Adjustable Forward Voltage Technique in LED Driver for High Efficiency

• Main Authors: Ke, Heng-Hsi, 柯恆熙
• Other Authors: Chen, Huang-Ming
• Format: Others
• Language: en_US
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/69985002095267363227

碩士 === 國立交通大學 === 電機學院電子與光電學程 === 102 === In recent year, light emitting diodes (LEDs) are widely used for display of various products, such as television, cellular phones, NB, tablet computer, etc. The advantages of LED backlight liquid are listed below. Firstly, it is more energy saving. LED backlight products save 40% energy, comparing with products with CCFL backlight in civilian industry. LED backlight technology, LED backlight display will be more energy saving in the future. Secondly, it is green and environment-friendly. Mercury in CCFL backlight is considerable damage to the environment, but LED backlight does not contain it. If LED backlight displays are popular in the future, it will be very helpful to improve the global environment. Thirdly, it has a wider color gamut. LED backlight module has a more pure white light and a wider color gamut, comparing with conventional CCFL backlight module. LED backlight display can display more vivid color and make a better color representation.Fourthly, it has a longer serving time. Theoretically, LED backlight has a long serving time and a longer brightness decreasing cycle, comparing with CCFL backlight. And it still can extend the serving time with the development of the technology. Fifthly, it is lighter and thinner. LED backlight products are much lighter and thinner than CCFL backlight products. The selling point of LED backlight displays in the market is ultra-thin which meets the fashion needs of consumers. This thesis proposes a LED driver with adjustable forward voltage technique in LED driver for High efficiency, and it was suitable for the LED backlight. This LED driver utilized a constant current regulator to support the LED string a stable current without color shift and a PWM dimming circuit to adjust the illuminate. Because the LED forward voltage variation occurred by time and manufacture, this driver utilized an adjustable forward voltage to overcome this problem. Then use a reference voltage tracking circuit with soft start to avoid the inrushing current issue. This LED driver circuit was simulated by TSMC 0.6um BCD 40 V process.