Joule Thief 101

[MileHigh]

If you wish to explore this further, the only place I CAN send you is to the bench.

https://wiki.analog.com/university/courses/electronics/comms-lab-isr
This is the very basics of resonance, and pertains mostly to the effects on the coil.
The core used in this experiment assumes the permeability of free space. (air).

Adding a magnetically inductive core, like a ceramic ferrite, can be examined in a similar manner.
Here is someone elses benchwork on this subject.
http://g3rbj.co.uk/wp-content/uploads/2015/08/Self-Resonance-in-Toroidal-Inductors.pdf

In the first link they also model a coil as a parallel LC resonator.   That means at the self-resonant frequency the coil blocks the resonant AC frequency and will not let it pass through the coil.  The coil is acting as a notch filter and will shut down and block any AC activity at the resonant frequency.

That means that when you observe a hacked Joule Thief "in a resonant mode" it almost certainly has nothing to do with the SRF of the coil.  Rather, it is like I said to you before, the resonant oscillation requires the transistor to power the resonance in some kind of positive feedback loop and the resonant frequency is determined by some of the components in the circuit, but not by the SRF of the coil itself.

Even if you add a ferrite core, the coil is still modeled as a parallel LC resonator and will act like a narrow notch filter.  It is all fine and dandy to find the self-resonant frequency of a coil, and depending on the coil and the frequency, it might sometimes also be modeled as a series LC resonator and then act like a narrow band pass filter.

The bottom line is it really does not matter.  In the real world of electronics nobody is too interested in coil self-resonance because there is nothing magical or special that you can do with it.  If they need a parallel or a series resonator, they will do it with discrete capacitors and inductors.  That way you have full control over what you are doing.

To repeat, there is nothing special about a self-resonating coil.  There are dozens of threads about self-resonating coils and they are mainly fanboy threads that imagine all sorts of amazing things but they are not true.  A self-resonating coil is sort of like a coil undergoing a spastic seizure and failing to do what it is supposed to do which is be an inductor.

MileHigh

[sm0ky2]

Smoky2:

A computer is typically clocked by a crystal oscillator, but that is about as far as it goes.

MileHigh

so theres absolutely no reason for a computer engineer to concern themselves with concepts like:
angle of incidence
wavelength, with respect to the thickness of the semiconductor
and im sure it's just a coincidence that both Green's function and the Hemholtz equations coorespond precisely to Maxwell's equations and the Huygens principal....

we can throw away all these textbooks now, and tell the guys down in the Intel Lab to go home..

[sm0ky2]

In the first link they also model a coil as a parallel LC resonator.   That means at the self-resonant frequency the coil blocks the resonant AC frequency and will not let it pass through the coil.  The coil is acting as a notch filter and will shut down and block any AC activity at the resonant frequency.

That means that when you observe a hacked Joule Thief "in a resonant mode" it almost certainly has nothing to do with the SRF of the coil.  Rather, it is like I said to you before, the resonant oscillation requires the transistor to power the resonance in some kind of positive feedback loop and the resonant frequency is determined by some of the components in the circuit, but not by the SRF of the coil itself.

again you are missing the point.  "hacking" a non-resonant JT to cause it to resonate, - yes, this is far from a symmetrical balance between the SRF of the coil and the SRF of the core (ideal situation). What is being done here, is changing the capacitance of the coil, with respect to the parasitic capacitance of the core. This, in effect, brings the two waveforms into a resonant node. Meaning, both waveforms have a displacement in the same vector.
This is observable in the scope image (even partially in abrupt non-linear switching), as well as in the brightness of an indicator (LED), or a measurement of the intensity of the field around the inductor.

Even the most adamant debater against the concept of resonance and constructive interference in electronics circuits, can easily demonstrate the frequency-based efficiency response of biasing the base resistor of a JT.
thus what I have stated above corresponds to experimental results across the board.
Regardless of your perspective of "what is occurring", it still occurs.

the SRF of the coil, by itself means nothing, we can't actually use it, because at SRF the coil no longer does what we want it to do. lower than it does what we want, higher than it does the opposite, but at the SRF it does not.

the SRF of Core material behaves like the exact inverse of the coil in these regards.
Inverse is the important key word here. One is magnetic, the other is electric, and they cross at 90-degrees.

when the two are set to resonate, in an LRC tank circuit, they behave the closets to the ideal tank that we humans can build. mathematically, experimentally, and in practice. When coordinated with an external parallel capacitance, and resistance of appropriate value, this tank can be demonstrated to continue resonant oscillations until all of the energy is dissipated as heat. A direct function of circuit resistance.
This has been known in electronics theory since the time of the radio.
We can argue about the whys and why nots until we are old and grey,
but the whats still occur when you build them.

