Electronic – What resistor to use with this RGB LED


i have this led, and im not sure what resistor to use to drop the 5v current to an appropriate voltage and produce the appropriate current.

the LED is rated at 200mA, but the data sheet says i should apply 150mA through it. my micro-controller outputs 5v i think, but im not sure as i do not have a multimeter, but i apply 5v to the vcc of the micro-controller.

RGB LED voltage

my questions are:

  • what resistor should i use with this led? (i got 33 ohms as the
    answer, making me thing i dont need a resistor).
  • if i do need a resistor, would a 1/2 watt rated resistor work? the lowest value i have is 100 ohm, is that close enough?
  • the data sheet does not explain how to solder the LED- do i just connect the b- and r- points to ground and the b+ and r+ to micro-controller outs, and if i want blue i do low r+ and high b+?

Sorry about the extensive questions, i never had any formal education or experience in this field. thanks!

Best Answer

You should use 3 different resistors, one for each color, although the blue and green have the same specs.

At 150mA the forward voltage for the red is 2.2v, green is 3.5v and blue is 3.5v. So you should use a 22ohm 1watt resistor for the red, and 10ohm .5watt resistor for the green and blue. You have a bit of wiggle room on these figures, and if you don't have a resistors that can handle that wattage you can use more than one in parallel just make sure you calculate the correct resistance between them.

Also I doubt your microcontroller can provide 150mA (it's probably more like 20mA,) so you will probably need to use a transistor on each color so that they can pull enough power. Take a look at this image for how to hook up the transistor to your system. Although ignore the 12v and multiple LEDs.

enter image description here

You may also want to have each color driven by a PWM pin, so that you can alter the brightness of each color to change the overall color at will.