JP5733798B2 - Liquid crystal display device and luminance control method - Google Patents

Description

  The present invention relates to a liquid crystal display device that reduces power consumption and a luminance control method.

  Some liquid crystal display devices (liquid crystal displays) are referred to as rear projection types in which the amount of light emitted from a backlight provided on the back surface of the liquid crystal panel is modulated by controlling the transmission amount of the liquid crystal panel according to the image to be displayed. . As a technique for reducing the power consumption of the liquid crystal display, a method for controlling the lighting of the backlight is known. A technology is disclosed that reduces power consumption by turning on only a backlight corresponding to a part of a region necessary for content display according to the display size of the content displayed on the screen (see Patent Document 1). .

  In addition, a technique for reducing power consumption by dividing the screen of the liquid crystal display into a plurality of areas and changing the luminance of the backlight corresponding to each area according to the maximum display luminance of each area is disclosed (patent). Reference 2).

  On the other hand, CCFLs (Cold Cathode Fluorescent Lamps) are widely used as backlights for liquid crystal displays, and CCFLs have become longer with the recent increase in size of liquid crystal displays. When the CCFL is lengthened, a temperature difference between the hot (HOT) side and the cold (COLD) side wall surface of the CCFL due to leakage current occurs, and the cataphoresis phenomenon is known in which the HOT side is bright and the COLD side is dark. . When the cataphoresis phenomenon occurs, a luminance difference occurs on the screen of the liquid crystal display, and the display quality is impaired. Therefore, in a liquid crystal display using a long CCFL, it is necessary to prevent the luminance from being affected even if a temperature difference occurs, and the output current of the inverter circuit that lights the CCFL is limited so as not to decrease.

JP 2004-91147 A JP 2008-71603 A

  However, in a liquid crystal display using a long CCFL for the backlight, the lower limit value of the output current of the inverter circuit is limited as described above, and thus the luminance of the backlight does not fall below a certain luminance value. When the entire display screen of the liquid crystal display is set to a brightness lower than the lower limit value of the brightness, a lower brightness display is realized by adjusting the contrast of the liquid crystal panel in addition to the brightness of the backlight. Therefore, there is a problem that even if the entire display screen of the liquid crystal display has a luminance lower than the lower limit value of the luminance, the power consumption cannot be reduced.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a liquid crystal display device and a luminance control method that can reduce power consumption.

In order to solve the above problems, the present invention provides a light source unit having a plurality of cold cathode fluorescent lamps, a liquid crystal display unit that modulates light from the light source unit to display an image, and supplies the light source unit to the light source unit The power source is controlled, and the light source is selectively switched between a partially turned off state in which some of the cold cathode fluorescent lamps are turned off and a fully turned on state in which all of the cold cathode fluorescent lamps are turned on. A display signal for displaying the image on the liquid crystal display unit based on display information supplied from outside and an inverter circuit unit for driving the unit, and for each pixel in the display signal according to the partial extinction state When the luminance conversion information for correcting the luminance information indicating the luminance value and the luminance setting information indicating the setting value of the screen luminance of the entire display screen supplied from the outside is a value lower than a predetermined threshold value, Inverter A control unit for shifting the signal conversion unit and the road section the part turned off, the signal conversion unit, the correction amount the defined display signal in advance of the cold cathode fluorescent lamp near lit The brightness is reduced based on the correction, the brightness is maintained without correcting the display signal in the vicinity of the cold cathode fluorescent lamp that is turned off, or the brightness is increased by correcting based on the predetermined correction amount, a liquid crystal display device which is characterized that you performs correction processing to equalize the luminance of the entire display screen.

  According to the present invention, the control unit thins out some of the plurality of cold cathode fluorescent lamps when the luminance information based on the luminance setting information supplied from the outside is lower than a predetermined threshold value. Turn on (partially off). Thereby, a signal conversion part correct | amends the luminance information of a display signal according to a partial light extinction state. Therefore, the liquid crystal display device can reduce power consumption without impairing display quality when the luminance information based on the luminance setting information is lower than the threshold value.

1 is a schematic block diagram illustrating a liquid crystal display device according to a first embodiment of the present invention. It is explanatory drawing which shows the correction | amendment operation | movement of a brightness | luminance and screen brightness distribution in the embodiment. It is a schematic block diagram which shows the liquid crystal display device in the 2nd Embodiment of this invention. It is a flowchart which shows the power save transfer operation | movement in the embodiment. It is a schematic block diagram which shows the liquid crystal display device in the 3rd Embodiment of this invention. It is a flowchart which shows the power save transfer operation | movement in the embodiment.

<First Embodiment>
A liquid crystal display device according to a first embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic block diagram showing a liquid crystal display device according to the first embodiment of the present invention.
The liquid crystal display device (liquid crystal display) 1 includes a backlight unit 10, an inverter unit 20, a panel unit 30, a signal conversion unit 40, and a control unit 50.

The backlight unit 10 includes a plurality of cold cathode fluorescent lamps (hereinafter referred to as CCFLs), is provided on the back surface of the panel unit 30, and is arranged in parallel. This figure shows a form in which four CCFLs CCFLs 101 to 104 are arranged. Further, here, in the description, the CCFLs 101 to 104 have the odd-numbered CCFL 101 and CCFL 103 as the A group and the even-numbered CCFL 102 and CCFL 104 as the B group. That is, the A group and the B group have a complementary relationship. Group A CCFLs 101 and 103 receive power from the inverter unit 20 through the signal line 71, and group B CCFLs 102 and 104 receive power from the inverter unit 20 through the signal line 72. Thereby, the backlight unit 10 is turned on and functions as a light source of the liquid crystal display 1.
The inverter unit 20 includes an output switching unit 201. The inverter unit 20 generates power for driving the backlight unit 10 based on the output control signal and the switching signal J supplied from the control unit 50, and supplies power to the backlight unit 10. To do.
In addition, the output switching unit 201 supplies all CCFLs 101 to 104 with electric power, and supplies power to either one of the A group or the B group and partially turns off the other power supply state (or The thinning-out lighting state is switched based on the switching signal J supplied from the control unit 50.

