JP2006330158A - Led display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LED display device capable of correcting the degradation of luminance in an LED with the lapse of time with a simple configuration. <P>SOLUTION: Whether or not preset luminance variation time (cumulative lighting time) arrives at the LED 11 is judged (S3). As a result of a step S3, when the luminance variation time arrives (YES in S3), luminance degradation ratio is calculated by referring to the cumulative lighting time of a lighting time storage part 20 (S4). Then, duty ratio is raised for the degradation ratio (S5). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a display device in which a plurality of LEDs (light emitting diodes) are arranged in a matrix and displays characters and figures by blinking control of the individual LEDs, and more particularly to an LED brightness control technique.

  2. Description of the Related Art Conventionally, LED display devices are used for advertising purposes in storefronts of shopping streets, and characters and graphics are displayed by LED blinking control.

  FIG. 4 is a block diagram showing an internal configuration of a conventional LED display device.

  As shown in FIG. 4, the display device 1 includes a display unit 3 in which a plurality of LEDs (nine examples are illustrated in the figure) 2 are arranged in a matrix shape to display characters and figures, A drive unit 4 that causes a drive current to flow through each LED 2, a control unit 5 that controls a display pattern of characters and figures, and a storage unit 6 that stores a program for the control unit 5 to operate. .

  Here, the drive signal from the drive unit 4 to the LED 2 does not always flow the drive current to the LED 2, but uses the afterimage effect of the human eye, and the pulse signal as shown in FIG. LED2 is driven, and the luminance becomes higher and brighter as the duty ratio between the period T and the time t1 of “H (High)” is larger.

In addition, in LED display devices, there is a problem that it becomes difficult to see the display due to the difference in ambient brightness, such as day and night, even in the same luminance. According to the brightness, a technique for setting the brightness to be easy to see when viewed from an observer is also disclosed (for example, Patent Document 1).
Japanese Patent Laid-Open No. 10-187096

  However, the LED has a problem that the luminance decreases as the lighting time becomes longer due to a change over time, and as a result, the LED becomes darker with time than the luminance at the time of installation.

  In order to cope with such a problem, it is possible to increase the luminance by using the technique described in Patent Document 1, but in order to cope with all of the plurality of LEDs constituting the display unit, the illuminance Since a plurality of sensors must be arranged, the configuration is complicated, resulting in an increase in the size of the display device.

  An object of the present invention is to provide an LED display device that can correct a decrease in luminance of an LED due to a change with time with a simple configuration.

  In order to achieve the above object, the invention according to claim 1 is an LED display device that includes a plurality of LEDs and drives the LEDs to display characters and figures, and accumulates lighting times of the individual LEDs. A lighting time storage unit for storing the respective cumulative lighting times; and a control unit for controlling the duty ratio of the drive signal to the LED whose cumulative lighting time has reached a preset time. To do.

  According to a second aspect of the present invention, in the LED display device according to the first aspect, the LED luminance reduction rate is calculated based on the cumulative lighting time, and the duty ratio is controlled to increase in accordance with the calculated reduction rate. It is characterized by that.

  According to a third aspect of the present invention, in the LED display device according to the first aspect, the duty ratio is set in advance corresponding to the cumulative lighting time.

  According to a fourth aspect of the present invention, in the LED display device according to the first aspect, the set time is preset in a plurality of stages.

  With such a configuration, it is possible to correct the luminance in response to a decrease in luminance of each LED due to a change over time, and it is possible to realize this with a simple configuration.

  According to the present invention, the luminance can be reduced in response to a decrease in the luminance of individual LEDs due to changes over time with a simple configuration without using a detection means such as an illuminance sensor in a conventional device and without increasing the size of the display device. It can be corrected.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing an internal configuration of an LED display device according to an embodiment of the present invention.

  As shown in FIG. 1, an LED display device 10 according to the present embodiment includes a display unit 12 in which a plurality of LEDs (nine examples are illustrated in the figure) 11 are arranged in a matrix and display characters and figures. , A drive unit 13 for driving the individual LEDs 11 of the display unit 12, a control unit 14 for performing various controls such as display patterns of characters and figures, and a storage unit 15. The storage unit 15 includes a control unit 14. In addition to a program for operating the unit 14, a lighting time storage unit 20 for accumulating the lighting times of the individual LEDs 11 constituting the display unit 12 is provided.

