I've recently acquired a new motherboard for my PC which features RGB strip control. That's well and good but I have particular need to control a single RGB diode with that same header.

The issue I'm facing now is that I'm not sure what form of resistors I need for my single RGB diode. I know I will need 3 of them. I plan to use a female to male connector then into a ribbon cable to the diode.

My motherboard is an ASUS HERO Maximus Alpha: LINK HERE

This is noted on the Asus page: *The Aura RGB-strip header supports standard 5050 RGB LED strips with a maximum power rating of 2A (12V)

Here is the data sheet for said diode:

enter image description here

How do I calculate the resistors required to control this LED?


1 Answer 1


The datasheet gives you the forward voltage of each LED at 20 mA and you have a 12 V supply. Your series resistor, therefore has to drop \$ 12 - V_f \$ volts at 20 mA. From Ohm's Law we can calculate the series resistance for each LED as

$$ R = \frac {V}{I} = \frac {12 - V_f}{0.02} $$

@Passerby is right that we should check the power dissipation in the resistors too. For example, your red LED calculation (in comments) gave a value of 500 Ω for a \$ V_f \$ of 2.0 V:

$$ P = \frac {V^2}{R} = \frac {(12-2)^2}{500} = \frac {10^2}{500} = \frac {100}{500} = 0.2~W $$

A 1/4 W resistor will suffice (although it will be hot to touch). Give it some breathing space.

  • \$\begingroup\$ Thanks so much! From that equation it looks like: Red: 500ohm Green: 440ohm Blue: 440ohm Or is my math off? \$\endgroup\$ Jun 20, 2016 at 19:14
  • \$\begingroup\$ You should add t he formulas for calculating the wattage of the resistors as well. \$\endgroup\$
    – Passerby
    Jun 20, 2016 at 20:20

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