JP2013200518A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of reducing power consumption and capable of elongating the life of a light source.SOLUTION: A liquid crystal display device 10 includes: a liquid crystal panel 11; a backlight unit 12 in which in each unit area A set in a bottom plate part 21a, an LED 25 is installed at each of a plurality of predetermined arrangement positions; a plurality of power sources 41 each being so provided as to be associated with each of the arrangement positions; a plurality of LED driver 42, each of which is so provided as to be associated with each power source 41 and drives the LED 25 associated with the power source 41 by means of power supplied from the associated power source 41; a storage part 35 for storing a brightness level of a display screen; and a brightness control part 40 for controlling supply/shutdown of power to each LED driver 42 in such a manner that power is supplied to LED drivers 42 of the number corresponding to the brightness level, and that power is not supplied to rest of LED drivers 42.

Description

  The present invention relates to a liquid crystal display device.

  Conventionally, image display devices such as liquid crystal display devices have been equipped with a function that can adjust the brightness (brightness) of the display screen in order to reduce power consumption and improve the visibility of the display screen. The user operates a remote control device (hereinafter abbreviated as “remote control”) or the like, and selects one of a plurality of brightness levels provided in advance, whereby the brightness of the display screen is displayed. Can be changed to a desired brightness.

  In the case of a liquid crystal display device, the brightness of the display screen is adjusted by dimming the backlight provided on the back side of the liquid crystal panel according to the brightness level set by the user. Recently, as a backlight of a liquid crystal display device, a light emitting diode (Light Emitting Diode; hereinafter abbreviated as “LED”) arranged in a plane is used. Pulse width modulation (hereinafter abbreviated as “PWM”) dimming method is adopted.

  FIG. 12 is a diagram showing the lighting state of each LED when the brightness level is changed stepwise in a conventional liquid crystal display device in which a plurality of LEDs are controlled by PWM dimming, and FIG. The lighting state of each LED when the brightness level is set to the maximum value is shown, and FIG. 12D shows the lighting state of each LED when the brightness level is set to the minimum value.

  As shown in FIG. 12, the conventional liquid crystal display device is configured by disposing an LED as a light source for each section q obtained by equally dividing the display screen Q in the vertical direction and the horizontal direction, and according to the brightness level set by the user. When adjusting the brightness of the display screen Q, the duty ratio of the PWM signal commonly supplied to each LED is changed to a duty ratio corresponding to the set brightness level, so that the entire surface of the backlight can be adjusted. PWM dimming is performed evenly. The duty ratio of the PWM signal is the ratio of the LED lighting period to one cycle of the PWM signal.

  As described above, in the conventional liquid crystal display device, the backlight is dimmed by the time division processing using the PWM signal. However, in such a dimming method, there is a limit in reducing the power consumption of the liquid crystal display device. In addition, there is a limit to extending the life of the LED as the light source.

  For example, in Patent Document 1, in a backlight device including a plurality of LEDs, by driving to repeat alternately a state in which all LEDs are lit and a state in which any one LED is unlit, It is described that the power consumption of the backlight device is reduced. However, Patent Document 1 does not describe or suggest a function for adjusting the brightness of the display screen according to the brightness level set by the user and a method for realizing the function.

JP 2008-22503 A

  An object of the present invention is to provide a liquid crystal display device capable of reducing power consumption as much as possible and extending the lifetime of a light source.

The present invention is a liquid crystal display device comprising a liquid crystal panel having a display screen capable of displaying an image, the brightness of the display screen being adjustable in a plurality of stages,
A backlight unit in which a plurality of unit areas of a predetermined size are set and a light source is installed at each of a plurality of predetermined arrangement positions in each unit area of the light source installation part;
A plurality of power supply units provided in association with each arrangement position of the unit region;
A plurality of light source driving units provided in association with each power supply unit, wherein each light source driving unit is installed at an arrangement position associated with the power supply unit by power supplied from the associated power supply unit. A plurality of light source driving units for driving the light source;
A setting unit for setting one stage among a plurality of brightness stages associated with the number of light source driving units to which power is supplied;
A storage unit for storing the one stage set by the setting unit;
A luminance control unit that controls power supply to each light source driving unit so that power is supplied only to a predetermined number of light source driving units corresponding to the one stage stored in the storage unit. This is a liquid crystal display device.

  According to the present invention, the luminance control unit changes the light source driving unit to which power is supplied at a predetermined cycle.

In the invention, the light source driving unit drives the light source by a pulse width modulation signal,
The luminance control unit may change a duty ratio of the pulse width modulation signal in accordance with one stage of brightness stored in the storage unit.

  According to the present invention, the brightness of the display screen is adjusted by changing the number of light sources to be turned on in the unit area, and the light sources are turned off by shutting off the supply of power to the light source driving unit. ing. Therefore, compared with the conventional dimming method by changing the duty ratio of the PWM signal, the power consumed by the light source driving unit can be reduced, and thus the power consumption of the liquid crystal display device is reduced as much as possible. be able to.

  Further, according to the present invention, the brightness of the display screen is adjusted to a predetermined brightness by changing the combination of light sources to be turned on for each unit area at a predetermined cycle. The life of the light source can be extended.

  Further, according to the present invention, the dimming method by changing the number of light sources to be lit in the unit area and the dimming method by changing the duty ratio of the pulse width modulation signal are used in combination. You can finely adjust the brightness.

