JP2010060746A - Liquid crystal display device - Google Patents

Liquid crystal display device Download PDF

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JP2010060746A
JP2010060746A JP2008225308A JP2008225308A JP2010060746A JP 2010060746 A JP2010060746 A JP 2010060746A JP 2008225308 A JP2008225308 A JP 2008225308A JP 2008225308 A JP2008225308 A JP 2008225308A JP 2010060746 A JP2010060746 A JP 2010060746A
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led
luminance
backlight
liquid crystal
brightness
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JP2008225308A
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Japanese (ja)
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Hiroharu Iwasaki
Motoyuki Oniki
弘治 岩崎
基行 鬼木
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Sharp Corp
シャープ株式会社
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Abstract

[PROBLEMS] To reduce the power consumption when adjusting the brightness of an LED to an intermediate brightness while allowing the brightness of a backlight using an LED as a light source to be adjusted in a wide brightness range including the maximum brightness.
The main control circuit 8 switches the level Di of the current supplied to the LED 9 to any one of a plurality of predetermined current levels, and the dimming circuit 7 and the LED power supply circuit 5 PWM control of current supply to the LED whose level Di has been switched is performed to adjust the luminance of the LED backlight 6 to the target luminance.
[Selection] Figure 1

Description

  The present invention relates to a liquid crystal display device including a backlight that illuminates a liquid crystal panel using an LED as a light source.

  In recent years, liquid crystal display devices represented by liquid crystal television receivers have a strong demand for higher image quality by expanding the color reproduction range than before. In order to meet the demand, a liquid crystal display device having a backlight using a light emitting diode (LED) having a high color purity as a light source and a liquid crystal panel illuminated by the backlight is becoming widespread. A liquid crystal display device using LEDs as a light source for backlight has a wider color reproduction range than the conventional general sRGB standard color reproduction range, and can display images with brighter (higher saturation) colors than conventional ones. is there.

On the other hand, fluorescent tubes and LEDs have non-linear emission luminance characteristics with respect to the level of the supplied current, and therefore it is difficult to perform fine luminance adjustment by adjusting the level of the supplied current. In particular, the fluorescent tube has a narrow range of brightness that can be adjusted according to the level of the supply current, and is not suitable for brightness adjustment by adjusting the level of the supply current. For this reason, the backlight of the liquid crystal display device is generally adjusted to a target luminance by PWM (Pulse Width Modulation) control for supplying a current to a light source such as a fluorescent tube or an LED. Hereinafter, the brightness adjustment of the light source by such PWM control is referred to as PWM dimming.
According to PWM dimming, since the light emission luminance of the light source is substantially proportional to the duty ratio of the pulse current, the luminance adjustment is easy.
In addition, in Patent Document 1, the LED brightness is stabilized by changing the LED drive voltage according to the temperature while maintaining the LED drive current level constant when performing PWM light control of the LED. The technology to be shown is shown.
JP 2006-235565 A

By the way, as a method of setting the LED in a light emission state with an intermediate luminance, a method of reducing the duty ratio in PWM dimming by maximizing (higher) the level of the supply current and lowering the level of the supply current. Either of increasing the duty ratio in PWM dimming or making the current constant is conceivable.
FIG. 6 is a diagram illustrating the relationship between the light control method and power consumption in a backlight using LEDs as light sources. In the example shown in FIG. 6, the supply current to the LED is maximum (40 mA) and medium (30 mA) when the light emission luminance of the backlight using the LED is set to three states (slightly dark, dark, and extremely dark). In this example, the power consumption of the LED is compared when the duty ratio of PWM dimming is set so as to obtain a desired light emission luminance under the minimum (11 mA) condition. The three types of light emission brightness are about 37% (slightly dark), about 20% (dark), and about 10% (roughly dark) with respect to the brightness (cd) when the duty ratio is 100% at the maximum current (40 mA). Extremely dark).

