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You start by checking the forward voltage and rated current for the LED. 20mA is the usual industry standard for regular LEDs and the forward voltage will be specified for that rated current. In t...
Answer
#1: Initial revision
by
Lundin
·
2021-09-01T20:57:00Z (about 3 years ago)
You start by checking the forward voltage and rated current for the LED. 20mA is the usual industry standard for regular LEDs and the forward voltage will be specified for that rated current. In this case the datasheet says V<sub>F</sub> = 2.0V typical @ 20mA. So now we know the current and the voltage will be supply voltage minus forward voltage. Applying Ohm's Law, we get: **R = (V<sub>supply</sub> - V<sub>forward</sub>) / I** In this case R1 = (9 - 2) / (20*10<sup>-3</sup>) = 350 ohm.