Maximum current rating for blue led?

them yet

for

and

potentiometer/multitester

so I

Don't expect too much from Digi-key.

In general the 5mm LED package can dissipate 100mW, so for a 4V maximum, that's 25mA. But a lot depends on how well the heat is conducted away fhru the leads. That being said, the usual white or blue LED is usually rated for 20mA max. But it's common to see them run at 30mA, which at

3.3V drop gives 100mW dissipation. See for specs on some commonly used LEDs. See Don K's LED pages for a lot more info.

Thanks a mil watson, thanks!

>

You are not interpreting the listings correctly.

Every LED in the Digikey catalog has a listed "IF (mA)". This is the maximum continuous current.

The forward voltage drop (VF) is not the "maximum voltage", it's the typical voltage at the given I_F. V_F is usually not a guaranteed parameter, solid state physics makes determines it.

Most (but not all) components in the Digi-Key catalog have a PDF data file on their website. Very useful.

Tim.

Maybe you can help me. I have seen your question, or a variation quite often. Personally, I am too chicken to run a LED at or near its maximum current, except experimentally. What benefit do you see to running a blue LED near its max? Or is it a question of finding the max, so that you can run it well below that?

So far (again, aside from experimenting) I have seen no advantage to running LEDs "hard" (for lack of a better term). I figure 10 mA (or less) as the design figure, unless there is a specific reason to go over that. That's not a reccomendation, it's just to give you the background behind my question.

Ed

Anyway, there's not just one number here. It depends on the nature of the current (is it DC?) and the ambient temperature, and how close to the maximum you'd like to run the junction. Blue (and white) LEDs tend to have the highest voltage drop of all common colors, so they get the hottest at a given current.

Eg.

If (abs max.) is 30mA at 25°C.

But in Fig. 5 you can see that at 75°C you need to reduce that to

20mA. If you work at 50-70% of the maximum, you're at about 10-14mA. That's probably about right for most ordinary 5mm blue LEDs. If you put resistors or other parts nearby that raise the ambient you'll want to reduce the current further. They probably assume the leads are short and soldered into a PCB with certain characteristics. If its hanging out in mid-air on long legs you'll have to further reduce it or reduce the maximum ambient.

Or is it a question

Exactly what I am trying to do Ed. This project of mine is hobbyist-grade, I am not trying to make a military-grade weapon or anything like that - just to let you know. I do think it is awesome you guys are so precise - don't get me wrong about what I said before. Looking forward to trying out the previous information from you guys. I never plan on running any led "hard", in fact I need the maximum forward current specs so that I can make sure I never damage or destroy the leds I use. Interestingly I received an answer back from digikey and the rep. said that indeed the specs I am looking for are not on the web or in their catalog and he sent me a data sheet with his e-mail answer specifying the maximum forward current for the led I inquired about. I much prefer having all of the specs online in case I change my mind about what led to get and it keeps the bandwidth free for other questions instead of clogging up the internet with requests for specs, plus I prefer to not wait for a response. Later!

them yet

rating for

voltage

and

potentiometer/multitester

so I

get

I came across a receipt from Rat shack back in 2001 when I bought my first white LEDs. They were four bucks apiece, and I found some others at a local electronics store for even more. Out of the flashlights I was building I was trying to get an amount of light that was competitive with an incandescent lamp, but without spending a fortune. So pushing a few LEDs, maybe 3 to 6, to their maximum was the only way to go. When I bought the first hundred Nichias for over $200, I was under a bit less pressure, but still it's not easy to see most of the cost of a flashlight tied up in just the white LEDs.

Nwowadays the cost is a dollar each so it's not a ptoblem using twice as many, but still there's issues of space and complexity.