As shown in FIG. 6, when a backlight using an LED as a light source is in a relatively low luminance state, a dimming method for reducing the duty ratio in PWM dimming by setting the level of the supply current to the maximum (40 mA) is as follows. The power consumption is larger than that of the dimming method in which the level of the supply current is lowered (30 mA or 11 mA) to increase the duty ratio in PWM dimming or to a constant current (that is, the duty ratio is set to 100%). In other words, when a backlight using an LED as a light source is in a relatively low luminance state, a power saving effect can be obtained by lowering the level of supply current and increasing the duty ratio of PWM dimming. In the example shown in FIG. 6, by reducing the supply current level to the minimum (11 mA), a power saving effect of about 17 to 19% is obtained compared to the supply current level being set to the maximum (40 mA). I understand.
However, in the conventional PWM dimming of the LED, the level of the supply current to the LED is set to the maximum so that dimming is possible in a wide luminance range including the maximum luminance. Therefore, the conventional PWM dimming of the LED has a problem that the energy efficiency is poor under a situation where the luminance of the LED is adjusted to an intermediate luminance.
Further, as described above, there is a problem that it is difficult to finely adjust the luminance of the LED by adjusting the level of the supply current due to the nonlinearity of the luminance characteristic of the LED.
Accordingly, the present invention has been made in view of the above circumstances, and an object of the present invention is to make it possible to adjust the luminance of a backlight using an LED as a light source in a wide luminance range including the maximum luminance, and to adjust the luminance of the LED. An object of the present invention is to provide a liquid crystal display device capable of reducing power consumption when adjusting the brightness to an intermediate brightness.

In order to achieve the above object, a liquid crystal display device according to the present invention includes a backlight that illuminates a liquid crystal panel using an LED as a light source, and further includes the components shown in (1) and (2) below. It is.
(1) Current level switching means for switching the level of the current supplied to the LED to one of a plurality of predetermined current levels.
(2) PWM dimming means for adjusting the luminance of the backlight to the target luminance by PWM control of current supply to the LED whose current level has been switched by the current level switching means.
The liquid crystal display device according to the present invention performs PWM dimming after setting the level of the current supplied to the LED to, for example, one of a plurality of stages of current levels including the maximum current. Therefore, the luminance of the LED (backlight) can be easily adjusted in a wide luminance range including the maximum luminance. Further, the current level switching means can reduce the level of the current supplied to the LED when the target luminance of the LED is low. As a result, it is possible to reduce power consumption when adjusting the luminance of the LED (backlight) to an intermediate luminance, particularly a relatively low luminance.

For example, it is conceivable that the liquid crystal display device according to the present invention further includes a component shown in the following (3).
(3) A correspondence relationship between the target luminance of the backlight used by the PWM dimming unit and the control value of the PWM control is represented in accordance with the level of the current supplied to the LED switched by the current level switching unit. PWM control parameter setting means for setting the PWM control parameter.
In this case, the current level switching means determines in advance the level of the current supplied to the LED in the PWM control in accordance with the content of the parameter that limits the target luminance range (especially the upper limit) of the backlight. It is conceivable to switch to one of a plurality of current levels.
For example, the parameter for limiting the range (particularly, the upper limit) of the target luminance of the backlight may be one or more of the following (3-1) to (3-3). It is done.
(3-1) Video display mode information that is selected from a plurality of candidates according to an operation input, and the target luminance of the backlight or the upper limit of the target luminance is switched according to the content.
(3-2) Input information of the target luminance of the backlight input from an operation input.
(3-3) A level of brightness around the liquid crystal panel detected by a brightness sensor and used for automatic adjustment of the target brightness of the backlight.
On the other hand, the current level switching means determines the level of the current supplied to the LED according to which of a plurality of predetermined brightness categories the backlight target brightness in the PWM control belongs to. It is also conceivable to automatically switch to any one of a plurality of predetermined current levels.

