JP2003257694A - Brightness control device, liquid crystal display, and brightness control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a brightness control device capable of changing the apparent brightness smoothly. <P>SOLUTION: A liquid crystal display 1 according to the invention includes a PWM signal producing part 14 to produce PWM signals Sp to be fed to an inverter 3 for lighting up a fluorescent lamp 4, whereby the brightness of the fluorescent lamp 4 is increased or decreased under control to one of the N stages (N is a natural number of 2 or more) at given intervals by controlling the duty ratio or frequency of the PWM signals Sp at multiple stages, in which the PWM signal producing part 14 performs the increase-decrease control at stages with finer unit intervals than the specified intervals in the one-stage increase-decrease control using the given intervals. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a brightness control device and a brightness control method for controlling the brightness of an inverter type lighting device in multiple stages, and a liquid crystal display equipped with the brightness control device.

[0002]

2. Description of the Related Art For example, in a car-mounted monitor such as a car navigation system, in order to avoid dazzling by a lighting for transmissive lighting or indirect lighting and to improve the visibility of a displayed image, it is necessary to adjust the brightness depending on the ambient brightness. It is preferable to adjust the brightness of the illuminating light. Specifically, it is necessary to reduce the brightness of the lighting light to avoid dazzling at night when the surroundings are dark, or in a tunnel, and to increase the visibility by increasing the brightness of the lighting light when the surroundings are bright. There is. Therefore, this type of display device is, for example, of a type that changes the brightness of the illumination light in conjunction with the switching of the light switch in the automobile, or a light receiving level (ambient brightness) of the light receiving sensor. A brightness control device of a type that changes the brightness of the lighting light is installed.

A liquid crystal display 51 shown in FIG. 8 is conventionally known as a display device equipped with this type of brightness control device. The liquid crystal display 51 includes a brightness control device 52 having a built-in light receiving sensor and a PWM (Pulse Width Modulation) output by the brightness control device 52.
An inverter 3 that oscillates according to the signal Sp, a fluorescent lamp (backlight) 4 that is turned on by an output signal of the inverter 3, and a liquid crystal panel configured to be able to display various display images by being irradiated with light emitted from the fluorescent lamp 4. 5 and. In the liquid crystal display 51, the brightness control device 52
However, the built-in light receiving sensor receives the light around the liquid crystal display 51 and adjusts the brightness of the fluorescent lamp 4 according to the light receiving level. Specifically, as shown in FIG. 9, it is determined whether the light receiving level L (ambient brightness) of the light receiving sensor is from the brightest light receiving level L8 to the darkest light receiving level L0, and based on the determination result. And fluorescent lamp 4
The brightness step S (any of brightness steps S8 to S0) to be set as the brightness of is determined. In this case, the brightness control device 52 performs PWM according to the determined brightness step S.
The duty ratio of Hi / Low in the signal Sp is changed. Specifically, as shown in FIG. 10, in the luminance step S8, the PWM signal Sp of Hi level is constantly output, and as the luminance step S decreases, the dimmer period TD decreases.
In the brightness step S0, the PWM signal Sp is output by shortening the Hi level time in the inside (the duty ratio is made small), and the PWM signal Sp corresponding to each brightness step S during the Hi level in the dimmer cycle TD.
Among them, the PWM signal Sp having the shortest (the smallest duty ratio) is output.

On the other hand, the inverter 3 oscillates, for example, when the PWM signal Sp output by the brightness control device 52 is at the Hi level and stops the oscillation when it is at the Low level. Therefore, as shown in FIG. 10, the dimmer period TD
The oscillation time TON of the inverter 3 inside is the longest (continuous oscillation) when the brightness control device 52 outputs the PWM signal Sp corresponding to the brightness step S8, and the PWM signal Sp corresponding to the brightness step S0 is output. Sometimes the shortest. Further, the fluorescent lamp 4 is turned on during the period when the inverter output signal is being supplied and is turned off during the period when the inverter output signal is not being supplied. As a result, the fluorescent lamp 4 is blinked at high speed in the dimmer period TD. At this time, by setting the blinking cycle of the fluorescent lamp 4 (that is, the frequency of the PWM signal Sp) to about 100 Hz or more, human eyes cannot recognize the blinking of the fluorescent lamp 4, and as a result, the blinking light is time-averaged. It is recognized as light having a predetermined brightness. Therefore, the fluorescent lamp 4 emits light with the brightness according to the set brightness step S.

