Please bear with this thread for the detailed explanation. Need to get some clarity.
I have three voltages 7.5V/13.5V/16.5V.
This is my LED Datasheet
The Operating temperature of my board is -40degC/+25DegC/+80degC
So, I need to perform WCCA with these parameters.
How shall I go about this? I need Min/Typ/Max values.
Please check if my approach is correct :-
I figured out that the total current through the R, LED and Transistor is Typ I = 13.5/1200=11.25mA
Max I = 16.5/(1200*1.03)=13.35mA (3% tolerance taken for R)
Similarly for Min I = 7.5/(1200*0.97) = 6.4mA
So, once I have these currents, I will now figure out the Vf of the LED with respect to the LED datasheet graph. (Vf vs If). So, I will have the Vf of the diode also. And since I have different temperatures to consider, I need a graph in the LED datasheet with provides a graph of "Change in Voltage" vs "Temp". So that I can add the change in voltage to the min Vf and subtract the change in voltage to the max vf af the temp of -40 and +80 respectively. However, in the datasheet mentioned, i donot have such a graph. But I have this graph in This Datasheet but it is a green LED. What can I do in this situation.
Suppose, I had done this Vf and temp calculation, I can now perform one more correct iteration of current through the LED by this formula,
I = (Vin - Vf - Vce(sat)) / R. // for all the temp and input voltage.
So , I will now have the near accurate value of Worst case analysis current values. Is my approach correct?
Please help me if I am wrong and tell the correct method. Will be really helpful. And what about the missing temperature vs change in voltage graph of the LED.