JP7451037B2 - Liquid crystal display device and image freeze detection method - Google Patents

Description

The present invention relates to a liquid crystal display device, and more particularly to a method for detecting image freeze.

Needle-type meters such as speedometers, tachometers, and fuel gauges located in instrument panels are being replaced by cluster displays using liquid crystal panels. Since warnings are also displayed on the cluster display, the functional safety requirements are required. The functional safety requirement is to set the screen to a safe state (for example, a black screen) when a screen freeze (an abnormal event on the display screen) is detected, thereby preventing the driver from noticing a warning due to the screen freeze.

Regarding the screen freeze of a liquid crystal display device, for example, the liquid crystal display device disclosed in Patent Document 1 detects a freeze state from a frame-to-frame change in a detection signal included in display data. Further, the image display system disclosed in Patent Document 2 detects freezing based on the presence or absence of a change in image information. Further, in the vehicle display device of Patent Document 3, when the change pattern of the monitoring drive data differs from the control pattern, it is determined that there is an abnormality and the operating state of the display control system is reset.

Japanese Patent Application Publication No. 2006-267452 JP2008-252307A Japanese Patent Application Publication No. 2010-237287

As shown in FIG. 1A, a liquid crystal display device 10 using a liquid crystal panel is provided in front of the driver's seat. As shown in FIG. 1(B), the liquid crystal display device 10 includes a speedometer, tachometer, fuel gauge, etc., as well as a warning light 12 for displaying warnings such as fastening of seat belt, remaining amount of gasoline, door ajar, etc. Clusters containing . When screen freeze of the liquid crystal display device 10 is detected, the entire screen is displayed as a black screen, and the driver is notified that there is a screen abnormality.

FIG. 2 is a diagram showing a schematic configuration of a conventional liquid crystal display device. The liquid crystal display device 10 supplies power to a liquid crystal panel 20, a backlight 22, a liquid crystal drive circuit 30 for driving the liquid crystal panel 20, an image processing circuit 40 that supplies display data to the liquid crystal drive circuit 30, and a liquid crystal drive circuit 30. The LCD power supply circuit 50 includes an LCD power supply circuit 50 that supplies power to the backlight 22, an error detection section 70 that detects internal errors in the liquid crystal panel 20 and the liquid crystal drive circuit 30, and a control section 80 that controls each section.

When the error detection section 70 detects an error (abnormality) related to the liquid crystal panel 20 or the liquid crystal drive circuit 30, it outputs an internal error detection signal ER to the control section 80. Upon receiving the internal error detection signal ER, the control unit 80 determines that a screen freeze has occurred, and causes the backlight power supply circuit 60 to stop supplying power to the backlight 22. As a result, a black screen is displayed on the liquid crystal panel 20, that is, a safe state is displayed, and the user is notified that the screen has frozen.

Screen freeze is an event in which the image displayed on the screen of the liquid crystal panel 20 stops, and this event may be caused by, for example, a failure of a thin film transistor (TFT) of the liquid crystal panel 20 or a gate voltage applied to the thin film transistor by the liquid crystal drive circuit 30. This occurs due to an abnormality, etc. On the other hand, the detection function of the error detection unit 70 includes errors that are not directly related to screen freezing (for example, generation of high voltage due to static electricity, malfunction due to noise, etc.). Therefore, it is difficult for the control unit 80 to accurately detect screen freeze from the internal error detection signal ER. Further, if screen freeze is detected frequently in response to the internal error detection signal ER, the control unit 80 stops power supply to the backlight 22 each time, and displays a black screen as the liquid crystal panel 20 is in a safe state. As a result, there are too many black screen transitions on the liquid crystal panel 20, causing discomfort to the user.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device and a screen freeze detection method that can solve the above-mentioned conventional problems and improve screen freeze detection accuracy.

A method for detecting screen freeze in a liquid crystal display device according to the present invention includes the steps of: switching the screen of a liquid crystal display section from a first image to a second image; and a second current consumption by the liquid crystal display section when displaying the second image.