When the liquid crystal display 51 is mounted on an automobile, when the surroundings of the liquid crystal display 51 are sufficiently bright (at the light receiving level L7 as an example), the brightness control device 52 shows the configuration shown in FIG. As described above, the brightness step S (in this case, the brightness step S7) according to the light reception level L is controlled. At this time, the duty ratio of the PWM signal Sp is controlled to be large, and as a result, the oscillation time TON of the inverter 3 becomes long. Therefore, the fluorescent lamp 4 is in a state close to continuous light emission and is perceived brightly by the human eye, so that the visibility of the display image displayed on the liquid crystal panel 5 is improved. On the other hand, at time t11 in the figure, for example, when the automobile enters the tunnel and the surroundings become dark (when the light receiving level is L1 as an example), the brightness control corresponding to the brightness step S1 is performed. At this time, the duty ratio of the PWM signal Sp is controlled to be small, and as a result, the oscillation time TON of the inverter 3 is shortened. Therefore, since the emission stop time of the fluorescent lamp 4 becomes long and the human eye feels dark, the dazzling caused by the emitted light of the fluorescent lamp 4 is avoided. In this case, in the liquid crystal display 51, when the ambient brightness sharply changes from the light receiving level L7 to the light receiving level L1 at time t11 in FIG.
Luminance step S6, S5 ...
Is decreased stepwise, and at time t12, the brightness is controlled to the brightness corresponding to the brightness step S1. Therefore, the brightness of the fluorescent lamp 4 changes smoothly as compared with the method of changing all at once from the brightness step S7 to the brightness step S1.

[0006]

However, the brightness control device 52 mounted on the conventional liquid crystal display 51 has the following problems. That is, the conventional brightness control device 52
Then, the brightness step S for which the brightness of the fluorescent lamp 4 should be controlled is determined according to the ambient brightness (light reception level L), and the PWM signal Sp of the duty ratio corresponding to the determined brightness step S is output to the inverter 3. The fluorescent lamp 4 is caused to blink at a brightness corresponding to each light receiving level L. However, since the human eye is sensitive to sudden changes in brightness,
Although the liquid crystal display 51 controls the brightness accurately, it feels awkward if the brightness change amount is large. Specifically, as shown in FIG. 12, for example,
When changing from the brightness step S7 to the brightness step S6, the brightness step S7 is performed at time t11 shown in FIG.
It is felt that the brightness B5a, which is darker than the brightness B6 corresponding to 6, is once controlled, and then is controlled to the original brightness B6. Similarly, from the brightness step S6 to the brightness step S6.
Even when the brightness is changed to 7, it is felt that the brightness B7a is once brighter than the brightness B7 corresponding to the brightness step S7 and then is controlled to the original brightness B7. As described above, in the conventional liquid crystal display 51, the apparent luminance change of the fluorescent lamp 4 is awkward although the duty ratio of the PWM signal Sp is accurately controlled according to the ambient brightness. There is a problem that

The present invention has been made in view of the above problems, and a main object of the present invention is to provide a brightness control device, a liquid crystal display, and a brightness control method capable of smoothly changing apparent brightness. And

[0008]

In order to achieve the above object, a brightness control device according to the present invention comprises a control signal generation part for generating a brightness control signal to be output to an inverter type lighting device, and the control signal generation part. Is a brightness control that controls the duty ratio or frequency of the brightness control signal in multiple steps to increase or decrease the brightness of the lighting device in any of N steps (N is a natural number of 2 or more) within a predetermined brightness change width. In the device, the control signal generation unit performs the stepwise increase / decrease control with a unit luminance change width finer than the predetermined luminance change width, in the one-step increase / decrease control with the predetermined luminance change width.

Further, a brightness control device according to the present invention is the brightness control device, further comprising a light receiving sensor for detecting a light amount, and the control signal generating section sets the brightness of the lighting device according to a light receiving level of the light receiving sensor. Is controlled to any one of the N stages.