It is a disassembled perspective view which decomposes | disassembles and shows the structure of the liquid crystal display device 10 which concerns on one Embodiment of this invention. It is sectional drawing which shows the structure of the liquid crystal display device 10 which concerns on this embodiment. FIG. 3A is a diagram illustrating a configuration of a backlight unit 12 in the liquid crystal display device 10, and FIG. 3A illustrates a plurality of LEDs 25 arranged on the bottom plate portion 21 a as viewed from the liquid crystal panel 11 side, and FIG. ) Is an enlarged view of one unit region A among the plurality of unit regions A in FIG. It is a block diagram which shows the structure of the liquid crystal display device 10 which concerns on this embodiment. It is a timing chart which shows the switching timing of lighting / extinguishing of each LED25A, 25B, 25C, 25D when the setting value of a brightness level is set to 75. It is a figure which shows the drive state of each LED25A, 25B, 25C, 25D when the setting value of a brightness level is set to 75. FIG. It is a figure which shows the drive state of each LED25A, 25B, 25C, 25D when the setting value of a brightness level is set to 50. FIG. It is a figure which shows the drive state of each LED25A, 25B, 25C, 25D when the setting value of a brightness level is set to 25. FIG. It is a figure which shows the drive state in each period T1-T4 of each LED25A, 25B, 25C, 25D. It is a flowchart which shows the operation | movement procedure of the setting process of the switching period of LED25 in an area light control system. It is a flowchart which shows the operation | movement procedure of the adjustment process of the brightness of a display screen by an area light control system. It is a flowchart which shows the operation | movement procedure of the adjustment process of the brightness of a display screen by an area light control system. It is a figure which shows the lighting state of each LED when the brightness level is changed in steps in the conventional liquid crystal display device in which a plurality of LEDs are PWM dimming controlled.

  FIG. 1 is an exploded perspective view showing an exploded configuration of a liquid crystal display device 10 according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing the configuration of the liquid crystal display device 10 according to the present embodiment. In FIG. 1, the frame 15, the plurality of substrates 16, and the back cabinet 17 are omitted.

  The liquid crystal display device 10 according to the present embodiment generally includes a rectangular liquid crystal panel 11, a backlight unit 12 provided on the back side of the liquid crystal panel 11, a plurality of optical members 13, and a bezel 14. In addition, the brightness of the display screen displayed on the liquid crystal panel 11 can be adjusted by dimming control of the backlight 22 mounted on the backlight unit 12. Hereinafter, in the liquid crystal display device 10, a direction parallel to the long side of the liquid crystal panel 11 is referred to as “lateral direction X”, and a direction parallel to the short side of the liquid crystal panel 11 is referred to as “vertical direction Y”.

  The liquid crystal panel 11 is an active matrix driving type liquid crystal panel, and a pair of light-transmitting insulating substrates formed in a horizontally long rectangular shape and an optical field applied between the pair of insulating substrates along with the application of an electric field. A liquid crystal layer formed by encapsulating liquid crystal molecules, which are substances whose properties change, and a pair of insulating substrates are bonded together with a sealant while maintaining a gap corresponding to the thickness of the liquid crystal layer And has a rectangular flat plate shape as a whole.

  Of the pair of insulating substrates, one substrate is a CF (Color Filter) substrate and the other substrate is a TFT (Thin Film Transistor) substrate. The TFT substrate has a plurality of gate bus lines extending parallel to each other as a plurality of display wirings on the inner surface side facing the liquid crystal layer, and a plurality of source bus lines extending parallel to each other in a direction intersecting each gate bus line. In the vicinity of the intersection of each gate bus line and each source bus line, a thin film transistor (Thin Film Transistor; hereinafter referred to as “TFT”) as a switching element connected to each gate bus line and each source bus line. Each TFT is connected to a plurality of pixel electrodes provided in a matrix corresponding to each pixel. The pixel electrode is made of a transparent electrode such as ITO (Indium Tin Oxide) or ZnO (Zinc Oxide).

  On the other hand, the CF substrate is provided with a plurality of color filters on the inner surface facing the liquid crystal layer so as to overlap each pixel electrode of the TFT substrate, and a light shielding layer (black matrix) for preventing color mixture between the color filters. ) Is formed. The color filter is provided so that, for example, subpixels of three colors of R (red), G (green), and B (blue) are alternately arranged. A common electrode is provided so as to cover the color filters and the black matrix. In addition, an alignment film for aligning liquid crystal molecules contained in the liquid crystal layer is formed on the inner surface side of each substrate, and a polarizing plate is pasted on the outer surface side opposite to the inner surface side of each substrate. It is attached.

  The backlight unit 12 is formed in a substantially box shape that opens to one side, and includes a backlight chassis 21 that holds the liquid crystal panel 11 between an end portion on the opening side and the bezel 14, and an interior of the backlight chassis 21. The liquid crystal panel 11 includes a backlight 22 to be accommodated and a reflection sheet 23 laid inside the backlight chassis 21, and is disposed so as to face the back surface 11 b that is the surface of the liquid crystal panel 11 on the TFT substrate side.

  The backlight 22 is installed on the inner surface 24a that is the surface facing the liquid crystal panel 11 in the bottom plate portion 21a of the backlight chassis 21, and irradiates the liquid crystal panel 11 with light when supplied with electric power. The light applied to the liquid crystal panel 11 passes through the liquid crystal panel 11, whereby an image is displayed in a visible state on the front surface 11 a that is the surface of the liquid crystal panel 11 on the CF substrate side.

  The backlight 22 is realized by a plurality of LEDs (Light Emitting Diodes) 25. As will be described in detail later, the plurality of LEDs 25 are mounted on the LED substrate 26, installed on the inner surface 24a of the bottom plate portion 21a, and arranged in a matrix along the inner surface 24a.

