Abstract:
A display device according to an aspect of the present invention includes: a display configured to have a backlight; a driver configured to drive the backlight; first and second temperature measurement modules, configured to measure temperatures of the display device, disposed in different positions in the display; a first comparison module configured to compare the temperature measured in the first temperature measurement module with a first threshold value; a second comparison module configured to compare the temperature measured in the second temperature measurement module with a second threshold value different from the first threshold value; and a controller controlling an output current value of the driver based on a comparison result in the first comparison module and the second comparison module.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2009-230311, filed on Oct. 2, 2009; the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a display device having a backlight and a display method. 
     2. Description of the Related Art 
     In some of conventional display devices, a plurality of temperature sensors are disposed in a liquid crystal display panel, and when a difference between respective temperatures measured by the plural temperature sensors exceeds a predetermined threshold value, a driving condition of a liquid crystal element of the above-described liquid crystal display panel is altered (JP-A 2007-298957 (KOAKI)). 
     BRIEF SUMMARY OF THE INVENTION 
     In recent years, some casings covering display panels are formed of metal such as aluminum in order to improve design. Since metal has a high thermal conductivity, heat of a backlight is easily conveyed to the casing, thereby raising a temperature of a casing surface. However, in a convention display device, though a driving condition of a liquid crystal element is altered, a temperature of a casing surface is not taken into consideration. In view of the above, the present invention is made to solve such a conventional problem and an object of the present invention is to provide a display device and a display method capable of suppressing a temperature rise of a casing surface effectively. 
     A display device according to an aspect of the present invention includes: a display configured to have a backlight; a driver configured to drive the backlight; first and second temperature measurement modules, configured to measure temperatures of the display device, disposed in different positions in the display; a first comparison module configured to compare the temperature measured in the first temperature measurement module with a first threshold value; a second comparison module configured to compare the temperature measured in the second temperature measurement module with a second threshold value different from the first threshold value; and a controller controlling an output current value of the driver based on a comparison result in the first comparison module and the second comparison module. 
     A display method according to an aspect of the invention includes: measuring temperatures of first and second positions different from each other in a display having a backlight; comparing the temperature of the first position with a first threshold value; comparing the temperature of the second position with a second threshold value different from the first threshold value; and suppressing an output current value to the backlight based on a result of the comparison. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing a display device according a first embodiment. 
         FIG. 2  is a diagram showing a configuration of the display device according to the first embodiment. 
         FIG. 3  is a diagram showing a configuration of an LED backlight. 
         FIG. 4  is a diagram showing arrangement positions of temperature sensors. 
         FIG. 5  is a diagram showing table data of a memory. 
         FIG. 6  is a diagram showing a functional configuration of the display device according to the first embodiment. 
         FIG. 7  is a flowchart showing an operation of the display device according to the first embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 
     First Embodiment 
       FIG. 1  is a view showing a display device according to a first embodiment.  FIG. 2  is a diagram showing a configuration of the display device according to the first embodiment. In the first embodiment, a liquid crystal television  1  (hereinafter, liquid crystal TV  1 ) is described as a concrete example of the 0020 display device. It should be noted that the display device is not limited to the liquid crystal TV  1 . The display device can be one having a backlight such as a cellular phone and a PDA for example. 
     The liquid crystal TV  1  has a display panel  108 , speakers S 1 , S 2  and the like in a front surface. The liquid crystal TV  1  decodes a digital broadcast signal inputted from a not-shown antenna, thereby reproducing a video and an audio. Metal such as aluminum is used for a casing  10  to cover surroundings of the display panel  108  in order to improve design. A material of the casing  10  is not limited to the metal but other materials such as plastic for example can be used. 
     Since the metal has a high thermal conductivity, there is a tendency that heat can be easily felt when a surface of the casing  10  is touched. A main cause of a temperature rise of the display panel  108  and its casing  10  is a backlight. The liquid crystal TV  1  according to the first embodiment suppresses the temperature rise of the display panel  108  and its casing  10  by suppressing an illuminance of the backlight. 
     As shown in  FIG. 2 , the liquid crystal TV  1  has a channel selection module  101 , a separation module  102 , a microcomputer  103 , a BEP (back end processor)  104 , an LED driver  105 , a backlight LED  106 , a liquid crystal driver  107 , the display panel  108 , a temperature measurement module  109 , a memory  110 , and a decoder  111 . 
     The channel selection module  101  selects a desired channel from the broadcast signal received by the antenna. The channel module  101  demodulates the selected broadcast signal, thereby generating a TS (transport stream). 
     The separation module  102  separates the broadcast signal, SI/PSI and the like from the TS generated in the channel selection module  101 . The TS is a multiplexed signal which includes the broadcast signal and SI/PSI. The broadcast signal is a broadcast signal of MPEG-2 for example. The broadcast signal is constituted by an audio ES (audio elementary stream) and a video ES (video elementary stream) made by encoding a video and an audio respectively. The PSI is information which records what program exists in the TS and what program each ES which is included in the TS belongs to. Further, the SI includes EPG (electric program guide) information (hereinafter, program information). 