Further, in the brightness control device according to the present invention, in the brightness control device, the control signal generating section continuously increases or decreases the brightness of the illumination device in multiple steps with the predetermined brightness change width. At this time, each luminance state corresponding to each predetermined luminance change width is maintained for a longer time than each luminance state corresponding to each unit luminance change width.

Further, in the brightness control device according to the present invention, in the brightness control device, the control signal generating section corresponds to each of the unit brightness change widths during one-step increase / decrease control by the predetermined brightness change width. Each of the brightness states is gradually maintained for a long time.

Further, a liquid crystal display device according to the present invention is lit with the brightness control device according to any one of the above, and a brightness according to the duty ratio or the frequency of the brightness control signal output by the brightness control device. It is configured to include the illuminating device that is configured as possible and a liquid crystal panel that is irradiated with light emitted from the illuminating device.

Further, the brightness control method according to the present invention controls the duty ratio or frequency of the brightness control signal output to the inverter type lighting device in multiple stages.
The brightness of the lighting device is divided into N levels (N is 2) within a predetermined brightness variation range.
A brightness control method for controlling an increase / decrease to any one of the above natural numbers), wherein the increase / decrease is controlled in one step by the predetermined brightness change width, the increase / decrease is performed stepwise with a unit brightness change width finer than the predetermined brightness change width. Control.

Further, the brightness control method according to the present invention is the brightness control method described above, wherein the brightness of the illuminating device is controlled to any one of the N levels according to the light receiving level of the light receiving sensor for detecting the light amount.

Further, in the brightness control method according to the present invention, in the brightness control method described above, when the brightness of the illuminating device is continuously increased / decreased in multiple steps with the predetermined brightness change width, each of the predetermined brightness changes. Each brightness state corresponding to each brightness change range is maintained for a longer time than each brightness state corresponding to each unit brightness change range.

Further, in the brightness control method according to the present invention, during the one-step increase / decrease control by the predetermined brightness change width, each brightness state corresponding to each unit brightness change width is gradually maintained for a long time.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a brightness control device, a liquid crystal display and a brightness control method according to the present invention will be described below with reference to the accompanying drawings.

First, the structure of the liquid crystal display 1 will be described with reference to the drawings. The same components as those of the conventional liquid crystal display 51 are designated by the same reference numerals, and duplicate description will be omitted.

The liquid crystal display 1 is a display device that can be used as, for example, a vehicle-mounted monitor, and includes a brightness control device 2, an inverter 3, a fluorescent lamp 4 and a liquid crystal panel 5, as shown in FIG. The brightness control device 2 includes a light receiving sensor 11, a filter 12, an A / D converter 13, a PWM signal generator 14, and a changeover switch 15. The light receiving sensor 11 receives light around the liquid crystal display 1 and outputs a level detection signal SI1 corresponding to the light receiving level. In this case, the light receiving sensor 11 also detects an irregular noise component (high frequency component) that captures a slight change in ambient light that cannot be recognized by human eyes. The filter 12 is the light receiving sensor 1
By averaging the level detection signal SI1 output by 1 with a relatively large time constant, the level detection signal SI1
The noise component contained in is removed and the level detection signal SI2 of a voltage corresponding to the average brightness is output. The A / D converter 13 digitally converts the level detection signal SI2 to generate level detection data DI and outputs it to the PWM signal generator 14.

The PWM signal generator 14 corresponds to the control signal generator in the present invention, and is based on the level detection data DI output from the A / D converter 13 (ie, the signal level of the level detection signal SI1). It is determined which of the light receiving levels L0 to L8 the brightness around the display 1 is. Further, the PWM signal generation unit 14 determines the luminance (luminance step S) of the fluorescent lamp 4 based on the determination result, and outputs the PWM signal (luminance control signal) Sp of the duty ratio corresponding to the determined luminance step S. To do. In this case, each brightness step S corresponds to the brightness of N steps in the present invention, and the liquid crystal display 1 is configured to be able to control the brightness of the fluorescent lamp 4 in 9 steps of brightness steps S0 to S8 as an example. There is. Further, the change width of each brightness step S corresponds to the predetermined brightness change width in the present invention, and in the liquid crystal display 1, when increasing or decreasing one brightness step S,
The PWM signal generation unit 14 controls the change step Sm (unit brightness change width in the present invention) as one change width unit and gradually increases or decreases in four steps. The changeover switch 15 is a switch for manually changing the brightness of the fluorescent lamp 4,
The PWM signal generator 1 outputs the switching signal Sc according to the switching state.
Output to 4. In addition, the PWM signal generation unit 14 outputs the switching signal Sc when the switching switch 15 outputs the switching signal Sc.
The brightness step S corresponding to the switching signal Sc is determined, and the PWM of the duty ratio corresponding to the determined brightness step S
The signal Sp is output.

