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How to work out a required resistor value using Ohms Law.
First of all we need to collect the following information:
-
The voltage of the supply
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The forward voltage of the component eg L.E.D
-
The current the component uses
We can then apply Ohms law to calculate the value of resistor needed.
For calculating resistance we use the formula R= V ÷ I
lets take the following as an example:
Blue LED = 3.4V Forward voltage and 30mA maximum current, The supply voltage is 12V DC.
Step 1
We first need to work out the difference in the voltage between the source and the component this is 12V - 3.4V = 8.6V
Step 2
We convert the current rating from mA into A we simply divide by 1000.
We now have R = 8.6 ÷ 0.03
Therefore R = 286 Ohms
However the nearest carbon film value would be 330 Ohms and the nearest metal film resistor would be 300 Ohms
Or... simply use the function below! We hope this helps!
