Research and application of low-cost direct-lit TV backlight system

Figure 4 New large-angle optical LENS solution design and test model sample

2.3 Research and solve the optimization of rectangular spot

At present, when designing rotationally symmetrical large-angle direct-down LED lenses, in order to improve the illumination uniformity of the receiving area, the double free-form surface design method is often used. This design method can avoid the suppression of total reflection and reduce Fresnel loss. The double free-form surface lens structure allows the light to be refracted twice to reach the receiving target surface.

A better simulation result of the receiving surface spot, the model and simulation results are shown in Figure 4. The results show that the light emitted by the LED light source is refracted by the lens to form a uniform rectangular spot of about 230 mm × 230 mm on the target receiving surface 35 mm away from the light source, which is significantly improved compared with the simulation results of the initial structure of the lens.

The above method realizes the design and optimization of a rectangular uniform spot lens. It starts from the spatial intensity distribution relationship before and after the light shape is shaped by the lens, and takes multiple sets of curves corresponding to the rotationally symmetric lens to form a circular spot with uniform illumination on the receiving surface as the optimization goal. The traditional design method of optimizing discrete points on the surface is transformed into the optimization of multiple sets of fitting curves, which overcomes the problem that the traditional method is difficult to optimize due to the large number of discrete points on the surface to a certain extent.

Figure 5 The maximum edge angle of reflective paper

2.4 Study the thinning design scheme of the whole machine

After backlight optoelectronic parameter design and prototype installation, the limit edge angle of reflective paper was evaluated as follows:

According to the edge trimming angle, the edge trimming dimensions of back panels of various sizes are shown in Table 2:

3 Feasibility Assessment and Verification

1) Based on the thermal analysis and actual reliability test of Ansys software, the steady-state thermal analysis and test of the backlight source SMC3030 packaged in dual-crystal and flip-chip single-crystal packaging were carried out. By comparing the analysis results of the two, it was found that the flip-chip large-chip LED has better thermal performance than the upright dual-crystal.

2) Based on the comparison of different light sources in the same module, the influence of the crystal gap of the backlight source in the flip-chip large chip packaging form on the thermal performance of the lamp beads was studied. It was found that the thermal resistance of the 3030 backlight source in the large chip flip-chip packaging form can be minimized by controlling the solder void rate.

3) Based on the phosphor simulation module of Lightools optical design software, the color temperature of SMC3030 lamp beads in flip-chip and upright dual-crystal packaging forms is simulated and analyzed to explore the change law of the phosphor characteristic parameters of dual-crystal lamp beads under the same color temperature conditions. The simulation results show that in order to obtain the same color temperature as the flip-chip large-chip LED light source, the flip-chip LED light source needs to increase the particle size of the phosphor or increase the density of the phosphor.

4) Based on the phosphor simulation module of Lightools optical design software, the effect of the crystal gap of the SMC3030 backlight source in a large chip flip-chip package on the light output of the lamp beads is studied. The maximum luminous flux of the LED lamp beads in the flip-chip package can be obtained by controlling the crystal gap.

5) Based on the non-imaging edge ray theory and the shearing design principle of free-form surfaces, Zemax Optic Studio optical design software and its optimization module Visual Optimizer were used to design and optimize a reflective backlight lens with a mixed light distance of 35mm. Based on the nine-point test method, a surface imaging colorimeter was used to test the lens when it was applied to a 55-inch direct-type LED LCD backlight module. The test results basically met the main requirements of the backlight module for optical performance.

6) Based on Zemax Optic Studio optical design software and its optimization module Visual Optimizer, a backlight lens with uniform rectangular light spot is designed. Starting from the spatial intensity distribution relationship before and after the light shape is shaped by the lens, multiple sets of curves corresponding to the rotationally symmetric lens form a circular light spot with uniform illumination on the receiving surface as the optimization goal. The traditional design method that requires the optimization of discrete points on the surface is transformed into the optimization of multiple sets of fitting curves. To a certain extent, it overcomes the problem that the traditional method is difficult to optimize due to the large number of discrete points on the surface.

4 Conclusion

32-inch, 43-inch, and 55-inch screens are the first to use new backlight technology, which is the first low-cost backlight solution in the industry. This technology can be applied to mid- and low-end products. Its backlight parameters and performance can reach the level of current multi-light strip solutions, and the price flexibility is large year-on-year. This technology caters well to the cost reduction advantages of direct-type backlight technology in the TV series, improves the company's brand reputation and product competitiveness, brings profit growth to mid- and low-end products, and leads the development trend of the industry.

With the expansion of the company's overseas brands and the increase in ODM business volume, logistics costs have become a key cost consideration. It is necessary to comprehensively evaluate the optimization design of the whole machine and module structure. The simplified design combined with optoelectronic technology can provide a large design expansion space for the structure, which has a strong guiding significance for increasing the cabinet loading volume.

References:

[1] Liu Chuanfang. Design and optimization of large-size direct-lit LED LCD backlight system[D]. Guangzhou: South China University of Technology, 2012.

[2] Liang Dejuan. Research on high-efficiency side-entry LED flat panel light without light guide plate[D]. Xiamen: Huaqiao University, 2014.

[3] Li Liang. Study on the characteristics of white light LED package phosphor[D]. Hangzhou: China Institute of Metrology, 2012.

[4] Song Jidong. Light distribution design of high-power LED lighting based on free-form surface[D]. Hangzhou: Zhejiang University, 2010.