     The decoder  111  decodes the audio ES and the video ES separated in the separation module  102 , thereby generating an audio signal and a video signal. The decoder  111  inputs the generated video signal to the BEP  104 . The decoder  111  inputs the generated audio signal to the speakers S 1 , S 2 . The speakers S 1 , S 2  output an audio based on the inputted audio signal. 
     The microcomputer  103  suppresses an output current to the backlight LED  106  based on a temperature measured in the temperature measurement module  109 . As a result, an illuminance of the backlight is suppressed. Suppression of the illuminance of the backlight leads to suppression of the temperature rise of the display panel  108  and its casing  10 . It should be noted that a suppressing method of an output current by the microcomputer  103  will be described later. 
     The BEP  104  controls the LED driver  105  and the liquid crystal driver  107  based on the video signal inputted from the decoder  111  and displays an image corresponding to the video signal in the display panel  108 . 
     The LED driver  105  drives the backlight LED  106  based on control from the BEP  104 . The LED driver  105  has thirty-two driver ICs of a driver IC  1  to a driver IC  32 . Each of the driver IC  1  to the driver IC  32  adjusts an output current to the backlight LED  106  by PWM (pulse width modulation) control. 
       FIG. 3  is a diagram showing a configuration of the backlight LED  106 . The backlight LED  106  has thirty-two LED units of an LED unit L 1  to an LED unit L 32  corresponding to the driver IC  1  to the driver IC  32 . Further, though not shown, the LED units each have sixteen LED blocks and a plurality of LEDs are arranged in each LED block. 
     The respective driver IC  1  to the driver IC  32  independently drive the sixteen LED blocks which the corresponding LED unit L 1  to LED unit L 32  each have. It should be noted that the number of the driver ICs and the LED units is not limited to thirty-two. Further, the number of the LED blocks each LED unit has is not limited to sixteen, and the number of the LEDs in the block is not limited, either. 
     The liquid crystal driver  107  drives a liquid crystal element of the display panel  108  based on control from the BEP  108 . 
     The temperature measurement module  109  has a plurality of temperature sensors of a temperature sensor A to a temperature sensor F disposed in the display panel  108 .  FIG. 4  is a diagram showing arrangement positions of the temperature sensor A to the temperature sensor F.  FIG. 4  shows a rear surface of the display panel  108 . In the rear surface of the display panel  108 , there are disposed a driver unit  21 , fans  22 ,  24 , a TCON unit  23 , a main unit  25 , a power supply unit  26 , and the like. 
     The driver unit  21  has a driver (for example, the LED driver  105 ) for driving the display panel  108 . The fans  22 ,  24  are cooling fans disposed on the back of the display panel  108 . The TCON (timing controller) unit  23  is a logic circuit for taking timing of video display and outputs a pulse such as a shift clock. The main unit  25  processes the inputted broadcast signal. More specifically, the main unit  25  has the channel selection module  101 , the separation module  102 , the microcomputer  103 , the BEP  104 , the decoder  111  and the like shown in  FIG. 2 . The power source unit  26  converts an alternating current supplied from a household power source and the like into a direct current and supplies to the respective portions (for example, the driver unit  21 , the fans  22 ,  24 , the TCON unit  23  and the like) of the liquid crystal TV  1 . 
     The temperature sensors A, B are disposed above and beneath the driver unit  21 , respectively. The temperature sensor C is disposed in an upper right part of the fan  22 . The temperature sensor D is disposed in an upper part of the TCON unit  23 . The temperature sensor E is disposed in an upper left part of the fan  24 . The temperature sensor F is disposed in an upper right side of the display panel  108 . Each of the temperature sensor A to the temperature sensor F detects a temperature of the disposed position. In an example shown in  FIG. 4 , the temperature sensor A to the temperature sensor F are disposed mainly in an upper part (upper side of the center) of the display panel  108 . This is because the upper part of the display panel  108  tends to have a higher temperature and the temperature rise of the casing  10  can be suppressed more effectively when the temperature sensor is disposed in the upper part of the display panel  108 . It should be noted that the number of the temperature sensors and the arrangement positions of the respective temperature sensors are not limited to the example shown in  FIG. 4 . 
       FIG. 5  is a diagram showing table data stored in the memory  110 . The memory  110  stores table data in which the temperature sensor A to the temperature sensor F and threshold values are made to correspond to each other. In an example shown in  FIG. 5 , the threshold values of the temperature sensor A to the temperature sensor F are set to 75° C., 78° C., 76° C., 69° C., 76° C., and 72° C., respectively. The respective threshold values of the table data are set so that surface temperatures of the display panel  108  and the casing  10  covering the display panel  108  become equal to or lower than 65° C. 
