Smart LS current regulator

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bikeNomad

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This LED stuff is fun, eh?

Flush with success after my recent Coleman 2-AA LS mod (which used my constant-current LT1308B regulator), I started to think about how I'd improve it. Some things came to mind: <UL TYPE=SQUARE><LI> improve its efficiency
<LI> make it not destroy rechargeable batteries if left on for a long time
<LI> automatically switch to "moon mode" if the voltage gets somewhat low to extend runtime
[/list]

And then I realized that there was a simple, fun solution: use a microcontroller!

I found an AVR microcontroller called the ATtiny15L that runs from 2.7 to 5.5V and has everything I need to make a nice constant-current step-up circuit (a step-down one will follow).

Look at the schematic and board for more details.

Note that because of the input voltage requirements, this is aimed more at running 2 or 3 LS from 3 cells. The step-down one will deal with the 3 or 4 cells to 1 LS.

Is anyone interested in using such a beast? What would your requirements be?
Would anyone like to buy such a thing?
 

bikeNomad

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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by lambda:
Have two things I'd like; run Luxeons from 2 cell and also on three cells with current control.

So, your saying the current circuit could provide 650-700ma from 2 cells; I want one!
<HR></BLOCKQUOTE>
You don't really want 700mA, do you? What are you going to run it into? If you want to run 2 LS's, you want 350mA at around 6.8V (which can be done with the LT1308B circuit I just did).

Of course, you need to think about your battery life; at (say) 80% efficiency, it will take 3W to run 2 LS's at 1.2W each. At 2.5V, this is 1.2A.

So you are only going to get an hour or so on NiCd AA cells (if you're lucky).

This would be better used with two D cells; the 8000mAH cells might last 6 hours or so at that rate.
 

lambda

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Yes, run one Luxeon 600 to 750ma, depending on light. Most would be 2D MagLite with one Luxeon running that much current.

I've made a couple with 3D cell Mags - direct connect, 1 ohm, and 2 ohm resistors, and they barely even get warm. High current draw seems to be Luxeon specific, so each is tested and resistored accordingly.
 

lambda

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On your original circuit, and the new one, what is the max current it could produce running on 4.5 to 3V? Does it need more voltage than this to run?
 

bikeNomad

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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by lambda:
On your original circuit, and the new one, what is the max current it could produce running on 4.5 to 3V? Does it need more voltage than this to run?<HR></BLOCKQUOTE>

Both circuits are probably capable of about an amp output, depending on the voltage. But since they're step-up, you'd run multiple LEDs in series, not in parallel. I've driven 3 LS in series, for instance, from 2 AA cells (on my original one).

The input voltage requirement on my first one (the LT1308B one) is 0.92V minimum (though below about a volt it doesn't drive the LS very brightly), and 10V maximum.

The microcontroller one (the new one) requires 2.7V to 5.5V on the input.

Both will output as much as 16V on their outputs. They're pre-set at 300-350mA output. So you could drive 4 LS in series (12-14V).

Since they're both step-up circuits, you have to have a lower voltage (by about 0.5V) on the input than on the output, so if you're driving 1 LS you can't have any more than 2.3-3.5V (depending on the voltage of the individual LS).

The upcoming step-down has to have a higher voltage at its input than output. So you could drive 1 LS from batteries in excess of 2.8-4V (depending again on LS). I figure that a step down is good for 3 or 4 cell applications.

What are you trying to do?
 

lambda

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Have two things I'd like; run Luxeons from 2 cell and also on three cells with current control.

So, your saying the current circuit could provide 650-700ma from 2 cells; I want one!
 

JollyRoger

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You know, I'd probably buy some of these, as well as your Coleman mods (as I emailed you).

If you could increase the efficiency of the Coleman mod to atleast 85%, that would be excellent!!!!

And then find a way to fit this regulator in a smaller light...like the minimag..and I think you'll have one of the better regulator mods out there.

Here's another thought. You might even be able to use the step down in the Coleman flashlight if you file away the inside of the battery holder barrel (aluminum) so that 2 CR123 3V's fit????

Interesting...
shocked.gif
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