Joule Thief 101

[sm0ky2]

Thanks farmhand.   Its been buggin me for some time. We see all these diagrams/drawings of toroid and other closed core transformers that do not depict this. And the idea that the core would leak due to an over abundance of field when the transformer is working hard, calling it over saturation.

Ok. Question answered in the best way.

Thanks again

Mags

yes. In fact, in engineering, the self-resonant frequency of the ferrite inductive core is understood to be
the frequency at which saturation peaks at a maximum (with no oversaturation) in the minimum time.
It is kind of a funny way of looking at things, but this is what occurs at that freq.

When the ferrite reaches saturation, it can hold no more field. (all else is wasted EMF radiation)
When the switching occurs right at this point, the resultant field collapse is precisely timed with the oscillations.
1/2T + 1/2T = T

In the case of undersaturation - there is a shorter charging time of the core material (or correspondingly weaker field)
clean waveforms can be transferred in this case, however it is not "resonant" with the ferrite.

In the case of oversaturation - there is a longer charging time of the core material, and a shorter discharge.
this leads to an imbalanced (asymmetrical) waveform. Also not "resonant" with the ferrite.

There are certain nodal frequencies in the case of undersaturation, where resonance can occur.
Not the case with oversaturation.

These conditions are in addition to what has been stated about the resonant frequency of the ferrite in previous posts.
It is not often looked at from this perspective, except by those that manufacture ferrite materials.

[sm0ky2]

I don't see a transformer and I don't know what you mean when you say efficiency.

I second this position.

What I see is two coils wound around the same core, (in series-parallel-ish)
such that their corresponding N and S poles are on the opposite sides of the core.
meaning one coil is would in the opposite direction(-ish?)

I would expect something similar to this, to occur:
with the field biased towards the green arrows, due to the unclosed loops on the inside.
We would need a second coil to do any sort of "efficiency" measurements, or calculations.
unless we are measuring the induced magnetic field strength through the core.
and "efficiency" being the energy used to saturate the core material.
seems kind of vague, and would be difficult to measure.

[Magluvin]

Was going through my toroid cores. If you take a ferrite bead, most have seen, a medium dark grey, and use an ohm meter, you dont get any resistance reading. So they would appear to have the least amount of eddy currents and would be best for high freq operation. At least ones available locally or from a scavenged device.

Some cores do have continuity. Ones that are coated in various colors, if you scrape away some of the coating in 2 different places then measure, you would be surprised at what you find. Some may be 0ohm. Some like one I just checked, 214ohm, one at 1.4mohm.  Ones that measure very low down to 0ohm, you can see they are shiny after scraping the coating, like if it is just solid iron. Probably used for low power/freq requirements.

So Im going for the known 'ferrite' core this round. Will do 11 turns, windings on opposite sides of the core.  I have a bunch of the blue coated 1.4mohm cores that I want to try something leaning towards EMjunkys opposing coils by winding 2 identical transformers, but one has 1 winding wound in the opposite direction to see it that affects things with the circuit. Naturally I will have to reverse the polarity connection on the EMj winding to make it work. But just interested in what might happen, if it affects freq, etc.

Mags

[Magluvin]

In my post above I made a mistake and corrected it. Where you see 'ferrite' I had '0ohm'   which would have not been the core I intended to use after posting all that.

Mags

[Pirate88179]

Mags:

Yes, the colored ones are powdered iron.  I always got better results with ferrite...with a high permeability if possible.  It all depends upon the goal.

Bill