  ADVANTAGE OF THE INVENTION According to this invention, the power consumption at the time of adjusting the brightness | luminance of the LED to an intermediate | middle brightness | luminance can be reduced, enabling the brightness | luminance of the backlight which uses LED as a light source to be adjustable in the wide brightness | luminance range including maximum brightness | luminance.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
FIG. 1 is a block diagram showing a schematic configuration of the liquid crystal display device X according to the embodiment of the present invention. FIG. 2 shows a procedure for setting the target luminance of the LED backlight and the LED supply current in the liquid crystal display device X. FIG. 3 is a diagram illustrating an example of a target luminance setting table in the liquid crystal display device X, FIG. 4 is a diagram illustrating a first example of a dimming table in the liquid crystal display device X, and FIG. 5 is a dimming table in the liquid crystal display device X. FIG. 6 is a diagram illustrating the relationship between the light control method and power consumption in a backlight using LEDs as light sources.

First, the configuration of the main part of the liquid crystal display device X according to the embodiment of the present invention will be described with reference to the block diagram shown in FIG.
As shown in FIG. 1, the liquid crystal display device X includes a video signal input unit 1, a video processing circuit 2, a liquid crystal driving circuit 3, a liquid crystal panel 4, an LED power feeding circuit 5, an LED backlight 6, a dimming circuit 7, a main circuit. A control circuit 8 and a brightness sensor 10 are provided.
The LED backlight 6 is arranged on the back side of the liquid crystal panel 4 for displaying images, and illuminates the liquid crystal panel 4 using a plurality of white LEDs or a plurality of sets of RGB three-color LEDs (hereinafter referred to as LEDs 9) as a light source. It is the illumination means to do.

The video signal input unit 1 is an interface for inputting a video signal. Hereinafter, the video signal input through the video signal input unit 1 is referred to as an input video signal.
In addition, the video processing circuit 2 determines the video brightness (pixel gradation) of each of the three primary colors (R, G, B) of each pixel constituting one frame image in the moving image based on the input video signal for one frame. Are sequentially generated, and the frame signal is transmitted to the liquid crystal driving circuit 3.
Further, each time the input video signal for one frame is inputted, the video processing circuit 2 uses the input video signal for the one frame as an index value of the video luminance (gradation level) for the one frame. The average luminance level (so-called APL (Average Picture Level)) Db, which is the average value of the image luminance of each pixel, is calculated, and the calculation result is transmitted to the dimming circuit 7. The average luminance level Db is a weighted average value of video luminances (gradation levels) of the three primary colors (R, G, B) of each pixel in the input video signal for one frame.

Based on the frame signal sequentially transmitted from the video processing circuit 2 at a predetermined cycle, the liquid crystal driving circuit 3 displays one frame of video (one frame image) corresponding to the frame signal on the liquid crystal panel 4. This is a circuit that sequentially displays.
More specifically, the liquid crystal driving circuit 3 responds to the gradation levels (also referred to as luminance levels) of the R, G, and B3 primary colors for the liquid crystal elements of the respective pixels provided in the liquid crystal display panel. A gradation signal having a predetermined voltage (gradation voltage) is supplied. Thereby, the liquid crystal panel 4 displays a video (moving image) based on the input video signal.

In accordance with control commands from the main control circuit 8 and the dimming circuit 7, the LED power supply circuit 5 controls the supply power to each of the LEDs 9, that is, the brightness of the LED backlight 6, and the switching control of the level of the supply current. It is a circuit that adjusts in combination with PWM control.
More specifically, the LED power supply circuit 5 supplies current to each of the LEDs 9, and the level of the current (hereinafter referred to as LED supply current) is specified current level Di inputted from the main control circuit 8. Adjust to. However, the specified current level Di is one of a plurality of predetermined current levels including the rated current (maximum current) of the LED 9.
Further, the LED power supply circuit 5 periodically turns on / off the pulse current whose current value is adjusted to the specified current level Di according to the duty ratio Dr that is an instruction value input from the dimming circuit 7. PWM dimming supplied to the LED 9 is performed. The duty ratio Dr is automatically set by the dimming circuit 7 according to the target brightness of the LED backlight 6.
That is, the LED power supply circuit 5 adjusts the luminance of the LED backlight 6 to the target luminance by PWM control of current supply to the LED 9 whose current level is switched according to the specified current level from the dimming circuit 7. It is an example of a PWM light control means.

