More on the likes of a buck boost dc-dc converter. Chip makers actually
have specific circuits now that will take 4.5 to 6 volts input and boost
up to 25 to 30 volts at 100ma. Most of the high numbered LED flashlights
use a series-parrallel configuration to get 10 or 15 LEDs with a 50 to
75 ma draw. Thats how they get the long run times.

I use a 4 LED model cheapo that uses 3 AA's. Good for most work in
cabinets and computer chassis. 6 months of normal use and I'm still on
the original set of batteries that it came with it. Normally I would be
changing batteries every month. I think Harbor Freight is now selling them.

Regards

Jim Vrzal
Holiday,Fl.

william_b_noble wrote:
the answer is a PWM circuit that manages the current to the LED - they
didn't say 24 hours a max brightness - the ones for spelunking, for example,
operate at reduced brightness most of the time. Just use a 555, or the CMOS
equivalent with some current feedback
"AL A." wrote in message
...

Hi all,
I know this is not strictly on topic, but this crew seems to know

something

about everythig, so here goes:

I am looking to build a "task" lamp (think dentist-type light) that uses
high output white LEDs for a friend who often does
work for extended periods of time in very remote places. I was looking at
the NTE electronics "lightwave" flashlights
http://www.nteinc.com/lightwave/ and they claim that they have circuitry
that makes it possible to run one of the 10
led lights for 24 days, continuously, on 3 D cells.

Any idea how they accomplish that? Most of the high output LEDs I have

seen

seem to want to run between 20 and 40 mA
current draw. Given the amp-hour ratings I find for D cells, I don't see

how

that would work out. Do they modulate the power to the LEDs
in some way that helps extend the battery life so dramatically?

I looked at just modifing a lightwave flashlight for the task at hand,

but

the beam is a bit too wide for what he needs. So I am hoping to
build something with maybe 3 LEDs and appropriate optics to give a fairly
narrow, even beam, mounted on a gooseneck type thing,
with a remote battery pack on a cord.

Any thoughts on the electronics involved? I can handle that part of it,

if

I know what I am trying to accomplish.Of course the body
of the thing will be METAL, nicely turned, naturally. (obligatory
metalworking content...)

Thanks for any ideas you can offer.
-AL








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