  The reflection sheet 23 is a sheet-like member made of a synthetic resin such as PET (polyethylene terephthalate) that exhibits a white color with excellent light reflectivity. The reflection sheet 23 exposes a plurality of LEDs 25, and the inner peripheral surface of the backlight chassis 21 is entirely formed. It is laid so as to cover. By this reflection sheet, most of the light emitted from the backlight 22 is guided to the opening side of the backlight chassis 21.

  The plurality of optical members 13 are disposed between the liquid crystal panel 11 and the backlight unit 12. The optical member 13 includes a diffusion plate that diffuses light emitted from the backlight 22 in the surface direction of the liquid crystal panel 11 and a plurality of functional resin sheets that are provided with various functions for improving display image quality. included. Examples of the functional resin sheet include a diffusion sheet, a lens sheet, and a polarizing reflection sheet. These optical members 13 are held at appropriate positions between the liquid crystal panel 11 and the backlight unit 12 by a resin frame 15.

  A plurality of substrates 16 are attached to the outer surface 24 b of the bottom plate portion 21 a in the backlight chassis 21. The plurality of substrates 16 include, for example, a main interface substrate that controls the overall operation of the liquid crystal display device 10 and performs predetermined processing such as scaling processing on a video signal input from the outside. A power supply circuit board that supplies power to each part, an LED driver board that drives a plurality of LEDs 25, an LCD-TCON (Liquid Crystal Display-Timing Controller) board that controls driving of the liquid crystal panel 11, and received radio waves and external input And a tuner for generating a video signal and an audio signal of a predetermined channel based on an input signal from the. The plurality of substrates 16 are respectively covered with a cover member (not shown). Further, a back cabinet 17 made of resin is mounted on the back side of the liquid crystal display device 10 to configure the appearance of the back side of the liquid crystal display device 10.

  The bezel 14 includes a rectangular frame-shaped covering portion 14a that covers the peripheral edge portion of the front surface 11a of the liquid crystal panel 11 from the outside, and a rectangular tube-shaped side wall that is connected to the covering portion 14a and is erected on the outer edge portion of the covering portion 14a. Part 14b, and is formed of a resin material or a metal material.

  FIG. 3 is a diagram illustrating a configuration of the backlight unit 12 in the liquid crystal display device 10, and FIG. 3A illustrates a plurality of LEDs 25 arranged on the bottom plate portion 21a as viewed from the liquid crystal panel 11 side. FIG. 3B shows an enlarged view of one unit region A among the plurality of unit regions A in FIG.

  As shown in FIG. 3A, in the present embodiment, the LED 25 is provided for each rectangular divided region d obtained by equally dividing a predetermined rectangular region D in the bottom plate portion 21a in the horizontal direction X and the vertical direction Y. Has been placed. That is, the plurality of LEDs 25 are arranged in a matrix along the horizontal direction X and the vertical direction Y on the bottom plate portion 21 a of the backlight chassis 21.

  The plurality of LEDs 25 are grouped into a predetermined number. The predetermined number corresponds to the number of brightness levels of the display screen that can be adjusted by an area dimming method described later.

  In the present embodiment, as shown in FIG. 3A, the plurality of LEDs 25 are divided into groups for each unit area A defined by vertical and horizontal 2 × 2 divided areas d. Four LEDs 25 are included. That is, the liquid crystal display device 10 according to the present embodiment can adjust the brightness of the display screen in four stages by an area dimming method described later.

  Here, as shown in FIG. 3B, among the four LEDs 25 in each unit region A, the LED 25 arranged near the X1 in the horizontal direction and near the Y1 in the vertical direction is expressed as “LED25A”. The LED 25 arranged near the other X2 in the horizontal direction and near the other Y2 in the vertical direction is expressed as “LED25B”, and the LED 25 arranged near the other X2 in the horizontal direction and near the one Y1 in the vertical direction is expressed as “LED25C”. The LED 25 arranged near the one side X1 in the horizontal direction and near the other side Y2 in the vertical direction will be referred to as “LED 25D”. Therefore, for example, the LEDs 25A are provided every other one in the horizontal direction X and the vertical direction Y in the LEDs 25 arranged in a matrix. The same applies to the LEDs 25B, 25C, and 25D.

  In the present embodiment, a plurality of LEDs 25 are grouped for each unit area A defined by a vertical and horizontal 2 × 2 divided area d. In other embodiments, the LEDs 25 are defined by a vertical and horizontal 3 × 3 divided area d. A plurality of LEDs 25 may be grouped for each unit area. In this case, the brightness of the display screen can be adjusted to nine levels by an area dimming method described later. In still another embodiment, a plurality of LEDs 25 may be grouped for each unit area defined by a vertical and horizontal 4 × 3 divided area d. In this case, the brightness of the display screen can be adjusted to 12 levels by an area dimming method described later.

  FIG. 4 is a block diagram showing a configuration of the liquid crystal display device 10 according to the present embodiment. In addition to the liquid crystal panel 11 and the LEDs 25A, 25B, 25C, and 25D, the liquid crystal display device 10 includes a video input unit 31, a display control unit 32, an OSD (On Screen Display) drawing unit 33, a clock 34, Storage unit 35, communication unit 36, temperature sensor 37, operation input unit 38, CPU (Central Processing Unit) 39, luminance control unit 40, power supplies 41A, 41B, 41C, 41D, and LED drivers 42A, 42B, 42C, 42D.

  A video signal to be displayed on the liquid crystal panel 11 is input to the video input unit 31 from the outside. When the display control unit 32 acquires a video signal via the video input unit 31, the display control unit 32 performs various processes such as scaling processing, gamma correction processing, color space conversion processing, synchronization detection processing, and OSD display processing on the video signal. Then, source drive data and gate drive data for driving the liquid crystal panel 11 are generated, and the liquid crystal panel 11 is driven based on the generated drive data.

