Design of LED backlight components for notebook computers

　　introduction

　　With the development of LED technology, especially the improvement of luminous efficiency, energy-saving and environmentally friendly LED products have been more and more widely used in the display field. LED packaging, SMT patch, and light strip production have all developed to a high level, and the manufacturing and industrialization level of LED backlight has also reached a fairly high level. At present, the market demand for small-size products is increasing at a rate of about 20% per year. The application of LED backlight in notebook computers has become the leader, and the application of CCFL backlight in notebook computers will gradually withdraw from the stage of history. At present, major manufacturers around the world are actively developing LED backlight products, and almost all mainstream notebook computers on the market currently use LED backlight technology.

　　This article introduces the design and development of LED backlight components for notebook computers, and explains the development process from the perspectives of optics, circuits, and structure. In terms of optics, STAMPER technology is used to form an integrated injection light guide plate to reduce printing steps and eliminate printing pollution; in terms of circuits, LED light strips are designed according to the specifications and number of LEDs to drive the entire backlight source; in terms of structure, a backboard-free structural design is used to achieve an ultra-thin effect. The LED backlight for notebook computers designed in this article is ultra-thin, high-brightness, and low-power, reaching the industry-leading level.

　　1 Optical Design

　　1.1 LED Light Source

　　The function of the backlight module is to transform the light emitted by a point light source into a surface light source through diffuse reflection. In order to obtain a qualified surface light source, the first thing to do is to select a suitable LED. The specification of the LED usually used in the notebook computer backlight component is 3014. By presetting the white field photometric index and combining the research and analysis of factors affecting the LCD screen, optical film, etc., the calculation of the luminous flux required for the entire backlight source is completed. Based on the calculated luminous flux, combined with the optical characteristics of the LED, the number of LEDs required is calculated.

　　1.2 LGP design and processing

　　Using STAMPER technology, the light guide plate is molded in one piece, which reduces the printing process and reduces printing pollution. The dots are formed by mold injection. The incident surface design can destroy the total reflection of the light source and control the distribution of the angle of the light source exiting the light guide plate. The number of dots can effectively control the light source. The dots can be designed in any shape according to the mold. If the dots are extremely small and smooth mirrors, the loss of light in the dots and the light guide plate can be minimized. Optical design software is used for dot design. Figure 1 shows the brightness uniformity of the simulated backlight component.

    2 Circuit Design

　　In the edge-lit backlight component, a long LED light-bar is used as the light source of the entire component. The LED light-bar uses white top-emitting LEDs. Taking a certain product as an example, the power consumption of a single LED is: 3.2V×0.02A=0.064W. The power consumption of the entire light-bar is: 0.064W×42=2.69W. The LED backlight circuit design mainly includes the light bar design and the drive control circuit design. The drive circuit uses a DC/DC constant current drive chip to drive the light bar with constant current. Figure 2 shows the driving principle diagram of the LED light-bar.

　　3. Structural design

　　The LED backlight components for notebook computers usually adopt an edge-lit structure. The backlight component structure includes: LED light strips, film materials, light guide plates, driver boards, and plastic frames. The backlight component uses white light LEDs. The entire structural design takes the center point of the Active Area as the design center of all components. Other dimensions are designed based on the size of the LCD screen used in the notebook computer. The structure is designed by comprehensively considering the requirements of circuit design and optical design. The structural design starts with the LAYOUT layout diagram to express the overall structure and the assembly relationship between the various components, and then proceeds to the parts drawing structure design. The thickness of a certain model of backlight product can reach 2.35mm. Structural features of the designed LED backlight source for notebook computers:

　　(1) The backlight source has a single short-side input, and the light input method is short-side input, which reduces the size of the light strip and reduces the cost;

　　(2) Using thin flat LGP requires higher LGP dot technology;

　　(3) Rubber frame structure, no back plate, no lampshade structure, using high reflectivity reflective sheet for shading, and aluminum foil for heat dissipation;

　　(4) During assembly, there are strict requirements for the alignment of the LED light-emitting surface and the LGP light-entering part.

　　4 Testing

　　The LED backlight component for notebook computers designed in this paper uses white light LEDs. The assembled LED backlight source is tested with 13 points using BM-7. The average brightness at 5 points is 4,019nit, the brightness uniformity is 85.33%, and the color reproduction reaches 95% @CIE 1976. The overall power of the backlight source is 3.2W, of which the LED power consumption is 2.69W. The driving circuit of the backlight system is simple and the current consistency is good. Table 1 shows the optical test data of the backlight source.

Table 1 Optical test data of LED backlight

Figure 3 Cross-sectional view of backlight source

　　5 Conclusion

　　This paper designs and develops an LED backlight for notebook computers. It uses STAMPER technology and an integrated injection light guide plate to reduce printing steps and reduce printing pollution. The LED light strip is designed according to the specifications and number of LEDs to drive the entire backlight source. In terms of structure, a backboard-free structure design is adopted to achieve an ultra-thin effect. The LED backlight component for notebooks designed in this paper is ultra-thin, high-brightness, and low-power, reaching the industry-leading level.