The panel unit 30 includes a signal reception unit 301 and displays an image on a display unit (not shown) based on the video signal M supplied from the signal conversion unit 40. The signal receiving unit 301 receives the video signal M, and the panel unit 30 receives image information to be displayed through the signal receiving unit 301.
The signal conversion unit 40 converts the display signal K into a video signal M based on the luminance correction signal supplied from the control unit 50 and supplies the video signal M to the panel unit 30. The display signal K is supplied from the external device 2 and includes display information of an image to be displayed on the panel unit 30. The video signal M is a signal converted to display an image on the panel unit 30 based on display information included in the display signal K.
The control unit 50 includes a luminance control unit 501 and a storage unit 502, and controls the inverter unit 20 and the signal conversion unit 40 based on a control signal supplied from the external device 2. Further, the control unit 50 supplies the output control signal and the switching signal J to the inverter unit 20, and supplies the luminance correction signal to the signal conversion unit 40.
The brightness control unit 501 of the control unit 50 performs control related to the screen brightness, which is the brightness of the entire display screen, based on the brightness setting information included in the control signal supplied from the external device 2. The luminance control unit 501 determines whether the CCFL is fully turned on or partially turned off. The luminance control unit 501 instructs the inverter unit 20 to change the light source luminance of the backlight unit 10 and instructs the signal conversion unit 40 to correct the luminance of the display signal included in the display signal K.
The storage unit 502 includes a brightness setting unit 5021 that stores a brightness threshold that is a threshold of screen brightness. The luminance setting unit 5021 stores a threshold value for determining whether or not the CCFLs 101 to 104 are in the thinned lighting state. Further, the luminance threshold value stored by the luminance setting unit 5021 is a predetermined value. The luminance threshold value stored in the luminance setting unit 5021 is, for example, equal to or higher than the limit value of the screen luminance that does not cause the catalysis phenomenon when the screen luminance is lowered by changing only the light source luminance while the CCFLs 101 to 104 are all turned on. Value.

Next, the operation of this embodiment will be described. In FIG. 1, when changing the screen brightness of the entire display screen of the liquid crystal display 1 based on the control signal supplied from the external device 2, the set value of the screen brightness (hereinafter referred to as the set brightness) is controlled by the control unit through the control signal. 50. The luminance control unit 501 of the control unit 50 controls the output power of the output lines 71 and 72 of the inverter unit 20 based on the supplied set luminance. In addition, the luminance control unit 501 instructs to supply an output control signal to the inverter unit 20.
In addition, the brightness control unit 501 compares the brightness threshold stored in the brightness setting unit 5021 of the storage unit 502 with the supplied set brightness, and determines whether or not the set brightness is equal to or less than the brightness threshold. The luminance control unit 501 supplies the switching signal J to the inverter unit 20 when determining that the set luminance is equal to or lower than the luminance threshold value. Based on the switching signal J, the output switching unit 201 of the inverter unit 20 switches to the thinned-out lighting state where only one of the A group or the B group of the backlight unit 10 is lit. That is, the output switching unit 201 stops power supply to either one of the output lines 71 and 72. For example, the output switching unit 201 supplies power only to the output line 71, turns on the A group, and turns off the B group.
When the switching signal J is not supplied from the control unit 50, the output switching unit 201 supplies power to both the signal lines 71 and 72 and lights all the CCFLs 101 to 104 (all lighting state).

When the external device 2 instructs to change from the set brightness value X with screen brightness to the set brightness value (X-1) with low one-step brightness in the full lighting state, the control unit 50 sets the set brightness value X to The corresponding output control value Y is changed to (Y−ΔY) and supplied to the inverter unit 20 by the output control signal. The inverter unit 20 changes the output power W corresponding to the output control value Y to the output power (W−ΔW) corresponding to the output control value (Y−ΔY), and supplies it to the backlight unit 10. As a result, the backlight unit 10 is changed from the screen brightness Z corresponding to the power W to the screen brightness (Z−ΔZ) corresponding to the power (W−ΔW). That is, the change amount of the output control value Y with respect to one step of the set luminance X is ΔY, and the change amount of the output power W supplied from the inverter unit 20 is ΔW. Further, the change amount ΔZ of the screen luminance of the backlight unit 10 with respect to one step of the set luminance X.
For example, when switching from a fully lit state to a partially unlit state in which the group B is turned off, the number of CCFLs that are turned on decreases, resulting in a change in the brightness of the screen display. When the brightness change of the screen display occurs, the display quality is deteriorated. In view of this, a sudden change in screen brightness is prevented from occurring even when switching to the partially off state. That is, when switching from the all-point lighting state to the partial lighting state, it is necessary to increase the luminance of the group A that is lit so that the amount of change ΔZ in screen luminance is constant. Therefore, the control unit 50 instructs the inverter unit 20 by the output control signal, and the inverter unit 20 increases the output power W to the output line 71.

  When the external device 2 instructs to change the screen brightness, the screen brightness change amount ΔZ with respect to one step of the set brightness value X is in a fully lit state or in a partially unlit state. It is preferable to set the amount of change to be the same. Since the number of lighting of the CCFLs 101 to 104 is smaller than the number of lighting when the CCFLs 101 to 104 are all lit, the screen luminance change ΔZ with respect to the output change ΔW of the output line 71 is Smaller than the case. Accordingly, in order to make the change amount ΔZ of the screen luminance for one step of the set luminance equal, when the output luminance value is set to one step of the set luminance value X in the case of the partial light-off state in contrast to the case of the full-on state. The change amount ΔY or the output change amount ΔW of the output line 71 is increased. For example, when the screen is partially turned off, the change amount ΔY of the output control value for one step of the screen brightness setting X is set to a value twice as large as that when the screen is lit. Thereby, the brightness | luminance of the whole display screen can be changed continuously.