  When a predetermined operation signal is input to the CPU 39, the OSD drawing unit 33 generates image information of various OSD screens according to a command from the CPU 39. For example, when an operation signal for changing the setting value of the brightness level of the display screen is input to the CPU 39, the OSD drawing unit 33 causes the user to select the brightness level of the display screen according to a command from the CPU 39. Image information of the brightness setting screen is generated and transmitted to the display control unit 32. When the display control unit 32 receives the image information of the OSD screen from the OSD drawing unit 33, the display control unit 32 performs OSD display processing and displays the OSD screen corresponding to the image information at an appropriate place on the display screen.

  The clock 34 measures the current time, and outputs the measured current time to the CPU 39. The temperature sensor 37 is provided in the backlight unit 12 and outputs detected temperature information to the CPU 39.

  The communication unit 36 has a wired or wireless communication function, and exchanges various information and signals with an external device. The communication unit 36 includes a light receiving unit (not shown) capable of receiving infrared light emitted from a remote control device (hereinafter abbreviated as “remote controller”). An operation signal corresponding to the infrared ray is transmitted to the CPU 39.

  The operation input unit 38 includes a plurality of operation switches (not shown) that are directly operated by the user. When the operation switch is operated by the user, the operation input unit 38 transmits an operation signal corresponding to the operation switch to the CPU 39.

  The storage unit 35 is realized by a ROM (Read Only Memory), a RAM (Random Access Memory), and the like, stores a control program executed by the CPU 39 and data necessary for executing the control program, and is used as a work area of the CPU 39. It is done. In the present embodiment, the storage unit 35 is provided with a storage area for storing the setting value of the brightness level of the display screen and the switching cycle of the LED 25.

  The CPU 39 controls the entire liquid crystal display device 10 according to a control program stored in the storage unit 35. In the present embodiment, the CPU 39 notifies the brightness control unit 40 of the brightness level setting value based on the brightness level setting value of the display screen stored in the storage area of the storage unit 35. Send a brightness level notification signal. This brightness level notification signal is constantly transmitted from the CPU 39 to the luminance control unit 40 while the liquid crystal display device 10 is in operation.

  When the CPU 39 receives an instruction to change the setting value of the brightness level of the display screen via the communication unit 36 or the operation input unit 38, the CPU 39 sets the brightness level of the display screen stored in the storage area of the storage unit 35. The setting value is updated to the setting value of the brightness level of the display screen newly set by the user, and the setting value of the updated brightness level of the display screen is transmitted to the brightness control unit 40 by the brightness level notification signal. Notice. That is, the setting unit is realized by the communication unit 36 or the operation input unit 38 and the CPU 39.

  Based on the brightness level notification signal input from the CPU 39, the luminance control unit 40 adjusts the power sources 41A, 41B, and 41C so that the backlight 22 is dimmed to a predetermined brightness by an area dimming method that will be described later. , 41D to control power supply / cutoff to the corresponding LED drivers 42A, 42B, 42C, 42D.

  Specifically, the luminance control unit 40, for each power supply 41A, 41B, 41C, 41D, based on the brightness level notification signal input from the CPU 39, corresponds to the LED driver from each power supply 41A, 41B, 41C, 41D. The power supply state in which power is supplied to 42A, 42B, 42C, and 42D and the power cut-off state in which power supply is interrupted are switched.

  In addition, a failure notification signal for notifying that a failure has occurred in the corresponding power supplies 41A, 41B, 41C, and 41D is input to the luminance control unit 40 from failure detection units 51A, 51B, 51C, and 51D, which will be described later, A failure notification signal for notifying that a failure has occurred in the corresponding LEDs 25A, 25B, 25C, and 25D is input from LED failure detection units 52A, 52B, 52C, and 52D described later. When such a failure notification signal is input, the luminance control unit 40 disables the power sources 41A, 41B, 41C, 41D in which the failure has occurred or the LEDs 25A, 25B, 25C, 25D in which the failure has occurred. can do.

  Each power supply 41A, 41B, 41C, 41D supplies driving power to the corresponding LED driver 42A, 42B, 42C, 42D, respectively. That is, the power source 41A supplies driving power to the LED driver 42A, the power source 41B supplies driving power to the LED driver 42B, and the power source 41C supplies driving power to the LED driver 42C. The power supply 41D supplies driving power to the LED driver 42D.

  Each of the power supplies 41A, 41B, 41C, 41D is provided with a failure detection unit 51A, 51B, 51C, 51D for detecting an abnormality in its own power supply. That is, the power supply 41A includes a failure detection unit 51A for detecting an abnormality in the power supply 41A, the power supply 41B includes a failure detection unit 51B for detecting an abnormality in the power supply 41B, and the power supply 41C includes the power supply 41C. A failure detecting unit 51C for detecting an abnormality in the power source 41D is provided, and a power source 41D is provided with a failure detecting unit 51D for detecting an abnormality in the power source 41D.

  Each LED driver 42A, 42B, 42C, 42D supplies current to the corresponding LED 25A, 25B, 25C, 25D based on the driving power supplied from the corresponding power supply 41A, 41B, 41C, 41D, The corresponding LEDs 25A, 25B, 25C, 25D are driven.

  That is, the LED driver 42A is driven by supplying current to the LEDs 25A in each unit region A among the plurality of LEDs 25 based on the driving power supplied from the power source 41A, and the LED driver 42B is driven by the power source 41B. Based on the supplied driving power, among the plurality of LEDs 25, the LED 25B in each unit area A is supplied with current to be driven, and the LED driver 42C is based on the driving power supplied from the power supply 41C. The LED 25 is driven by supplying a current to the LED 25C in each unit area A among the plurality of LEDs 25, and the LED driver 42D is provided with each unit area among the plurality of LEDs 25 based on the driving power supplied from the power source 41D. A current is supplied to the LED 25D in A to drive it.

