Dear All,
Its been a while since I last posted, hope everyone is keeping well.
This question may be based on the naieve notion that IR diodes act pretty much the same as LE diodes.
I purchased 10 IR diodes from farnell (next day delivery - wow!)
https://www.electro-tech-online.com/custompdfs/2008/08/tsks5400.pdf
According to the documentation the maximum forward (continuous) current (If) is 100mA and the basic forward voltage (Vf) is between 1.3 and 1.7 volts.
So I set up a basic circuit with a 5 volt source, an IR diode in series with a 39 ohm resistor, because:-
(5 Volts - 1.3Vf)/ 100mA = 37 (39 E12)
Ok, with a 39ohm resistor I would expect to see current of around 94mA which is close enough.
But the measurement I get is closer to 75mA.
The only way I may be able to account for this is if the Vf of the diode isn't 1.3, actually it wouldn't be 1.7 either - more like 2 Volts.
I have checked the resistor and it is bang on 39ohms so no problem with tolerance there.
Have I mis-read the datasheet, or am I making some bad assumptions?
Best Wishes
Mark