KR101216989B1 - Liquid crystal display using optical sensor in light emitting diode-back light unit - Google Patents

Abstract

The present invention relates to a liquid crystal display device, the configuration of the cover bottom; An optical sensor fixed below the cover bottom; A liquid crystal plate laminated on the light receiving unit of the optical sensor; A printed circuit board (PCB) attached to an upper portion of the cover bottom; A light emitting diode (LED) fixed to the substrate; And an LCD panel disposed on the optical sheet and spaced apart from the front surface of the substrate by a predetermined distance. As a result of the above configuration, the optical sensor accurately controls the light to improve the brightness and color characteristics of the liquid crystal display device to meet the needs of customers.

Optical sensor, side-emitter light emitting diode (LED), LED backlight

Description

Liquid crystal display using LED backlight light sensor {LIQUID CRYSTAL DISPLAY USING OPTICAL SENSOR IN LIGHT EMITTING DIODE-BACK LIGHT UNIT}

1 is a cross-sectional view of the LED backlight device of the present invention

2 is a cross-sectional view of a liquid crystal display device having an LED backlight device in which an optical sensor is deposited according to a first embodiment of the present invention.

3 is a cross-sectional view of a liquid crystal display device having an LED backlight device in which an LCD panel is stacked on a light receiving unit of an optical sensor according to a second embodiment of the present invention.

※ Explanation of main part of drawing ※

100: PCB for fixing LED 112: Light sensor

114: liquid crystal board 116: LED

120: PCB for fixing the optical sensor 122: LCD panel

124: adhesive 128: optical sheets

130: cover bottom

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device. In particular, in using a light emitting diode (LED) as a light source, an LED backlight device intended to maintain a constant light quantity and color by mounting an optical sensor therein or applying a constant deformation to the optical sensor. It relates to a liquid crystal display device configured to include.

The backlight of a general liquid crystal display reflects light from a cold cathode tube to a reflecting plate and arranges a milky white scattering plate in the reflection path of the light, so that light having a locally uniform illuminance is illuminated on the liquid crystal display.

However, this method has a disadvantage in that the thickness of the backlight cannot be reduced, which makes the liquid crystal display complicated and large. Therefore, in recent years, as a surface light source device, it is a two-pole device that emits light only when a current passes. By using LEDs with low power consumption and semi-permanent lifespan, the backlight is thinned and the brightness is improved.

In particular, it reproduces natural color and high-definition image compared to the existing cold cathode tube, solves the afterimage problem, and replaces the cold cathode tube backlight device with eco-friendly products that do not use mercury.

Briefly looking at the related art of the LED backlight device in this regard there is a structure in which a plurality of LED chips are arranged in a predetermined pattern on the driving circuit board for uniform light emission as an example of the surface light source LED backlight. In this case, the total thickness of the surface light source device was about 5 mm, which was relatively thin compared to the surface light source device of the conventional cold cathode tube type, but was still inadequate to meet the desired thickness for application to the liquid crystal display. Since the light emitting form is performed by a plurality of LED chips forming a dot, it is not easy to form a uniform illuminance on the whole surface.

In contrast, a backlight system as disclosed in US patent application Ser. No. 09 / 384,137 sometimes includes LEDs having any number of rows and columns. The system includes 10 x 12 matrix LEDs. However, it should be understood that any number of LEDs may be provided to form the matrix. The LEDs are placed in a cavity suitably formed by the connected wall. The cavity here is exactly called the 'backlit cavity'. In particular, the wall is coated with a high light reflectivity finish such as, for example, high gloss white paint or white reflective material. It will also be understood that side-lit or edge-lit applications include LEDs on one or more walls.

Of course, the LEDs here are current-controlling elements, whether surface-mount or thru-hole. As a result, each LED in the string is provided with the same current. Among other reasons, it is also common to form electrical LED strings in series connection to conserve power. Multiple strings of LEDs not only increase the brightness anyway, but also avoid higher voltage levels, increasing the safety margin of the LED's potential for failure and adjusting the various colors of the LED when color enhancement or color generation is required. It was expected to be used for.

However, contrary to such expectations, the above invention was not without problems. In other words, in the LCD device to which the LED backlight is applied, luminance gradually decreases over time.

After all, one of the reasons for this is the LED characteristics. Specifically, when all the LEDs are subjected to the same input current, the output temperature of the LED decreases as the junction temperature increases, which causes a decrease in luminance or a change in color. .

Accordingly, the present invention, in the conventional LED backlight, by attaching a light sensor therein, or by stacking a kind of liquid crystal board (board) on the light receiving portion of the light sensor to detect more accurate light, to control the change in brightness and color Its purpose is to.

