The Backlight's Composition And Upgrade Method of TFT Display

Views: 333     Author: Reshine Display     Publish Time: 2023-11-30      Origin: Site


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The Backlight's Composition And Upgrade Method of TFT Display

The backlight source's composition

A light source, a light guide plate, an optical module, and structural components comprise the backlight source.

1. Choosing a Light Source

Electroluminescent (EL) backlighting is thin and lightweight, delivering uniform and consistent illumination. It consumes very little power and requires an operating voltage of 80 100 Vac. The operating voltage can be provided by an inverter with a 5/12/24Vdc input converted to an AC output. However, the service life of EL backlighting is limited (the average service life under 50% brightness is 3000 to 5000 hours, and the service life will be greatly shortened at higher brightness levels), so the ideal inverter for EL backlighting allows the output voltage and frequency to be increased with the aging of the EL bulb, thereby extending the effective service life of displays employing the EL backlighting light source.

For small reflective LCD applications such as watches, digital desktop clocks, and monochrome PDAs that require extremely weak illumination for use in hazy or dimly lit conditions, EL backside illumination is preferable. However, their low efficiency, low brightness, and short lifetime make them unsuitable for use in transmissive backlighting applications such as the large LCDs required for laptop computers and flat-panel desktop monitors.

Small cold cathode fluorescent lamps (CCFLs) provide the brightness and lifetime (and light control) needed for large LCDs, but with the proliferation of LEDs that are more efficient and flexible in their design and use, CCFLs are becoming less and less common. However, heat buildup is a concern. Related product: TFT LCD Display.

LED backlighting has a service life of more than 5,000 hours and uses DC voltage. LED backlighting and CCFL backlighting in the structure are the same, where the main difference is that the CCFL is a line light source, while the LED is the first to be made into an LED light bar (LED light bar) and then put into the backlight.

2. Selection of light guide plate

The light guide's role is to direct the direction of light scattering, improve panel brightness, and ensure panel brightness uniformity. Because the quality of the light guide plate has a significant impact on the backlight panel, the design and production of the light guide plate are two key technologies in the side-light backlight panel. The injection molding method of acrylic pressed into a smooth surface of the plate, and then with highly reflective and non-absorbent materials, in the bottom surface of the guide plate with screen printing on the way to print the diffusion point, the CCFL or LED light bar is located in the side of the guide plate. When light is emitted into the interior using a reflective guide plate and shot to the point of diffusion, the reflection of the light is diffused to various angles, and the light then destroys the reflection conditions of the guide plate. When the light reaches the diffusion point, the reflected light diffuses to various angles before shooting out of the front side of the light guide plate, destroying the reflection condition. The use of a variety of sparse, varying-size diffusion points can help to uniformize the light guide plate. The reflector's purpose is to reflect the light exposed on the bottom surface back to the light guide plate, which is used to improve light efficiency.

Guide plates made by various processes can be classified as printed or non-printed (injection molding), printed on an acrylic plate with high reflectivity and non-absorbent materials on the bottom surface of the guide plate with screen printing printed on the circular or square diffusion points. The use of precision molds to make the light guide plate in injection molding, adding a small amount of different refractive index in the acrylic material in the granular material, the direct formation of densely packed tiny bumps, and its role as a dot are all examples of non-printing. The printing method is ineffective compared to the non-printing method.

Non-printing excellent; the method is excellent in that it employs fewer people, is quick, and efficient; You light guide components, with low development costs and the benefits of rapid production, more commonly and non-printed technical difficulties, but excellent brightness performance; Mold development technology for the bottleneck; additionally, they can be divided into a flat plate and a wedge-shaped plate based on shape; the flat plate is more commonly used in monitors and televisions, while the wedge-type plate is more commonly used in notebooks. The main purpose of diffusion plate production is to improve the brightness of the front; its role is to make light distribution more evenly distributed so that the front cannot see the shadow of the reflection point. As the light from the diffusion plate's directivity is very poor, we must use the prism sheet to correct the direction of the light, achieve the effect of concentrated light, and improve the brightness of the front.

In addition, there are also etching methods (mold kernel nibbles), that is, directly transferring the design of the printing point to the mold instead of the traditional printing method, and in terms of the actual performance of the luminance, the etching guide plate is not as good as the printed light guide plate.

Cutting SC processing, that is, in the front of the light guide plate to cut the way to create a long groove type of structure and prism sheet structure similar to the mirror design, can increase the effect of improving the brightness, but the uniformity of performance is not as good as the printing method of the structure of the light guide plate.

method involves the sandblasting method, which involves the use of fine sand material sprayed on the mold kernel to form a coarse surface distribution. In the injection molding under direct transfer to the light guide plate, the coarser the surface of the place, the more destruction of the light source will occur.

Visible, the role of the backlight module is nothing more than a point light source or line light source issued by diffuse reflection to make it a surface light source. But this backlight source has a lot to learn. With a different number of lamps, when the surface texture will have different changes, the design of the backlight plate covers the optical design, precision molds, etching, printing, and other precision technology.

3. Optical Film Selection

Prismatic films, reflective polarizers, and high-reflectivity reflectors will be used to improve the forward-looking brightness, or axial brightness, of the LCD module under certain light source output conditions. There are two ways to improve axial brightness without increasing the number of light sources: first, improve the angular distribution of light by focusing the light on the front view angle; second, reduce losses and improve the total light output luminous flux. There are more than 30 manufacturers of brightening films on the market, including LG, 3M, GE, Sony, Rohm, Haas, and others.

Backlight restoration technique

1. First, the backlight board should be overhauled to ensure that the power supply is operational.

That is, the standby power supply 3.3V or 5V, 12V, 24V, PFC circuit is working properly before you can overhaul the backlight system!

2. Repair can be removed wiring.BRI (dimming), and BL-ON (backlight control) 3 feet together, and the normal backlight board should be able to light up normally. This step can be judged to be a problem with the motherboard or the power board.

3. If the backlight tube still does not light up, there is no pulse signal added to the backlight inverter. We can repair the backlight circuit when the backlight system can be viewed as a line sweep circuit to repair!

4. The backlight control chip has a characteristic that the chip, just powered on for about 2 seconds, is not protected by any feedback pin control; there is an output pulse after the startup to get the normal feedback signal of its detection pins before entering the normal operating state. If you do not get the feedback signal after the start or an abnormal feedback signal, the chip will enter the protection state to stop outputting excitation signals!

5. The use of this feature first in the power-up now detects output. It should be noted that the chip protection needs to be powered off and restarted after the output will be about 2 seconds.)

6. If there is a signal output, the fault in the backstage drive part can be determined. Otherwise, the problem is with the backlight chip control circuit. We can measure the backstage of the excitation transformer output, whether the AC excitation signal output (there is no accurate voltage value because the operating frequency of the backlight circuit is 56 kHz or so beyond the frequency response of our ordinary multimeter), the digital table is generally 30 volts or so, and the mechanical table is 10 volts or so. We must emphasize that regardless of how much the voltage value of the two windings is used to obtain the voltage value, it must be the same; otherwise, there is a problem.

7. When the excitation transformer output pulse is normal, we continue with the backstage step-by-step measurement until we find the pulse of the short-circuit point.

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