White Light Sensing and Mixing of RGB LEDs

• Main Authors: Yu-Wei Hsu, 許煜偉
• Other Authors: Jia-You Lee
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/35885576473099514451

碩士 === 國立成功大學 === 電機工程學系碩博士班 === 97 === The purpose of this thesis is to develop red, green and blue light emitting diode (LED) mixed light driving circuit for the backlight in the liquid crystal display (LCD). Comparing with the cold cathode fluorescent lamp (CCFL) for backlight, LED can make the image more colorful and saturate. The thesis lets eight LED be a string and uses a LED to sense and mix for LED string. First, analyzes the influence of LED brightness intensity versus color sensor circuit and using integrating sphere measurement system to measure the mixing white light of RGB LED forward current in accordance with single chip control circuit. Then, a closed loop buck converter is designed to provide a stable voltage for LED. Besides, stable current circuit can control the forward current of LED. According to the analysis and measurement result, the brightness intensity of LEDs under a specific current ratio would be transfer to the voltage signal by the color sensor circuit. The voltage signal would be send to the single chip control circuit to control the forward current of every LED. Experimental results show that the sensing and mixing can control the forward current of LED under the mixing current.