  Each LED driver 42A, 42B, 42C, 42D detects the failure of the LEDs 25A, 25B, 25C, 25D by detecting the forward voltage drop Vf of the corresponding LEDs 25A, 25B, 25C, 25D. Detectors 52A, 52B, 52C, and 52D are provided.

  That is, the LED failure detection unit 52A detects the forward drop voltage Vf of each LED 25A to detect that the LED 25A has failed, and the LED failure detection unit 52B detects the forward drop voltage Vf of each LED 25B. The LED failure detection unit 52C detects the failure of the LED 25C by detecting the forward voltage drop Vf of each LED 25C, and the LED failure detection unit 52D detects the failure of the LED 25D. The direction drop voltage Vf is detected to detect that the LED 25D has failed.

  Hereinafter, the operation of the liquid crystal display device 10 according to the present embodiment will be described. The liquid crystal display device 10 according to the present embodiment is configured to be capable of adjusting the brightness of the display screen, and adopts an area dimming method as the dimming method of the backlight 22 for adjusting the brightness of the display screen. Yes.

  Here, the area dimming method means that a plurality of LEDs 25 provided in the backlight unit 12 are grouped into a plurality of predetermined unit areas A as shown in FIG. Among the plurality of LEDs 25, the light is adjusted by controlling the number of LEDs 25 to be lit.

  In the present embodiment, as described above, the plurality of LEDs 25 are grouped for each unit area A defined by the vertical and horizontal 2 × 2 divided areas d. In each unit area A, four LEDs 25 are provided. include. Therefore, in this embodiment, the brightness of the display screen can be adjusted in four stages by changing the number of LEDs 25 to be lit between 1 to 4 in each unit area A.

  Turning on / off the LEDs 25A, 25B, 25C, and 25D is controlled by supplying / cutting off power from the power sources 41A, 41B, 41C, and 41D to the corresponding LED drivers 42A, 42B, 42C, and 42D. For example, when the LED 25A is switched from the unlit state to the lit state, power supply from the power source 41A is started to the LED driver 42A, and when the LED 25C is switched from the lit state to the unlit state, the power source 41C is switched to the LED driver 42C. The power supply of is cut off.

  Here, the setting value of the brightness level when the display screen is brightest is defined as 100. That is, when the set value of the brightness level is set to 100, all the LEDs 25 included in each unit area A are turned on.

  In the present embodiment, four setting values 100, 75, 50, and 25 are prepared in advance as brightness level setting values that can be selected by the user, and the brightness level setting value is set to 100. All four LEDs 25 are turned on. When the brightness level setting value is set to 75, three LEDs 25 are turned on in each unit area A, and when the brightness level setting value is set to 50, in each unit area A, When the two LEDs 25 are turned on and the set value of the brightness level is set to 25, one LED 25 is turned on in each unit area A.

  Moreover, when driving the plurality of LEDs 25 using such an area dimming method, the liquid crystal display device 10 according to the present embodiment replaces the LEDs 25 to be lit at predetermined intervals for each unit region A. In other words, the combination of the LEDs 25 to be lit is sequentially changed. Here, the predetermined cycle may be, for example, a cycle set by the user or a cycle that matches one cycle of the vertical synchronization signal.

  FIG. 5 is a timing chart showing the switching timing of turning on / off the LEDs 25A, 25B, 25C, and 25D when the brightness level setting value is set to 75. 5A shows the vertical synchronization signal, FIG. 5B shows the switching timing of turning on / off the LED 25A, and FIG. 5C shows the switching timing of turning on / off the LED 25B. 5 (d) shows the switching timing for turning on / off the LED 25C, and FIG. 5 (e) shows the switching timing for turning on / off the LED 25D. 5B to 5E, the high level corresponds to the lighting state of the LED 25, and the low level corresponds to the lighting state of the LED 25.

  FIG. 6 is a diagram illustrating the driving state of the LEDs 25A, 25B, 25C, and 25D when the brightness level setting value is set to 75, and FIG. 6A is a period T1 in FIG. 6 (b) shows the driving state of each LED 25A, 25B, 25C, 25D, FIG. 6 (b) shows the driving state of each LED 25A, 25B, 25C, 25D in period T2 in FIG. 5, and FIG. FIG. 6D shows the driving state of each LED 25A, 25B, 25C, 25D in the period T3 in FIG. 5, and FIG. 6D shows the driving state of each LED 25A, 25B, 25C, 25D in the period T4 in FIG. .

  With reference to FIGS. 5 and 6, the switching process when the brightness level setting value is set to 75 will be described. First, at the rise time t1 of the pulse of the vertical synchronization signal, the supply of power from the power source 41A to the LED driver 42A is cut off, whereby the LED 25A is switched from the on state to the off state, and from the power source 41D to the LED driver 42D. Supply of electric power is started, and thereby the LED 25D is switched from the unlit state to the lit state. At this time, the LEDs 25B and 25C are kept on. Therefore, in the period T1 from the time t1 to the pulse rising time t2 immediately after that, as shown in FIG. 6A, the LEDs 25B, 25C, and 25D are turned on and the LED 25A is turned off in each unit area A.

  Then, at the rise time t2 of the pulse of the vertical synchronization signal, the supply of power from the power source 41B to the LED driver 42B is cut off, whereby the LED 25B is switched from the on state to the off state, and from the power source 41A to the LED driver 42A. Supply of electric power is started, and thereby the LED 25A is switched from the unlit state to the lit state. Therefore, in the period T2 from the time t2 to the pulse rising time t3 immediately after that, as shown in FIG. 6B, the LEDs 25A, 25C, and 25D are turned on and the LED 25B is turned off in each unit area A.