  Further, when the CCFL is arranged in a direct type, if the CCFL is thinned and turned on, the uniformity of the screen luminance of the entire display screen is affected. Therefore, the signal conversion unit 40 corrects the luminance of the video signal M based on the luminance correction signal from the control unit 50. Specifically, since the place where the screen luminance is not uniform is known in advance, the signal conversion unit 40 changes the level of the video signal M transmitted to the panel unit 30 and corrects the luminance to be uniform. To do.

Next, the luminance correction operation by the signal conversion unit 40 will be described with reference to FIG.
FIG. 2 is an explanatory diagram showing luminance correction operation and screen luminance distribution in the present embodiment.
FIG. 2A is a diagram of the panel unit 30 in a partially unlit state as viewed from the display surface (front side). Since the screen is partially off, the screen in the vicinity of the CCFL that is turned off is dark, and the screen in the vicinity of the CCFL that is lit shows a non-measured state in which bright screen luminance is uneven.
FIG. 2B shows a cross-sectional view of the panel unit 30 taken along the line AA ′ (FIG. 2A). In addition, a waveform 601 indicating the distribution of screen luminance is shown in accordance with FIG. A waveform 601 shows a state in which the luminance is higher toward the left. That is, the waveform 601 shows a state where the screen luminance is uneven. Of the CCFLs arranged on the back surface of the panel unit 30, the screen brightness is high in the vicinity of the lit CCFLs 101 and 103, and the screen brightness is low in the vicinity of the CCFLs 102 and 104 that are unlit.

  FIG. 2C shows a voltage waveform of the video signal M supplied from the signal conversion unit 40 to the panel unit 30. In this figure, the horizontal axis represents time, and the vertical axis represents voltage. The voltage waveforms V102 to V104 are an example of the video signal M supplied to the signal receiving unit 301 of the panel unit 30 in order for the signal conversion unit 40 to perform luminance correction in the state of FIG. In the waveform 601, the signal conversion unit 40 corrects the signal level of the video signal M so that the corrected screen brightness matches the lowest level of the screen brightness before correction. The voltage waveforms V102 to V104 correspond to the waveforms of the video signal M in the vicinity of the CCFLs 102 to 104, respectively.

  As shown in the waveform 601, the difference in luminance level when the light is partially turned on can be determined in advance. For example, the brightness of each part of the screen may be measured in advance in a fully lit state, a state where only group A is lit, and a state where only group B is lit, and may be calculated from the measured values. Based on the determined luminance level difference, the signal conversion unit 40 calculates a correction amount for correcting the signal level of the video signal M in either the state in which only the group A is lit or the state in which only the group B is lit. Each gradation of the display signal K is stored in a conversion table (not shown). For each gradation of the display signal K, for example, all gradations from black to white may be set by dividing each gradation into five, and the gradation between them may be calculated by linear interpolation or the like. Note that if the number of divisions is increased, correction can be performed more smoothly, but more storage capacity is required. The correction amount is determined so that the screen luminance after correction of each gradation is matched with the lowest level of the screen luminance before correction. This is because, when the vicinity of white in the display image is displayed, luminance correction by the video signal M cannot be performed in a low screen luminance portion (near the CCFL that is turned off), and when the vicinity of black in the display image is displayed. In addition, the contrast is prevented from deteriorating. Accordingly, in the intermediate gradation between white and black of the display image, the gamma characteristic of the video signal M may be taken into consideration and the luminance may be set appropriately.

When converting the display signal K supplied from the external device 2 into the video signal M, the signal conversion unit 40 refers to the conversion table (not shown) corresponding to the lighting state (Group A or Group B) of the CCFL, and displays the waveform. In the area where the screen luminance of 601 is high, the signal level of the video signal M is converted to a low level (V103). When the screen brightness is low, the signal level of the video signal M is output as it is (V102, V104). However, as described above, the signal level of the video signal M may be converted to a high level when the screen luminance is low (V102, V104).
A waveform 602 in FIG. 2D is a luminance distribution when the signal conversion unit 40 corrects the screen luminance shown in FIG. The waveform 602 is uniformly corrected according to the lowest level of the screen luminance of the waveform 601.

  As described above, when the set brightness lower than the brightness threshold stored in advance in the brightness setting unit 5021 is set, the liquid crystal display 1 described above thins out a part of the plurality of CCFLs (lights one). Part off). Therefore, even when the entire display screen of the liquid crystal display 1 is set to a lower setting luminance than the lower limit value of the screen luminance, the power consumption can be reduced. In addition, since the threshold value stored in advance is set to a value equal to or higher than the screen luminance at which the cataphoresis phenomenon occurs, the cataphoresis phenomenon does not occur. Further, when shifting to a partly extinguished state, the power supplied to the CCFL in which the inverter unit 20 is lit is increased, so that display quality is not impaired by the catalysis phenomenon. As described above, even when the CCFL is arranged in a direct type, the signal conversion unit 40 corrects the video signal M so that the screen luminance is uniform, so that the display quality is not impaired. , Power consumption can be reduced. From the above, it is possible to provide the liquid crystal display 1 that can satisfy power consumption regulations such as environmental regulations typified by the newly required energy star.

<Second Embodiment>
A liquid crystal display device according to a second embodiment of the present invention will be described below with reference to the drawings.
FIG. 3 is a schematic block diagram illustrating the liquid crystal display device according to the present embodiment. The liquid crystal display 1a includes a backlight unit 10, an inverter unit 20a, a panel unit 30, a signal conversion unit 40, and a control unit 50a.
In this figure, the same components as those in FIG.

  The inverter unit 20a supplies power to the backlight unit 10 based on the output control signal and switching signals J1 and J2 supplied from the control unit 50a. The inverter unit 20a includes an output switching unit 201a, transformers 202 and 203, a switching circuit unit 204, and a control circuit unit 205.