The dimming circuit 7 is a circuit including an arithmetic circuit 71 and a register 72.
The arithmetic circuit 71 includes a reference luminance (hereinafter referred to as a reference BL luminance (Da)) of the LED backlight 6 input from the main control circuit 8 and the average luminance level input from the video processing circuit 2. Based on Db and information stored (stored) in the register 72 (target brightness setting table DTa described later), a target brightness (hereinafter referred to as target BL brightness) of the LED backlight 6 is determined (set). To do.
FIG. 3 is a diagram illustrating an example of the target brightness setting table DTa used by the arithmetic circuit 71 to determine the target BL brightness.
The target brightness setting table DTa is a look-up table showing the correspondence between the average brightness level Db and the correction coefficient of the reference BL brightness (Da).
As shown in FIG. 3, the arithmetic circuit 71 corrects the target BL luminance to be lower than the reference BL luminance (Da) when the average luminance level Db is high. The arithmetic circuit 71 corrects the target BL luminance to be higher than the reference BL luminance (Da) when the average luminance level Db is low.
In the liquid crystal display device X, the visual brightness (brightness perceived by the viewer) of the display image depends on the balance between the image brightness level of the entire display image and the brightness of the light source for the backlight. Therefore, the arithmetic circuit 71 reduces glare by lowering the luminance of the LED backlight 6 when the average luminance level Db increases, and the LED backlight 6 when the average luminance level Db decreases. The brightness of the image is sufficiently secured by increasing the brightness of the image.

Further, the arithmetic circuit 7 calculates the duty ratio Dr of the pulse current in the PWM dimming based on the target BL luminance and information (dimming table DTb described later) stored (stored) in the register 72. Determine (set). The duty ratio Dr is transmitted to the LED power supply circuit 5.
The dimming table DTb is a look-up table that represents the correspondence between the target BL brightness and the duty ratio Dr.
FIG. 4 is an example of the dimming table DTb used by the arithmetic circuit 7 when determining the duty ratio Dr.
In the liquid crystal display device X, the designated current level Di is switched according to the situation, that is, the level of the supply current to the LED 9 is switched. Therefore, the duty ratio Dr is changed according to the designated current level Di. The dimming table DTb used for determination is switched.
FIG. 4A shows an example of the dimming table DTb0 employed (selected) when the specified current level Di is the maximum current level.
FIG. 4B is an example of a dimming table DTb1 that is employed (selected) when the specified current level Di is an intermediate current level that is the second highest after the maximum current.
Similarly, the thick solid line in FIG. 4C is a graph line showing an example of the dimming table DTb4 employed (selected) when the specified current level Di is the minimum current level.
Also, the broken lines in FIG. 4C are employed when the specified current level Di is the highest current level and the first to third higher current levels among the lower intermediate current levels. It is a graph line showing an example of the light control table DTb0-DTb3 to be selected.
The arithmetic circuit 7 selects the dimming table DTb according to the specified current level Di in accordance with a command from the MPU 81.
As shown in FIG. 4, in the dimming table DTb, the relationship of the PWM duty ratio Dr with respect to the target BL luminance is linear for at least the specified current level Di set in stages.
Here, the reference BL brightness Da is set with a relatively long cycle, and the target BL brightness and the duty ratio Dr based on the reference BL brightness Da are set with a relatively short cycle (for each frame of the video). The
The dimming circuit 7 is embodied by, for example, an FPGA or an ASIC.