In one aspect, the first image is black or white, and the second image is white or black. In one embodiment, the determining step determines that the screen is frozen when a difference between the first current consumption and the second current consumption is equal to or less than a certain value. In some aspects, the detection method further includes turning off the backlight when switching the screen from the first image to the second image. In one aspect, the detection method further includes the step of detecting an internal error in the liquid crystal display section, and the switching step and the determining step are performed when the internal error is detected. In one embodiment, the detection method further includes the steps of: storing reference current consumption for each display mode in the storage unit; and current consumption when an image of the selected display mode is displayed on the screen of the liquid crystal display unit and the display mode. and a reference current consumption corresponding to the reference current consumption, and when a certain difference is detected in the comparing step, the switching step and the determining step are performed.

The liquid crystal display device according to the present invention includes a liquid crystal display section, a detection means for detecting current consumption of the liquid crystal display section, and a screen freeze detection means for detecting screen freeze of the liquid crystal display section, The means includes an image switching means for switching the screen of the liquid crystal display unit from a first image to a second image, and a first current consumption detected by the detection means when the first image is displayed. and determining means for determining screen freeze based on the second current consumption detected by the detecting means when displaying the second image.

In one aspect, the first image is black or white, and the second image is white or black. In one aspect, the determining means determines that the screen is frozen when the difference between the first current consumption and the second current consumption is less than a certain value. In one aspect, the image switching means turns off the backlight when switching the screen from the first image to the second image. In one embodiment, the liquid crystal display device further includes internal error detection means for detecting an internal error in the liquid crystal display section, and the screen freeze detection means is implemented when the internal error detection means detects an internal error. In one embodiment, the liquid crystal display device further includes a storage means for storing a reference current consumption for each display mode, and a storage means for storing a reference current consumption for each display mode, and a storage means for storing a reference current consumption for each display mode, and a storage means for storing a reference current consumption for each display mode, and a storage means for storing a reference current consumption when displaying an image in a selected display mode on the screen of the liquid crystal display unit. and a comparison means for comparing the current consumption with a corresponding reference current consumption, and when a certain difference is detected by the comparison means, the screen freeze detection means is executed.

According to the present invention, the screen is switched from the first image to the second image, and the screen freeze is caused by the first current consumption when the first image is displayed and the second current consumption when the second image is displayed. Since the determination is made, it is possible to improve the accuracy of detecting screen freeze compared to the conventional method.

2 is a diagram illustrating an example of cluster display on a liquid crystal panel. FIG. 2 is a diagram illustrating a conventional method for detecting screen freeze of a liquid crystal display device. 1 is a diagram showing the configuration of a liquid crystal display device according to an example of the present invention. FIG. 3 is a diagram showing a connection relationship between a thin film transistor and a liquid crystal forming a sub-pixel. 1 is a diagram showing the configuration of a screen freeze detection function of a liquid crystal display device according to a first embodiment of the present invention; FIG. 3 is an operation flow of the screen freeze detection function according to the first embodiment of the present invention. It is a figure which shows the structure of the screen freeze detection function based on the 2nd Example of this invention. It is an operation flow of the screen freeze detection function according to the second embodiment of the present invention.

The liquid crystal display device of the present invention has a function of detecting screen freeze, and is used, for example, as an instrument panel for displaying vehicle meters. The liquid crystal display unit works with the vehicle's engine control unit to display information about the vehicle's status (speed, tachometer, remaining fuel level, warning lights), and works with in-vehicle devices to display information such as the navigation screen, audio screen, and in-vehicle equipment. It is also possible to display a screen imaged by a camera.

Next, examples of the present invention will be described. FIG. 3 is a diagram showing the configuration of a liquid crystal display device according to an embodiment of the present invention. Components that are the same as those in FIG. 2 are given the same reference numbers. The liquid crystal display device 100 of this embodiment includes a current monitoring section 110 in addition to the configuration shown in FIG. The current monitoring unit 110 monitors the current that the LCD power supply circuit 50 supplies to the liquid crystal drive circuit, in other words, monitors the current consumption of the liquid crystal drive circuit 30. The current monitoring unit 110 detects the current of the LCD power supply circuit 50 according to an instruction from the control unit 80 and provides the detected current to the control unit 80. The control unit 80 determines the presence or absence of a screen phrase based on the current consumption detected by the current monitoring unit 110, as described later.

The liquid crystal panel 20 has, for example, a TFT (Thin Film Transistor) liquid crystal structure. The TFT liquid crystal structure includes a TFT array substrate in which a plurality of thin film transistors are formed in a matrix. On this substrate, a liquid crystal, an RGB color filter, a polarizing plate, etc. are provided. Below the array substrate, a polarizing plate, a backlight, etc. 22 etc. are provided. One pixel constituting the screen of the liquid crystal panel 20 includes three sub-pixels corresponding to RGB of the RGB color filter, and one sub-pixel includes one thin film transistor.

