Joule Thief 101

[MileHigh]

Go ahead Brad and complete the current loop for the red dots.  It's your claim.

Chet?

[TinselKoala]

Well maybe we should have a JT distance run of 2 circuits, one with the led across the coil and one with the led across the transistor.  Use fresh, quality batteries to start and no base resistor to shorten testing time.

Ill wip up a board with 2 identical JTs and give it a go.     

See, I have an assumption about an assumption that I am assuming is assumptionless assumption.

Mags

Didn't I already do this test for you, a few weeks ago? Sorry, I didn't take a video but as I recall, I reported the results in this thread, including light-meter readings. But please, repeat the test as necessary, of course.

[TinselKoala]

Yes Mags, I noticed that too...hmm....ringing.  That video is fairly recent too...I think within the past year.  The thing that amazes me to this day about "this simple circuit" is that it turns out to not be all that simple after all.

I do agree that we have seen many variants of the legendary JT circuit and I have no problem with them being called JT's.  I have used many different ones myself so, how could I argue?  I just wanted folks to see the original circuit from the guy that named it...even though he gave credit to a Russian guy for the design.  I really like how Clive graphed the battery depletion which really demonstrates the real purpose for this circuit.  That is what got me involved early on was to be able to use 90%+ of an AA battery instead of 20%.

It is a fairly long video but worth watching.

Transformer Ringing...hmm....


Bill

PS  Clive also talks about how the circuit will run way below the voltage level that it will start at.  I have seen this myself many times.  The circuit will self-fire at say .6 volts but not .4.  If allowed to run it will continue to oscillate down to .3 or so but it will not start that low.  That alone shows something is ringing around back and forth to keep it going right? I believe it was TK that demonstrated that the oscillations continue long after the led is no longer illuminated. I had never even thought to look for that.

That's right. You may find this video of mine of interest:
http://www.youtube.com/watch?v=K7msKzlNzKw

However... I don't think that "ringing" (as in resonant ringing) is the proper word to describe this oscillatory behaviour. So MH is right.   


However x2: Joule Thiefs of a particular design can certainly exhibit _true_ resonant ringing. See the scopeshots below for examples of this. So MH is wrong.   

But note that the ringing (true resonance) is of a much higher frequency than the basic JT pulse-oscillations. So... MH is right. 


(If you search my YT channel for Joule Thief videos you will find lots and lots of demonstrations and explorations of various variants, far too many to list here.)

[Magluvin]

Didn't I already do this test for you, a few weeks ago? Sorry, I didn't take a video but as I recall, I reported the results in this thread, including light-meter readings. But please, repeat the test as necessary, of course.

ya did?  Must have missed it. Was waiting on it. Was it more eff with the led across the transistor?


Mags

[TinselKoala]

ya did?  Must have missed it. Was waiting on it. Was it more eff with the led across the transistor?


Mags

I can't find the report at the moment using the forum's Search function, but I think it's back in this thread somewhere, about where you first mentioned your idea about the efficiency of the two variants. Maybe someone else remembers where it is.