Structural analysis of direct-lit, side-in LED backlight modules

1. Background and purpose

The market share of LED backlights has expanded rapidly. At present, the technology of LED backlight modules is developing, and the structure of LED backlight modules is developing.

According to Yiguang, Samsung plans to further reduce the thickness of the direct-lit LED-backlit LCD TV. Of course, it still needs to overcome many technical difficulties. In addition, there are opportunities to combine the technology of side-lit LED backlight and direct-lit LED backlight. Launched (side-lit LED-backlit LCD TVs are the driving force for ultra-thin design).

Hisense believes that the first is to directly occupy the high-end LED, while the side-entry type occupies the low end of the LED; then the side-in type gradually replaces the CCFL backlight, while the direct-down type gradually replaces the side-entry type ("The 4th China International New Light Source & New Energy Lighting Forum").

Lin Xiujie of Techno System Research of Japan introduced the next development trend of high-growth LED-backlit LCD TVs in the "7th TSR Seminar 2010" (the next trend of LED-backlit LCD TVs). According to reports, many panel manufacturers plan to cut the light guide instead of unilaterally equipped with LEDs to reduce costs. Straight-down type In order to reduce the number of LEDs used, a lens cap (Lens Cap) is generally used. Through the improvement of the lens cover, the thickness of the backlight unit can be "thinned to 1.5 cm".

Therefore, research and development is being carried out in the following aspects:

First, the existing side-entry backlight module is improved.

Second, the existing direct type backlight module is improved.

Third, a new type of backlight module that designs and develops the main advantages of both direct-type and side-entry backlight modules without the major drawbacks of both. The main disadvantage of the side-lit backlight module is the main advantage of the direct-lit backlight module. The main disadvantage of the direct-lit backlight module is the main advantages of the side-lit backlight module. The two are highly complementary.

"China Electronics News" has separately counted the patents of important components of the backlight module, such as light guide plate, diffuser plate, reflector plate and light source. As of March 31, 2009, there were 2,381 Chinese patent applications in the field of TFT-LCD backlight module technology. Among them, the number of invention patent applications was 1,885, and the number of utility model patent applications was 466.

2, side-entry LED backlight module

The main disadvantages of the side-lit 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 conventional side-entry LED backlight module includes that the LED light source is disposed on a side of the light guide plate, and a mesh point is formed on a 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 reflection and scattering of the reflection sheet and the dots.

For the traditional side-entry LED backlight module, the light emitted by the LED chip cannot enter the light guide plate. On the one hand, a part of the light (a large angle of light, about 20%-30%, depending on the package structure) is due to total internal reflection. Cannot be emitted from the light exit surface of the LED package. On the other hand, even if the light emitted from the light surface of the LED package has been partially reflected, 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. The coupling and efficiency between the LED package and the light guide plate needs to be further improved.

Figure 1 sectional view

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, the light-emitting surface of the LED package 102 is adhered to the light-incident surface of the light guide plate by using the transparent glue 210, as shown in FIG. 2 . Since the refractive index of the silica gel, the transparent adhesive and the light guide plate of the LED package are substantially the same, there is substantially no total internal reflection at the light exit surface of the LED package, and substantially no reflection at the light incident surface of the light guide plate, and the LED chip emits The light basically enters the light guide plate substantially, and the coupling efficiency is improved to substantially reach 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, and the uniformity of brightness is easily achieved.

Figure 2 sectional view

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% to 30%.

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

(4) When the same brightness is ensured, the number of LED packages used is reduced by about 16%-23%, which reduces the cost.

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

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

(7) The light-emitting angle of the LED package is increased.

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