The brightness sensor 10 is, for example, a sensor that is provided in a frame portion around the liquid crystal panel 4 and detects the brightness level around the liquid crystal panel 4. The detection level of the brightness sensor 10 is used for automatic adjustment of the target luminance of the LED backlight 6, as will be described later.
The main control circuit 8 includes an MPU 81 that is a calculation means, an EEPROM 82 that is a nonvolatile memory, and the like, and the MPU 81 executes a control program stored in a ROM (not shown), whereby each liquid crystal display device X includes The control process of the component is executed.
For example, the main control circuit 8 performs video display mode switching processing, input of target luminance information of the LED backlight 9, and target luminance based on the input information in accordance with an operation input through a remote controller (not shown). Perform the setting process.
Here, the video display mode is selected from three types: wall picture mode, standard mode, and dynamic mode.
The wall picture mode is a video display mode in which the video processing circuit 2 displays the video on the liquid crystal panel 4 based on a video signal representing a still image or a moving image with little motion stored in the memory in advance. The wall picture mode is selected when the liquid crystal display device X is not used (when a moving image based on a video signal input through the video signal input unit 1 is not viewed), and is in a state like a wall hanging picture. Is the mode.
The dynamic mode is a mode that is selected when the liquid crystal display device X is installed in a store or the like at a store. In this dynamic mode, the video signal is corrected by the video processing circuit 2 so that the color of the display video is brighter than usual.
The normal mode is a mode that is selected when the liquid crystal display device X is installed in a normal use environment such as a room in a general household.
The main control circuit 8 performs an automatic adjustment process of the target luminance of the LED backlight 6 based on the detection level of the brightness sensor 10. Details thereof will be described later.

Next, with reference to the flowchart shown in FIG. 2, the procedure for setting the target brightness and LED supply current of the LED backlight 6 in the liquid crystal display device X will be described. Note that the processing shown in FIG. 2 is repeatedly performed as needed while the liquid crystal display device X is activated. Further, S1, S2,... Shown below represent identification codes of processing procedures (steps).
[Step S1]
First, the MPU 81 in the main control circuit 8 sets a preset manually set backlight luminance to an initial value of the reference BL luminance (Da) that is used as a reference for the target luminance of the LED backlight 6 (S1). ). Thereafter, the initial value is corrected as necessary, and the final reference BL luminance (Da) is obtained.
The manually set backlight luminance is a reference value of the luminance of the LED backlight 6 set based on a manual operation by the user.
That is, the manually set backlight luminance is the luminance level of the LED backlight 6 that is manually input by the MPU 81 through an operation input through a remote controller (not shown). For example, when any of 33 levels of information from −16 to +16 is input through the remote controller, the manually set backlight luminance corresponding to the level information is set and recorded in the EEPROM 82. .

[Step S2]
Next, the MPU 81 corrects the reference BL luminance (Da) according to the detection level of the brightness sensor 10 (S2). More specifically, the MPU 81 corrects the reference BL luminance (Da) to be increased within a predetermined range as the detection level of the brightness sensor 10 is higher (the brighter the surroundings are), The lower the detection level of the brightness sensor 10 (the darker the surroundings), the lower the reference BL brightness (Da) within a predetermined range.
Thereby, it is possible to prevent the user from feeling that the display image is dark when the surroundings become bright or that the display image is dazzling when the surroundings become dark.

[Step S3]
Next, when the video display mode is the wall picture mode, the MPU 81 limits the reference BL luminance (Da) to a predetermined intermediate luminance (hereinafter referred to as a first designated intermediate luminance). . That is, when the video display mode is the wall picture mode, the MPU 81 determines that the reference BL luminance (Da) is the first designated intermediate luminance if the reference BL luminance (Da) is higher than the first designated intermediate luminance. Otherwise, the reference BL brightness (Da) is not corrected. Further, when the video display mode is other than the wall picture mode, the reference BL luminance (Da) is not corrected.
When the wall picture mode is selected, the brightness and clearness of the display image are not particularly required. Therefore, in order to reduce the power consumption by suppressing the brightness of the LED backlight 6 to a relatively low brightness, this step S3 Is performed.
Thus, the video display mode is an operation mode for switching the upper limit of the target luminance of the LED backlight 6. Note that, when the video display mode is the wall picture mode, it is conceivable to correct the reference BL luminance (Da) in the direction of decreasing (switch the target luminance).