The liquid crystal drive circuit 30 drives each of a plurality of thin film transistors arranged in a matrix. FIG. 4 illustrates thin film transistors arranged in two rows and two columns as part of the structure. A drive signal line Xi from the liquid crystal drive circuit 30 is commonly connected to each gate of the thin film transistors Q1 and Q2 in the i row, and a drive signal line Xi from the liquid crystal drive circuit 30 is connected to each gate of the thin film transistors Q3 and Q4 in the j row. Lines Xj are commonly connected. A data line Di is commonly connected to the drain electrodes of the thin film transistors Q1 and Q3 in the i column, and a data line Dj is commonly connected to the drain electrodes of the thin film transistors Q2 and Q4 in the j column. A liquid crystal element Ca and an auxiliary capacitor Cb are connected to the source electrode of each thin film transistor.

The liquid crystal drive circuit 30 generates a gate voltage for driving the gates of the thin film transistors via drive signal lines Xi and Xj, and also generates a voltage corresponding to display data provided from the image processing circuit 40. A voltage is applied to the drain electrode of the thin film transistor via the data lines Di and Dj. For example, when an H-level gate voltage is applied to the thin film transistors Q1 and Q2 via the drive signal line Xi, the thin film transistors Q1 and Q2 are turned on, and the liquid crystal element Ca of the thin film transistor Q1 is supplied from the data line Di in response to display data. A voltage corresponding to the display data is applied from the data line Dj to the liquid crystal element Ca of the thin film transistor Q2. The liquid crystal element Ca changes the direction of molecules according to the applied voltage, and varies the amount of light transmitted from the backlight 22. In this way, the gradation display is controlled according to the voltage applied to the liquid crystal element Ca, and an image according to the display data is displayed on the liquid crystal panel 20. On the other hand, when an L-level gate voltage is applied to the thin film transistors Q1 and Q2 via the drive signal line Xi, the thin film transistors Q1 and Q2 are turned off, and no voltage is applied to the liquid crystal elements Ca of the thin film transistors Q1 and Q2. In this case, the amount of light transmitted from the backlight 22 is completely blocked, and black is displayed on the screen of the liquid crystal panel 20.

The current monitoring unit 110 detects the current consumption of the liquid crystal drive circuit 30 as described above. In one aspect, the current monitoring unit 110 detects current consumption when the liquid crystal drive circuit 30 drives the gate voltage. When displaying an image corresponding to display data on the liquid crystal panel 20, all thin film transistors are driven with an H-level gate voltage to turn on, which results in a certain amount of current consumption. On the other hand, when displaying the entire screen of the liquid crystal panel 20 in black, the gate voltage is set to L level (GND level) so that all thin film transistors are turned off, so in this case almost no current consumption occurs.

In another aspect, the current monitoring unit 110 may detect current consumption when the liquid crystal drive circuit 30 drives a voltage corresponding to display data. Since the voltage applied to the drain electrode of the thin film transistor differs depending on the display data, current consumption when driving the voltage applied to the drain electrode differs depending on the display color. For example, when displaying white on an LCD panel screen, a voltage is generated that maximizes the amount of light transmitted from the backlight, and when displaying black, the amount of light transmitted from the backlight is minimized. voltage like that. The voltage difference when displaying white and black on the liquid crystal panel screen is maximum, and the current consumption difference at that time is maximum.

The control unit 80 controls the operation of the liquid crystal display device 100 using hardware and/or software. The control unit 80 controls the image processing circuit 40, the LCD power supply circuit 50, the backlight power supply circuit 60, and the like. Further, the control unit 80 performs error processing based on the internal error detection signal ER from the error detection unit 70. In this embodiment, the control unit 80 has a function of detecting screen freeze in addition to display control of the liquid crystal display device 100.

FIG. 5 shows the configuration of the screen freeze detection function according to the first embodiment of the present invention. The screen freeze detection function 200 includes an LCD error detection section 210, a screen switching section 220, a current consumption detection section 230, a screen freeze determination section 240, and a safety state display section 250.

