At present, CRT (cathode ray tube) TV is gradually replaced by LCD TV. At the same time, the number of family purchases is also growing steadily. Today, the average American family has 2.4 LCD TVs, which is far greater than the average number of one CRT TV per family in 1990. Although the power consumption of each LCD TV is decreasing year by year, the improvement of its popularity increases the total power consumption of each family year by year. Among household appliances, LCD TV has become the main power consumer after refrigerator.

Therefore, a series of energy-saving standards for LCD TV came into being, especially for super large screen LCD TV with more than 50 inches, and the upper limit of energy consumption of 108 watts is mandatory. The energy star energy saving standard also regulates the absolute energy consumption of TV for the first time, which is different from the previous relative standard corresponding to screen size.

LED backlight design scheme of LCD TV

Figure 1: 64 channel fully integrated LED area backlight driving chip

In the past 10 years, we have witnessed the development of the signal processing path of LCD TV: a variety of functional modules are gradually integrated into a single chip, which not only rapidly reduces the cost, but also gradually reduces the energy consumption. Similar developments and innovations have also occurred in the power path of LCD TV in recent years. The most important is the unit function with the largest energy consumption in LCD TV, that is, the LCD backlight with more than 60% of the total energy consumption of LCD TV.

Just as the backlight of notebook computers has basically completed the conversion from CCFL (cold cathode fluorescent lamp) to LED backlight in the past two years, the conversion of LCD TV backlight will be completed in recent years. Its main energy-saving effect comes from the photoelectric conversion efficiency of LED higher than CCFL. With the rapid development of LED luminous material technology, its energy-saving effect will become more and more obvious?? Wait.

The most straightforward LED backlight method of LCD TV is to follow the LED backlight scheme of notebook computer, arrange multiple LEDs in a row and place them on the upper and lower sides of LCD display screen. In this way, the advantages of low cost and thin volume of LED backlight of notebook computer can be retained on LCD TV, and its existing production line and process can be retained and simply extended to a considerable extent, especially for small and medium-sized LCD TV. In order to further reduce the cost, even the LED backlight scheme with only one side below has been used in small screen LCD TV.

LED backlight design scheme of LCD TV

Figure 2: side down and straight down area dimming

After this edgelit LED backlight TV entered the market, it was widely favored by the market because of its thin popular style, which further improved the market position of LED backlight LCD TV and catered to the needs of price sensitive customers. At the same time, from a technical point of view, scientific and technological personnel have used the fast photoelectric conversion speed of led to invent the local dimming technology, which is combined with the side down or direct lit LED backlight structure to divide the whole screen image into 1-dimensional or 2-dimensional areas, and dynamically adjust the regional LED backlight brightness according to the content of the displayed image in each area, It greatly improves the image contrast and color saturation. While further reducing the energy consumption of LCD TV, it improves the image quality of LCD TV to a level far better than CCFL TV and PDP (plasma) TV, meeting the needs of customers who are more sensitive to image quality.

IWatt is a leading technology enterprise in the field of led regional 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 market, iWatt has promoted its digital power control technology to the LED backlight application of LCD TV. IWatt’s original adaptive intelligent patent 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. Combined with the powerful function of its digital power supply, it solves the well-known problem of integrated heat loss of high-voltage switch and rectifier resistance. In 2010, it launched the world’s first 64 channel fully integrated LED driver chip, replacing all the functions traditionally realized by 4 16 channel chips, 32 double encapsulated high-voltage switches and 64 current detection resistors, reducing the number of main pins of key devices from 576 pins to 88 pins (as shown in Figure 1). At the same time, it has strong SPI programmable ability, The chip is 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 TV, and provides customers with the lowest cost and smallest LED backlight scheme.

Responsible editor; zl

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