LED not dying without resistor
April 22, 2024, 20:09
Hi!
I have a quick question regarding LEDs. My understanding has been that whenever using an LED I should use it in combination with a resistor to limit the current.
I have a bunch of different coloured LEDs and have noticed (accidentally) that when I wire up a blue LED directly to 5V, with no resistor, it seems to work fine. A yellow or green LED for examples dies effective immediately.
What could explain the blue LED not dying?
For reference the 5V source I'm using is a 65 watt capable USB PD power supply at 5V.
Also just FYI, I am going to be using a resistor with my LEDs in the project in question, I'm just wondering what gives, what makes it that the LED seems to be seemingly okay without one.
Blue LEDs do just use more power
I know that they have a higher forward voltage drop, but this should be around the 3 to 3.3 volt mark, I expected it to still die at 5V with no resistor
Me to but guess we both just learnt something
Still can just be explained that blue LEDs require more energy since the gap in the transistor has to be bigger
The Blue LED is a different composition of materials than the other colors.
And its not a transistor, its a diode, that's the D in Light Emitting Diode.
Forgot the proper wording it seems. Thank you
Well you where half right as a transistor can be described as two diodes 😉
I'll take the half win 😅
All components can tolerate a bit more that the datasheet recommend. And depending on what kind of components that can be just a few % to 100% outside the spec.
And mostly that will either damage them or shorten the lifespan of the component.
And I can tell you that applying 30volt to a LED can cause it to explode, I had a pupil that did that and the plastic cover dome of the LED was embedded in the ceilings soundproofing tiles 2m above the lab bench.
Correct attitude 😉
So when you say shorten lifespan, what kind of lifespan shortening would you be talking about? Like I said I don't intend do actually use it without a resistor in my project, but I've kept it running side by side with a resistor-using blue LED for about 48 hours now to see if it would die quickly, as an experiment.
Because I've found one other source online of someoneexperiencing the same "issue", or making the same observation. And they mentioned it would probably die within hours, which doesn't seem to be the case here.
30 volt shorten the lifespan to some milli seconds. And I have never seen a chart over what your asking for.
But I know of some design that has ben suffering from design flaws like what your asking for and they have been operational for a couple hundred hours but should have been operational for several 10k hours befor failing.
Interesting, that's far better than I expected
Still no reason to not just chuck in a resistor
Learn how to design correct and use components as they are supposed to be used. And that is the reason to use a current limiting resistor!
Oh yeah absolutely, all my designs included the resistor. I just forgot when doing the soldering, and though "Oh fuck", but then realised it was still "fine".
Well its outside the spec and it is just a question of time before it dies... I have learn the hard way, if you make a mistake, correct it! And when I was young we had a song "Börja om från början, gör rätt med en gång" and ruffly translated, "Restart from the beginning and do it correctly from the start!".
That's exactly why I did splice a resistor into the wire that I had running to my LED, so it's resolved now. It's just that I was quite surprised that it didn't instantly die.