The LCD error detection section 210 receives the internal error detection signal ER from the error detection section 70, and stores an error code indicating that an error has occurred inside the LCD in a register or the like. The error detection unit 70 detects internal errors in LCDs such as the liquid crystal panel 20 and the liquid crystal drive circuit 30. In this embodiment, not all internal errors detected by the error detection unit 70 are determined to be screen freezes. Therefore, even if the LCD error detection section 210 receives the internal error detection signal ER, it does not stop the power supply to the backlight power supply circuit 60 at this point and does not turn off the backlight 22.

The screen switching unit 220 switches the screen of the liquid crystal panel 20 when the LCD error detection unit 210 detects an internal error in the LCD. For example, the screen switching unit 220 displays black on the screen of the liquid crystal panel 20, and then switches the black screen to white. This order may be reversed and may be switched from a white screen to a black screen. When displaying a black screen on the liquid crystal panel 20, the screen switching unit 220 sets all gate voltages driven by the liquid crystal drive circuit 30 to L level (GND). In another embodiment, all gate voltages are driven to H level to turn on the thin film transistors, display data representing black is supplied from the image processing circuit 40 to the liquid crystal drive circuit 30, and the liquid crystal element transmits light from the backlight 22. The amount may be completely blocked.

It is desirable that the screen switching time be short so as not to cause any inconvenience to the user. If the screen of the liquid crystal panel 20 is displayed using, for example, 30 frames per second, the screen switching unit 220 allocates two frames, a black screen frame and a white screen frame, to screen switching. be able to. However, the number of frames of the black screen and the white screen may be greater than one frame, and the black screen and the white screen do not necessarily have to be displayed consecutively. Furthermore, in order to reduce the influence of screen switching, the screen switching unit 220 stops the power supply from the backlight power supply circuit 60 and turns off the backlight 22 when switching the screen, so that an apparently black screen is displayed. You can do it like this.

The current consumption detection unit 230 causes the current monitoring unit 110 to detect the current consumption when displaying a black screen and the current consumption when displaying a white screen at a timing synchronized with the screen switching by the screen switching unit 220.

The screen freeze determination unit 240 compares the current consumption when displaying a black screen detected by the current monitoring unit 110 with the current consumption when displaying a white screen, and when the difference is below a certain level, Or, if there is no change, it is determined that the screen is frozen. As mentioned above, when all thin film transistors are turned off to display a black screen (when the gate voltage is set to GND), the current consumption is equal to that when all thin film transistors are turned on to display a white screen. (driving gate voltage to H level). If the screen switching of the liquid crystal panel 20 is normal, there should be a certain difference in current consumption between a black screen and a white screen. If the difference in current consumption between the black screen and the white screen is below a certain level, the gate voltage may not be generated normally due to a failure in the liquid crystal drive circuit 30, or the thin film transistor may be functioning normally due to a failure in the thin film transistor. It is thought that the screen is not working properly and the screen is freezing.

When the screen freeze determination unit 240 determines that the screen is frozen, the safety state display unit 250 stops the power supply to the backlight power supply circuit 60, turns off the backlight 22, and displays a black screen on the liquid crystal panel 20 as a safety state. let On the other hand, if it is determined that the screen is not frozen, the display on the liquid crystal panel 20 continues without turning off the backlight 22.

Next, FIG. 6 shows the operation flow of the screen freeze function of this embodiment. When the liquid crystal display device 100 starts operating, the screen freeze detection function 200 starts operating. The LCD error detection unit 210 monitors the internal error detection signal ER of the error detection unit 70 and detects whether an error has occurred inside the LCD (S100). When an internal error of the LCD is detected, the screen switching unit 220 causes the liquid crystal panel 20 to display a black screen (S110), and the current consumption detection unit 220 causes the current monitoring unit 110 to detect the current consumption when displaying the black screen. Detection is performed (S120). Next, the screen switching unit 210 switches the screen from the black screen to the white screen (S130), and causes the current monitoring unit 110 to detect the current consumption when displaying the white screen (S140). Next, the screen freeze determination unit 240 compares the current consumption for the black screen and the current consumption for the white screen (S150), and if the difference is greater than a certain value, it determines that the screen has not frozen, and continues displaying the image. Let it continue. On the other hand, if the difference is less than a certain value, it is determined that the screen is frozen (S160), and in response to the determination result, the safety state display unit 250 stops the power supply from the backlight power supply circuit 60, and turns on the backlight 22. It is turned off and a black screen in a safe state is displayed (S170).

