I got interested in the flashlight and then i found all the info on

this site about different flashlights and tests and all, so i thought i

would contribute to the information pool also by determining how the

flashlight circuit was made and how it worked so that others could

build their own home made flashlights and power them up with circuits

similar to this one and install them in whatever flashlight they wanted

to. Having posted the schematic and brief explanation, i feel i have

acheived that goal.

Some of the points you made were interesting, and i would like to

explain a few things pertaining to those remarks.

First, the definition of 'linear' is:

the multiplication of the voltage by a constant k results

in the multiplication of the current by the same constant k.

The LED is certainly not linear, and doing a nonlinear analysis

anyway, i saw no need to use a piecewise linear approximation.

If you still are not comfortable with calling the LED v/i curve

nonlinear, then simply substitute the words

"v/i curve of the LED"

for the words

"nonlinearity of the LED"

and re-read the sentence.

Secondly,

when i say "average" i mean "average". Whenever someone says average, they

mean the arithmetic average and not the geometric average, harmonic average,

square root of the mean of the square, ninth root of the velocity of

the speed of light in a vacuum times the current cubed, or anything else

Third,

when i said the pulsed current produces the same light as about

the same average current through the LED would produce, i meant just that too.

The reason for this is quite simple: when you half the time of the light output

you half the total amount of light being output, and when you double the current

to the LED you approximately double the light output from the LED. When you do

both, you get the same output as if you supplied about the same continuous current

to the LED as the average of the pulsed current. Yes the led is more inefficient

at higher currents, but it will be hard to notice a difference. Also, 'about'

means just that too.

For most practical purposes, when you supply 'about' the same constant current

to the LED as an averaged pulsed current, you get 'about' the same light output.

Lastly, i will post updates when i do more with this circuit.

I did find already that the circuit can operate on a single

AA battery with slight mod's. I built up a similar circuit

using the parts list shown (with the schematic) and wound

a toroidal coil measuring about 220uH. I got about the same

results as the original circuit. The thing i really like

about this circuit is that the parts are so dirt cheap. Its

much cheaper then buying evaluation boards for parts that will

cost $4.00 just for the ic. Im thinking of using a MOSFET

output transistor to increase efficiency. Only problem is,

that will raise the price tag a little. With the transistors

in the parts list, this circuit can be built for under

75 cents.

As i do more tests ill post the results here so everyone can

build the circuit and modify it to fit any number of LEDs

and battery cells they wish to use with their flashlights.

I would hope that anyone else working with this circuit would

post their results as well.

Good luck with it,

--Al

PS. Special thanks to Stingmon for the use of the WCT graphic.