The backlight technology of large-size LCD screens is divided into two types: side-down (or edge) and direct-down (or matrix). Due to its low cost and simple architecture, the side-down backlights account for more than 90% of the large-size LCD backlight market share. At present, domestic first-line brands such as Hisense, Haier, Konka, Skyworth, TCL, Changhong, etc. are all committed to the development of LED TVs with side-down backlight architecture. However, due to the advantages of more power-saving, simpler heat dissipation, better image contrast, and local dimming, the discussion on switching to a direct-type (or matrix) LED backlight architecture has also begun to emerge in the industry.
According to Displaybank, the global LED market will grow at a rate of 19% per year. The most important growth driver comes from large-size LCD screens, including the backlight market for liquid crystal displays and LED TVs. There is no doubt that if the LED backlight architecture is changed from the current mainstream edge-type large-scale to direct-type (or matrix), the demand for LEDs in the industry will surge.
The most important growth driver for the global LED market comes from large-size LCD screens.
At present, Sharp Corporation of Japan has been pushing the concept of direct-sense and developing a solution for LED+LENS. However, since only high-end models use direct-type technology, major domestic manufacturers have not responded positively, so the shipment of this technology product is not large.
Yang Zhiyong, TV project manager of Ruifeng Optoelectronics Co., Ltd., analyzes this. There are three main reasons: First, the cost problem, the direct cost is still slightly higher than the side type; the second is the volume problem, compared with the side type, the direct type The thickness of TV increases more; the third is the process problem, and the production process of FULL LED & LENS is more complicated than the side.
Considering the possibility of a shortage of light guide plates and the direct features of local dimming, Ruifeng is actively developing and stocking this technology (COB, Full LED, Lens+LED mode). Yang Zhiyong revealed that Ruifeng Optoelectronics has jointly developed direct-type projects with Konka, Skyworth and TCL.
Looking forward to this year, direct-lit backlight technology will remain weak. Zhao Donghui, vice president of Fairchild's Korea Power Conversion Division, said that the current direct-source (matrix) LED backlights account for less than 5% of total LED TV production, and the proportion of direct-lit LED backlights is not expected to increase because of the price adjustment of LEDs this year. Slower, and LCD TV manufacturers are focusing on reducing the cost of BLU Back Light Unit TVs to replace LCD TVs with CCFL backlights.
Wu Tao, a power product business development engineer in TI China, estimates that more models of direct-lit backlight technology will be developed in the market in 2012. Therefore, the phenomenon of large-scale adoption of the direct-lit LED backlight architecture TV will not occur until at least two years later.
In terms of side-down backlight technology, with the full investment of domestic first-line brand manufacturers such as Hisense, Haier, Konka, Skyworth, TCL, and Changhong, the LED TV development of the side-down backlight architecture is getting better. Due to the increase in LED brightness, the price of single lamps has been greatly reduced, and the backlight strips have quickly transitioned from the previous multilateral to the current narrow unilateral, which is almost equal to the CCFL in overall cost. At present, the number of LED TV projects developed by major manufacturers is also significantly redundant with CCFL.
Kin Shum, CEO of Xinkai Electronic Technology Co., Ltd. believes that the main reason for the low cost of side-down backlights is that it can connect dozens or more LED lights in one LED string, thus reducing the cost of the system. Therefore, the high-voltage LED driver chip will become the mainstream driver chip for the side-lit backlight.
Kin Shum, CEO of Kaikai Electronic Technology, said that due to its leading high-voltage process, Kaikai can provide a series of high-voltage LED driver chips that can drive up to 60 LEDs per string. "In terms of efficiency, our competitor's LED driver chip can only drive 10 to 15 LEDs in a single string, so using our LED driver chip will greatly reduce system cost." He stressed that high system cost is hindering the LED market. The bottleneck of faster development, so with the decline in the production cost of LED itself, the core LED driver chip will have no small cost competitiveness.
Number of LED backlight driver ICs
There is currently no standard LED chip requirement for a specific size TV in the industry. In fact, the number of LEDs used in different LED TV backlighting schemes varies, depending on the LED characteristics such as Forward Current and Luminous Intensity. Wu Tao estimates that about 200 to 300 LED chips can meet the needs of 42-inch or 47-inch LED TVs. Zhao Donghui believes that many TV manufacturers only need to use 70~140 LED chips in 42-49-inch LED-backlit TVs.
The number of LED drivers depends on the light bar configuration. Zhao Donghui said that most TV manufacturers use 1-4 LED driver ICs in their systems. Wu Tao from TI has different opinions. "We usually choose to use one LED driver for all the light bars. Although sometimes 2 will be used, we will never use 3 LED drivers in the same TV." Wu Tao said.
The configuration of LED strips in different schemes is also very different, and customers may have different considerations for cost, dimming requirements or maximum luminous intensity. Wu Tao introduced that one of the common configurations is 4 strings of LEDs, each with 50 LEDs.
