Structure analysis of direct-type and side-type LED backlight module

1. Background and purpose

The market share of LED backlights is expanding rapidly. At present, the technology of the LED backlight module is developing, and the structure of the LED backlight module is developing.

According to Everlight, Samsung intends to further reduce the thickness of direct-lit LED-backlit LCD TVs. Of course, many technical difficulties need to be overcome. In addition, there are opportunities to combine edge-lit LED backlights and direct-lit LED backlights. Launched (edge-lit LED-backlit LCD TVs are popular with ultra-thin design is the motivation).

Hisense believes that first the direct type occupies the high end of the LED, and the side type occupies the low end of the LED; then the side type gradually replaces the CCFL backlight, and the direct type gradually replaces the side type ("The 4th China International New Light Source & New Energy Lighting Forum").

At the "7th TSR Symposium 2010", Lin Xiusuke of Japan's Techno System Research introduced the next development trend of the high-growth LED backlight LCD TV (the next development trend of the LED backlight LCD TV which is the general trend). According to reports, many panel manufacturers plan to cut light guide plates instead of unilaterally equipped with LEDs to reduce costs. In order to reduce the number of LEDs used in the direct-type method, a lens cap (Lens Cap) is generally used. Through the improvement of the lens cover, the thickness of the backlight unit can be "reduced to 1.5cm".

Therefore, research and development are being carried out in the following areas:

First, the existing edge-type backlight module is improved.

Second, the existing direct type backlight module is improved.

Third, design and develop a new type of backlight module that has the main advantages of both direct-type and edge-type backlight modules without the main disadvantages of the two. The main disadvantage of the side-type backlight module is the main advantage of the direct-type backlight module, and the main disadvantage of the direct-type backlight module is the main advantage of the side-type backlight module. The two are highly complementary.

"China Electronics News" separately counted the patents of important components of the backlight module, such as light guide plates, diffusers, reflectors, and light sources. As of March 31, 2009, there were a total of 2,381 Chinese patent applications in the field of TFT-LCD backlight module technology. Among them, the number of invention patent applications was 1885, and the number of utility model patent applications was 466.

2. Side-in LED backlight module

The main disadvantages of the side-type backlight module are:

(1) The coupling efficiency of the LED package and the light guide plate can also be improved;

(2) It is challenging when applied to large sizes;

(3) Local dimming cannot be performed.

2.0. Traditional side-entry LED backlight module

The structure of the traditional side-lit LED backlight module includes that the LED light source is arranged on the side of the light guide plate, and dots are formed on the bottom surface of the light guide plate. The light emitted by the LED package is coupled into the light guide plate, and propagates toward the liquid crystal screen through the reflection and scattering of the reflective sheet and the dots.

For traditional edge-lit LED backlight modules, all the light emitted by the LED chip cannot enter the light guide plate. On the one hand, part of the light (large-angle light, about 20%-30%, depending on the package structure) is caused by total internal reflection. It cannot be emitted from the light-emitting surface of the LED package. On the other hand, even if the light has been emitted from the light emitting surface of the LED package, part of the light cannot enter the light guide plate due to the reflection of the light incident surface of the light guide plate, as shown in FIG. 1. The coupling method and efficiency between the LED package and the light guide plate need to be further improved.

2.1. Improve the coupling efficiency between the LED package and the light guide plate

In order to make all the light emitted by the LED chip enter the light guide plate, a transparent glue 210 is used to glue the light emitting surface of the LED package 102 to the light incident surface of the light guide plate, as shown in FIG. 2. Since the refractive index of the silica gel, transparent glue and light guide plate of the LED package is basically the same, there is basically no total internal reflection at the light exit surface of the LED package, and there is basically no reflection at the light entrance surface of the light guide plate, and the LED chip emits Almost all of the light enters the light guide plate, and the coupling efficiency is improved, basically reaching 100%. In addition, since there is no total internal reflection, the large-angle light emitted by the LED chip also enters the light guide plate, which is easy to achieve the uniformity of brightness.

Advantages: (1) The coupling efficiency between the LED package and the light guide plate is improved.

(2) The extraction efficiency of the LED package is increased by about 20%-30%.

(3) The heat generated by each LED package is reduced by about 8%-13%.

(4) Under the condition of ensuring the same brightness, the number of LED packages used is reduced by about 16%-23%, reducing costs.

(5) The total heat generated by the LED backlight module is reduced by approximately 23%-33%.

(6) Energy consumption is reduced by approximately 16%-23%.