Parallel LEDs

Why we don't Parallel LEDs

[jonathanhughes]

Chris i just wanted to thank you for showing the Math equation's and explaining them alot of you videos helped me to better understand the math in my Basic circuits 1 AC college Class. thank you sir.

[Enigma]

Would you agree though that parallel LEDs, with a resistor for each branch is fine?

[td]

Thank you for this video! It is very timely for me, because I am in the middle of building a night light with parallel LEDs. Forgive me, please, I am not an EE... Just a self-taught hobbyist, with massive holes in my learning and understanding... Therefore, I did not follow very well the problem with placing LEDs in parallel. Here is my setup... I have a MCU demo board driving transistors, which sink the current from a pair of parallel RGB LEDs/Common Anode. Each color pair has a single current limiting resistor - around 40mA at 12V. However, for convenience, I am only driving the (entire) circuit at 5V, because that is what the MCU requires. (The project just doesn't warrant the work/cost of dual rails.) Because the resistors were calculated for 12V (for future adaptability) and the LEDs are only supplied 5V, they will see much less than 40mA, per color pair. I am using parallel LEDs to gain more light output... With a fixed 5Vs, I can only adjust the current. I am doing that by using parallel LEDs. Ahh... A little illumination, if you will pardon the bad pun... I do understand that a single color pair will have slight power consumption differences. And, that even using two resistors per color pair, I will never get them perfectly matched. Meaning that one of the two will do most of the work and it might end up in a "run-away" condition. Is that the gist of the issue? I am thinking so. If correct, I am going to have to engage in a major redesign that moves away from the fixed constraints of the demo board... Or, just live with the limited brightness of a single LED... Yep, that would keep the project moving forward. After all, it's just a toy night light, stylized as a robot and made from repurposed garbage. Thanks! Cheers!

[RexxSchneider]

The point you didn't really make is that LEDs get warm as they pass current, and the voltage across the LED drops a little as the temperature increases just as in any diode. If you try to match two LEDs and put them in parallel, one will draw slightly more current, get warmer and take a greater share of the current, which warms it more, etc. until most of the current is passing through one of the LEDs. But you can run multiple LEDs in parallel by using a separate current limit resistor in series with each LED. That swamps out the small change in voltage caused by heating and maintains a relatively constant current through each LED. The larger the limiting resistance, the more constant the current is, but you then need a larger supply voltage, of course.