Joule theif not working at 0.5 v ?

[conradelektro]

The germanium transistors work at 0,2V flat. At that voltage led is not very bright. I will tomorow post pictures. One strange thing also ocurs - joule tief with germanium transistor don't work at 1,4 - 1,5v, don't know why. Work with more and less but not with 1,5v exactly

Interesting, which germanium transistors did you use? I would like to try them myself.

I think that the 1.5 V problem could be overcome by changing the number of turns of the windings on the toroid. May be you could post the exact circuit you were using, and specially the windings on the toroid.

Greetings, Conrad

[omdano]

Interesting, which germanium transistors did you use? I would like to try them myself.

I think that the 1.5 V problem could be overcome by changing the number of turns of the windings on the toroid. May be you could post the exact circuit you were using, and specially the windings on the toroid.

Greetings, Conrad

You have the BC547 which can allow you to get low to 0.136v
with a 100:10 toroid windings , i will try that as it seems like a solution

[MarkE]

Interesting, which germanium transistors did you use? I would like to try them myself.

I think that the 1.5 V problem could be overcome by changing the number of turns of the windings on the toroid. May be you could post the exact circuit you were using, and specially the windings on the toroid.

Greetings, Conrad

There are two things that are needed to make the device start:

1) The transistor must turn on with the available bias voltage.
2) The transformed bias voltage must be enough to turn the transistor off.

JFETs will turn on with zero bias voltage.  Smaller Vgs values are needed to meet the second requirement.  For junction transistors the first requirement is the limiting factor.

[xee2]

You may want to look at this video >>> http://www.youtube.com/watch?v=LQinhM1CxkM


The Vbe scope shot shows that the circuit needs less than 0.5 volts to work. However, I do not know if the circuit will start at 0.5 volts.

[SeaMonkey]

What MarkE said above is quite true.

For low voltage startup with a bipolar transistor,
either silicon or germanium, the base drive must
be adequate to assure that the transistor turns
"on" sufficiently.  This usually means that the
base current limiting resistor will need to be
reduced in value.

Or, some sort of switch can be placed across the
resistor to temporarily and briefly "short" it to
start the oscillator.  Once running it may continue
to run at the low voltage of 150 to 200 milliVolts
or even less.

In some very low voltage Joule Thief oscillators
the base resistor is not used at all.