Re: [Phys-l] led flashlights

[Brian Whatcott <betwys1@sbcglobal.net>]

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!