How to deal with very voltage-specific amber LEDs?

I have a light (which I'm building from scratch) that uses 19 amber LEDs tucked neatly into a 1.2" circular pattern.

I chose these particular LEDs bacause they throw the most tightly collimated spot of any I have seen. They are claimed to have an 8 degree beam, but in fact they cast an image of the LED die, square with a round central hole and two leads on opposite sides. That, combined with the fact that they are quite bright, should give them a longer throw than any normal 5mm LED light. I have arranged all the diodes with the negative lead towards the outside of the pattern, so all the square beams blend into a bright round spot.

Here is the datasheet on the LEDs I'm using: 5mm AlInGaP LED datasheet

My problem is that these LEDs are very finicky about drive voltage. They do not reach 20mA or anything like full brightness until 2.2x volts, and by the time I deliver a whole 2.40 volts, they are pulling around 50 mA each and dimming/reddening from the heat.

They really, really want just 2.3V, no more or less.

If I use 2 NiMH cells with a low ohm limiting resistor, either the initial voltage will fry them or the flat voltage portion of the discharge will be undesirably dim. If I use alkalines with a resistor it's just hopeless.

What I really need is a current limiter in the 500mA range, but all the LED-specific ones I know of are intended to send between 3 and 4V.

Is there a current-limiting board available that will send 500mA at 2.3V reliably? What choices do I have other than wasting batteries using a converter board WITH a limiting resistor? ('Cause that just don't set right with me.) /ubbthreads/images/graemlins/thinking.gif

Chalo Colina

I would assume a bb500 would work as long as your input voltage going to it is less than the Vf of the leds. But I'm not sure what the cut off min voltage in of the BB is...
EDIT: actually a DB500 would be what you need. It's like a constnat varible resistor.. /ubbthreads/images/graemlins/thumbsup.gif

Actually, seeing as how he's looking for a voltage regulator, I would recommend a MadMax module. It's voltage regulated, not current. It will operate on .8-5V, and can supply up to 700mA. Sounds like a winner to me! /ubbthreads/images/graemlins/smile.gif

Chris

I think a DowbBoy biased to 500ma is exactly what you need.

It makes sense to use more batteries for full brightness with a longer run-time. Maybe the DownBoy will work.

Re: How to deal with very voltage-specific amber L

[ QUOTE ]
StoneDog said:
I think a DowbBoy biased to 500ma is exactly what you need.

[/ QUOTE ]

So is changing the current on a DownBoy a matter of swapping out a sense resistor? I have not seen a DownBoy set for that current. Is this something I can just buy?

Also, I assume since the LEDs only want 2.3V, I could use a DownBoy with 3 volts from the batteries. Am I correct? One CR123A or two AA alkalines are both very tidy, easily packaged options.

Chalo Colina

Re: How to deal with very voltage-specific amber L

I belive you can custom configure them when you order them. I know you can for the BB's. You select which resistors (they have a calc to tell you what you need for X current) and then you can also select 3.00 option for them to be solderd on there for you.

Yes either power source will work fine. Keep in mind though some might have a lower Vf than others and you might run into the same problem. e.g. total draw is 500ma, some are dim (high vf) and some are being overdriven (low vF). So I think you might still encounter your problem, depending on how consitant the LEDS are. Best solution would be to measure each one and put appropraite resistors for each one in addition to the drive circuit /ubbthreads/images/graemlins/icon3.gif