Electronic – Is it OK to put LEDs in parallel?


I wonder if it's a good idea to put LEDs in parallel, as below:

enter image description here

I've heard that it might not be because the voltage threshold won't be exactly the same for each LED, so they'll shine all with very different brightness and you don't have a way to balance that. Is that true? So does it mean it's a bad idea?

Best Answer

It's not a good idea. Look how a (generic red) LED conducts current when you apply a voltage to it: -

enter image description here

At 2 volts, the LED is taking 20 mA. If the LED was manufactured slightly differently it might require 2.1 volts or maybe 1.9 volts to push 20 mA thru it. Imagine what happens when two LEDs are in parallel - if they "suffer" from normal manufacturing variations, an LED that only needs 1.9 volts across it would hog all the current.

The device that needs 2.1 volts might only receive 5 mA whilst the 1.9 volt device would take maybe 35mA. This assumes a "common" current limiting resistor is used to provide about 2 x 20 mA to the pair.

Now multiply this problem out to 8 LEDs and the one that naturally has the lowest terminal voltage will turn into smoke taking the best part of over 150mA. Then the next one dies then the next etc...