  The output switching unit 201a has a fully lit state in which power is supplied to all CCFLs 101 to 104 and a partially unlit state in which power is supplied to one of the A group or the B group and the power supply is stopped to the other (or thinning-out state). The lighting state and the all-off state in which power is stopped for all CCFLs 101 to 104 are switched based on switching signals J1 and J2 supplied from the control unit 50a. The output switching unit 201a includes switches 206 and 207, and whether or not the drive signal supplied from the switching circuit unit 204 through the signal line 73 is supplied to the transformers 202 and 203 is switched from the control unit 50a. Switching is performed based on the signals J1 and J2. The switch 206 switches whether to connect the signal lines 73 and 74 based on the switching signal J1 supplied from the control unit 50a. Further, the switch 207 switches whether or not the signal lines 73 and 75 are conducted based on the switching signal J2 supplied from the control unit 50a.

The transformers 202 and 203 convert the drive signal supplied from the switching circuit unit 204 via the output switching unit 201a into electric power for lighting the CCFLs 101 to 104. The transformer 202 supplies power to the CCFLs 101 and 103 in the A group through the signal line 71, and the transformer 203 supplies power to the CCFLs 102 and 104 in the B group through the signal line 72.
The switching circuit unit 204 generates a drive signal to be supplied to the transformers 202 and 203 based on the enable signal EN supplied from the control circuit unit 205.
The control circuit unit 205 controls whether or not to operate the switching circuit unit 204 based on the switching signals J1 and J2 supplied from the control unit 50a.

The control unit 50a includes a luminance control unit 501a and a storage unit 502a, and controls the inverter unit 20a and the signal conversion unit 40 based on a control signal supplied from the external device 2. Further, the control unit 50a supplies the output control signal and the switching signals J1 and J2 to the inverter unit 20a, and supplies the luminance correction signal to the signal conversion unit 40.
The storage unit 502a includes a luminance setting unit 5021 and a setting storage unit 5022 that store a threshold value of luminance, and the setting storage unit 5022 stores the output states of the switching signal J1 and the switching signal J2.
Further, the luminance control unit 501a of the control unit 50a performs control related to the screen luminance, which is the luminance of the entire display screen, based on the luminance setting information included in the control signal supplied from the external device 2. The luminance control unit 501a selects switching between the fully lit state and the partially unlit state of the CCFL. The luminance control unit 501a instructs the inverter unit 20a to change the light source luminance of the backlight unit 10, and instructs the signal conversion unit 40 to correct the luminance of the display signal included in the display signal K.

Next, the operation of this embodiment will be described.
In FIG. 3, when changing the screen brightness of the entire display screen of the liquid crystal display 1a based on the control signal supplied from the external device 2, the set brightness is supplied to the control unit 50a. The luminance control unit 501a of the control unit 50a supplies an output control signal for controlling the output power of the outputs 71 and 72 of the inverter unit 20a to the inverter unit 20a based on the supplied screen luminance information.
In addition, the brightness control unit 501a compares the supplied set brightness with the brightness threshold that is the screen brightness threshold stored in the brightness setting unit 5021 of the storage unit 502a, and determines whether the set brightness is equal to or less than the brightness threshold. To do. When it is determined that the set brightness is higher than the brightness threshold, the brightness control unit 501a supplies the switching signals J1 and J2 to the inverter unit 20a. When it is determined that the set brightness is equal to or lower than the brightness threshold, the brightness control unit 501a supplies the switching signal J1 (or J2) to the inverter unit 20a. Here, the signal states of the switching signals J1 and J2 indicate a case where the L (low) state is output when the CCFL is turned off. The control circuit unit 205 of the inverter unit 20a supplies an enable signal EN to the switching circuit unit 204 based on the supplied switching signal J1 (or J2). The enable signal EN is an enable signal for controlling whether or not to operate the switching circuit unit 204, and the switching circuit unit 204 operates in the H (high) state. The control circuit unit 205 supplies a signal obtained by performing a logical sum (OR) operation of the switching signals J1 and J2 to the switching circuit unit 204 as an enable signal EN. Accordingly, when both the switching signals J1 and J2 are in the H state, or when one of them is in the H state and the other is in the L state, the enable signal EN is in the H state.

Next, the switching circuit unit 204 that has received the enable signal EN supplies a drive signal to the transformers 202 and 203. The drive signal is supplied to both the switch 206 and the switch 207. The switch 206 of the output switching unit 201a conducts the signal lines 73 and 74 when the switching signal J1 is in the H state, and interrupts the signal lines 73 and 74 when the switching signal J1 is in the L state. The switch 207 conducts the signal lines 73 and 75 when the switching signal J2 is in the H state, and interrupts the signal lines 73 and 75 when the switching signal J2 is in the L state. Accordingly, when the set luminance is higher than the luminance threshold, both the switching signals J1 and J2 are in the H state, and the signal line 73 is conducted to both 74 and 75. Further, when the set luminance is equal to or lower than the luminance threshold value, either the switching signal J1 or J2 is in the L state, and either one of 74 or 75 is cut off for the signal line 73.
When the switching signal J1 (or J2) is in the L state, the drive signal generated by the switching circuit unit 204 is not supplied to the signal line 74 (or 75), so the transformer 202 (or 203) stops. As a result, the CCFLs 101 and 103 in the A group (or the CCFLs 102 and 104 in the B group) are turned off and partially turned off.

Next, in the present embodiment, an operation when shifting to the power saving state and returning again will be described with reference to the drawings. The power saving state is a state in which all the CCFLs 101 to 104 of the backlight unit 10 are turned off.
FIG. 4 is a flowchart showing power control of the backlight unit 10 in accordance with the set luminance described above. It is a flowchart which shows the operation | movement which transfers to a power saving state from the state (partial light extinction state) from which CCFL was thinned and lighted when setting brightness | luminance is below the threshold value of screen luminance, and returns to a partial light extinction state again. For example, an operation when the inverter unit 20a supplies power to the CCFLs 101 and 103 of the A group as an initial state is shown. That is, in the initial state, the switching signal J1 is in the H state and the switching signal J2 is in the L state. When the external device 2 is not operated for a certain period in this initial state, the external device 2 supplies an instruction to shift to power saving to the liquid crystal display 1a through a control signal. Alternatively, the external device 2 may stop outputting the display signal K, and the liquid crystal display 1a may detect that there is no input of the same signal included in the display signal K and shift to the power saving state.

