TV manufacturers have introduced LED backlight market

LCD LED backlight has been expected by the market

LED backlight module is already one of the technologies expected by the market. The high power consumption problem faced by LED backlight has already been solved, because for large-size LCD TV, there is nearly 60% of power. It is consumed on the backlight module, but to reduce the total power consumption is not only a single aspect of LED backlight, but also includes changing the driving circuit technology, enhancing the light guiding efficiency, reducing the thermal effect phenomenon, etc., and also assisting to reduce the total consumption. The technology of electricity.

At present, depending on the application, LED lighting methods are also different. Most LCD TVs use direct-lit backlights, while monitors and small-size applications are mainly side-lit, which is due to both sides. The difference between luminance and color rendering needs. In general, most of the monitors use the RGB3 primary color of the sidelight type. If it is a smaller size application, such as a car navigation panel, a mobile phone panel, a PDA panel, etc., most of them use white LEDs. Side-light mode, but the backlight method of side-light white LED has gradually developed towards large-scale development. At present, some notebook computers have also begun to use backlight modules with side-light white LEDs, so the design of the exterior can be more achieved. The goal of thinning and high elasticity, although the white LED is in the red part, there is a problem of lack of color rendering, but because the notebook computer is mostly used for static display of documents and the like, it is expected to reach the same quality as the LCD TV. After all, not much, so basically the lack of color rendering is not too big a problem, but of course there are ways to overcome, such as adding red LEDs in the array of white LEDs, etc., these methods are also one by one by the backlight module The industry has overcome it.

Leading the neck to expect high efficiency and high brightness LED

However, if the actual popularity of the 3 primary color LED backlights is expected, it is believed that there are still many problems to be solved, and it may take several years. In fact, the fundamental key is to wear the cost, because for LCD TVs, what is needed is high brightness, so it is necessary to use high-efficiency, high-brightness LEDs of 1W or more, plus because it is a direct-lit light, so 3 The number of primary color LEDs used may increase the number of LEDs used due to the increase in panel size. However, this approach brings another problem, that is, the thermal effect will increase due to the increase in the number of LEDs used in the three primary colors. In the first place, more heat sink fins, fans, heat pipes, etc. must be used to maintain the temperature inside the module. In addition, a large number of LEDs are used, and in order to uniform color tone, in addition to strict screening of LEDs with the same wavelength of illumination In addition, Color Sensor must be used to adjust the RGB chromatic aberration, but the effect is increased cost, so it can not effectively make the price meet the expectations of consumers. However, this is not absolute, and other techniques can be used to achieve an increase in panel size without having to use too many 3 primary color LEDs.

However, it is not the backlight module and LCD TV system industry to strive to reduce the power consumption of the LED backlight module. In fact, it also plays a very important role for the LED chip industry, because if the chip industry's efforts can strengthen the LED, If the luminous efficiency is used, then the LED's demand for electricity will be greatly reduced, and the benefits will be directly reflected in the LED backlight module.

The thermal effect problem is a common problem but not easy to solve

In recent years, LED chip manufacturers have been actively developing high-brightness LED chips. The most practical way is to let LEDs support larger currents to make LEDs produce greater brightness. In current specifications, one The maximum current that an area of ​​30um2 LED can withstand is about 30mA. This result is still not in line with the application of "making LEDs have greater brightness" because the market expects LEDs with an area of ​​1mm2. The introduction of 350mA current into the chip allows the single chip to produce higher internal quantum efficiency. If the driving voltage is 3V, then the power that flows into the LED will be nearly 1W.

However, it is not enough to increase the amount of current, because according to experience, about 3/4 of the power flowing in will have a thermal effect, that is, only 1/1 (0.25W) will be converted into light. And about 0.75W of electricity will become a thermal effect. The trouble caused by the thermal effect is well known. LEDs change the wavelength of light due to temperature, and reduce the luminous efficiency, resulting in color deviation of image quality.

For the development of white LEDs for LCD backlights, it is not only to improve the brightness of LEDs, but also to include the advantages of luminance uniformity, high color rendering, longevity, etc., so high-current LED chips are completed. After that, how to encapsulate it on a material with a large thermal conductivity and a large heat capacity has become a very important issue for the industry.

Increase optical output power by encapsulation

At present, the Lighting Promotion Association expects that 100 lm/W white LED will reach the practical stage of 1 lumen per lumen. The average color rendering evaluation of LEDs has been improved, and the development of phosphor powder has played a very important role, because the simulated white LEDs obtained by using phosphor powder with blue LEDs have weaker ability to display red and green at wavelengths, so Some companies have begun to use ultraviolet LEDs with RGB phosphors. However, this practice still has its complexity, because it is not possible to simply mix the phosphors of each color, because how to achieve the output close to natural white light is a problem. However, regarding the uniformity of the luminescent characteristics, it is generally considered that it is only necessary to improve the uniformity of the concentration of the fluorescent powder material of the white LED, and the production technique of the luminescent powder should overcome the above problems.

Technically, if the light output efficiency of the blue LED chip reaches 360mW, it is not difficult to obtain a white light output of 100lm/W in combination with the packaging capability of high-order technology. It is not a difficult problem in today's technology, for example, including CREE , In 2006, companies such as Nichia have developed high-brightness blue LED chips. How to reduce the loss of external quantum efficiency immediately afterwards is the ability of the tester's packager.

However, while increasing the current input, the thermal effect is a very rigorous problem, because it is necessary to try to reduce the thermal impedance, improve the heat dissipation and so on. Current practices include: reducing the thermal impedance of the chip, controlling the thermal impedance of the module and the printed circuit board, improving the heat dissipation of the chip, and the like.