Introduction to interface backlight and bad points of liquid crystal display

by:Genyu     2019-12-14
At present, the market is full of liquid crystal displays, and the maintenance of liquid crystal displays is more difficult than CRT displays. This article will explain some knowledge and technologies of liquid crystal display maintenance. Liquid crystal is a substance between solid and liquid, and is an organic compound with regular molecular arrangement. If it is heated, it will appear a transparent liquid state, and if it is cooled, it will appear a turbid solid state of crystalline particles, which has the characteristics of liquid and crystal, so it is called 'liquid crystal '. The principle of liquid crystal display is simply to electrify the liquid crystal placed between the two electrodes, and the arrangement sequence of liquid crystal molecules will change when the electrodes are energized, thus changing the light path of transmitted light, realize the control of the image. TFT liquid crystal panel consists of surface protection glass, ternary color filter plate, polarizing plate, FET transistor deposited on glass substrate (Thin Film Transistor) Electrodes, liquid crystals, common electrodes also deposited on glassy substrates, underlying polarizing plates, backlight plates (Light guide)And a backlight. Light is transmitted from the bottom layer and controlled by the liquid crystal and the polarizing plate to produce colorful images with the help of the filter plate. Digital interfaces can be divided into 3. 3V and 5V can be divided into 18-digit interfaces and 24-digit interfaces if they are classified according to color. There are also two types of analog interfaces, one is analog RGB signal input and the other is NTSC/PAL video signal input. Backlight is talked about backlight here, so we will classify the angle of looking at liquid crystal from the other side. We can divide it into three types of liquid crystal, namely transmission type, reflection type and semi-transparent type. The reason why we divide it this way is that the liquid crystal display is passively luminous, so it has to rely on external light sources to display the content. In this case, what kind of light do the three types of liquid crystals need? The transmissive liquid crystal needs to add background light, and the reflective liquid crystal needs stronger ambient light, the semi-transparent liquid crystal requires strong ambient light or a backlight. For character-type liquid crystal, the backlight source is basically LED backlight source, mainly yellow, which drives small dot matrix liquid crystal with 5V monochrome STN, the most used backlight is LED or EL, and the common color of EL backlight is mainly yellow-green. EL's AC drive is basically 400-800Hz, 70- 100 V, the more commonly used drive requires 1W power in large dot matrix STN liquid crystal and TFT Liquid Crystal: mostly cold cathode fluorescent tubes (CCFL/CCFT) The common color of the backlight is white, and the AC drive is generally 25 k-100 kHz, above 300 V. The performance indicators of the bad point LCD screen can be found in the supplier's information and specifications, but the 'bad point' on the screen needs to be observed before it can be found. What is the 'bad point'? We call some pixels on the liquid crystal display screen that continue to emit light or are completely different the 'bad point '. The bad points always exist on the screen, so when we buy the LCD screen, we have to choose clearly. How can we find the 'bad points, we can adjust the screen to a pure white or pure black state, and then we can see if there are any pixels that continue to glow or are completely different. Under normal circumstances, no more than three bad display screens can be regarded as qualified products. Of course, when we choose, we will definitely choose a product that is not available, which is a-a product.
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