| Title |
Thermal effects in high-power light-emitting diodes / |
| Translation of Title |
Šiluminiai reiškiniai didelės galios šviestukuose. |
| Authors |
Vaitonis, Zenonas |
| Full Text |
|
| Pages |
36 |
| Keywords [eng] |
light-emitting diode ; junction temperature ; chromaticity ; electroluminescence |
| Abstract [eng] |
The thesis is devoted to the investigation of thermal effects and their influence on the variation of electrical and output characteristics in commercial high-power light-emitting diodes (LEDs). The method of the measurement of junction temperature from the high-energy wing of the electroluminescence spectrum in AlGaInP and InGaN LEDs has been validated and compared to other methods. The dynamics of junction temperature under the pulse-width modulation and pulse-frequency modulation driving modes has been investigated both experimentally and theoretically. The pulse-frequency modulation mode has been found to result in smaller junction temperature oscillations and to be advantageous in terms of a higher efficiency and steadier output characteristics. A simple numerical model for the simulation of the chromaticity coordinates of white phosphor-conversion LEDs as functions of ambient temperature and forward current has been proposed. The accuracy of the model is better than the subjectively perceived chromaticity difference. The spectral distribution of electroluminescence modulation depth in high-power AlGaInP and InGaN LEDs has been investigated and explained in terms of thermal and athermal effects. The frequency response of the LEDs in the regions of spectrum that are sensitive to the modulation of junction temperature has been applied for the estimation of thermal relaxation time constants. An alternation of electrical characteristics of InGaN LEDs during aging under rated conditions has been observed and attributed to long-term annealing at operating junction temperature. |
| Type |
Summaries of doctoral thesis |
| Language |
English |
| Publication date |
2011 |