  The data stored in the lighting time storage unit 20 is the accumulation of the time when each LED 11 is lit, and is accumulated every certain unit time. For example, if the unit time is 1 hour and the luminance is 10%, the lighting time storage unit 20 stores a lighting time of 6 minutes every hour.

  As shown in FIG. 2, the relationship between the lighting time and the luminance of the LED 11 decreases with time. With the above configuration, the control unit 15 can be installed by referring to the time of the lighting time storage unit 20. Since it becomes possible to grasp the rate of decrease in the brightness of the individual LEDs 11 compared to that time, the control unit 15 changes the duty ratio of the individual LEDs 11 whose brightness has decreased, and thereby the installation time at that time. Light emission luminance can be maintained.

  Next, the brightness control method of the control unit 14 in the embodiment having the above configuration will be described in detail.

  FIG. 3 is a flowchart showing the brightness control method of the display device of the present invention.

  In FIG. 3, it is first determined whether or not the unit time has passed for each LED 11 (S1). If the unit time has elapsed in a certain LED 11 as a result of the determination in step S1 (YES in S1), the lighting time of the LED 11 is stored in the lighting time storage unit 20 (S2), and the determination result in step S1. If the unit time has not elapsed (NO in S1), the determination in step S1 is performed again.

  After the process of step S2, it is determined whether or not a preset brightness change time (cumulative lighting time) has arrived at the LED 11 (S3). As a result of the determination in step S3, when the luminance change time has come (YES in S3), the luminance reduction rate is calculated with reference to the accumulated lighting time in the lighting time storage unit 20 (S4). Then, the duty ratio described in FIG. 5 is increased by the decrease rate (S5), and the determination in step S1 is performed again.

  If the result of determination in step S3 is that the brightness change time has not come (NO in S3), the determination in step S1 is performed again.

  As described above, according to the present embodiment, since it is possible to grasp the luminance decrease of each LED 11 due to a change with time, the duty ratio of the drive signal is increased by the decrease amount with respect to the LED 11 whose luminance has decreased. Thus, the display as a whole can be adjusted to the same brightness as at the time of installation.

  In addition, the LED of the LED display device may be turned on or off depending on the display content, but even if the display content is changed, it is possible to reduce variations in the brightness of individual LEDs. become.

  It should be noted that the luminance change time (set time) of the present embodiment is preferably set to a time of, for example, about a 100-hour cycle, which is a luminance reduction rate at which a difference in luminance can be seen with human eyes. Then, if the LED driving current is set in advance corresponding to the cumulative lighting time for each period, the control is simply performed.

  The present invention is a technique for reducing a decrease in luminance due to changes with time of LEDs, and is effective for use in a display device that performs display using a plurality of LEDs.

The block diagram which shows the internal structure of the LED display apparatus for describing embodiment of this invention The figure which shows the time-dependent change of the brightness | luminance of LED which concerns on this embodiment. Flow chart related to luminance control in this embodiment The block diagram which shows the internal structure of the conventional display apparatus Explanatory drawing of the drive signal of LED in a display apparatus

Explanation of symbols

10 LED display device 11 LED
12 Display unit 13 Drive unit 14 Control unit 15 Storage unit 20 Lighting time storage unit

Claims (4)

  In an LED display device that includes a plurality of LEDs and displays characters and figures by driving the LEDs, the lighting time storage unit that accumulates the lighting times of the individual LEDs and stores the respective cumulative lighting times; and An LED display device comprising: a control unit that controls a duty ratio of a drive signal for an LED whose cumulative lighting time has reached a preset time.   2. The LED display device according to claim 1, wherein an LED luminance reduction rate is calculated based on the accumulated lighting time, and the duty ratio is controlled to increase in accordance with the calculated reduction rate.   The LED display device according to claim 1, wherein the duty ratio is set in advance corresponding to the cumulative lighting time.   2. The LED display device according to claim 1, wherein the set time is preset in a plurality of stages.

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