  First, the luminance control unit 501a of the control unit 50a stores the states of the switching signals J1 and J2 in the setting storage unit 5022 (step S1). Subsequently, the luminance control unit 501a sets both the switching signals J1 and J2 to the L state. As a result, the control circuit unit 205 outputs an L state to the enable signal EN, and the switching circuit unit 204 stops operating. Further, both the switches 206 and 207 are turned off, and both the transformers 202 and 203 stop the power supplied to the backlight unit 10. Thereby, all the CCFLs 101 to 104 of the backlight unit 10 are turned off, and the power saving state is entered (step S2).

The controller 50a determines whether or not there is a return request from the power save state based on a control signal from the external device 2. As a result of the determination, when determining that there is no return request, the control unit 50a repeats the determination in step S3 and maintains the power save state (step S3). The determination in step S3 is performed based on whether or not the return request message is included in the information included in the control signal supplied from the external device 2 by the control unit 50a. Alternatively, the determination may be performed based on the presence or absence of a synchronization signal included in the display signal K. If it is determined in step S3 that there is a return request, the process proceeds to step S4, and the luminance control unit 501a of the control unit 50a refers to the states of the switching signals J1 and J2 stored in the setting storage unit 5022.
Next, the brightness controller 501a reverses the stored switching signals J1 and J2 (step S5). Further, the conversion table is changed to a correction table for correcting the signal level of the video signal M corresponding to the lighting state of the CCFL (group A or group B). For example, the luminance control unit 501a sets the switching signal J1 to the L state and the switching signal J2 to the H state. As a result, the enable signal EN of the control circuit unit 205 becomes the H state, the switching circuit unit 204 enters the driving state, and the driving signal is supplied to the signal line 73. On the other hand, since the switch 206 is turned off and the switch 207 is turned on, only the output line 71 of the transformer 203 supplies power to the backlight unit 10. As a result, the CCFLs 101 and 103 of the A group are turned off, and the CCFLs 102 and 104 of the B group are returned to the partially turned off state. In addition, since the correction table for the video signal M is switched to the correction table in which only the group B is lit, the screen luminance is uniform.

  In addition, when the set brightness based on the brightness setting information included in the control signal supplied from the external device 2 is higher than the brightness threshold, the brightness control unit 501a sets the first switching signal J1 and the second switching signal J2. Both are set to the H state, and all CCFLs of the first CCFL 101 to the fourth CCFL 104 are turned on. Further, the video signal M is not corrected by the signal conversion unit 40.

As described above, in the present embodiment, when a set brightness lower than the brightness threshold stored in advance in the brightness setting unit 5021 is set, a part of the plurality of CCFLs is thinned out (partially turned off). . Therefore, even when the entire display screen of the liquid crystal display 1a is set to a lower setting luminance than the lower limit value of the screen luminance, the power consumption can be reduced. In addition, since the threshold value stored in advance is set to a value equal to or higher than the screen luminance value at which the cataphoresis phenomenon occurs, the cataphoresis phenomenon does not occur. Further, when shifting to the partially off state, the power supplied to the CCFL in which the inverter unit 20a is lit is increased, so that display quality is not impaired by the catalysis phenomenon. As described above, even when the CCFL is arranged in a direct type, the signal conversion unit 40 corrects the video signal M so that the screen luminance is uniform, so that the display quality is not impaired. , Power consumption can be reduced.
Further, the setting storage unit 5022 of the control unit 50a stores the setting state (partial switching signals J1 and J2) in a partly off state, and based on the information stored in the setting storage unit 5022, the CCFLs 101 and 103 of the A group are stored. A partially unlit state in which is turned on and a partially unlit state in which CCFLs 102 and 104 of the B group are lit are used alternately. Therefore, the lifetime of the backlight unit 10 can be extended.

<Third Embodiment>
A liquid crystal display device according to a third embodiment of the present invention will be described below with reference to the drawings.
FIG. 5 is a schematic block diagram showing the liquid crystal display device in the present embodiment.
The liquid crystal display 1b includes a backlight unit 10, an inverter unit 20a, a panel unit 30, a signal conversion unit 40, and a control unit 50b.
In this figure, the same components as those in FIGS. 1 and 3 are denoted by the same reference numerals.
The control unit 50b includes a luminance control unit 501b, a storage unit 502b, and timers 503 and 504. The control unit 50 b controls the inverter unit 20 a and the signal conversion unit 40 based on the control signal supplied from the external device 2. Further, the control unit 50b supplies the output control signal and the switching signals J1 and J2 to the inverter unit 20a, and supplies the luminance correction signal to the signal conversion unit 40.
The storage unit 502b includes a luminance setting unit 5021 and a setting storage unit 5022b that store a threshold value of luminance. The setting storage unit 5022b stores the output state of the switching signal J1 and the switching signal J2, and the cumulative lighting time of each of the A group and the B group.
Further, the luminance control unit 501b of the control unit 50b relates to the cumulative lighting time of the A group and the B group of the backlight unit 10 based on the measured values of the timers 503 and 504, in addition to the control in the luminance control unit 501b of FIG. Take control.
The timer 503 measures the lighting duration time during which the CCFLs in the A group are continuously turned on. In addition, the timer 504 measures a lighting duration time during which the group B CCFLs are continuously lit.

