Joule Thief 101

[MileHigh]

Yes I think it would make perfect sense for Magluvin to make a thread called "Joule Thief in Resonance Mode" or something akin to that and give it a go.

I would only ask Magluvin when he has his Joule Thief operating normally that he post a nice scope shot of TP1 and TP2 like was previously discussed.

I for one will assure you that I won't touch it or I will barely touch it because I am only interested in seeing if it is going to be possible for this thread to reach its logical conclusion and arrive at an understanding about how a Joule Thief really works.

I will just repeat from here that if the hacked Joule Thief manages to oscillate or resonate the big questions will be "So what?" and "What's next?"  In the long run "finding the delicate balance of resonance in a Joule Thief" will mean absolutely nothing.  Instead of twisting pots and fiddling with your coil like Smoky2 is saying, you may as well look up a single-transistor based oscillator and put it together and you are done.

Or perhaps there is something out there and "they" don't want you to know.  After all, the X-Files is coming back on TV.

The whole thing is nothing more than chasing the resonance fetish and as if you were going to strike gold or something.  It's nothing more than fool's gold.

So, presuming that Magluvin makes another thread and sees sine waves on his scope with a Joule Thief circuit, are big things supposed to happen?  Super efficiency?

The real question will be whether or not the proponents of a "resonant Joule Thief" will account for the final results or will the thread just die with the key players just "running away" for lack of a better term.

A "resonant Joule Thief?"  Bring it on and I will watch from the peanut gallery.

MileHigh

[MileHigh]

Brad:

So the ball is still in your court.  You mentioned stuff about transistor junction capacitance and "RLC."

Please explain exactly how a regular Joule Thief works and give it your best shot and leave no stone upturned.

The floor is yours.

MileHigh

[Magluvin]

Below is MH test point scope shot.

Also a shot of the circuit running at 320mv and a pic of the led. looks brighter on camera. (Mislabeled (named) the 320mv pics as 360mv.)

And a pic of another transformer or say filter choke from a pc power supply.

Also a shot of the original test point at 100kohm showing a dip after led pulse. Then another showing something resembling a sine at about 160kohm. Will do more and also with the original transformer I made.

Mags

[sm0ky2]

Bring it on and I will watch from the peanut gallery.

MileHigh

So, despite the mathematics, and solid foundations in electronics theory,
despite all that has thus been discussed here,

you set in stone your ridiculous opinion, before even considering the experimentation?

[MileHigh]

Magluvin:

Thanks for the scope shot.  You can see the how the Joule Thief transformer is an inverting transformer relative to the two test points.  If I assume that the winding is a 1:1 ratio then I can even see the battery voltage in the scope shot.  The LED voltage peaks at about 6.5 volts and the feedback volage peaks at about -5.3 volts.  So the battery voltage must be about 1.2 volts.

More importantly, this scope shot of a Joule Thief operating normally confirms everything I said about how it operates including the copy-paste articles.  There is no "resonance," there is just the energizing cycle time and then the discharge into the LED cycle time.  Add those two values together and invert it and you get the operating frequency for the Joule Thief.  The positive-feedback "snap ON" and "snap OFF" events are nice clean very-high-slew-rate events.  Finally you can see it is running at a nice "low" frequency of 4.2 kHz.

You can also see that potential issue that I raised on the other thread.  How bright is the LED at 6.5 volts?  (Actually the LED is probably over-driven at 6.5 volts and and you are getting less bang for your current buck at that operating point.  The LED would probably burn up with a constant 6.5 volts across it.)  How bright is the LED at 5 volts?  How bright is the LED at 3.8 volts?  Is this an issue?  Is the decaying voltage/current discharge curve though the LED resulting in a lot of "lost" inductor energy that is not really contributing to the brightness of the LED?  If so, how can you improve upon this?

MileHigh