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Topic: Multi colored LED (Read 686 times) previous topic - next topic


I purchased few LEDs, rgb, red and blue.
I was just playing with them powering them with 3v lithium battery, and I found something interesting. When Red and RGB are powered together I only get red color from the rgb LED, I tried to light blue and the RGB together, but blue didnt affect the RGB, I get ll three lights from  the RGB LED. Am just curious about this. Is there a reason for this phenomenon??

Tom Carpenter

Its all to do with forward voltages.

If you put a blue and red LED in parallel, only the red will light up. This is because the Red led has a typical Vf of 2.2V while the blue has a Vf around 3.3V. That means in parallel you will only have 2.2V across the blue LED which is not enough to make it light up.

Red and Green have similar Vf's so both tend to light up.


Tom Carpenter

Worth mentioning is that you can have all 3 in parallel as long as they each have their own current limiting resistor.

Ascii circuit diagram ahoy:
Code: [Select]
   Resistor  LED

+ o--+---[]----|>"|---+----o -


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