The inverter 3 oscillates according to the PWM signal Sp output by the brightness control device 2. This inverter 3 is similar to the conventional liquid crystal display 51 in that the PW
It oscillates when the M signal Sp is at the Hi level, and stops the oscillation when it is at the Low level. The fluorescent lamp 4 constitutes the lighting device of the present invention together with the inverter 3, is disposed on the back surface side of the liquid crystal panel 5, and blinks at high speed in synchronization with the output signal of the inverter 3. The liquid crystal panel 5 is configured by a liquid crystal module of a transmissive display as an example, and is configured to display various display images by being irradiated with the light emitted from the fluorescent lamp 4. It should be noted that there are many existing brightness control devices of the type in which a filter, a duty controller, or the like is interposed between parts corresponding to the PWM signal generation unit 14 and the inverter 3 in the brightness control device 2. The liquid crystal display 1 according to the invention is configured so that the PWM signal Sp generated by the PWM signal generation unit 14 can be directly output to the inverter 3. As a result, the manufacturing cost is reduced by reducing the number of parts.

Next, assuming that the liquid crystal display 1 is mounted on an automobile, the brightness control method according to the present invention will be specifically described with reference to the drawings. As described above, the liquid crystal display 1 is also configured to be able to execute the brightness control based on the changeover signal Sc output from the changeover switch 15, but the fluorescence is detected based on the output signal of the light receiving sensor 11. The automatic brightness control (so-called auto dimmer control) for controlling the brightness of the lamp 4 will be described below as an example.

When the liquid crystal display 1 is turned on,
By the PWM signal generation unit 14 of the brightness control device 2, FIG.
The brightness control process 20 shown in is executed. In the brightness control process 20, first, a brightness step S for changing the brightness of the fluorescent lamp 4 according to the brightness of the surroundings of the liquid crystal display 1.
Is determined (step 21). Specifically, the level detection signal SI1 output by the light receiving sensor 11 is averaged by the filter 12 and output as the level detection signal SI2. At this time, the A / D converter 13 converts the level detection signal SI1 into an analog signal. -Digital conversion is performed to generate level detection data DI and output to the PWM signal generation unit 14. In this case, as shown in FIG. 3, the PWM signal generation unit 14 determines the brightness step S7 when the surroundings of the liquid crystal display 1 are bright (at the light reception level L7 as an example). Next, the PWM signal generation unit 14 determines the brightness step S
(In this case, the brightness step S7) and the brightness step S currently set (current brightness step S) are determined to be the same (step 22). When they are determined to be the same, the brightness step S7 is performed. Corresponding duty ratio P
The WM signal Sp is output to the inverter 3 (step 2
3) Returning to step 21, the brightness step S determination process based on the new light reception level L is executed. At this time, the inverter 3 oscillates in synchronization with the PWM signal Sp, so that the fluorescent lamp 4 blinks at high speed. As a result, as shown in the figure, the brightness of the fluorescent lamp 4 is the brightness B7.
Controlled by.

On the other hand, when, for example, an automobile equipped with the liquid crystal display 1 enters a tunnel and the surroundings of the liquid crystal display 1 suddenly darken (when the light receiving level L1 is reached as an example), the PWM The signal generation unit 14 determines the luminance step S to be the luminance step S1 in step 21.
Next, the PWM signal generation unit 14 determines that the determined brightness step S (in this case, the brightness step S1) and the current brightness step S (in this case, the brightness step S7) are not the same (step 22), It is determined whether or not the current brightness step S is larger than the determined brightness step S (step 24). At this time, since the current brightness step S is larger than the determined brightness step S, the PWM signal generation unit 14 reduces the brightness to the brightness step S determined from the current brightness step S (in this case, the brightness step S7). Perform brightness control.