First, the configuration of the liquid crystal display device according to the first embodiment of the present invention for achieving the above object is a cover bottom; An optical sensor fixed below the cover bottom; A printed circuit board (PCB) attached to an upper portion of the cover bottom; A light emitting diode (LED) fixed to the substrate; An optical sheet spaced at a predetermined distance from the front surface of the substrate; And a liquid crystal display (LCD) panel provided on the optical sheet.

In addition, the liquid crystal display according to the second embodiment of the present invention includes a cover bottom; An optical sensor fixed below the cover bottom; A liquid crystal plate laminated on the light receiving unit of the optical sensor; A PCB attached to an upper portion of the cover bottom; An LED fixed to the substrate; And an LCD panel disposed on the optical sheet and spaced apart from the front surface of the substrate by a predetermined distance.

First, before going into the configuration of the present invention, the characteristics of the LED that serves as a light source and a photodiode that recognizes light in a specific region, that is, the characteristics of the optical sensor will be described.

The luminescence properties of LEDs are very dependent on the LED's semiconductor material. Therefore, the LED characteristics vary for various manufactured parts. Luminescence always depends on the LED current. The ratio of the emitted light to the LED current is one of the key variables that vary from product to product. Accordingly, various groups with similar ratios of converting current into light generally select LEDs first. Among these LED groups, the LED forward voltage can vary.

For example, to use a LED light source to illuminate a picture, the image sensor must be activated and simultaneously generate a light pulse. In order to optimize the system for power dissipation and heat dissipation, it is important to keep the LEDs on as short as possible. Therefore, synchronization with the image sensor is required. Typically light pulses of 100 ms or more are used, but depend on the LED light-emitting ability and the way the image sensor and flash device work together. There are two things to address. In other words, the LED current must be controlled and the light pulse and image sensor must be synchronized.

On the other hand, when the temperature of the P / N junction rises, the LED itself changes its light characteristics due to a decrease in luminous flux and a wavelength shift, that is, movement to a long wavelength region. Therefore, it is no exaggeration to say that the failure rate of a semiconductor element is determined by the junction temperature of the element. And this can often be proved by the following equation, which represents the relationship between ambient temperature and junction temperature.

P / N junction temperature in LED

T _J (° C) = T _A (° C) + θ _JA P _AVG

Where T _A is the ambient temperature, θ _JA Is the temperature resistance around the junction and P _AVG Denotes average power dissipated, respectively.

Next, a brief look at the optical sensor. This means that the light receiving device, which is the opposite concept to the light emitting device described above, may be considered to be the opposite. In other words, the light receiving element senses light from the outside and thus restricts the flow of current.

Specifically, in the energy band structure of the PN junction, the Fermi level coincides with the P layer and the N layer in the thermal equilibrium state, and a potential barrier is formed inside. When light (E = hv) having a larger energy than the energy gap Eg is irradiated thereto, the electrons are attracted to the conduction band, and the electrons and the remaining holes are formed in pairs. When the electron hole pair thus formed is formed in the depletion layer, it is accelerated by the electric field, electrons move to the N layer, and holes move to the P layer. In the case of the P layer and the N layer, the electrons of the P layer and the holes of the N layer diffuse and reach the depletion layer, which is further accelerated by the electric field, and the charges in the N and P layers are accumulated.

In addition, if the characteristics are seen, the light receiving element is a planar structure, i.e., a specific element is engraved on the surface of a flat semiconductor plate called a wafer, so the diode characteristics are good, and the operation characteristics under load are particularly excellent. In addition, the linearity of the photocurrent from low illuminance to high illuminance is good, and the variation in light output between devices is small in the same assembly state. In addition, the device uses a photovoltaic effect having many characteristics such as fast response speed and wide sensitivity wavelength.

In particular, in terms of spectral sensitivity, the optoelectronic light-receiving element is a silicon substrate, and since the chip itself has a wide spectral sensitivity ranging from the visible region to the near infrared ray, it can be combined with most light sources.

Then, the configuration of the LED backlight according to the present invention will be described in detail with reference to the drawings. Therefore, FIG. 1 is intended to show only the LED backlight device of the liquid crystal display device of the present invention. The cover bottom 40 of the backlight device, i.e., the inside of the cover, may be, for example, a printed circuit board 20, but there are a plurality of LEDs arranged in a string, ie two or three or more rows. In particular the LEDs herein may be side-emitter type LEDs with red, green and blue LEDs.

And the optical sensor 26 is mounted in the middle of the board | substrate 20, or any point of a side surface. Although illustrated in the drawings as being fixed in the middle position in the present invention does not substantially limit the position.

