Joule Thief

[SeaMonkey]

A certain amount of reverse bias across the Base-Emitter
junction is beneficial as it aids transistor turn-off and
enhances switching efficiency.

If the reverse voltage is too great (ordinarily more than
about 8 Volts) the junction will go into breakdown because
its doping is very similar to a Zener Diode.  If breakdown
occurs at the reverse voltage peaks then undesired and
unpredictable things may happen.

[TinselKoala]

Sometimes the NPN transistor will work when it's wired backwards, too: E where C should be and C where E should be. This gives some interesting effects too. Not all transistors in all JT circuits will do this, but when you find one that does it's pretty interesting to fool around with.

I also have one transistor, a 2n2222a, that is "partially failed" and it also does some very interesting things in the Basic JT circuit.

[Farmhand]

Ok Fixed that problem, clamped it at less than 1 volt, and I'm thinking of adding a small inductor (see drawing) I found with a enormous inductance for it's size and turns, must be special core material.

Anyway if I add this inductor at the spot indicated as (A) on the circuit it might help a bit more.

The transistor isn't wired backwards it's 1) emitter, 2) base, 3) collector. all good.  with pnp the emitter goes to most positive, is that right ? Could be confusing.
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At the moment to get the initial boost to over 5 volts in C3 for the logic circuit I have to stop the pulses from the CD4049 chip by manually holding one of the gate inputs low momentarily, only takes a touch. Needs a fix.
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Base is blue trace collector is yellow.
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[MarkE]

Beware that small coils with large inductance usually also have high resistance and/or low saturation currents.  You should also replace at least D2 with a good Schottky.  A 10BQ015 type such as MicroSemi LSM115 has almost no forward voltage.  The leakage shouldn't hurt you in this application.

[Farmhand]

Yes Mark that coil won't work in a JT for some reason, the resistance is not high, it's fairly thick wire, might need to wind one, maybe a resistor will do. I don't have any Schottkys yet, some ordered but I might get more, this is fun and useful. I need to order the small gate chips so I'll get some of those Schottkys too.

Tinsel I think when I adjust the circuits so that the switch turns on just before the coil finishes discharging then the current is already flowing in the right direction and it gives that push along with it. Even the JT wave form shows that now. You can see that the slope on the decline of the discharge gets clipped by the switch turning back on.

Is that good or better when voltage is zero ?

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Oh I see, is that transistor bad maybe ? I thought it was happening because of the extra turns on the base trigger coil, the yellow turns are extra ones two blue coils the same on there with the yellow added to the end of one for the base trigger.

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Tinsel with the Logic circuit I can cramp up the wave form by adjusting the frequency/pulse width and clip the back of the discharge off square, which increases the amplitude of the output, and makes it "square" or rectangle.

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P.S.Here's a pic of a few of my small inductors, the little one beside the one with blue tape is about a half inch diameter and
has 1.2 mH inductance but only a few turns and hardly any resistance.
Only 7 turns or so and it is really light, like it's core is not made of normal "metallic like" material.
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The shot below shows the current through the inductor sensed by a 1 Ohm resistor in the place I marked (A) on the drawing. 1.2 mH.
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