Specifically, in the liquid crystal display 1, for example, the brightness to be set is defined by 5-bit data, and any of the brightness steps S0 to S8 is specified by the upper 3 bits, and each brightness step. The luminance step S divided into four by the change step Sm of the minute change amount rather than the change amount of S is specified by the lower 2 bits. In this case, the change step Sm means the minimum change amount of the duty ratio in the PWM signal Sp when the brightness of the inverter 3 is controlled to increase or decrease by the unit brightness change width in the present invention. Further, for example, the luminance steps S50 to S53 are the luminance steps S
The luminances obtained by further dividing 5 to S6 in the change step Sm are shown. Regarding the luminance step S50, the luminance step S5 is shown.
Therefore, it is simply referred to as a brightness step S5. Therefore, as shown in FIG. 4, the PWM signal generation unit 14 determines the brightness step S63 obtained by subtracting the change step Sm from the brightness step S7 at the time t1 in the figure, and determines the duty corresponding to this brightness step S63. Ratio PWM
The signal Sp is output (step 25). As a result, the inverter 3 oscillates according to the PWM signal Sp corresponding to the brightness step S63 to blink the fluorescent lamp 4. In this case, the PWM signal Sp corresponding to the brightness step S63
Indicates that the time of Hi level is slightly shorter than the PWM signal Sp corresponding to the brightness step S7. Therefore, the visual brightness B of the fluorescent lamp 4 is slightly darker than that at the brightness B7.

Next, the PWM signal generator 14 determines whether the brightness step S (in this case, brightness step S1) determined in step 21 and the current brightness step S (in this case, brightness step S63) are the same. It is determined (step 26). When it is determined that they are not the same, the PWM signal generation unit 14 returns to step 25 and proceeds to the brightness step S (that is, the brightness step S62) obtained by subtracting the change step Sm from the current brightness step S (in this case, the brightness step S63). Performs brightness control to reduce brightness. The PWM signal generation unit 14 repeats steps 25 and 26 to obtain brightness steps S62 and S6.
1, S6, S53, S52, ..., the brightness step S is stepwise reduced in units of the change step Sm, and the PWM signal Sp of the duty ratio corresponding to each brightness step S is supplied to the inverter 3 each time. Output. As a result, the oscillation time TON of the inverter 3 is gradually shortened by a slight change amount, and as a result, as shown in FIG. 4, the visual brightness B of the fluorescent lamp 4 is gradually darkened from the time point of time t1. The brightness corresponding to the brightness step S1 is reached at time t2.

In this case, in the conventional liquid crystal display 51, during the brightness control, the brightness control device 52 controls the decrease in units of a large change width change step S. Therefore, the visual brightness B of the fluorescent lamp 4 changes in a stepwise manner, as shown by the broken line in FIG. 4, and also changes awkwardly such that the brightness once becomes dark and then becomes the normal brightness. felt. On the other hand, in this liquid crystal display 1,
The brightness step S is controlled to decrease in increments of a slight change step Sm. In this case, it is extremely difficult for the human eye to recognize the change in brightness of the fluorescent lamp 4 with the change step Sm as a unit. Therefore, the visual brightness B of the fluorescent lamp 4 is recognized as a linear smooth change as shown by the solid line in the figure. After that, when it is determined that the determined brightness step S is the same as the current brightness step S at the time t2 in FIGS. 3 and 4 (step 26), the PWM signal generation unit 14 returns to step 21. The determination process of the brightness step S based on the new light reception level L is executed.

Further, as shown in FIG. 3, when the automobile exits the tunnel at the time t3 and the surroundings of the liquid crystal display 1 suddenly become bright (as an example, the light receiving level L7
(When returning to step 1), the PWM signal generation unit 14 determines the brightness step S7 in step 21. Then P
The WM signal generation unit 14 determines the determined brightness step S (in this case, brightness step S7) and the current brightness step S.
(In this case, it is determined that the luminance step S1) is not the same (step 22), and it is determined whether the current luminance step S is larger than the determined luminance step S (step 24). At this time, since the current brightness step S is smaller than the determined brightness step S, the PWM signal generation unit 1
As shown in FIG. 5, 4 determines a brightness step S obtained by adding a change step Sm to the current brightness step S (in this case, the brightness step S1) at time t3, and corresponds to this brightness step S. The duty ratio PWM signal Sp is output (step 27). As a result, the inverter 3
However, it oscillates in synchronization with the PWM signal Sp to blink the fluorescent lamp 4. In this case, the PWM signal Sp corresponding to the brightness step S11 is the PWM signal corresponding to the brightness step S1.
The time of Hi level is slightly longer than that of the signal Sp. Therefore, the visual brightness B of the fluorescent lamp 4 is the brightness B1.
It feels slightly brighter than when.