According to this embodiment, when an internal error in the LCD is detected, screen freeze is determined based on the difference in current consumption when switching between a black screen and a white screen. Detection accuracy can be improved. As a result, it is possible to reduce erroneous detection of screen freeze, and to suppress unnecessary display of safety conditions from occurring frequently.

In the above embodiment, the screen freeze detection function 200 is executed when the error detection unit 70 detects an internal error in the LCD, but this is just an example, and the present invention is not limited to this. isn't it. The screen freeze detection function 200 of this embodiment may be performed independently of the error detection operation of the error detection section 70. For example, the screen freeze detection function 200 may be performed according to a predetermined schedule, or may be performed periodically while the liquid crystal display device is in operation.

Further, in the above embodiment, the screen switching unit 220 switches the screen from a black screen to a white screen or from a white screen to a black screen, but the screen switching unit 220 may use the difference in current consumption caused by driving the gate voltage of a thin film transistor. In this case, the screen to be switched may be any color other than the white screen, and the color displayed on the screen does not need to be one color. In other words, when displaying something other than a black screen, the thin film transistor is operated, so the current consumption due to driving the gate voltage is constant no matter what is displayed.

Furthermore, when using the difference in current consumption for driving the voltage corresponding to display data, rather than using the difference in current consumption due to driving the gate voltage of the thin film transistor, switching the screen can be performed using a screen other than a black screen. The screen may be of any other color. The difference in current consumption is greatest when displaying a black screen and when displaying a white screen, but if you can easily detect the difference in current consumption other than this, you can switch between screens with other display colors. It may be.

Further, in the above embodiment, the screen switching unit 220 prepares a black screen and a white screen for switching the screen screen, but the present invention is not limited to this. It may also be possible to switch to another screen. For example, when meters as shown in FIG. 1B are displayed, the meter screen may be switched to a black screen or a white screen. In this case, screen freeze is determined based on the difference between the current consumption when the meters are displayed and the current consumption when the black screen or white screen is switched. Note that the screen that displays the meters shown in FIG. 1B generally has a black background, so it is desirable that the screen to be switched is a white screen or a bright screen that increases the difference in current consumption.

Next, a second embodiment of the present invention will be described. In the second embodiment, a liquid crystal display device 100 has a plurality of display modes, and has a function of switching each display mode according to instructions from a user or the like.

FIG. 7 is a diagram showing the configuration of a screen freeze detection function 200A according to the second embodiment, and the second embodiment further includes a display mode identification section 260 and a reference current consumption storage section 270. The display mode identification unit 260 identifies the display mode of the liquid crystal panel 20. Display modes include, for example, a navigation mode that displays a road map etc. when the navigation function is executed, a camera mode that displays images of the surrounding area of the road taken by an in-vehicle camera, and a playback screen when the audio playback function is executed. This is the audio mode that displays. These display modes display those images in addition to the images of the meters shown in FIG. 1(B). For example, in navigation mode, a navigation screen is displayed in addition to the meters.

The reference current consumption storage unit 270 stores in advance a reference current consumption value when each display mode is operating normally. For example, reference current consumption in navigation mode, reference current consumption in camera mode, and reference current consumption in audio mode are stored. Since the display color of a screen including meters as shown in FIG. 1(B) is fixed, the reference current consumption is generally constant. Since these reference current consumptions vary from product to product, it is desirable to actually measure the current consumption for each product and determine the reference current consumption based on the measured value.

FIG. 8 shows an operation flow of the screen freeze detection function according to the second embodiment. First, the reference current consumption storage unit 270 stores the reference current consumption for each display mode in the storage unit (S200). Next, the current consumption detection unit 230 detects the current consumption by the display screen currently displayed on the liquid crystal panel (S210), and then the display mode identification unit 260 identifies the display mode of the current display screen. (S220). When the display mode is identified, the screen freeze determination unit 240 reads the reference current consumption of the corresponding display mode from the storage unit (S230), compares the read reference current consumption with the detected current consumption (S240), If the difference in current consumption exceeds a certain level, it is determined that there is a possibility of screen display abnormality (S250), and the detection in the first embodiment is subsequently performed (S260). That is, the screen freeze determination unit 240 switches the current display screen to another screen, detects the current consumption of the switched screen, and determines whether or not the screen freezes based on the difference between the current consumption and the current consumption detected in step S210. .

