Study on optical and electrical characteristics of hybrid warm white high voltage light-emitting diodes

• Main Authors: Kuo, Hsuan-ting, 郭炫廷
• Other Authors: Kuo, Hao-chung
• Format: Others
• Language: zh-TW
• Published: 2012
• Online Access: http://ndltd.ncl.edu.tw/handle/77212908804638385440

碩士 === 國立交通大學 === 光電工程學系 === 100 === In this thesis, we designed the hybrid warm white structure of high-voltage light-emitting diodes (HV-LEDs) to reduce the wall plug conversion losses and improve both the warm white efficiency and light quality. First, we designed the series connected micro-diodes array in single chip to form the HV-LEDs which operated at relative low injection current at high forward voltage. The high forward voltage is able to reduce the voltage-conversion loss from wall plug. The simulation results demonstrated that such micro-diodes can effectively enhance the uniformity of current distribution. Consequently, the HV-LEDs with micro-diodes array exhibited higher light output power and lower current crowding ratio measured by the electroluminescence and the beam view separately at high current density, as compared to conventional LED. Second, we demonstrated the hybrid warm white structure with InGaN LEDs, AlGaInP LEDs and yellow phosphor. Different from the conventional full phosphor conversion warm white LEDs, the proposed structure replace the red phosphor by the red AlGaInP LEDs and successfully solve the efficiency gap between cool and warm white LED with an excellent color rendering index (CRI=90). Furthermore, the droop behavior would also be reduced dramatically 18% in the proposed system. However, there is a correlated color temperature (CCT) instability problem observed at different temperatures. The simulation results show that the thermal-dependent intensity drop of red LEDs is the main reason for CCT instability. Thus, the current compensation method is applied and successfully improved the CCT stability factor from 0.83 to 0.99.