Next, the PWM signal generator 14 determines that the brightness step S (in this case, brightness step S7) determined in step 21 and the current brightness step S (in this case, brightness step S11) are not the same. (Step 28), returning to Step 27, the current luminance step S
(In this case, brightness step S11) change step Sm
Luminance step S (that is, luminance step S1
2) is determined, and the PWM signal Sp having the duty ratio corresponding to the brightness step S is output (step 27). In this way, by repeatedly executing steps 27 and 28, the PWM signal generation unit 14 causes the brightness step S12,
As in S13, S2, S21, S22, ..., the brightness step S is stepwise increased in units of the change step Sm, and the PWM signal Sp of the duty ratio corresponding to each brightness step S is supplied to the inverter 3 each time. Output. As a result, the oscillating time TON of the inverter 3 is gradually lengthened by a slight change amount, and as a result, as shown in FIG.
The visual brightness B of gradually becomes brighter from the time t3, and reaches the brightness corresponding to the brightness step S7 at the time t4.

In this case, in the conventional liquid crystal display 51, when the brightness is controlled, the brightness control device 52 performs the increase control in units of the change step S having a large change width. Therefore, the visual brightness B of the fluorescent lamp 4 changes in a stepwise manner, as shown by the broken line in FIG. 5, and changes awkwardly such that it becomes normal brightness after becoming bright once. felt. On the other hand, in the liquid crystal display 1, the luminance step S is controlled to be increased in increments of a small variation step Sm. Therefore, the visual brightness B of the fluorescent lamp 4 is recognized as a linear smooth change as shown by the solid line in the same figure as in the brightness control from the brightness step S7 to the brightness step S1 described above. After that, when it is determined that the determined brightness step S is the same as the current brightness step S at the time t4 in FIGS. 3 and 5 (step 28), the PWM signal generation unit 14
Returns to step 21 and executes the determination process of the luminance step S based on the new light reception level L.

As described above, according to the liquid crystal display 1,
The PWM signal generation unit 14 of the brightness control device 2 uses the fluorescent lamp 4
When increasing or decreasing the brightness of the PWM signal by one step, the duty ratio of the PWM signal Sp is changed stepwise by a change step Sm finer than the change width of one brightness step S.
Unlike the brightness control method in which the amount of change corresponding to one brightness step S is changed all at once, the visual brightness B of the fluorescent lamp 4 can be changed smoothly. Also,
According to this liquid crystal display 1, the PWM signal generation unit 14 causes the light reception level of the light reception sensor 11 (in this case, the A / D conversion unit 1).
The brightness of the liquid crystal panel 5 can be automatically adjusted by determining the brightness step S according to the value of the level detection data DI output by the signal 3 of FIG. 3, so that the brightness of the fluorescent lamp 4 can be automatically adjusted according to the ambient brightness. Can be set to an appropriate luminance, and as a result, it is possible to surely and easily avoid dazzling and improve visibility.

The present invention is not limited to the above-described embodiments of the present invention. For example, in the embodiment of the present invention, when changing the brightness step S, the brightness step S
63, S62, S61, S6, S53, etc., the respective lighting times of the fluorescent lamps 4 (the respective times for maintaining the respective brightness states corresponding to the respective brightness steps S) are equally controlled. It is not limited to this. Specifically, as shown in FIG. 6, when changing from the brightness step S7 to the brightness step S4, for example, the respective lighting times corresponding to the brightness steps S6 and S5 are set to the brightness steps S63, S62, S61, S53, S52, The lighting time can be maintained longer than each lighting time corresponding to S51. According to this brightness control method, the fluorescent lamp 4
Since the visual brightness B of the fluorescent lamp changes stepwise like the brightnesses B6, B5, and B4, the user can surely recognize the stepwise brightness change of the fluorescent lamp 4. Even with this brightness control method, the brightness steps S7 and S6 are changed, and the brightness steps S6 and S5 are changed.
Unlike the conventional liquid crystal display 51, the apparent brightness B can be changed smoothly by gradually controlling the decrease in m. In this case, even when the brightness is increased, each lighting time corresponding to each brightness step can be similarly maintained at a long time.