  Then, at the rise time t3 of the pulse of the vertical synchronization signal, the power supply from the power source 41C to the LED driver 42C is cut off, whereby the LED 25C is switched from the on state to the off state, and from the power source 41B to the LED driver 42B. Supply of electric power is started, and thereby the LED 25B is switched from the unlit state to the lit state. Therefore, in the period T3 from the time t3 to the pulse rising time t4 immediately after that, as shown in FIG. 6C, the LEDs 25A, 25B, and 25D are turned on and the LED 25C is turned off in each unit area A.

  Then, at the rise time t4 of the pulse of the vertical synchronization signal, the supply of power from the power source 41D to the LED driver 42D is cut off, whereby the LED 25D is switched from the on state to the off state, and from the power source 41C to the LED driver 42C. Supply of electric power is started, and thereby the LED 25C is switched from the unlit state to the lit state. Therefore, in the period T4 from the time t4 to the pulse rising time t1 immediately after that, as shown in FIG. 6D, the LEDs 25A, 25B, and 25C are turned on and the LED 25D is turned off in each unit area A.

  When the setting value of the brightness level is set to 75, as described above, the combination of the three LEDs 25 that are lit is sequentially changed at a predetermined cycle.

  FIG. 7 is a diagram showing a driving state of each of the LEDs 25A, 25B, 25C, and 25D when the set value of the brightness level is set to 50. FIG. 7A is a period T1 and T3 in FIG. FIG. 7B shows the driving states of the LEDs 25A, 25B, 25C, and 25D in the periods T2 and T4 in FIG.

  When the brightness level setting value is set to 50, the LEDs 25A and 25B are extinguished and the LEDs 25C and 25D are lit whenever the vertical sync signal pulse rises (FIG. 7). (A)) and the state (FIG. 7B) in which the LEDs 25A and 25B are turned on and the LEDs 25C and 25D are turned off are switched.

  FIG. 8 is a diagram showing the driving state of each LED 25A, 25B, 25C, 25D when the set value of the brightness level is set to 25, and FIG. 8 (a) shows each of the periods T1 in FIG. FIG. 8B shows the driving state of the LEDs 25A, 25B, 25C, and 25D, FIG. 8B shows the driving state of the LEDs 25A, 25B, 25C, and 25D in the period T2 in FIG. 5, and FIG. FIG. 8D shows the driving state of the LEDs 25A, 25B, 25C, and 25D in the period T4 in FIG. 5, and FIG. 8D shows the driving state of the LEDs 25A, 25B, 25C, and 25D in the period T3.

  Similarly to the above, when the set value of the brightness level is set to 25, as shown in FIG. 8, one LED 25 to be lit is sequentially turned on every time the vertical synchronization signal pulse rises. Be changed.

  FIG. 9 is a diagram showing driving states of the respective LEDs 25A, 25B, 25C, and 25D in the periods T1 to T4. FIG. 9A is a table in the case where the brightness level setting value is set to 100. FIG. FIG. 9B shows a table h2 when the brightness level setting value is set to 75, and FIG. 9C shows that the brightness level setting value is set to 50. FIG. 9D shows the table h4 when the brightness level setting value is set to 25. FIG.

  FIG. 10 is a flowchart showing the operation procedure of the setting process of the switching cycle of the LED 25 in the area dimming method. When a user operates the remote controller to input an instruction to change the switching cycle of the LED 25 to the CPU 39 via the communication unit 36, the process is started and the process proceeds to step s1.

  In step s1, the CPU 39 transmits a command to the OSD drawing unit 33, and generates image information of the OSD screen for allowing the user to select a switching cycle setting method. Upon receiving this command, the OSD drawing unit 33 generates image information of the OSD screen for allowing the user to select whether to set the switching cycle according to one cycle of the vertical synchronization signal or a predetermined time cycle, and performs display control. It transmits to the part 32. Thereby, the OSD display process is performed in the display control unit 32, and when the OSD screen is displayed, the process proceeds to step s2.

  In step s2, the CPU 39 monitors an operation signal input via the communication unit 36, and determines whether or not one cycle of the vertical synchronization signal is selected by the user among the two selection items. If it is determined that one period of the vertical synchronizing signal is selected, the process proceeds to step s3. If it is determined that one period of the vertical synchronizing signal is not selected, the process proceeds to step s4.

  In step s3, the CPU 39 stores a numerical value indicating one period of the vertical synchronization signal as the switching period of the LED 25 in the storage area of the storage unit 35, and ends the process. In step s4, the CPU 39 stores the time period selected by the user among a plurality of predetermined time periods as the switching period of the LED 25 in the storage area of the storage unit 35, and ends the process. In this embodiment, it is configured such that any one of 5 milliseconds, 10 milliseconds, 15 milliseconds and 20 milliseconds can be selected as a plurality of predetermined time periods.

  FIG. 11A and FIG. 11B are flowcharts showing the operation procedure of the brightness adjustment processing of the display screen by the area dimming method. When the liquid crystal display device 10 is powered on, the process is started and the process proceeds to step s11.

  In step s11, the luminance control unit 40 is provided in the luminance control unit 40, and each stage of the four-stage annular shift register VCNT (D0: D3) in which the driving conditions of the LEDs 25A, 25B, 25C, and 25D are described. Set the initial value to. Here, the driving condition of each LED 25A, 25B, 25C, 25D is set by a value of “0” or “1”, “0” indicates that the LED 25 is turned off, and “1” indicates that the LED 25 is turned off. Indicates that it is lit.

