My Luxeon Star Projects

I have to admit it. I got impatient. I couldn't wait any longer for Gransee to start shipping ARC-LS flashlights. So I made my own. (But I still want an ARC-LS when they come out).

I bought a white LS LED from Gransee, and a double-barrel AAA from WalMart. I put them together just like all the flashoholics here on the forums did.

WOW, great light! I love it.

Then I say my friend's PALights that are always on in a very dim mode. I had to have that too.

So I added a 10K resistor bypassing the on/off switch on the DB.

WOW, greater light! I love it even more. I keep it on my night stand and can always find my way to and from bed. I suspect it will last for years this way, and can always be turned full on whenever I need all the available candlepower.

But it needs to be improved. AAA cells in series-parallel are only supplying 180mA to the LS. It really wants more.

So, as luck would have it, the Texas Instruments sales engineer paid a call on me, and dropped off a couple of sample evaluation boards of the TPS61016.

This 95% efficient boost converter should pump the AAA cells to 3.3volts to the LS. Even though it is rated to drive 200mA, I ran it into a load and found it good to 440mA. It should be really happy pumping 350mA (maybe a bit less for safety) through the LS.

That being the case, I just ordered five more Luxeon Stars from Future-Active (only because Gransee is out of stock).

After I get the LS and the TPS61016 properly married, they go into another DB (I'm off to WallMart tomorow), and later retrofit my first DB/LS.

Oh, are you wondering why I bought five LS LEDs? It's for my crowning glory project! (I hope)

I plan to mosiac them together on an aluminum plate, wire them in series, and drive them with a Maxim MAX-1698.

Yes, I am getting the MAX1698EVM for free from the Maxim sales engineer.

It looks to be capable of driving the four series-wired LS's to a full 350mA. This should be one bright LED flashlight.

After I get the basic 4-LS module working, I'll be looking into flashlights or housings to hold it, probably running from 2 C or D cells. I'd also like to use the MAX-1698 feedback feature to dim the light when the battery runs low, and may also add a manual dimming control.

If I get really ambitious, I might even monitor the LS heatsink temperature and go to a low power mode when it gets hot. But chances are that's not necessary since the MAX-1698 is a consant current converter.

I'll keep you posted with my progress.

Tom

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by tomlang:
That being the case, I just ordered five more Luxeon Stars from Future-Active (only because Gransee is out of stock).
<HR></BLOCKQUOTE>

Which ones did you order? colour? flood/spot? high/low dome?

I want to try one white spot, one amber spot, one white flood and one amber flood together (waiting for the high domes). When I have time, probably not before Easter.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by tomlang:
The TPS61016 should be really happy pumping 350mA (maybe a bit less for safety) through the LS.
<HR></BLOCKQUOTE>

I doubt it will be really happy. The MSOP-10 package is only rated for 424mW, and 3 volts times 300mA is over twice that.

But it might work for intermittent use.

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>
After I get the basic 4-LS module working, I'll be looking into flashlights or housings to hold it, probably running from 2 C or D cells. I'd also like to use the MAX-1698 feedback feature to dim the light when the battery runs low, and may also add a manual dimming control.
<HR></BLOCKQUOTE>

You won't need the dimming feature.

The MAX1698 only puts out a max ~25mA through a string of four LEDs.

Good thing you're getting the eval board for free

I am using only white spotlight LS's

The TPS61016 is a switching regulator, so the chip doesn't have to dissipate the full LED power. The chip data sheet rates it at 200mA, while the eval kit data sheet rates it at 250mA. I'd probably be happy running an LS at 250mA, but tests show the TPS61016 will run over time without problems at 350mA or more.

Yes, the MAX1698 chip itself is rated at 21mA and 444mW. But again, it is a switcher. The total circuit, with external FET and inductor, is rated at 5 watts (which would be enough to light five Luxeon Stars). The inductor current is limited to 1.5A. We'll see how well it works. If it works, great. If not, I can use it to light it's onboard 9 LEDs and drive my cluster of 4 LS just like I did in my first DB conversion.

Eigher way, I'm a happy camper.

Tom