  The switching operation between the fully lit state and the partially unlit state is the same as in the second embodiment. The timer 503 starts measurement when the switching signal J1 switches from the L state to the H state, and measures the time (lighting duration) until the switching signal J1 switches from the H state to the L state. When the switching signal J1 is switched to the L state, the luminance control unit 501b reads the cumulative lighting time of the group A stored in the setting storage unit 5022b, adds the lighting duration time measured by the timer 503, and stores the setting again. Stored in the unit 5022b. The timer 504 starts measurement when the switching signal J2 switches from the L state to the H state, and measures the time (lighting duration) until the switching signal J2 switches from the H state to the L state. When the switching signal J2 is switched to the L state, the luminance control unit 501b reads the cumulative lighting time of the group B stored in the setting storage unit 5022b, adds the lighting duration time measured by the timer 504, and stores the setting again. Stored in the unit 5022b. Note that the cumulative lighting time of the A group (or B group) is reset by replacing the CCFL. For example, when the CCFL is replaced, the luminance control unit 501b executes an initialization process, and initializes the cumulative lighting time of the setting storage unit 5022b.

Next, in the present embodiment, an operation when shifting to the power saving state and returning again will be described with reference to the drawings.
FIG. 6 is a flowchart showing power control of the backlight unit 10 in accordance with the set luminance described above. It is a flowchart which shows the operation | movement which transfers to a power saving state from the state (partial light extinction state) from which CCFL was thinned and lighted when setting brightness | luminance is below the threshold value of screen luminance, and returns to a partial light extinction state again. For example, an operation when the inverter unit 20a supplies power to the CCFLs 101 and 103 of the A group as an initial state is shown. That is, in the initial state, the switching signal J1 is in the H state and the switching signal J2 is in the L state. When the external device 2 is not operated for a certain period in the initial state, the external device 2 supplies an instruction to shift to power saving to the liquid crystal display 1b through the control signal. Alternatively, the external device 2 may stop outputting the display signal K, and the liquid crystal display 1b may detect that there is no input of the same signal included in the display signal K and shift to the power saving state.
First, the luminance control unit 501b of the control unit 50b stores the states of the switching signals J1 and J2 in the setting storage unit 5022b (step S1a). Subsequently, the luminance control unit 501b sets both the switching signals J1 and J2 to the L state. The luminance control unit 501b stores the cumulative lighting time calculated from the lighting duration time measured by the timers 503 and 504 in the setting storage unit 5022b. As a result, the control circuit unit 205 outputs an L state to the enable signal EN, and the switching circuit unit 204 stops operating. Further, both the switches 206 and 207 are turned off, and both the transformers 202 and 203 stop the power supplied to the backlight unit 10. Thereby, all the CCFLs 101 to 104 of the backlight unit 10 are turned off, and the power saving state is entered (step S2a).

The controller 50b determines whether or not there is a return request from the power save state based on the control signal from the external device 2. As a result of the determination, when determining that there is no return request, the control unit 50b repeats the determination in step S3a and maintains the power saving state (step S3a). If it is determined in step S3a that there is a return request, the process proceeds to step S4a, and the luminance control unit 501b of the control unit 50b determines the state of the switching signals J1 and J2 stored in the setting storage unit 5022b and Refer to the cumulative lighting time corresponding to each.
Next, the luminance control unit 501b compares the accumulated lighting times corresponding to the stored switching signals J1 and J2. As a result of the comparison, the luminance control unit 501b sets the switching signal J1 or J2 having a shorter cumulative lighting time to the H state (step S5a). Further, the conversion table is changed to a correction table for correcting the signal level of the video signal M corresponding to the lighting state of the CCFL (group A or group B). Further, when the switching signal J1 or J2 is set to the H state, the timer 503 or 504 starts measuring the lighting duration time. Subsequent operations are the same as those in the second embodiment.

The number of timers 503 and 504 for measuring the time of the switching signals J1 and J2 in the H state may be one. The switching signals J1 and J2 are both in the H state, one of them is in the H state, and both are in the L state. This state is referred to as state 1 (J1 = L state, J2 = L state), state 2 (J1 = H state, J2 = L state), state 3 (J1 = L state, J2 = H state), state 4 (J1 = H state, J2 = H state). For example, first, both the switching signals J1 and J2 are set to the L state (state 1).
From state 1 (J1 = L state, J2 = L state) to state 2 (J1 = H state, J2 = L state), state 3 (J1 = L state, J2 = H state), and state 4 (J1 = H) State, J2 = H state), the measurement of the lighting duration time is started.
When the state 2 (J1 = H state, J2 = L state) is changed to the state 1 (J1 = L state, J2 = L state), the measured lighting duration is the accumulated lighting time corresponding to the switching signal J1. It is added and the measurement of the lighting duration time is finished. When the state 2 (J1 = H state, J2 = L state) is changed to the state 3 (J1 = L state, J2 = H state), the measured lighting duration is the accumulated lighting time corresponding to the switching signal J1. The measurement of the lighting duration time is started again. When the state 2 (J1 = H state, J2 = L state) is changed to the state 4 (J1 = H state, J2 = H state), the measured lighting duration is the accumulated lighting time corresponding to the switching signal J1. The measurement of the lighting duration time is started again. That is, the measured lighting duration is added to the switching signal of the H state immediately before, and the measurement of the lighting duration is started or ended again.

When the state 3 (J1 = L state, J2 = H state) is changed to the state 1 (J1 = L state, J2 = L state), the measured lighting duration is the accumulated lighting time corresponding to the switching signal J2. It is added and the measurement of the lighting duration time is finished. When the state 3 (J1 = L state, J2 = H state) is changed to the state 2 (J1 = H state, J2 = L state), the measured lighting duration is the cumulative lighting time corresponding to the switching signal J2. The measurement of the lighting duration time is started again. When the state 3 (J1 = L state, J2 = H state) is changed to the state 4 (J1 = H state, J2 = H state), the measured lighting duration is the accumulated lighting time corresponding to the switching signal J2. The measurement of the lighting duration time is started again. That is, the measured lighting duration is added to the switching signal of the H state immediately before, and the measurement of the lighting duration is started or ended again.
When the state 4 (J1 = H state, J2 = H state) is changed to the state 1 (J1 = L state, J2 = L state), the measured lighting duration is the cumulative lighting corresponding to the switching signals J1 and J2. It is added to the time, and the measurement of the lighting duration time is finished. When the state 4 (J1 = H state, J2 = H state) changes to the state 2 (J1 = H state, J2 = L state), the measured lighting duration is the cumulative lighting corresponding to the switching signals J1 and J2. It is added to the time and the measurement of the lighting duration time is started again. When the state 4 (J1 = H state, J2 = H state) changes to the state 3 (J1 = L state, J2 = H state), the accumulated lighting time corresponding to the switching signals J1 and J2 is measured. It is added to the time and the measurement of the lighting duration time is started again. That is, the measured lighting duration is added to the switching signal of the H state immediately before, and the measurement of the lighting duration is started or ended again.
By controlling as described above, it is possible to have one timer for measuring the lighting duration corresponding to the switching signals J1 and J2.

