LED backlight drive energy efficiency priority

LED as LCD backlight is not what new things, its driving technology has been very mature. However, the small size of the portable applications to expand the size of the LCD TV, the new field of application on the LED drive circuit also made more stringent requirements. At the same time, due to the LCD TV backlight LED is also faced with the choice of different modes, so the design of the driver circuit should also compare the pros and cons of various programs.

With the support of LED price decline and green energy concept, using LED as the application field of backlight source by mobile phone and other portable products rapidly expand to the notebook computer and desktop computer monitors and LCD televisions in large size display field. Traditional, large size LCD display using CCFL (cold cathode fluorescent lamp) backlight faces a LED offensive offensive. The difference between LED and traditional CCFL backlight lighting source is that the former has better image quality, more slim design, low power consumption and environmental protection, which is the rapid adoption of LED lighting solutions and replace the CCFL lighting solution where. Said Li Zaipeng, director of Fairchild Semiconductor PCIA lighting. AnalogicTech CEO RichardWilliams also said: the use of LED backlight will be about 30% less than CCFL backlight. The use of CCFL is not only high energy consumption, but also the use of mercury pollution of the environment. At present, more and more LCD TVs use LED as backlight. "

However, the large size LCD backlight LED driver circuit requirements are more stringent. The general manager of Hangzhou Mao Power Semiconductor Technology Co Ltd and MPS Hangzhou R & D center Ren Yuancheng in an "China electronic newspaper" interview with reporters, said: "with the increase of the panel size, power LED backlight is also increasing rapidly, also put forward new requirements for LED driving circuit. The driving circuit can be 12V or 24V voltage into a higher voltage to drive more series of LED; to ensure the flow of current between each series LED backlight to achieve high precision uniform; conversion efficiency to be higher, thereby reducing production in a limited space to achieve strict heat; open circuit and short circuit protection. "

"LED backlight from portable applications to LCD TV applications, the change is very large. Hangzhou Silan microelectronics Limited by Share Ltd power supply and power driven product line general manager Wu Jianxing told reporters, "change the screen size lead to the change of power from the mobile phone backlight, LCD TV to hundreds of milliwatts or even tens of watts is hundreds of watts. In addition, the power supply changes, the phone uses a lithium battery power supply, the typical value of 3.7V~4.2V; and in the LCD TV applications, power supply is generated by AC-DC 12V or 24 power supply system. So LCD TV backlight and mobile phone backlight is completely different two product platform, in terms of reliability, efficiency, current matching, dimming and other aspects of LCD TV backlight LED driver has a new requirement. "

There are two forms of LCD TV LED backlight, namely, the edge and dot matrix (direct). RichardWilliams told reporters: "LED edge type backlight solution, is actually in the edge of the LCD is arranged before CCFL place to install some LED, the formation of a number of LED'band'; and the dot matrix is in the form of LED dot matrix LCD display in the layout below. "The LED dot matrix backlight scheme, intelligent control LED current absorber for individual parts based on image content provides accurate brightness, and can provide more pure black for the viewer, while improving the contrast, in order to obtain better and more natural viewing.

In addition, its dynamic LED backlight can also meet the stringent energy consumption standards for large flat-panel tvs. "RichardWilliams says. "Edge has the advantages of simple structure and cheap price, and the dot matrix has the characteristics of good image quality and high contrast, but the driving circuit is relatively complex, which requires a digital interface and an image decoding chip to communicate. "Any remote said," the edge of the backlight three driver circuit has matured, the industry is now focused on how to reduce costs and improve efficiency. MPS proposed the "driving energy processing 'design concept, through this design, about 80% of the energy only two received LED, while only about 20% of the energy to be handled 3 times; the drive efficiency reached more than 97%, compared with the three level architecture improves the 5%~6%; at the same time, because can be used in low voltage devices, but also reduces the cost of many. If the number of LED strings in the edge architecture is reduced from the current 4 series to the next 1, then the level of the drive line in the cost and drive efficiency will be more attractive. "

Wu Jianxing also compared to the edge of the reporter and dot matrix backlight LED program pros and cons. "Edge backlight has the advantages of low cost and low power consumption. Its disadvantage is that the backlight uniformity is not enough, and the backlight color gamut is close to the CCFL backlight. Dot matrix has the advantages of even backlight and wide color gamut. Disadvantages are high cost, power consumption, the model can not be ultra-thin. "Wu Jianxing said," the edge type backlight scheme composed independently by driving circuit specifications is relatively simple, focuses on the design of topology (step-up / step-down), single or multiple output (LED series and dimming way), and output power. Direct type backlight is a system, the control part and driving part, such as the control part to consider local dimming edge processing and intelligent backlight function, the whole system can be complicated; only the drive circuit, in addition to increasing the control part of the interface, in the constant current light matching and blending ratio on a more demanding. "