workexperience.ms (1749B)
1 .TL 2 Notes from work experience day 2 3 .AU 4 Lucas Standen 5 .AI 6 30/5/24 7 .NH 1 8 The voltage over an LED 9 .NH 2 10 The experiment 11 .LP 12 Continuing on from yesterdays study of The wavelength of LEDs and how it change as the current was 13 increased, today I have taken results showing how time effects the voltage across the LED. 14 15 I would predict that the LED's voltage will fall over time as the temperature increases, which will 16 cause the die to "slow down" so to say, or stop behaving as once intended. 17 18 My results were taken on a green LED with a 10mA current provided at 2.2V. A multimeter was used to 19 capture data from the LED, it takes 2000 readings and outputs them in a csv file (my results can be 20 found in results.csv). 21 22 I found it took on average 45 seconds for the multimeter to take 2000 results. 23 The data was taken at 1 nplc (1 nplc = 1/50hz) 24 25 .NH 2 26 Results 27 .LP 28 As expected the voltage over the LED fell slightly over time, the graph of these results can be seen 29 bellow. 30 .PSPIC graph.ps 31 .LP 32 Another graph showing the first 450ms can be seen here, this relates to how our pulse mesurements 33 from yesterday 34 .PSPIC graph2.ps 35 .LP 36 As you can see, this is experiencing exponential decay, falling quickly at first and then levelling 37 out. This was about as expected. The voltage falls, as the LED is too hot, then it reaches closer 38 and closer to equilibrium, where the total thermal output is the same as the power input. 39 .NH 2 40 Takeaways 41 .LP 42 From my data I can take away that LED's are definitely thermally limited, one can see this from 43 today's data and yesterdays data. I have found it interesting how the LED can heat up so slightly 44 and yet it still have an effect on the voltage input. One would suppose there is a formula to model 45 this decay in voltage. 46