  In this embodiment, the luminance control unit 40 sets “0” in the first-stage register VCNT (D0) representing the driving condition of the LED 25A in step s11, and registers the second-stage register representing the driving condition of the LED 25B. “0” is set to VCNT (D1), “0” is set to the third stage register VCNT (D2) representing the driving condition of the LED 25C, and the fourth stage register VCNT (D3) representing the driving condition of the LED 25D is set. Set “0” to.

  That is, four-digit data “0000” is set in the annular shift register VCNT (D0: D3). In this 4-digit data, the leftmost numerical value corresponds to the value of the first-stage register VCNT (D0), the second numerical value from the left corresponds to the value of the second-stage register VCNT (D1), and from the left The third numerical value corresponds to the value of the third-stage register VCNT (D2), and the rightmost numerical value corresponds to the value of the fourth-stage register VCNT (D3). When the initial value is set, the process proceeds to step s12.

  In step s12, the luminance control unit 40 acquires the setting value of the brightness level of the display screen included in the brightness level notification signal input from the CPU 39, and proceeds to step s13. In step s13, the brightness control unit 40 determines whether or not the brightness level setting value acquired in step s12 is different from the brightness level setting value stored in the storage area in the brightness control unit 40. If it is determined that they are different, the process proceeds to step s14. If it is determined that they are the same, the process proceeds to step s22.

  In step s14, the luminance control unit 40 determines whether or not the brightness level setting value acquired in step s12 is 25. If it is determined that the setting value is not 25, the process proceeds to step s15, where the setting value is 25. If it is determined that, it proceeds to step s20.

  In step s15, the luminance control unit 40 determines whether or not the setting value of the brightness level acquired in step s12 is 50. If it is determined that the setting value is not 50, the process proceeds to step s16, where the setting value is 50. If it is determined that, it proceeds to step s19.

  In step s16, the luminance control unit 40 determines whether or not the setting value of the brightness level acquired in step s12 is 75. If it is determined that the setting value is not 75, the process proceeds to step s17, where the setting value is 75. If it is determined that, it proceeds to step s18.

  In step s17, since the brightness level setting value acquired in step s12 is 100, the brightness control unit 40 sets 4-digit data “1111” in the annular shift register VCNT (D0: D3), Proceed to step s21.

  In step s18, since the brightness level setting value acquired in step s12 is 75, the luminance control unit 40 sets 4-digit data “0111” in the annular shift register VCNT (D0: D3), Proceed to step s21.

  In step s19, since the brightness level setting value acquired in step s12 is 50, the luminance control unit 40 sets 4-digit data “0011” in the annular shift register VCNT (D0: D3), Proceed to step s21.

  In step s20, the brightness control unit 40 sets the four-digit data “0001” in the annular shift register VCNT (D0: D3) because the brightness level setting value acquired in step s12 is 25. Proceed to step s21.

  In step s21, the brightness control unit 40 stores the set value of the brightness level acquired in step s12 in the storage area in the brightness control unit 40, and returns to step s12.

  In step s22, the luminance control unit 40 determines whether or not the value of the first-stage register VCNT (D0) in the annular shift register VCNT (D0: D3) is “1” and not “1”. Then, the process proceeds to step s23, and if it is determined to be “1”, the process proceeds to step s24.

  In step s23, the luminance control unit 40 turns off the respective LEDs 25A by cutting off the supply of power from the power source 41A to the LED driver 42A, and proceeds to step s25. In addition, when the supply of power to the LED driver 42A is already cut off, the state is maintained.

  In step s24, the luminance control unit 40 starts supplying power from the power source 41A to the LED driver 42A, thereby lighting each LED 25A, and proceeds to step s25. Note that when the supply of power to the LED driver 42A has already started, the state is maintained.

  In step s25, the luminance control unit 40 determines whether or not the value of the second-stage register VCNT (D1) in the annular shift register VCNT (D0: D3) is “1”, and does not determine “1”. Then, it progresses to step s26, and if it determines with being "1", it will progress to step s27.

  In step s26, the luminance control unit 40 shuts off the power supply from the power source 41B to the LED driver 42B, thereby turning off each LED 25B, and proceeds to step s28. Note that when the supply of power to the LED driver 42B has already been cut off, the state is maintained.

  In step s27, the luminance control unit 40 starts supplying power from the power supply 41B to the LED driver 42B, thereby lighting each LED 25B, and proceeds to step s28. Note that when the supply of power to the LED driver 42B has already started, the state is maintained.

  In step s28, the luminance control unit 40 determines whether or not the value of the third-stage register VCNT (D2) in the annular shift register VCNT (D0: D3) is “1” and not “1”. Then, it progresses to step s29, and if it determines with being "1," it will progress to step s30.

  In step s29, the luminance control unit 40 turns off each LED 25C by cutting off the supply of power from the power source 41C to the LED driver 42C, and proceeds to step s31. In addition, when the supply of power to the LED driver 42C is already cut off, the state is maintained.

  In step s30, the luminance control unit 40 starts supplying power from the power source 41C to the LED driver 42C, thereby lighting each LED 25C, and proceeds to step s31. Note that, when the supply of power to the LED driver 42C has already started, the state is maintained.

  In step s31, the luminance control unit 40 determines whether or not the value of the fourth-stage register VCNT (D3) in the annular shift register VCNT (D0: D3) is “1”, and does not determine “1”. Then, it progresses to step s32, and if it determines with it being "1", it will progress to step s33.

  In step s32, the luminance control unit 40 shuts off the power supply from the power source 41D to the LED driver 42D, thereby turning off each LED 25D, and proceeds to step s34. Note that, when the supply of power to the LED driver 42D has already been cut off, that state is maintained.

