I’m building an IR LED light out of these IR 950nm LEDs:
https://www.digikey.com/product-detail/en/osram-opto-semiconductors-inc/SFH-4725S/475-3012-1-ND/3767470
Using this LED driver which is purposely overkill:
https://www.digikey.com/product-detail/en/stmicroelectronics/LED2001PHR/497-13825-1-ND/4250490
You can calculate passive component values for the LED driver using a GUI called Estudio by STM. The two values I need help calculating and understanding are:
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The Forward Voltage of the LED. According to Digikey (Vf) is 2.75V. However, a table in the datasheet says the forward voltage for I(f) = 1A and T(p) = 100uS is “typically 2.65V and a max of 3.2V”. So what voltage do I need to apply for the LED to turn on? Somewhere between 2.65V and 3.2V when I(f) =1A for one LED? I'm not sure why they give it for a 100uS pulse, see attached table.
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The Gui asks me for a Rd value, what is the Rd for this LED?
My approach: The datasheet only gives a graph of the forward current versus the forward voltage for a 100uS pulse. However, I will have my LED on for many minutes at a time if not longer, not a pulse so I'm unclear if I can use this data for calculations but no other information is provided. The datasheet says this LED has a forward current max of 1A. So if I look at the chart for a 100uS pulse where the voltage intercepts 1A of current I get 2.66V. Therefore: 2.66V/1A = 2.66 Ohms. Is that a reasonable number for R(d) and should I expect that the resistance will change dramatically if I have the LED on for a long time (not pulsed). Why do they only provide a 100uS pulse and not a sustained V vs I graph? I attached a picture of the graph I used from the datasheet.
Any help appreciated!
