LED backlight zone dimming for energy-saving LCD TVs

　　CRT (cathode ray tube) TVs are gradually being replaced by LCD TVs, and the number of TVs purchased by households is also growing steadily. Today, the average number of LCD TVs per household in the United States is 2.4, far more than the average number of CRT TVs per household in 1990. Although the power consumption of each LCD TV is decreasing year by year, the increase in its popularity has increased the total power consumption of each household year by year. Among household appliances, LCD TVs have become the main power-consuming appliance after refrigerators.

　　Therefore, a series of energy-saving standards for LCD TVs have emerged. The most stringent of these standards is the EPA Energy Star 5.0 standard, which will take effect on May 1, 2012. It specifically stipulates an upper limit of 108 watts of energy consumption for large-screen LCD TVs over 50 inches. The Energy Star energy-saving standard also regulates the absolute energy consumption of TVs for the first time, which is different from the previous relative standard corresponding to the screen size.

　　Figure 1: 64-channel fully integrated LED area backlight driver chip

　　Over the past 10 years, we have witnessed the development of LCD TV signal processing pathways: multiple functional modules have been gradually integrated into a single chip, rapidly reducing costs while also gradually reducing energy consumption. Similar developments and innovations have also occurred in the power supply pathways of LCD TVs in recent years, with the most important being the LCD backlight, which is the unit function with the largest energy consumption in LCD TVs and accounts for more than 60% of the total energy consumption of LCD TVs.

　　Just as notebook computer backlights have basically completed the transition from CCFL (cold cathode fluorescent lamp) to LED backlights in the past two years, the transition of LCD TV backlights will be completed in the next few years. Its main energy-saving effect comes from the higher photoelectric conversion efficiency of LED than CCFL, and with the rapid development of LED luminous material technology, its energy-saving effect will become more and more obvious.

　　The most straightforward method of using LED backlight for LCD TVs is to use the LED backlight solution for laptops, arranging multiple LEDs in a row and placing them on the upper and lower sides of the LCD display. In this way, the advantages of low cost and slim size of the notebook LED backlight can be retained on LCD TVs, and the existing production lines and processes can be retained and simply extended to a considerable extent. This is an effective solution, especially for small and medium-sized LCD TVs. In order to further reduce costs, even the LED backlight solution with only one side at the bottom has been used in small-screen LCD TVs.

　　Figure 2: Side-lit and direct-lit local dimming

　　After this edge-lit LED backlight TV entered the market, it was widely favored by the market due to its slim and popular style, further improving the market position of LED backlight LCD TVs and catering to the needs of price-sensitive customer groups. At the same time, from a technical perspective, scientific and technological personnel used the rapid photoelectric conversion speed of LED to invent local dimming technology, which was combined with edge-lit or direct-lit LED backlight structures to divide the entire screen image into 1D or 2D areas, and dynamically adjust the regional LED backlight brightness according to the content of the image displayed in each area, greatly improving the image contrast and color saturation, while further reducing the energy consumption of LCD TVs, and improving the image quality of LCD TVs to a level far superior to CCFL TVs and PDP (plasma) TVs, catering to the needs of customer groups who are more sensitive to image quality.

　　iWatt is a technology leader in the field of LED area backlight. With its successful experience in the field of digital power supply for many years and its leading position in the LED lighting and smart power supply market, it has extended its digital power supply control technology to the LED backlight application of LCD TV. iWatt's original adaptive smart patented technology can automatically detect and compensate for the mismatch of LED voltage drop (VF), making it possible for many channel LEDs to share the same power supply, and combined with the powerful functions of its digital power supply, it solves the well-known integrated heat loss problem of high-voltage switches and rectifier resistors. In 2010, the world's first 64-channel fully integrated LED driver chip was launched, replacing all the functions that were traditionally implemented using four 16-channel chips, 32 dual-package high-voltage switching tubes, and 64 current detection resistors, reducing the total number of pins of key components from the original 576 pins to only 88 pins (as shown in Figure 1). At the same time, its powerful SPI programmable capability makes the chip also suitable for side-down and direct-down regional dimming (as shown in Figure 2). While providing high-quality and low-cost LED backlight, it further reduces the energy consumption of LCD TVs and provides customers with the lowest cost and smallest LED backlight solution.

　　If the 170 million LED-backlit LCD TVs expected to be sold worldwide in 2012 all adopted edge-down or direct-down local dimming, 30 megawatts of electricity would be saved, enough to supply the total electricity consumption of all households in New York City for 10 months.