     It should be noted that a correlation between a temperature detected by the temperature sensor and surface temperatures of the display panel  108  and the casing  10  covering the display panel  108  differs depending on the arrangement positions of the temperature sensor A to the temperature sensor F. In the first embodiment, by giving the threshold value per temperature sensor, an optimal threshold value is set in correspondence with the arrangement positions of the temperature sensor A to the temperature sensor F. 
       FIG. 6  is a diagram showing a functional configuration of the liquid crystal TV  1  according to the first embodiment. Hereinafter, the functional configuration of the liquid crystal TV  1  according to the first embodiment will be described with reference to  FIG. 6 . The liquid crystal TV  1  has an obtaining module  201 , a comparison module  202 , a controller  203  and the memory  110 . 
     The obtaining module  201  obtains the temperatures detected in the temperature sensor A to the temperature sensor F which the temperature measurement module  109  has at regular time intervals. 
     The comparison module  202  compares the temperature obtained in the obtaining module  201  with the threshold value with reference to the memory  110 . The comparison module  202  compares the temperatures detected in the temperature sensor A to the temperature sensor F with the corresponding threshold values, respectively. 
     The controller  203  controls output currents of the driver IC  1  to the driver IC  32  which the LED driver  105  has, based on a comparison result in the comparison module  202 . More specifically, the controller  203  alters duty ratios of the driver IC  1  to the driver IC  32  while the temperatures detected in the temperature sensor A to the temperature sensor F exceed the corresponding threshold values, thereby reducing the output currents by one percent at regular time intervals (for example, every several seconds). 
     When the temperatures detected in the temperature sensor A to the temperature sensor F become equal to or lower than the threshold values, the controller  203  sets the duty ratios of the driver IC  1  to the driver IC  32  back to duty ratios before alteration. On this occasion, the controller  203  raises the output currents by one percent at regular time intervals (for example, every several seconds). 
     By setting the duty ratios of the driver IC  1  to the driver IC  32  back to the duty ratios before alteration when the detected temperatures become equal to or lower than the threshold values, it is possible to shorten a time during which an image displayed in the display panel  108  becomes dark. 
       FIG. 7  is a flowchart showing an operation of the liquid crystal TV  1  according to the first embodiment. 
     The obtaining module  201  obtains the temperatures detected in the temperature sensor A to the temperature sensor F which the temperature measurement module  109  has (step S 101 ). 
     The comparison module  202  compares the temperature obtained in the obtaining module  201  with the threshold value with reference to the memory  110  (step S 102 ). 
     If the temperature obtained in the obtaining module  201  exceeds the threshold value of the table data stored in the memory  110  (Yes in the step S 102 ), the controller  203  alters the duty ratios of the driver IC  1  to the driver IC  32  which the LED driver  105  has, thereby reducing the output currents by one percent at regular time intervals (step S 103 ). 
     If the temperature obtained in the obtaining module  201  does not exceed the threshold value of the table data stored in the memory  110  (No in the step S 102 ), the controller  203  judges whether or not the output voltages of the driver IC  1  to the driver IC  32  which the LED driver  105  has are suppressed (step S 104 ). 
     If the output voltages are suppressed (Yes in the step S 104 ), the controller  203  sets the duty ratios of the driver IC  1  to the driver IC  32  back to the duty ratios before alteration (step S 105 ). On this occasion, the controller  203  raises the output currents by one percent at regular time intervals. 
     Further, in a case that the output voltages are not suppressed (No in the step S 104 ), if an action of the step S 103  or the step S 105  is finished, a procedure goes back to an action of the step S 101 . The obtaining module  201  to the controller  203  repeat the actions of the step S 101  to the step S 105  at predetermined time intervals. 
     As stated above, the liquid crystal TV  1  according to the first embodiment has the plurality of temperature sensors of the temperature sensor A to the temperature sensor F disposed in the display panel  108  and compares the temperatures detected in these temperature sensor A to temperature sensor F with the threshold values. Then, if the detected temperature exceeds the threshold value, the output current of the driver IC driving the backlight is suppressed. 
     Accordingly, even if a material having a high thermal conductivity such as metal is used for a casing covering a display panel  108 , a rise of a surface temperature of a casing  10  can be suppressed. Further, when the temperatures detected in the temperature sensor A to the temperature sensor F become equal to or lower than the corresponding threshold values, the controller  203  sets the duty ratios of the driver IC  1  to the driver IC  32  back to the duty ratios before alteration. It is possible to shorten a time during which an image displayed in the display panel  108  becomes dark. 
     Other Embodiment 
     It should be noted that the present invention is not limited to the above-described embodiment as it is, and can be concretized by modifying components in a range not deviating from the gist in an execution phase. For example, in the first embodiment the output currents of the driver IC  1  to the driver IC  32  are suppressed when the temperatures detected in the temperature sensor A to the temperature sensor F exceed the threshold values, but the output currents of the driver IC  1  to the driver IC  32  can be independently suppressed. More specifically, it can be constituted to suppress only an output current to a driver IC outputting a current to an LED unit in a region close to a position where the temperature sensor whose measured temperature exceeds a threshold value is disposed.