As described above, in the present embodiment, when a set brightness lower than the brightness threshold stored in advance in the brightness setting unit 5021 is set, a part of the plurality of CCFLs is thinned out (partially turned off). . Therefore, even when the entire display screen of the liquid crystal display 1b is set to a lower setting luminance than the lower limit value of the screen luminance, the power consumption can be reduced. In addition, since the threshold value stored in advance is set to a value equal to or higher than the screen luminance value at which the cataphoresis phenomenon occurs, the cataphoresis phenomenon does not occur. Further, when shifting to the partially off state, the power supplied to the CCFL in which the inverter unit 20a is lit is increased, so that display quality is not impaired by the catalysis phenomenon. As described above, even when the CCFL is arranged in a direct type, the signal conversion unit 40 corrects the video signal M so that the screen luminance is uniform, so that the display quality is not impaired. , Power consumption can be reduced.
Further, in the present embodiment, timers 503 and 504 are provided, and the setting storage unit 5022b of the control unit 50b is partially turned off (the state of the switching signals J1 and J2 and the cumulative lighting time corresponding to the switching signals J1 and J2). ) Is memorized. Based on the information stored in the setting storage unit 5022b, the brightness control unit 501b includes a partially unlit state in which the CCFLs 101 and 103 of the A group are lit and a partially unlit state in which the CCFLs 102 and 104 of the B group are lit. Use the shorter cumulative time. Therefore, the cumulative lighting times of the A group and the B group of the backlight unit 10 are substantially equal, and the luminance difference that changes according to the cumulative lighting time can be reduced. Moreover, since the usage time of A group and B group can be averaged, the replacement interval of CCFLs can be extended.

  The present invention is not limited to the above embodiments, and can be modified without departing from the spirit of the present invention. In each of the above-described embodiments, the number of CCFLs of the backlight unit 10 is described by using four examples, and two sets of groups are described. However, the present invention is not limited to this. The external device 2 may be any external device that supplies a display signal K for displaying an image, such as a personal computer, a workstation, a television tuner, and the liquid crystal displays 1, 1a, and 1b may be integrated with the external device 2. Further, in each of the above embodiments, the external device 2 that supplies the display signal K to the signal conversion unit 40 supplies the set luminance to the control units 50, 50 a, and 50 b, but is different from the external device 2. Another external device may be used, or the set luminance may be supplied by a switch operation by the user. Further, the signal conversion unit 40 may be in the form of a large scale integrated circuit (LSI), or may be in other forms. Moreover, although the example which performs the process of the brightness | luminance correction of the video signal M based on the conversion table of the signal conversion part 40 was demonstrated, another form may be sufficient.

  In the second and third embodiments, as a condition for shifting to the power saving state, when the external device 2 is not operated for a certain period of time or when the external device 2 stops outputting the display signal K, the liquid crystal Although an example in which the display 1a has no input of the same signal included in the display signal K has been described, the present invention is not limited to this. In the second and third embodiments, the power save state has been described as an example in which output to both the switching circuit unit 204 and the drive signal lines 74 and 75 to the transformers 202 and 203 is stopped. The present invention is not limited to this, and any other state may be used as long as the power supply to the output lines 71 and 72 of the transformers 202 and 203 is stopped and the backlight unit 10 is turned off. For example, the switching circuit unit 204 may be operated, the output switching unit 201a may be shut off, and power supply to the transformers 202 and 203 may be stopped. Further, the form of the inverter unit 20a is not limited to the second and third embodiments, and may have an output switching unit 201a and switch the power supply state to the output lines 71 and 72. For example, other forms may be used.

In the second and third embodiments, the operation in the case of shifting to the power saving state and returning again has been described. However, the liquid crystal display 1a (or 1b) shifts to the power-off state and returns to the power-on state again. It can also be applied to cases. However, when shifting to the power shut-off state, it is desirable to retain information to be retained before the transition even in the power shut-off state. The information to be held here is the state of the switching signals J1 and J2 in the second embodiment, the state of the switching signals J1 and J2 and the lighting duration time measured by the timers 503 and 504 in the third embodiment. is there. For example, another storage unit that temporarily stores information to be held is provided. In another storage unit, information to be held by the luminance control unit 501a (or 501b) at normal times is periodically stored (for example, every minute or every second). The storage unit different from the setting storage unit 5022 (or 5022b) is configured to be able to hold stored information even in a power-off state. When shifting to the power shut-off state, transition from two states can be considered. First, in step S1 (or S1a and S2a), the state of the switching signals J1 and J2 (and the cumulative lighting time) is shifted from the state where the processing for storing the setting signal in the setting storage unit 5022 (or 5022b) is completed to the power-off state. Is the case. In this case, when returning to the power-on state again, it can be dealt with by performing the processes of steps S4 and S5 (or S4a and S5a).
The other is a case where the state before the completion of the process of step S1 (or S1a and S2a) shifts to the power-off state. In this case, when returning to the power-on state again, the luminance control unit 501a (or 501b) first refers to information to be held stored in another storage unit. Next, the luminance control unit 501a (or 501b) causes the setting storage unit 5022 (or 5022b) to store the states of the switching signals J1 and J2 (and the cumulative lighting time calculated from the lighting duration time). Thereafter, steps S4 and S5 (or S4a and S5a) may be continuously performed. It should be noted that, when the power is shut off, whether or not the process of step S1 (or S1a and S2a) is being performed is determined by, for example, a flag determination process indicating that the switching signals J1 and J2 are in the L state. judge.

