Joule theif : try out !

[MarkE]

That's where a flyback variant would do better.  One could wind the 100T or so secondary bifilar with one winding directed at the output rectifier and LED load, and the other winding directed soley to drive the transistor gate timing circuit.

[Farmhand]

I realize this thread hasn't been posted in for a while but I thought I would post here because this is my first Joule Thief and I'm trying to work out if I have it right or working as it should.

I got a newer set of shots after some alterations and also made a drawing of what I "think" will work ok, the only things on the drawing that I have not got in the circuit is, I'm only using the 1 K resistor, I haven't tried it with 12 volts but I imagine with more resistance on the trigger and more load it could. I took out 2 LED's and am charging two AAA's in their place, so 4 LED's and the batteries in series.

Any hints on what I may be doing better ? 

First is collector to ground, second is base to ground and circuit proposed. I'm using 5 nF in series with the base at the moment.

.

[MarkE]

I recommend two changes to your design:

Change the 1N4007 diodes to 1N4148 diodes.
insert a Schottky diode sucn as a 1N5819 in series with the LEDs.

Both changes are to reduce losses due to the reverse recovery of the diodes.

[Vortex1]

I recommend two changes to your design:

Change the 1N4007 diodes to 1N4148 diodes.
insert a Schottky diode sucn as a 1N5819 in series with the LEDs.

Both changes are to reduce losses due to the reverse recovery of the diodes.

Those are worthy changes. Additionally ,few people give thought to the function of the two windings in a blocking oscillator. Since there is current gain available, this can be used to advantage to get fast switching of the transistor. Study some old schematics by Tektronix where blocking oscillators were properly designed. You will find that the base drive winding is properly sized to effect good switching, but not wasting power by over driving.

There are alternative circuits to the usual practice used in most JT's of a power wasting resistor in series with the base winding. This does not produce the best switching. You want a circuit which biases the winding to the base threshold yet still allows sufficient current flow into and out of the base, but not excessive. The base winding should have lower turns ratio than the collector winding.

In an ordinary poorly designed blocking oscillator such as a JT, switching can be improved by adding an series R-C speedup network across the bias resistor, but this is not the best improvement that can be made, as the circuit itself is not optimized topologically.

[MarkE]

Those are worthy changes. Additionally ,few people give thought to the function of the two windings in a blocking oscillator. Since there is current gain available, this can be used to advantage to get fast switching of the transistor. Study some old schematics by Tektronix where blocking oscillators were properly designed. You will find that the base drive winding is properly sized to effect good switching, but not wasting power by over driving.

There are alternative circuits to the usual practice used in most JT's of a power wasting resistor in series with the base winding. This does not produce the best switching. You want a circuit which biases the winding to the base threshold yet still allows sufficient current flow into and out of the base, but not excessive. The base winding should have lower turns ratio than the collector winding.

In an ordinary poorly designed blocking oscillator such as a JT, switching can be improved by adding an series R-C speedup network across the bias resistor, but this is not the best improvement that can be made, as the circuit itself is not optimized topologically.

I agree that the base drive as it is is wasteful.