[Step S4]
Next, the MPU 81 determines whether or not the reference BL luminance (Da) obtained by the processing in steps S1 to S3 is equal to or lower than a predetermined intermediate luminance (hereinafter referred to as second designated intermediate luminance). Is discriminated (S4). The second designated intermediate luminance is higher than the first designated intermediate luminance.

[Step S5]
When the reference BL luminance (Da) is not less than or equal to the second designated intermediate luminance, the MPU 81 executes the following three processes shown in (a1) to (a3) together, and thereafter To step S1 described above.
(A1) The designated current level Di (that is, the level of current supplied to the LED 9) is set to the maximum level (rated current level of the LED 9), and the designated current level Di is output to the LDE power supply circuit 5. .
(A2) The dimming table DTb used in the dimming circuit 7 is selected so that a candidate to be used when the specified current level Di is the maximum level is selected from a plurality of dimming table candidates. A command is output to the dimming circuit 7.
(A3) The reference BL luminance (Da) is output to the dimming circuit 7.

[Step S6]
On the other hand, when the reference BL luminance (Da) is equal to or lower than the second designated intermediate luminance, the MPU 81 executes the following three processes shown in (b1) to (b3) together, and then performs a process. To step S1 described above.
(B1) The designated current level Di (that is, the level of the current supplied to the LED 9) is determined in a plurality of stages (for example, about 2 to 5 stages) determined in advance according to the reference BL luminance (Da). Set (switch) one of the intermediate current levels.
(B2) For the dimming circuit 7, the dimming table DTb used in the dimming circuit 7 is selected so that a candidate corresponding to the specified current level Di is selected from a plurality of dimming table candidates. Output a command.
(B3) The reference BL luminance (Da) is output to the dimming circuit 7.

[Step S7]
As described above, the arithmetic circuit 71 in the dimming circuit 7 uses the reference BL luminance (Da) set by the MPU 81 as a reference and performs correction based on the average luminance level Db. To set the target BL brightness (S7, see FIG. 3). Further, the arithmetic circuit 7 applies the target BL brightness to the dimming table DTb set in step S5, that is, the dimming table DTb switched according to the designated current level Di, The duty ratio Dr in the PWM control of the LED 9 is automatically set (S7).
[Step S8]
The LED power supply circuit 5 adjusts the level of the current supplied to the LED 9 so as to coincide with the specified current level Di set in step S5 (S8).
Further, the LED power supply circuit 5 executes PWM control of the LED 9 according to the duty ratio Dr (S8).

As described above, the MPU 81 has a plurality of stages in which the designated current level Di is determined in advance based on the manually set backlight luminance, the video display mode, and the detection level of the brightness sensor 10. Switch to one of the current levels (S1, S2, S3, S5, S6). The rated current (maximum current) of the LED 6 is included in the plurality of current levels. Further, even if there is only one kind of intermediate current level that can be set in step S6, it is set to one of a plurality of stages of current levels as a whole together with the maximum current level set in step S5. It can be said.
Here, the manually set backlight luminance is input information of the target luminance of the LED backlight 6 input from an operation input.
The detection level of the brightness sensor 10 is a brightness level around the liquid crystal panel 4 used for automatic adjustment of the target luminance of the LED backlight 6.
The video display mode is video display mode information that is selected from a plurality of candidates according to an operation input, and the target luminance of the LED backlight 6 or the upper limit of the target luminance is switched according to the contents.
These parameters of the manually set backlight luminance, the detection level of the brightness sensor 10 and the video display mode are parameters for setting the reference BL luminance (Da) according to the contents thereof. Further, as shown in FIG. 3, the target BL brightness is set within a certain range based on the reference BL brightness (Da). Therefore, each parameter of the manually set backlight luminance, the detection level of the brightness sensor 10 and the video display mode is an example of a parameter for limiting the range of the target luminance of the LED backlight 6.

