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According to research by Strategies Unlimited, the market size of high-brightness LEDs is expected to reach US $ 8.2 billion in 2010, and by 2015, it is expected to grow to US $ 20.2 billion, with a compound annual growth rate (CAGR) of 30.6%. LEDs currently used to backlight display screens are the main drivers of this growth, and their applications include high-definition televisions, automotive display screens, and a large number of handheld devices. To maintain a high growth rate, LEDs not only need to provide higher reliability, lower power consumption, and smaller / flatter form factors, but also need to improve contrast, image quality clarity, and color accuracy. In addition, automotive, avionics, and marine displays must be suitable for a variety of environmental lighting conditions, such as bright daylight and dim nights. These transistor liquid crystal displays (TFT-LCD) are widely used, from infotainment systems, meters to a variety of instruments, when using LEDs to backlight these displays, in order to optimize the display under a variety of ambient lighting conditions The ease of readability will bring some unique LED IC driver design challenges, which requires the LED driver to provide a very wide dimming range and high efficiency, and withstand the relatively harsh and harsh automotive electrical and physical environments. Finally, these solutions must be flat and have a compact footprint to increase cost efficiency.
The rapid growth of LEDs in the automotive lighting market stems from the following factors: First, the luminous efficiency of LEDs is more than 10 times higher than incandescent lamps, almost twice the efficiency of fluorescent lamps, including cold cathode fluorescent lamps (CCFL), thus reducing the supply of The amount of electrical power required for a certain amount of light output (in lumens) and the amount of heat it generates. With the further development of LEDs, the efficiency of generating lumen with electrical power will only continue to increase. Secondly, LED lighting does not need to handle, contact and remove the toxic mercury vapor common in CCFL / fluorescent lamps, which satisfies the requirements of environmental protection. Third, about every 1000 hours, the incandescent lamp needs to be replaced, and the continuous use time of the fluorescent lamp reaches 10,000 hours. In contrast, the life of the LED exceeds 100,000 hours. In most applications, this allows the LED to be permanently embedded in the end application without the need for ancillary equipment. This is especially important for the backlighting of instrument / navigation / infotainment system displays embedded in the interior of the car, because they never need to be replaced during the life of the car. In addition, LEDs are smaller and flatter than other lights by orders of magnitude, so LCD displays can be very thin, so the space required inside the car is minimal. In addition, by using red, green, and blue LED configurations, an unlimited variety of colors can be provided. LEDs can also dim and turn on / off at a much faster rate than the human eye can detect, thereby significantly improving the backlighting of LCD displays while achieving extremely high contrast and resolution.
One of the biggest challenges facing automotive lighting system designers is how to optimize all the advantages of the latest generation of LEDs. Since LEDs generally require an accurate and efficient DC current source and a dimming method, the design of LED driver ICs must meet these requirements under various conditions. Power solutions must be efficient, reliable, compact, and affordable. It can be said that for LED drivers, the most demanding applications will be found in TFT-LCD backlighting applications in avionics, marine and automotive infotainment systems, because these applications must face the harsh automotive electrical environment and must compensate for changes A wide range of ambient lighting conditions must be placed in very restricted spaces, while at the same time maintaining an attractive cost structure.
Automotive LED backlighting
Advantages such as small size, extremely long life, low power consumption, and enhanced dimming capabilities have led to the widespread use of LED TFT-LCD backlighting in today's cars, airplanes, and ships. Infotainment systems usually have an LCD display mounted somewhere in the center of the dashboard, so that drivers and passengers can easily check the location, perform audio tuning, and complete other various tasks. In addition, many cars have LCD screens in the rear seats to provide entertainment for passengers, providing movies, video games and so on. Historically, these displays have used CCFL backlighting, but the replacement of these relatively large CCFL lamps with very flat white LED arrays is becoming more common. White LEDs provide more accurate and adjustable backlighting, and It is easy to exceed the life of the car life.
The benefit of using LEDs in this environment is that they can have several positive effects. First, they never need to be replaced, because their reliable life span is more than 100,000 hours (the service life is 11.5 years), which exceeds the life of the car itself. This allows car manufacturers to permanently embed them into the backlighting system in the car without having to consider the ease of replacement. The style may also be a significant change, because the LED lighting system does not need to occupy as much space or such a large area as CCFL lamps. LEDs are also generally more efficient than fluorescent lamps in providing light transmission from input power (in lumens). This has two positive effects. First, it consumes less electrical power provided by the car bus. Also importantly, this reduces the heat that needs to be dissipated in the display screen, eliminating the need for any bulky and expensive heat sinks.
Another important benefit of LED lighting is the wide dimming ratio capability provided by high-performance LED driver ICs. Since the ambient lighting conditions inside a car vary widely, including every change from direct sunlight to complete darkness, the LED backlight lighting system must be able to provide a very large dimming ratio, generally up to 30,000: 1. With a suitable LED driver IC, this large dimming ratio is relatively easy to achieve, but it is not possible to use CCFL backlighting. Figure 1 illustrates a typical LCD-based analog dashboard.
Figure 1 analog dashboard
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