As cost and power efficiency drive the development of new system architectures and overcome design challenges, the backlights of large-size LCD TVs in the industry are constantly transitioning from cold cathode fluorescent lamps (CCFLs) to white LEDs . The main challenge for LCD TV designers in LED backlighting is how to balance system design complexity, component cost, and power conversion efficiency. The overall system efficiency of LCD TV LED backlighting is affected by several factors. The new LED backlight driver IC is striving to solve these challenges and provide practical solutions for LCD TV designers.
LED backlight type
Two major types of white LED backlighting solutions emerged during the transition of CCFL backlights to white LED backlights. Most solutions are typically "direct-down" or "side-in" LED backlighting solutions.
“Direct-down†LED backlighting means that the LED directly projects light behind the LCD panel. Direct-lit backlight systems typically consist of short strings of LEDs, typically 8 to 12 sets of white LEDs arranged in multiple channels or "modules." The number of modules or channels used per LCD panel is as many as 64 to 128. Compared to the original CCFL system, the direct-lit backlight system has the advantage of better contrast because each LED string or module itself is an independent source of illumination for the LCD screen. Disadvantages of direct-lit backlight systems are higher system cost and control complexity.
Figure 1: Direct-lit backlit LCD TV LED strings arranged in a group of backlight "module" cells
Figure 2: Direct-lit backlight single LED channel icon
• Side-lit backlighting systems arrange LEDs into long strings or “light bars†on the sides or top and bottom of the LCD panel. The LED string of each light bar can contain up to 20 to 50 sets of LEDs. The advantages of side-lit backlights are lower system cost and complexity. However, since the illumination of the liquid crystal panel is not straight, the contrast quality is often the same as that of the original CCFL system. One of the advantages of side-lit backlights is that they can be used to replace traditional CCFLs that have little or no adjustment to backlight system signals or hardware.
Figure 3: Side-lit backlight LCD panel icon
Under the AC system series, we have two different waves system, modifed sine wave and pure sine wave. The pure sine wave AC system is more stable, but the Modified Sine Wave system will has cheaper price and smaller size. Use series connection PWM charge circuit. Charge efficiency is 3%-6% higher than witnout PWM, gives longer life to products.
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