GaN基高压直流发光二极管制备及其性能分析

GaN基高压直流发光二极管工艺制备,采用蓝宝石图形衬底(PSS)外延片制备正梯形芯粒结构的GaN基高压直流LED.相对其他结构器件,该结构器件发光效率最高,封装白光后,在色温4500 K,驱动电流20 mA时,光效116.06 lm/W,对应电压50 V.测试其I-V曲线表明,开启电压为36 V,对应驱动电流为1.5 mA;在电流15 mA至50 mA时,光功率随驱动电流增加近似于线性增加,在此区域光效随电流增加而降低的幅度比较缓慢,表明GaN基高压直流LED适宜于采用大电流密度驱动,而不会出现驱动电流密度增加导致量子效率明显下降(efficiencydroop),为从芯片层面研究解决量子效率下降难题提供了一种新思路.

一种新型LED驱动器的分析与设计

传统的具有功率因数校正(power factor correction,PFC)功能的DC输出LED驱动器需要在输出端用容值较大的电解电容来减小输出电流纹波。为解决电解电容的使用寿命短而造成驱动器寿命低于LED寿命的问题,采用一种新型的AC LED拓扑电路结构,理论分析了该拓扑电路结构以及参数的选取。由于该驱动器的输入电压和输出电压都是脉动的,驱动器的输入输出滤波可采用容值较小的薄膜电容,从而提高了驱动器的使用寿命。通过仿真和试验的结果表明,该拓扑电路结构是可行的,其参数的选取是正确的。

Development of the Operating Circuit for a LED Lamp Based on the Cockcroft-Walton Circuit

The operating circuits for LED （light emitting diode） lamp composed of diodes and DC capacitors only are proposed. The proposed circuit is based on a double-voltage rectifier circuit and a Cockcroft-Walton circuit. The circuit can operate LED without flicker, and is free from switching noise since high frequency switching circuit is not used. To replace an AC capacitor by a DC capacitor for the ballast, a diode is connected across the capacitor in parallel, and the operating voltage of LED unit is kept at the value greater than the peak voltage of the input power source. The circuit realizes high efficiency and high input power factor compared with the operating circuits on the market. Cockcroft-Walton-type circuit can operate many LED devices in series connection. Series connection is preferable for fabricating LED unit of a constant voltage characteristic. Moreover, fairly flat waveform of LED operating current is realized by Cockcrofl-Walton-type circuit, even though capacitor ballast is used.