Further, as shown in FIG. 7, for example, when increasing control from the brightness step S4 to the brightness step S7, each lighting time corresponding to each of the brightness steps S41, S42, S43 is gradually maintained to be a long time. You can also
According to this brightness control method, the visual change in the brightness B of the fluorescent lamp 4 becomes a gentle curve as shown in the figure, so that a display device of high display quality can be provided.
In this case, for example, even when the brightness is lowered, each lighting time corresponding to each brightness step S can be gradually maintained to be a long time. Further, in the embodiment of the present invention, the brightness control method for controlling the brightness of the fluorescent lamp 4 by changing the duty ratio in the PWM signal Sp having a constant frequency according to the determined brightness step S has been described. Is not limited to this, and by changing the frequency of the brightness control signal without changing the Hi level output time (oscillation time TON of the inverter 3) of the brightness control signal (pulse signal) output to the inverter 3, as a result, It is also possible to control the brightness of the fluorescent lamp 4 by a brightness control method in which the duty cycle of the brightness control signal is changed to control the oscillation cycle of the inverter 3. In addition, in the embodiment of the present invention, each change step Sm in one luminance step S
Although the example in which the (unit brightness change width) is made equal to each other has been described, the change width of each unit brightness change width can be changed appropriately. In addition, in the embodiment of the present invention, the brightness control device 2 for turning on the fluorescent lamp 4 of the liquid crystal display 1 has been described as an example, but the illumination device to be brightness controlled is not limited to this. Starting with discharge lamps for projectors,
Various lighting devices such as indoor and outdoor lighting fixtures are included. In this case, when controlling the brightness of the luminaire, the brightness of the luminaire is reduced (the brightness step S is lowered) when the surroundings are bright, and the brightness of the luminaire is increased (the brightness step S is raised) when the surroundings are dark. There is a need. For this reason,
Unlike the brightness control method illustrated in the embodiment of the present invention, it is preferable to determine the brightness step S in inverse proportion to the light receiving level L of the light receiving sensor 11.

[0034]

As described above, according to the brightness control device of the present invention, the visual brightness of the lighting device can be smoothly changed, unlike the method of changing the brightness at a predetermined change width. In this case, since the brightness of the lighting device can be automatically adjusted according to the ambient brightness by controlling the brightness of the lighting device according to the light receiving level of the light receiving sensor, the brightness of the lighting device can be adjusted to an appropriate brightness. As a result of being settable, it is possible to surely and easily avoid dazzling and improve visibility. In addition, by maintaining each luminance state corresponding to each predetermined luminance change width for a longer time than each luminance state corresponding to each unit luminance change width, the gradual luminance change of the lighting device can be performed to the user. Can be surely recognized. Furthermore, by gradually maintaining each brightness state corresponding to each unit brightness change width for a long time, it is possible to provide a display device with high display quality.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a liquid crystal display 1 according to an embodiment of the present invention.

FIG. 2 is a flowchart of a brightness control process 20 executed by a brightness control device 2 of the liquid crystal display 1.

FIG. 3 Brightness around the liquid crystal display 1 (light reception level L)
3 is a timing chart showing the relationship between the luminance step S determined by the PWM signal generation unit 14 and the visual luminance B of the fluorescent lamp 4.

FIG. 4 is a timing chart showing the relationship between the brightness step S determined by the PWM signal generator 14 and the visual brightness B of the fluorescent lamp 4.

FIG. 5 is another timing chart showing the relationship between the brightness step S determined by the PWM signal generator 14 and the visual brightness B of the fluorescent lamp 4.

FIG. 6 is a timing chart showing the relationship between the luminance step S determined by the PWM signal generator 14 and the visual luminance B of the fluorescent lamp 4 in another embodiment of the present invention.

FIG. 7 is a timing chart showing the relationship between the brightness step S determined by the PWM signal generator 14 and the visual brightness B of the fluorescent lamp 4 in yet another embodiment of the present invention.