In terms of LED power level selection, according to Yang Zhiyong, project manager of Ruifeng Optoelectronics Co., Ltd., the LED power used in the side-down 32" LED TV is mainly 0.4-0.8W, and the main 32-inch is 0.06-0.2. W-based; direct-down architecture is currently only 32" or more, and its LED power is mainly 0.06W. He revealed that in the field of medium-power LED, the current TV manufacturers are still evaluating.
At present, there are five main requirements for LED driver, including: 1) LED current accuracy between different channels; 2) efficiency of the overall backlight system; 3) PWM dimming function; 4) linearity of LED current; ) Protection when the LED is open or shorted.
Improving thermal performance, reducing EMI problems, and reducing the number of channels and LED strips are the main technical challenges facing LED system manufacturers. It is also a major problem to achieve the cost of lower 3D model design while maintaining visual quality, higher passive component requirements and trade-off balance.
O 2 Micro is believed that the future development trend of LED drivers is mainly concentrated on multi-channel equalization and regional dimming. Multi-channel equalization means that when multiple strings of LEDs are connected in parallel, if a string of LEDs fails or is damaged, in order to keep other string LEDs still functioning properly, it is necessary to consider the application of current matching in multiple LED strings, including series and parallel LED strings. . The bumpy LED driver chip allows for 3.1 to 3.5V LEDs forward voltage range (Tolerance in forward voltage of LEDs), and its consistency and efficiency are higher than CCFL.
Area dimming technology is used to dim the backlight portion of a specific area on the screen, or to illuminate different areas to make the picture look darker or brighter, while the edge-lit LED backlight technology can only be comprehensive. Brighten or dim. This dimming method is especially suitable for the design of high contrast TVs. Area dimming saves the number of light sources used and makes the picture area look more realistic. O 2 Micro can provide global dimming and local dimming control chips to support market demand.
LED prices stabilized in the first half of the year
The backlight of LCD TVs is gradually being replaced by LEDs. According to the prediction of the Topology Industry Research Institute, the penetration rate of LEDs has risen rapidly in 2011. For example, LED displays have risen from 20% to 48%, and LED TVs have climbed from 20.4% to 50%, which has become the main driving force for LED applications. Such a large market size has also attracted many LED drivers and packaging manufacturers to join them. Currently active LED backlight driver manufacturers include: O 2 Micro, MPS, AnalogicTech, TI, Fairchild, Li Wei, etc. The main LED packaging factories are: Yiguang, Dehao Runda, Ruifeng, Foshan Guoxing and so on.
The main markets for O 2 Micro are the LCD TV, LCD and notebook markets. The relevant person in charge of the company told the international electronic business reporter that in the third quarter and the fourth quarter of 2010, the above markets experienced some pressure on inventory adjustment; however, with the coming of Christmas and the Chinese New Year, the recent supply and demand in the market Already close to balance. With the increase in the ratio of LCD TVs with LEDs as backlights, the emergence of new TVs such as 3D TVs and smart TVs, and the demand for new NBs driven by the launch of Intel's new platform, O2 Micro considers the supply and demand of LED driver chips in the next six months. Maintain a balanced situation.
Ruizhi Optoelectronics TV project manager Yang Zhiyong said that Ruifeng Optoelectronics has 10 years of packaging process precipitation, and is also very concerned about the TV backlight market. The person in charge of the company disclosed to the international electronic business reporter that at present, domestic first-line brands such as Konka, Skyworth and Changhong are important customers, with monthly shipments of 10-15KK, and the delivery period has been relatively normal. It is reported that Ruifeng invested a large amount of funds in 2010 to purchase related equipment, and the production capacity has more room to play.
Due to the establishment of strategic partnerships with many well-known raw material manufacturers including Cree, Jingyuan and Yiquan, Ruifeng Optoelectronic TV Project Manager Yang Zhiyong expects that the price of Ruifeng Optoelectronics' 5730 and 3020 products will stabilize in the first half of 2011. In addition, due to the significant addition of MOVCD equipment from the Korean, Taiwanese and mainland epitaxial manufacturers in 2009-2010, "I believe that in the next few years, LED chips as the main material will definitely reduce prices, while the demand for LED TVs Increase, as well as the development of the lighting market, when the overall demand for LEDs is greatly increased, the price of LEDs is bound to be lowered to be closer to the requirements of ordinary people." Yang Zhiyong said.
Since TV brand manufacturers pay close attention to the reliability of LED chips, and LED TVs have only been launched in the market for about two years, there are still many problems that require time to verify. Yang Zhiyong said that Ruifeng Optoelectronics has always used Taiwanese chips and communicated with European and American chip manufacturers. As for why the local LED chip is not used, Yang Zhiyong said that local manufacturers need to continue their efforts in the following areas to meet the requirements of LED TV customers: 1) reliability; 2) productivity; 3) brightness; 4) patent issues.
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