Do people usually regulate 5mm LEDs?

[kuksul08]

I am building a little side project, which will incorporate about 4-6 of those cheap 5mm LEDs (20-30mA each). I planned on using 3 AA's to run them, for the short time they are on, about 15 minutes at a time.


Do people usually just use a resistor in this case? Or should I look into a home made current regulator (LM317?).

Also totally random, but are these supposed to get warm? I was direct driving a few white 5mm LEDs directly from ~4V and they got warm. I measured 80mA through them.

 

[Fallingwater]

I am building a little side project, which will incorporate about 4-6 of those cheap 5mm LEDs (20-30mA each). I planned on using 3 AA's to run them, for the short time they are on, about 15 minutes at a time.
Do people usually just use a resistor in this case? Or should I look into a home made current regulator (LM317?).

The simplest solution is a resistor, but nothing prevents you from using something else.
I just mounted a 1xAMC7135 board (used to be a 3xAMC, I just desoldered two chips) in a 9-LED 3-AAA flashlight. I now power it with a 18650 LiIon, and it even has a low mode.

Also totally random, but are these supposed to get warm? I was direct driving a few white 5mm LEDs directly from ~4V and they got warm. I measured 80mA through them.

No, they aren't supposed to get very warm. 80mA is about four times the energy a 5mm LED wants - no wonder they're getting warm! Don't worry though, they won't be warm for long

 

[kuksul08]

The simplest solution is a resistor, but nothing prevents you from using something else.
I just mounted a 1xAMC7135 board (used to be a 3xAMC, I just desoldered two chips) in a 9-LED 3-AAA flashlight. I now power it with a 18650 LiIon, and it even has a low mode.


No, they aren't supposed to get very warm. 80mA is about four times the energy a 5mm LED wants - no wonder they're getting warm! Don't worry though, they won't be warm for long

Ruh Roh!

Should I plan on running 20mA or 30mA through them? I see they are rated at 20mA with a 30mA max.... but I wonder if the brightness is any different.

I was looking at those LM317 voltage regulators, but they have a 3V dropout! Any suggestions? I don't mind building it (I prefer building it )


Did you use the standalone AMC7135 IC's or did you leave them intact on the boards with diodes?

 

[ledstein]

People usually don't and neither do most of china or other low cost producers. If lifetime is very important they should.

I really dont know the leds u use but if they are china leds even 20mA is too much. At 20mA lifetime for white or blue is 300-500 hours. For some thousands of hours 15mA is the choice.


At 80mA they will be gone real fast.

LED drivers for such leds are small, like this one: Constant current supply 20mA

 

[Fallingwater]

Should I plan on running 20mA or 30mA through them? I see they are rated at 20mA with a 30mA max.... but I wonder if the brightness is any different.

My modded AMC driver feeds about 39mA to each LED. I swapped the original LEDs with brighter Jeleds, which will hopefully last more at this current.

Did you use the standalone AMC7135 IC's or did you leave them intact on the boards with diodes?

I used one of these.

They work with anything from one to four AMCs; tthe board comes with three, but has solder pads for a fourth. Since each AMC is good for 350mA, just removing or adding AMCs allows you to set the desired current in four 350mA steps.

 

[JohnR66]

(Assuming white LEDs here)
In my experience...
Even cheapo 5mm LEDs will fade and/or color shift at only 15ma in a couple months.

Just about every 5mm LED I put my paws on faded at least some in my 30ma 192 hr test. Some cheap ones faded so bad I consider them as failed in that test.

If you don't need a tight beam, flux LEDs are a much better choice. The ones I tested did not fade and are brighter than typical 5mm LEDs.

5mm white LEDs are most efficient at 3 to 5 ma. Use more and underdrive them for more light plus good lifetime.

 

[kuksul08]

Thanks for the input. I will get some resistors to test a few different currents and see if the brightness difference is noticeable to warrant the decreased life.

 

[PCC]

I think it's all relative. Significantly overdriving a relatively cheap 5mm LED will shorten its life but it is just that: a cheap LED. I mean, I'm not about to drive 2 amps into an SSC P4 or 5 amps into a SSC P7 because of the cost of the emitter itself. At $0.35 cents per LED, it's not a big deal to me. Even paying too much for 5mm LEDs at Radio Shack ($2 for 2) it's not that big a deal to me. Prematurely killing a $5+ emitter starts to get expensive after a while.

You have to remember that most 5mm LEDs are put into cheap lights. Why would you double (or triple) the cost of a light by including expensive circuitry to increase the life of a $0.35 part? I've built a few small lights using 2 5mm LEDs, a 100 ohm resistor, and a recycled 9V battery connector. When the LEDs finally die I'll toss it out and make another one for less than $1. Would it have made a huge difference in light output to put in a 150 ohm resistor instead? Probably not, but for the use that I intend to use this light for, it is enough. The last one I made has a 68 ohm resistor to try to make it even brighter, though it really did not improve things by much. Next one will revert back to the 100 ohm resistor.

 

[Black Rose]

LED drivers for such leds are small, like this one: Constant current supply 20mA

Nice. Too bad you have to buy 500 at a time

 

[Fallingwater]

Why would you double (or triple) the cost of a light by including expensive circuitry to increase the life of a $0.35 part?

Because swapping LEDs often gets annoying.
With the Jeleds and driver the cost of my light doubled (from $2.5 to $5 or thereabouts), but it's now a decent light and one I'll (probably) keep, not a disposable one that I'll throw in the trash in a few months.

 

[PCC]

Yes, that is true for you or I and probably a lot of people on these forums but you have to remember that we are not your average Joe looking to buy a light. We have the desire for brighter, better quality, reliable lights and are willing to do what is needed to accomplish this, including modifying the lights to suit our needs. Most average people would not think about taking a flashlight apart to change out the emitter or circuit board.

Also, sometimes it's all about the simplicity of design. Less components to fail and, when it does fail, easy to repair or replace.

Don't get me wrong, I am looking for a simple, small circuit to boost either 1.5 or 3 volts to a single 5mm LED for a few cheap flashlights I'm currently direct driving (the 2AA ones, at least). The reality is that these are not readily available over the counter. It was when I was trying to find this that I realized that the simplest way to go was to either direct drive them or use a resistor when the voltage rose above 3.6V.

 

[ledstein]

Nice. Too bad you have to buy 500 at a time

Try www.leds.de or any other germany led shop. The ship everywhere also.

 

[RyanA]

This is a very interesting thread. Would I be ok with a shoppe bb converter at 40 ma (supposedly attainable w a single 1.2 resistor) and a high power 5mm like an mj led?