Power a Luxeon Star with two AA batteries?

I'd like to power a 1-watt Luxeon Star
http://www.lumileds.com/products/family.cfm?familyId=2
with two AA batteries.

And I'd like to be able to dim the light. I've found that the Luxeon
Star puts out useable light down to 50mA, or up to about 350 mA.

This is for a headlamp to be used for camping and backpacking. Most
manufacturers of these headlamps use 3 batteries and a voltage dropping
resistor. IMHO, this is pretty cheesy and besides I'd like to mod one
of my existing AA headlamps.

Actually I'd like to make it run off of a single AA battery because I'd
rarely use full brightness.

Has Maxim come out with any new IC'c in the last year that might be
right for the job? I just ran across this, don't know what's inside,
but it doesn't dim:
http://www.luxeonstar.com/item.php?id=415&link_str=89&partno=02009A

I'm no electronics expert but I'm smarter than the average bear in this
respect and I can solder.

Can anyone recommend a circuit?

Thanks for your help.

 

Build a switcher. There are lots of circuits available. Here is one:

(View with courier font)

VCC = .8 to 3V
,---o---------------------.
| | |
.-. | C|
470R| |<-' C| L1
p1 | | C|
'-' |
| ___ || | D2
o--|___|-----o------||----o-->|--o---------,
| R1 | || | | |
| | C1 | | |
| | |/c | |
o------------|----------| Q2 | |
| | |> | .----'----.
| | | | | |
c\| | | --- | Luxon |
Q1 |----------o | C2 --- | Star |
<| | | | '----.----'
| - D1 | | |
| ^ | | |
| | | | |
'------------o------------o------o---------'
Ground

C1 = 220pF
C2 = 100uF electrolytic
R1 = 10k
Q1,Q2 = 2N4401
D1 = 1N4001
D2 = Schottky Diode
L1 = 33uH High Q inductor, at least 1A rating.

Put a 100 ohm resistor where your Luxon goes
Then, adjust voltage to minimum value before putting on star

You might want to use a power transistor for Q2. This circuit puts
more than rated current across it

created by Andy´s ASCII-Circuit v1.25.250804 www.tech-chat.de

Its a simple boost switcher, based on a two transistor oscillator. The
input voltage should be less than the forward voltage of the luxon +
Schottky, or it won't oscillate, and the luxon and inductor will fry.

I'm not sure it'll get all the way up to 350mA.

Regards,
Bob Monsen

 

You might want to check out

http://www.streamlight.com

http://www.flashlights.com

Streamlight makes a 2 AA Luxeon flashlight
and a dimmable 3 AAA Luxeon headlight. I believe the flashlight
has a DC-DC voltage converter, so it runs well on NiMH rechargeables.

 

http://www.candlepowerforums.com

has a infinite amount of information on flashlights and led's

 

[...]
I'm making a small change:

R2 gives Q2 a little protection. If a huge current tries to go through
Q2, R2 will develop more than 2 diode drops of voltage and cut the "on"
part of the cycle short.

It doesn't add many parts (one) but its protection is not all that good.


[...]

I'd use something faster for D1

This is a good idea. Over current spikes can slowly kill a transistor.

 

The Linear Technology LT1618

http://www.linear.com/prod/datasheet.html?datasheet=736

Looks like a useful part for this application. Unfortunately like most
switchers for portable applications it is only available in tiny surface
mount packages.

 

It'll put out a lot more light at low average currents if you keep the
peak current at 350ma.

For most of the SMPS chips available, they are significantly more efficient
at a battery voltage of 2.4V, rather than 1.2V.
You can probably get away with a step-up only device, 2 fresh alkaline AA
cells won't provide enough current at ~3.5V to kill the luxeon device, even
neglecting diode drops.
Synch rectification will buy you a little bit, but not much.

 

What may also be useful would be a 3 cell device.
2 AA 1.5V cells, and 1AA 3V cell, for emergencies.

 

I have found the efficiency of red, orange and yellow Luxeons to be
maximized at instantaneous currents somewhat less, maybe around 200 mA.
For white and blue ones, the efficiency is maximized at even lower
instantaneous currents around 100 mA or less.
If your average current is around or over 50 mA and the Luxeon is a
white one, I recommend steady rather than pulsating current. But if the
average current is only a few milliamps, then you are better off using
pulses with a higher instantaneous current - perhaps 50-100 mA.

- Don Klipstein ()

 

Zetex (www.zetex.com) have a range of single and double cell LED
constant current drivers that are used in many commercial LED
headlamps.

Dave

 

What's that Lassie? You say that BruceW..1 fell down the old
sci.electronics.basics mine and will die if we don't mount a rescue by
Mon, 06 Sep 2004 00:33:27 GMT:

Ask here:
http://www.candlepowerforums.com/ubbthreads/ubbthreads.php?Cat=

Search in the electronics forum.
http://www.candlepowerforums.com/ubbthreads/postlist.php?Cat=&Board=UBB6

 

Check candlepower.com or ledmusuem.com reviews before buying the Argo
headlamp. One review alleged the 3 AA batteries lasted only an hour.
Would be very costly, if NiMH rechargeable batteries weren't used. The
new model Argo may have an improved (more efficient) driver.

What is the cost of building a LS 2-AA headlamp?

 

Well, the 1W LS with lens, AKA -NW98, is about $16 or maybe a bit less.
So I'd say that that's the most expensive part. You can also buy a kit
of a LS and a Micropuck for about $25 and put into yout own case. I
bought two of them from LED Supply and put them each in its own project
box.

Micropuck:
http://lib1.store.vip.sc5.yahoo.com/lib/ledsupply/LuxDrive-2009-MAR-04.p
df

sales:
http://shop.store.yahoo.com/ledsupply/02009a-ho.html

Just make sure you heatsink the LS to some copper or aluminum.

In my humble opinion, the candlepower guys are a bunch of elitists,
trying to make some bucks. They make these good looking flashlights,
but they all use CR123 lithium cells which cost up to $10 each or more,
and are hard to find. I think the only way to go is the two AA cells,
and use rechargeables if you use it a lot. Two AA cells are only fifty
cents on sale. See www.cheapbatteries.com.

 

What's that Lassie? You say that Watson A.Name - "Watt Sun, the Dark
Remover" fell down the old sci.electronics.basics mine and will die if
we don't mount a rescue by Thu, 23 Sep 2004 05:02:14 -0700:

You can get them for $1.00 at http://www.batterystation.com/cpf.htm