles. 
     Once the number of frames corresponding to the entry size is determined at operation (S 404 ), then at operation (S 405 ) the data driver  300  being driven by use of values in the first lookup table LUT 1  is gradually changed (e.g. transitioned) to be driven by use of values in the second lookup table LUT 2  over a plurality of frames. During the gradual change, a value corresponding to a median value of a value of the first lookup table LUT 1  and a value of the second lookup table LUT 2  may be used in the frames during the change. Furthermore, the inventive concept is not limited to the above case, and the value of the first lookup table LUT 1  can be gradually changed to the value of the second lookup table LUT 2  according to the degree of change. 
     When it is determined at (S 402 ) that the number of toggles included in each frame is equal to or greater than the reference number of toggles and at (S 403 ) that the data driver  300  is currently being driven by the second lookup table LUT 2  (e.g. LUT 1  is not being used at operation (S 403 ), then at operation (S 406 ) the data driver  300  is continued to be driven using the value(s) of the second lookup table LUT 2 . 
     When it is determined at (S 402 ) that the number of toggles included in each frame is less than the reference number of toggles, it is additionally determined (at operation S 407 ) whether the data driver  300  is currently being driven by the first lookup table LUT 1 . 
     If at operation (S 407 ) the determination is affirmative (LUT 1  is being used, then at operation (S 408 ) the data driver  300  is continued to be driven using value(s) from the first lookup table LUT 1  (operation S 408 ). 
     On the contrary, if at operation (S 407 ) it is determined that the data driver  300  is currently being driven by the second lookup table LUT 2  (e.g. the decision at S 407  is “no”), it is determined at operation (S 409 ) to set how many frames in the entry size. 
     At operation (S 410 ), once the number of frames corresponding to the entry size is set, the data driver  300  being driven by using value(s) from the second lookup table LUT 2  is gradually changed to be driven by using value(s) from the first lookup table LUT 1  over a plurality of frames. 
     In the current embodiment of the inventive concept, the conversion between the first lookup table LUT 1  and the second lookup table LUT 2  for driving the data driver  300  is performed not at a time, but gradually. Therefore, a brightness difference caused by the conversion between use of the first lookup table LUT 1  and use of the second lookup table LUT 2  to drive the data driver  300  results in a gradual change in the display that is not visible (e.g. noticeable) to a user. 
       FIG. 17  is a flowchart illustrating an example of the operation of an overheat prevention circuit according to an embodiment of the inventive concept. 
     First, at operation (S 501 ), a detector  121  (e.g. see  FIG. 10 ) counts the number of toggles included in each frame by using input image data signal DATA. 
     Next, at operation (S 502 ), a comparator  122  (e.g. see  FIG. 10 ) receives information about the number of toggles included in each frame from the detector  121  and determines whether the number of toggles included in each frame is equal to or greater than a reference number of toggles ( ). 
     When it is determined at operation (S 502 ) that the number of toggles included in each frame is equal to or greater than the reference number of toggles, at operation (S 503 ) it is additionally determined whether a power supply unit  500   a  (e.g.,  FIG. 10 ) is currently generating a first driving voltage AVDD 1 . 
     If it is determined that the number of toggles included in each frame is equal to or greater than the reference number of toggles (operation S 502 ) and that the power supply unit  500   a  is currently generating the first driving voltage AVDD 1  (operation S 503 ), at operation (S 504 ) it is determined whether to control the power supply unit  500   a  currently generating the first driving voltage AVDD 1  to generate a second driving voltage AVDD 2  according to the quantity of frames in an entry size. The number of frames corresponding to the entry size may be a predetermined number of frames. However, the number of frames corresponding to the entry size is not limited to the predetermined number of frames and can be variably determined according to the number of toggles. 
     Next, at operation (S 505 ) once the number of frames corresponding to the entry size is determined, the power supply unit  500   a  currently generating the first driving voltage AVDD 1  is gradually changed to generate the second driving voltage AVDD 2  over a plurality of frames. Thus, a person of ordinary skill in the art should understand and appreciate that the change from the first driving voltage AVDD 1  to the second driving voltage AVDD 2  is considered a gradual change when it occurs over a plurality of frames. The gradual change may not be noticed, or hardly noticed, by many users. Here, a value corresponding to a median value of the first driving voltage AVDD 1  and the second driving voltage AVDD 2  may be used in the frames during the change. Furthermore, the inventive concept is not limited to the above case, and the voltage level of the first driving voltage AVDD 1  can be gradually changed to the voltage level of the second driving voltage AVDD 2  according to the degree of change. 
     However, when it is determined at operations (S 502  and S 503 ) that the number of toggles included in each frame is equal to or greater than the reference number of toggles and that the power supply unit  500   a  is currently generating the second driving voltage AVDD 2  (e.g. S 503  is a “no”), then at operation (S 506 ) the power supply unit  500   a  keeps generating the second driving voltage AVDD 2 . 
     On the other hand, when it is determined at operation (S 502 ) that the number of toggles included in each frame is less than the reference number of toggles, it is additionally determined at operation (S 507 ) whether the first look-up table (LUT  1 ) is being used, thus determining whether the power supply unit  500   a  is currently generating the first driving voltage AVDD 1 . 
     If it is determined from operations (S 502 ) and (S 507 ) that the number of toggles included in each frame is less than the reference number of toggles and that the power supply unit  500   a  is currently generating the first driving voltage AVDD 1  (e.g. based on LUT  1  being used), then at operation (S 508 ) the power supply unit  500   a  keeps generating the first driving voltage AVDD 1 . 
     On the contrary, if it is determined from operations (S 502 ) and (S 507 ) that the number of toggles included in each frame is less than the reference number of toggles and that the power supply unit  500   a  is currently generating the second driving voltage AVDD 2 , then at operation (S 509 ) it is determined whether to control the power supply unit  500   a  currently generating the second driving voltage AVDD 2  to generate the first driving voltage AVDD 1  according to how many frames in the entry size (e.g. set the entry size). 
     At operation (S 510 ), once the number of frames corresponding to the entry size is determined at operation (S 509 ), the power supply unit  500   a  currently generating the second driving voltage AVDD 2  is gradually changed to generate the first driving voltage AVDD 1  over a plurality of frames. 
     In the current embodiment of the inventive concept, the conversion between the generation of the first driving voltage AVDD 1  and the generation of the second driving voltage AVDD 2  by the power supply unit  500   a  is performed gradually rather than at one time (e.g. change over one frame rather than a plurality of frames. Therefore, a brightness difference caused by the conversion between the first driving voltage AVDD 1  and the second driving voltage AVDD 2  may not be visible to a user. 
     According to at least the aforementioned embodiments of the inventive concept discussed herein above, a display device may be constructed so as to prevent overheating of a data driver. 
     It is also possible to provide a method of driving a display device which can prevent overheating of a data driver. 
     However, the breadth of the inventive concept is not restricted to the embodiment set forth herein above.