FIG. 8 is a block diagram showing a configuration of a conventional liquid crystal display 51.

9 is a timing chart showing the relationship between the ambient brightness (light reception level L) of the liquid crystal display 51 and the brightness step S determined by the brightness control device 52. FIG.

FIG. 10 shows P output by the brightness control devices 2 and 52.
6 is a timing chart showing the relationship between the WM signal Sp and the oscillation state of the inverter 3.

11 is another timing chart showing the relationship between the ambient brightness (light receiving level L) of the liquid crystal display 51 and the brightness step S determined by the brightness control device 52. FIG.

FIG. 12 is a timing chart showing the relationship between the brightness step S determined by the brightness control device 52 and the visual brightness B of the fluorescent lamp 4.

[Explanation of symbols]

1 Liquid crystal display 2 Brightness control device 3 inverter 4 fluorescent lamp 5 LCD panel 11 Light receiving sensor 12 filters 13 A / D converter 14 PWM signal generator 15 Changeover switch 20 Brightness control processing B, B0-B8 brightness DI level detection data L, L0 to L8 Light receiving level S, S0 to S8 brightness step Sc switching signal Sm change step SI1, SI2 level detection signal Sp PWM signal

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H091 FA42Z FD22 GA11 LA16                 2H093 NC42 NC49 NC55 ND07                 3K073 AA02 AA11 AA53 AA58 AA65                       AA67 AA85 BA28 CG10 CG11                       CG43 CH04 CH17                 3K098 CC42 CC44 CC49 DD20 DD35                       DD37 DD42 EE31 EE32 EE40

Claims (9)

[Claims] 1. A control signal generation unit for generating a brightness control signal to be output to an inverter type lighting device, wherein the control signal generation unit controls the duty ratio or frequency of the brightness control signal in multiple stages. , The brightness of the lighting device in N steps within a predetermined brightness change width (N is a natural number of 2 or more)
In the brightness control device for increasing / decreasing control to any one of the above, the control signal generation unit, in one-step increase / decrease control by the predetermined brightness change width, performs a step with a unit brightness change width finer than the predetermined brightness change width. A brightness control device that controls increase / decrease. 2. A light-receiving sensor for detecting a light amount, wherein the control signal generation unit controls the brightness of the lighting device to any one of the N levels according to a light-receiving level of the light-receiving sensor. Brightness control device. 3. The control signal generation unit, when continuously increasing / decreasing the brightness of the lighting device in multiple steps with the predetermined brightness change width, controls the brightness corresponding to the predetermined brightness change width. 3. The brightness control device according to claim 1, wherein the status is maintained for a longer time than each brightness status corresponding to each unit brightness change width. 4. The control signal generation unit gradually maintains each brightness state corresponding to each unit brightness change width for a long time during one-step increase / decrease control by the predetermined brightness change width. 4. The brightness control device according to any one of 3 to 3. 5. The brightness control device according to claim 1, and a structure capable of lighting with a brightness according to the duty ratio or the frequency of the brightness control signal output by the brightness control device. A liquid crystal display including the lighting device and a liquid crystal panel irradiated with light emitted from the lighting device. 6. The brightness of the lighting device is controlled in multiple steps by controlling the duty ratio or frequency of the brightness control signal output to the inverter lighting device in N steps (N is a natural number of 2 or more). ), The brightness control method for increasing / decreasing the brightness in a step of increasing / decreasing by a unit brightness change width finer than the predetermined brightness change width during the one-step increase / decrease control with the predetermined brightness change width. Control method. 7. The brightness control method according to claim 6, wherein the brightness of the illuminating device is controlled to any one of the N levels according to the light receiving level of the light receiving sensor for detecting the light amount. 8. When the brightness of the lighting device is continuously controlled to increase or decrease in the predetermined brightness change width in multiple steps, each brightness state corresponding to each predetermined brightness change width is changed to each unit brightness change. 8. The brightness control method according to claim 6, wherein the brightness is maintained for a longer time than each brightness state corresponding to each width. 9. The brightness state corresponding to each of the unit brightness change widths is gradually maintained for a long time during one-step increase / decrease control by the predetermined brightness change width. Brightness control method.