This is because the light emitted from the backlight will be uniform to the last, and the result of detecting the light probabilistically will not be very different no matter where the optical sensor is supposed to detect the light. Thus, the key to the position of the light sensor above is the fact that it fixes one light sensor anywhere on the substrate inside the backlight cover.

In addition, the backlight device basically includes optical sheets 28 on the front surface of the substrate.

The optical sensor 26 according to the above-described configuration senses about three kinds of light. In other words, optical sensors such as light directly received from the LEDs, or light reflected and received primarily before passing through the diffuser plate, and light passed through the diffuser plate and reflected from the optical sheet, that is, the prism sheet, may be provided. By sensing and controlling all the lights, it is possible to maintain the white light by appropriately mixing the light emitted by a plurality of red, green, and blue LEDs. This, in turn, concludes that the photosensor can collectively control the LEDs in the backlight to determine the overall brightness and color characteristics of the LCD device.

However, contrary to those expectations, the luminance and color characteristics of the liquid crystal display device shown in FIG. 2 as the first embodiment of the present invention have not been kept constant in addition to the processes up to now. Of course, the liquid crystal display device here is a thin film transistor liquid crystal display device having an additional LCD panel 30 on the front of the LED backlight device. As a result, the conclusion of the first embodiment according to the present invention is that even if the light sensor 26 maintains the brightness and the color accurately inside the backlight, the light properties from the inside of the backlight pass through the polarizer and the liquid crystal of the LCD, and thus the optical characteristics are changed. It was. In summary, the light transmission characteristics of LCD panels change over time due to temperature or applied voltage, because polarizers, liquid crystals, and color filters are affected by temperature or electric fields.

Accordingly, the present invention, if the above results may be a problem, the second embodiment also presents a solution as shown in FIG. The configuration is similar to that of the first embodiment, but the only difference is a structure in which a kind of crystal board 114 having the same characteristics as a so-called LCD panel is laminated on the light receiving portion of the optical sensor 112.

The configuration will be described in more detail with reference to the accompanying drawings. In any one of the cover bottom 130 and the kind of backlight case mentioned above, an optical sensor 112 and a comparison circuit chip are drilled by precisely drilling holes corresponding to the light receiving unit where the optical sensor is mounted on the side. C) is fixed to the PCB 120 is fixed to the site. Of course, the PCB 100 of the front portion that will correspond to the light-receiving portion also need to be punched. In particular, the remaining pieces 114 stacked on the light receiving unit remain after cutting the LCD panel, for example, using a double-sided tape or adhesive 124 or the like, the bottom of the PCB 100 to which the LEDs of the backlight case or string are fixed. Use a method of fixing to Although the drawings illustrate fixing to the PCB 100 as an example, the present invention is not limited thereto.

In this case, since the light finally read by the optical sensor 112 is detected as the same light as the light transmitted through the LCD panel, the effect according to the configuration of the second embodiment may be improved a little.

As a result of the above, according to the present invention, the optical sensor can provide a better quality product by constantly controlling the overall brightness and color of the liquid crystal display.

Claims (12)

Cover bottom; An optical sensor fixed below the cover bottom; A printed circuit board (PCB) attached to an upper portion of the cover bottom; A light emitting diode (LED) fixed to the substrate; An optical sheet spaced at a predetermined distance from the front surface of the substrate; And And a liquid crystal display (LCD) panel disposed on the optical sheet. The liquid crystal display of claim 1, wherein the LED comprises LEDs arranged in two or three or more rows. The liquid crystal display of claim 1, wherein the LED comprises one or more side emitting LEDs. The liquid crystal display of claim 1, wherein the LED is formed by mixing red, green, and blue LEDs. The liquid crystal display of claim 1, wherein the optical sensor is fixed to a side surface of the substrate. Cover bottom; An optical sensor fixed below the cover bottom; A liquid crystal plate laminated on the light receiving unit of the optical sensor; A PCB attached to an upper portion of the cover bottom; An LED fixed to the substrate; An optical sheet spaced at a predetermined distance from the front surface of the substrate; And And a LCD panel installed on the optical sheet. 7. The liquid crystal display device according to claim 6, wherein the LED comprises LEDs arranged in two or three rows or more. 7. The liquid crystal display of claim 6, wherein the LED comprises one or more side emitting LEDs. The liquid crystal display of claim 6, wherein the LED is formed by mixing red, green, and blue LEDs. The liquid crystal display of claim 6, wherein the optical sensor is fixed to a side of the cover bottom. 7. The liquid crystal display device according to claim 6, wherein the liquid crystal plate has the same optical characteristics as the LCD panel. The liquid crystal display device according to claim 6, wherein the liquid crystal plate is fixed by the cover bottom and a double-sided tape or an adhesive.

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