Solution: Large size ultra-thin side-lit LED backlight design

introduction

The LCD screen itself does not emit light. In order to clearly see the contents of the LED display , a certain white backlight is required. The backlight is an optical component present inside the liquid crystal display, consisting of a light source and the necessary optical auxiliary components. The conventional backlight uses a cold cathode fluorescent lamp (CCFL), which has poor color reproduction and contains mercury vapor which is harmful to the human body. LED backlights have good color reproduction, long life, no mercury, and are good for environmental protection. As far as the driving circuit is concerned, the conventional CCFL backlight driving circuit is very complicated, and requires a driving voltage of several thousand volts, which can be driven by a special inverter. The LED can work at low voltage, the response speed is fast, and the control is convenient. In recent years, LED has been gradually introduced into the existing liquid crystal display technology, and the backlight is very likely to become the next industry monopolized by LED. LED backlights are far superior to CCFL backlights by adding contrast and area control. At present, LED backlights have been popularized in small and medium-sized panels, such as mobile phones and digital photo frames. With the development of LED technology and the continuous maturity of LED chips , LED LCD TVs may gradually replace traditional CCFL LCD TVs.

The backlight is divided into a direct type backlight and an edge type backlight according to the position of the light source. The direct-type backlight directly places the LED light source under the light-emitting surface, and the light emitted by the light source is diffused and mixed by a space distance and a diffusion plate, and then becomes a surface light source, and the direct-type backlight needs a certain mixing distance. The edge-lit backlight structure is superior to the ultra-thin module design. With the “ultra-thin wind” blowing, large-size ultra-thin side-lit LED backlights have become the research of major TV manufacturers and upstream enterprises. Hot spot.

1 Structural design

The LED backlight designed in this paper is an edge-light ultra-thin structure. The whole structure includes: LED light bar, driving board, film material, light guide plate, heat sink block, upper frame and back plate. The backlight uses white LEDs. The entire structure is designed with the center point of the Active Area as the design center for all components. The other dimensions are designed on the premise of the size of the LCD screen used in LCD TVs. The structure is designed considering the requirements of circuit design and optical design. The structural design begins with the UIVOUT layout diagram, expressing the overall mechanism and the assembly relationship between the components, and then proceeding with the part drawing structure design. The upper frame adopts a segmented design and is segmented in the length direction to avoid lengths that are too long. The outlet end of the light bar is placed at the four corners of the back plate to reduce the length of the winding.

2 optical design

The function of the backlight module is to make the light emitted by the point source pass the diffuse reflection to make it a surface light source. In order to obtain a qualified surface light source, we must first select the appropriate LED. This design uses a white light two-chip LED. Through the preset white field photometric index, combined with the research and analysis of the influencing factors such as liquid crystal screen and optical film, the calculation of the luminous flux required for the entire backlight is completed. Based on the calculated luminous flux, the number of LEDs required is calculated in conjunction with the optical characteristics of the LED. Table 1 shows the electrical and optical characteristics of the selected LED.

Table 1 LED electrical and optical characteristics

LED electrical and optical properties

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