Download Joule Thief modern 5252F

It seems that many "Joule Thief" circuits depend on a clunky (bulky and heavy) toroid or "donut"
that has to be carefully wound with copper wire. But now there are several very small 4 legged
ICs available that do the job using only a simple inductor, single cell battery and a LED. In effect,
the 4 legged IC replaces the clunky toroid.
I came across these ICs when I disassembled some solar powered yard lights. I looked for a
toroid but only found a four legged IC and a part that looked like a resistor but actually was a
very physically small inductor (coil). Both of these parts along with wire attachment points were
soldered to a small circuit board. I was able to remove parts, attach wires to them and assemble
them on a Radio Shack type of "Breadboard" to test and better understand this circuit.
But then I created a very crude and minimal circuit to better understand some of the key parts of
a "Joule Thief."
I used a Yellow LED that requires 2 volts (or a little more). My 1.5 volt "Rocket
Battery" has been worn down to 1.4 volts. As a result, the LED is off and is not even close to
conducting any current. Points A and B on the inductor coil L are at pretty much the same
voltage, 1.4 volts compared to "ground" or the minus of the battery.
When the switch is pushed and and held ON, briefly, current flows through the coil and creates a
magnetic field around the coil. Points A and B are still positive with point A being slightly more
positive than point B.
But when the switch is released and turned OFF, the magnetic field suddenly collapses and
creates a 1.4 volt voltage with a reverse polarity. This means that point B is now 1.4 volts higher
(more positive) than point A. It is as if the coil has become like a temporary battery connected in
series with the actual battery, presenting 2.8 volts to the LED. The LED reacts to this by flashing
on for a very short moment. Pushing the switch again repeats this cycle. If I could push the
switch rapidly enough, the LED would appear to be solidly ON.
The pictures that follow will reveal how simple it would be to recreate this. The coil or inductor is
12 feet of 24 gage wire wrapped (200 turns) around a 1/4 inch diameter soft iron nail.
I reversed drew the schematic from a solar light "joule thief" and was stuck when I view what
look just like a resistor and nothing else. I had never seen an inductor that looked like a resistor.
I then made a crude "equivalent" circuit using only a battery, LED, switch and the mystery part.
My crude "equivalent" circuit was able to momentarily flash the LED that requires about three
volts. I asked myself, "if L were really a resistor, how could the LED ever get 3 volts?" Against
what I thought I knew, I decided that maybe L was an inductor. Then I looked up inductors in
parts catalogs and sure enuf, they had inductors for sale that looked like resistors...