Re: [Phys-l] led flashlights

[chuck britton <britton@ncssm.edu>]

Somewhere out there on the 'net is a simple circuit called the 'joule  
thief' (IIRC).
It uses a small ferrite toroid (bead) to give the voltage boost 'kick'.

Described as squeezing a 'dead' single cell to run an  LED for hours.

This circuit would make a flickering light - but the frequency is WAY  
higher than our ~30 HZ limit.

I wouldn't use it on a sensitive diode laser without some post- 
conditioning.

On Mar 5, 2008, at 1:17 PM, Brian Whatcott wrote:

> At 08:49 AM 3/5/2008, you wrote:
> > The newer led flashlights apparently have a voltage multiplier
> > circuit along with a voltage regulator that boosts the battery
> > voltage up to what the leds need. This means that you can use old
> > batteries to power the flashlight and get almost the same intensity
> > as with new batteries, although they don't last as long. I find this
> > to be a great use for my used AAA bateries that are too weak to
> > power my calculators. Old batteries work in small radios but they
> > last so long that i've accumulated a small box full of weak, but
> > still usable batteries. Mag-Lights@ with a tungsten filament that
> > use AAA batteries also work well but the light starts dim and gets
> > dimmer as the battery is used up. Leds keep the light level high for
> > a shorter time. Great! I found mine at Harbor Freight on sale for
> > under $2 apiece (not an advertisement, just a fact.)
> > Prof. Eric T. Lane   eric-lane@utc.edu
> > Physics Dept. 2352  423-265-7804
> > The University of Tennessee at Chattanooga  37403-2409
> > _______________________________________________
> > Forum for Physics Educators
> > Phys-l@carnot.physics.buffalo.edu
> > https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l
>
>
> The method now growing in popularity for holding onto high conversion
> efficiency for battery-powered devices, in face of a drooping source
>   voltage is the boost/buck regulator which drops or boosts the input
> voltage as needed. They usually rely on the inductive kick from
> switching an inductor in the output path at high audio frequency.
> Solar arrays also benefit from this approach.
>
>
>
> Brian Whatcott    Altus OK    Eureka!
>
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