The liquid crystal display device X performs PWM dimming after setting the level of the current supplied to the LED 9 to any one of a plurality of levels including the maximum current. Therefore, the luminance of the LED backlight 6 can be adjusted in a wide luminance range including the maximum luminance. At this time, the PWM duty ratio Dr can be set linearly and simply with respect to the target luminance at least for each of the designated current levels Di set stepwise (see FIG. 4).
The designated current level Di is lowered by the main control circuit 8 when the target brightness of the LED backlight 6 is low. As a result, it is possible to reduce power consumption when adjusting the luminance of the LED backlight 6 to an intermediate luminance, in particular, a relatively low luminance.

The embodiment described above is an example in which the dimming table DTb corresponding to the designated current level Di that is switched stepwise in a relatively long cycle is set (selected). Other embodiments are also conceivable.
For example, each time the dimming circuit 7 sets a new target BL brightness (for each frame of video), the dimming circuit 7 determines which of the plurality of predetermined brightness categories the target BL brightness belongs to Then, it is conceivable to automatically set (switch) the designated current level Di according to the determination result (luminance classification) (an example of current level switching means). In this case, the specified current level Di is transmitted from the dimmer circuit 7 to the LED power supply circuit 5.
However, the relationship between the target BL luminance and the duty ratio Dr represented by the dimming table DTb ′ used in this embodiment is linear as the target BL luminance is switched as shown in FIG. It becomes non-linear that breaks. The example shown in FIG. 5 is an example in which the target BL luminance is divided into five levels of luminance (L1 to L5), and the specified current level Di different for each division is set.
In such an embodiment, as shown in FIG. 5, since the duty ratio Dr in the PWM control of the LED 9 is always maintained at a high value, the energy efficiency is high and the power saving effect is further enhanced.

  The present invention is applicable to a liquid crystal display device.

1 is a block diagram illustrating a schematic configuration of a liquid crystal display device X according to an embodiment of the present invention. The flowchart showing the procedure of the setting process of the target brightness | luminance and LED supply current of LED backlight in the liquid crystal display device X. FIG. The figure showing an example of the target luminance setting table in the liquid crystal display device X. The figure showing the 1st example of the light control table in the liquid crystal display device. The figure showing the 2nd example of the light control table in the liquid crystal display device X. FIG. The figure which illustrated the relationship between the light control method and power consumption in the backlight which uses LED as a light source.

Explanation of symbols

X: Liquid crystal display device 1: Video signal input unit 2: Video processing circuit 3: Liquid crystal drive circuit 4: Liquid crystal panel 5: LED power supply circuit 6: LED backlight 7: Dimming circuit 8: Main control circuit 9: LED
10: Brightness sensors S1, S2,...: Processing procedure (step)

Claims (4)

  1. A liquid crystal display device having a backlight for illuminating a liquid crystal panel using an LED as a light source,
    Current level switching means for switching the level of the current supplied to the LED to any one of a plurality of predetermined current levels;
    PWM dimming means for adjusting the luminance of the backlight to a target luminance by PWM control of current supply to the LED whose current level has been switched by the current level switching means;
    A liquid crystal display device comprising:
  2. A PWM control parameter representing the correspondence between the target brightness of the backlight used by the PWM dimming means and the control value of the PWM control according to the level of the current supplied to the LED switched by the current level switching means PWM control parameter setting means for setting
    Based on the content of the parameter that limits the range of the target luminance of the backlight, the current level switching means changes the level of the current supplied to the LED in the PWM control to a plurality of predetermined current levels. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is switched to any one.
  3. A parameter for limiting the range of the target brightness of the backlight is
    Video display mode information that is selected from a plurality of candidates according to the operation input, and the target luminance of the backlight or the upper limit of the target luminance is switched according to the contents;
    Input information of the target brightness of the backlight input from the operation input;
    A level of brightness around the liquid crystal panel detected by a brightness sensor and used to automatically adjust the target brightness of the backlight;
    The liquid crystal display device according to claim 2, which is one or more of the above.
  4.   The current level switching means automatically changes the level of the current supplied to the LED depending on which of the plurality of predetermined brightness categories the backlight target brightness in the PWM control belongs to. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is switched to any one of a plurality of predetermined current levels.
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Cited By (3)

* Cited by examiner, † Cited by third party
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