How to calculate value of series Resistor value?
Following are the the assumptions made in this post for example sake:
- Supply voltage - 12 V
- LED minimum forward voltage - 2.3 V ( From LED datasheet )
- LED maximum forward voltage - 3.1 V ( From LED datasheet)
- Maximum current allowed to flow in the LED - 20 mA ( Care has to be taken here by considering the maximum operating temperature, if relevant, as normally there will be a derating in the amount of current allowed to flow through the LED at higher temperature)
- Size of LED - Not applicable
With all the above assumptions, the resistor value can be calculated as follows:
R min = (Supply max - Forward voltage min)/ Maximum Allowed LED current;
Rmax = (Supply min - Forward voltage max)/10% of Maximum LED
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