  Moreover, you may hold | maintain the power supply of the control part 50a (or 50b) only for the period when the process of step S1 (or S1a and S2a) is performed using an auxiliary power supply (for example, battery). In addition, if the process of step S1 (or S1a and S2a) can be continued at the time of shifting to the power-off state, an auxiliary power supply is not necessary. In the case of shifting to the power-off state, the setting storage unit 5022 (or 5022b) and another storage unit may be in any form as long as they hold information in the power-off state. For example, an electrically rewritable nonvolatile memory or an SRAM (Static Random Access Memory) having a backup power source may be used, or another form may be used. Another storage unit may be provided in the storage unit 502a (or 502b) as a storage area different from the setting storage unit 5022 (or 5022b).

  In the third embodiment, the timers 503 and 504 have been described as being provided in the control unit 50b. However, the present invention is not limited to this and may be provided outside the control unit 50b. In the third embodiment, the cumulative lighting time is stored in the setting storage unit 5022b in step S2a. However, the present invention is not limited to this, and may be stored in step S1a.

1, 1a, 1b Liquid crystal display 10 Backlight part 20, 20a Inverter part 30 Panel part 40 Signal conversion part 50, 50a, 50b Control part 101-104 CCFL
201, 201a Output switching unit 202, 203 Transformer 204 Switching circuit unit 205 Control circuit unit 206, 207 Switch 301 Signal receiving unit 501, 501a, 501b Luminance control unit 502, 502a, 502b Storage unit 5021 Luminance setting unit 5022, 5022b Setting storage Part 503, 504 Timer

Claims (6)

A light source unit having a plurality of cold cathode fluorescent lamps;
A liquid crystal display unit that displays an image by modulating light from the light source unit;
Generates power to be supplied to the light source unit, and selects a partially unlit state in which some of the cold cathode fluorescent lamps are turned off or a fully lit state in which all of the cold cathode fluorescent lamps are turned on. An inverter circuit unit that drives the light source unit,
Generates a display signal for displaying the image on the liquid crystal display unit based on display information supplied from the outside, and corrects luminance information indicating a luminance value for each pixel in the display signal according to the partial extinction state A signal converter to
When the luminance setting information indicating the setting value of the screen luminance of the entire display screen supplied from the outside is a value lower than a predetermined threshold value, the inverter circuit unit and the signal conversion unit are set to the partially off state. And a control unit for transition ,
The signal converter is
The display signal in the vicinity of the cold cathode fluorescent lamp that is lit is corrected based on a predetermined correction amount to reduce the brightness,
Maintaining the brightness without correcting the display signal in the vicinity of the cold-cathode fluorescent lamp that is turned off, or increasing the brightness by correcting based on the predetermined correction amount,
Performs correction processing to make the brightness of the entire display screen uniform.
A liquid crystal display device comprising a call. The inverter circuit section is
A switching unit that selectively switches between the two partially lit states, the first partially lit state and the second partially lit state, in which the cold cathode fluorescent lamps that are turned off are in a complementary relationship. With
The controller is
When the luminance setting information is lower than the threshold value, the inverter circuit unit and the signal conversion unit are shifted to the first or second partial turn-off state,
When returning from the first or second partially extinguished state to a state where power supply to the light source unit is stopped and then returning to the partially extinguished state again, the second or different from before the transition The liquid crystal display device according to claim 1, wherein the liquid crystal display device is shifted to a first partially unlit state. A timer for measuring the lighting duration of the cold cathode fluorescent lamp;
The inverter circuit section is
A switching unit that selectively switches between the two partially lit states, the first partially lit state and the second partially lit state, in which the cold cathode fluorescent lamps that are turned off are in a complementary relationship. With
The controller is
When the luminance setting information is lower than the threshold value, the inverter circuit unit and the signal conversion unit are shifted to the first or second partial turn-off state,
The cold cathode type measured by the timer when returning from the first or second partially extinguished state to a state in which power supply to the light source unit is stopped and then returning to the partially extinguished state again. 2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device shifts to the second or first partial light-off state based on an accumulated lighting time obtained by accumulating the lighting duration time of the fluorescent lamp. The plurality of cold cathode fluorescent lamps are:
4. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is arranged in parallel and has the partially turned off state in which one of the odd number and the even number is turned off according to the arrangement order. The controller is
When shifting from the fully lit state to the partially turned off state, increase the brightness of the lit cold cathode fluorescent lamp,
The amount of change for changing the luminance of the light source unit is set to a value larger than the amount of change determined in advance as the fully lit state for the amount of change after shifting to the partially extinguished state. The liquid crystal display device according to claim 4 . A brightness control method for an image displayed on a liquid crystal display unit using a light source unit having a cold cathode fluorescent lamp,
Power is supplied to the light source unit having the plurality of cold cathode fluorescent lamps, and a part of the plurality of cold cathode fluorescent lamps is partially turned off and all of the cold cathode fluorescent lamps are turned off. Selectively switching between all lighting states and driving the light source unit;
A process of generating a display signal of an image to be displayed on the liquid crystal display unit from display information supplied from the outside, and correcting luminance information indicating a luminance value for each pixel in the display signal according to the partial turn-off state;
When the luminance setting information indicating the setting value of the screen luminance of the entire display screen supplied from the outside has a luminance lower than a predetermined threshold value, the process of shifting to the partially extinguished state,
Only including,
In the process of correcting the luminance information,
The display signal in the vicinity of the cold cathode fluorescent lamp that is lit is corrected based on a predetermined correction amount to reduce the brightness,
Maintaining the brightness without correcting the display signal in the vicinity of the cold-cathode fluorescent lamp that is turned off, or increasing the brightness by correcting based on the predetermined correction amount,
Performs correction processing to make the brightness of the entire display screen uniform.
Luminance control method comprising the this.

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