According to this embodiment, when it is determined that there is a possibility of a screen display abnormality based on the reference current consumption prepared in advance and the current consumption of the actually displayed screen, the screen Since the image freeze is determined from the difference in current consumption by switching between the two, it is possible to improve the accuracy of detecting screen freeze.

Further, in the second embodiment as well, screen freezing may be determined on the condition that the internal error detection signal ER of the internal error detection section 70 is generated. For example, when the difference from the current consumption of the display mode is more than a certain value and an internal error occurs due to the internal error detection signal ER, the screen is switched as in the first embodiment, and the screen is Freeze may be determined.

Next, a modification of the second embodiment will be described. The control unit 80 stores in advance a normal setting value when the liquid crystal drive circuit 30 operates normally in the storage unit. When the error detection unit 70 detects an internal error in the LCD, it rewrites the contents of the register of the liquid crystal drive circuit 30 from a normal setting value to an error code. The control unit 80 executes the operations of steps S200 to S250 in FIG. 8, and if it is determined that there is a possibility of a screen display abnormality (S250), the control unit 80 reads the contents of the register of the liquid crystal drive circuit 30, and the read contents are If the value is different from the normal setting value, the operation in step S260 may be performed. Such a method is effective when the error detection section 70 is unable to notify the control section 80 of the error detection signal ER due to a failure.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to specific embodiments, and various modifications and variations can be made within the scope of the gist of the invention described in the claims. Changes are possible.

20: Liquid crystal panel 22: Backlight 30: Liquid crystal drive circuit 40: Image processing circuit 50: LCD power supply circuit 60: Backlight power supply circuit 70: Error detection section 80: Control section 100: Liquid crystal display device 110: Current monitoring section

Claims (12)

A method for detecting screen freeze in a liquid crystal display device, the method comprising:
a step of detecting an internal error in the liquid crystal display ;
switching the screen of the liquid crystal display unit from a first image to a second image different from the first image in response to the detection of the internal error;
Screen freeze occurs when the difference between the first current consumption by the liquid crystal display unit when the first image is displayed and the second current consumption by the liquid crystal display unit when the second image is displayed is below a certain level. a step of determining that
A detection method having The detection method according to claim 1, wherein the first image is black or white, and the second image is white or black. The detection method according to claim 1, wherein the first image is an image currently displayed on the liquid crystal display section . The detection method according to claim 1, further comprising the step of turning off a backlight when switching the screen from the first image to the second image. 2. The detection method according to claim 1, further comprising the step of turning off a backlight and displaying a black screen on the liquid crystal display when it is determined that the screen is frozen. The detection method further includes the step of storing reference current consumption for each display mode in a storage unit;
Comparing the current consumption when an image of the selected display mode is displayed on the screen of the liquid crystal display unit and the reference current consumption corresponding to the display mode ,
The detection method according to claim 1, wherein the switching step and the determining step are performed when a certain difference is detected in the comparing step. a liquid crystal display section;
internal error detection means for detecting an internal error in the liquid crystal display section;
detection means for detecting current consumption of the liquid crystal display section;
screen switching means for switching the screen of the liquid crystal display unit from a first image to a second image different from the first image in response to an internal error being detected by the internal error detection means ;
a difference between a first current consumption detected by the detection means when displaying the first image and a second current consumption detected by the detection means when displaying the second image; a liquid crystal display device, the liquid crystal display device comprising: determination means for determining that the screen is frozen when the value is below a certain level . 8. The liquid crystal display device according to claim 7, wherein the first image is black or white, and the second image is white or black. 8. The liquid crystal display device according to claim 7, wherein the first image is an image currently displayed on the liquid crystal display section . 8. The liquid crystal display device according to claim 7, wherein the screen switching means turns off a backlight when switching the screen of the liquid crystal display section. 8. The liquid crystal display device according to claim 7, further comprising safe state display means for turning off a backlight and displaying a black screen on the liquid crystal display section when the determination means determines that the screen is frozen. Display device. The liquid crystal display device further includes a storage means for storing reference current consumption for each display mode;
Comparing means for comparing the current consumption when an image of the selected display mode is displayed on the screen of the liquid crystal display unit and the reference current consumption corresponding to the display mode,
8. The liquid crystal display device according to claim 7, wherein the screen switching means and the determining means are executed when a certain difference is detected by the comparing means.

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