  In step s33, the luminance control unit 40 starts supplying power from the power source 41D to the LED driver 42D, thereby lighting each LED 25D, and proceeds to step s34. Note that, when the supply of power to the LED driver 42D has already started, the state is maintained.

  In step s34, the luminance control unit 40 determines whether or not the rising edge of the vertical synchronization signal pulse has been detected.

  In step s35, the luminance control unit 40 shifts the four-digit data set in the annular shift register VCNT (D0: D3) to the right, and the shifted four-digit data is converted into the annular shift register VCNT (D0: D3). ) And return to step s12.

  Specifically, when the set value of the brightness level stored in the storage area in the brightness control unit 40 is 100, 75, 25, it is set in the annular shift register VCNT (D0: D3). 4-digit data is shifted one step to the right. When the brightness level setting value stored in the storage area in the luminance control unit 40 is 50, the 4-digit data set in the annular shift register VCNT (D0: D3) is transferred to the right. Shift two directions in the direction.

  Such adjustment processing of the brightness of the display screen by the area dimming method is continuously performed while the liquid crystal display device 10 is in operation.

  As described above, according to the present embodiment, the brightness of the display screen in the liquid crystal display device 10 is adjusted by dimming the backlight 22 by the area dimming method. And in this area dimming system, when turning off LED25, it is comprised so that supply of the electric power from the power supply 41 to the LED driver 42 may be interrupted | blocked. Therefore, compared with the case where the brightness of the display screen is adjusted by the PWM dimming method as in the prior art, the power consumed in the LED driver 42 can be reduced, and the power consumption of the entire liquid crystal display device 10 can be reduced. Can be reduced.

  Further, according to the present embodiment, when driving the plurality of LEDs 25 using such an area dimming method, the combination of the LEDs 25 to be lit is sequentially changed for each unit region A at a predetermined cycle. It is configured. Therefore, the lifetime of each LED 25A, 25B, 25C, 25D can be leveled compared with the case where such a combination change is not performed, and therefore the lifetime of the backlight 22 can be extended. .

  In addition, according to the present embodiment, the predetermined period is configured so that the user can arbitrarily select either one period of the vertical synchronization signal or a predetermined time period. Therefore, even when a problem occurs in which the video displayed on the display screen interferes with the switching timing of turning on / off the LEDs 25A, 25B, 25C, and 25D, the setting of the predetermined cycle is changed. Thus, such a problem can be easily solved.

  In addition, according to the present embodiment, since the area dimming method is adopted, a failure has occurred in any one of the four LEDs 25A, 25B, 25C, and 25D constituting one unit region A. Even in this case, if the set value of the brightness level is other than 100, it is possible to avoid a decrease in luminance due to the occurrence of a failure.

  For example, when the setting value of the brightness level is set to 50 and a failure has occurred in the LED 25A, any one of the remaining LEDs 25C and 25D is replaced with the failed LED 25A at the lighting timing of the LEDs 25A and 25B. By illuminating one, it is possible to avoid a decrease in luminance due to the occurrence of a failure.

  In the above embodiment, the number of LEDs 25 included in each unit region A is set to four, so that the brightness of the display screen can be adjusted in four stages by the area dimming method. In the embodiment, by further increasing the number of LEDs 25 included in each unit region A, the brightness of the display screen can be adjusted to more stages than four stages.

  In the above embodiment, the brightness of the display screen is adjusted using only the area dimming method. Therefore, when the number of LEDs 25 included in each unit region A is small, the display screen can be adjusted. The number of brightness steps is also reduced. Therefore, in another embodiment, the brightness of the display screen can be adjusted more finely by using a combination of the area dimming method and the PWM dimming method.

  Specifically, each LED 25 is driven to be lit by a PWM signal, and the luminance control unit 40 adjusts the number of LED drivers 42 that supply power according to the brightness setting value of the display screen, and PWM This can be realized by adjusting the duty ratio of the signal between 0% and 100%. Thus, by using a combination of the area dimming method and the PWM dimming method, even if the number of LEDs 25 included in each unit area A is small, the number of brightness levels of the display screen is increased. Can do.

10 Liquid crystal display device 11 Liquid crystal panel 12 Backlight unit 25 LED
35 storage unit 40 brightness control unit 41A, 41B, 41C, 41D power supply 42A, 42B, 42C, 42D LED driver

Claims (3)

A liquid crystal display device comprising a liquid crystal panel having a display screen capable of displaying an image, the brightness of the display screen being adjustable in a plurality of stages,
A backlight unit in which a plurality of unit areas of a predetermined size are set and a light source is installed at each of a plurality of predetermined arrangement positions in each unit area of the light source installation part;
A plurality of power supply units provided in association with each arrangement position of the unit region;
A plurality of light source driving units provided in association with each power supply unit, wherein each light source driving unit is installed at an arrangement position associated with the power supply unit by power supplied from the associated power supply unit. A plurality of light source driving units for driving the light source;
A setting unit for setting one stage among a plurality of brightness stages associated with the number of light source driving units to which power is supplied;
A storage unit for storing the one stage set by the setting unit;
A luminance control unit that controls power supply to each light source driving unit so that power is supplied only to a predetermined number of light source driving units corresponding to the one stage stored in the storage unit. A liquid crystal display device.   The liquid crystal display device according to claim 1, wherein the luminance control unit changes a light source driving unit to which power is supplied at a predetermined cycle. The light source driving unit drives the light source by a pulse width modulation signal,
3. The liquid crystal display device according to claim 1, wherein the luminance control unit changes a duty ratio of the pulse width modulation signal according to one stage of brightness stored in the storage unit.