You keep reverting back to "standard use of components in electronic circuitry", when the very concept we are talking about is what Electronics as a whole teaches us NOT to do... Almost every electronics circuit in use today relies on the coherency of data. without the data the device is "useless". We cannot use resonant waveforms in electronics. Amplitudes build up in ways not always predictable by theory, at least not in a manner in which all values can be accounted for within a feasible device. And something as simple as sending a text message would result in garblygook on the other end. We wouldn't even get that far, because the software code itself wouldn't function properly. We can't save files, we can't READ files, error correction goes completely out the window.
on an even deeper level, the voltages and current values at the terminals of our IC chips would not be the expected values, and its very likely that we will burn up components all over our circuit.
There are reasons they teach us not to use the components in this manner.
Not to mention the fieldday the FCC would have from such a radiating computer system.

it seems we just keep going in circles, I tell you how to do it, and you tell me why you don't think it works they way I describe it. The results are the same, regardless of perspective. so,. (bangs head on wall)....

Even if you add a ferrite core, the coil is still modeled as a parallel LC resonator and will act like a narrow notch filter.  It is all fine and dandy to find the self-resonant frequency of a coil, and depending on the coil and the frequency, it might sometimes also be modeled as a series LC resonator and then act like a narrow band pass filter.

you're almost there, like standing on the edge of a cliff, but you don't quite see the magnitude of the drop to the bottom.

instead of thinking in terms of when it cuts and clips....
Think of the exact moment when the upper and lower limits of the filter balance each other out, and perfectly cancel.

In the ideal situation, wherin the SRF of the coil is the same frequency as the SRF of the core:

The ferrite core acts are an energy storage for the electric field of the coil, and the coil acts as an electric field storage of the magnetic flux from the core. (Thermodynamically conservative, in accordance to Maxwell's Equations)
At this frequency, the core material can be viewed as a resistor in the circuit as a function of its permeability.
This can be replaced by a resistor of the same value for circuit analysis and Fourier transform.
Magnetic Reluctance (resistance to change in magnetic flux over time) has no effective value in the circuit at SRF.
This is the ideal state in which the ferrite core switches flux at its natural resonant time intervals.
It is a direct function of the properties of the core material with respect to its' physical dimensions.
It is defined mathematically, and in practice the manufacturers of the ferrite cores determine the SRF in testing as the point where magnetic reluctance is effectively (nil).
This is measured by the change in flux with respect to a drop in a secondary applied field.
The point at which the core material behaves like a series resistor to the applied field, is its SRF.

It is a self-defined situation, inductance, reluctance, resistance, impedance, electric flux, magnetic flux.
They are all proportional, from whatever perspective. change one, you effectively change the other.

What I am describing is not anything "magical". It is the most efficient way to use electricity and magnetic flux.
It might not be the most useful in most applications, but for something like the Joule Thief, TPU, and the LED lightbulbs that are replacing the incandescent,  these concepts can prove to be very useful.

Not by "generating" energy, but by wasting LESS of it.

The bottom line is it really does not matter.  In the real world of electronics nobody is too interested in coil self-resonance because there is nothing magical or special that you can do with it.  If they need a parallel or a series resonator, they will do it with discrete capacitors and inductors.  That way you have full control over what you are doing.

MileHigh

and you wonder why I use a term like "indoctrination"

[MileHigh]

so theres absolutely no reason for a computer engineer to concern themselves with concepts like:
angle of incidence
wavelength, with respect to the thickness of the semiconductor
and im sure it's just a coincidence that both Green's function and the Hemholtz equations coorespond precisely to Maxwell's equations and the Huygens principal....

we can throw away all these textbooks now, and tell the guys down in the Intel Lab to go home..

It all depends on the scope of the discussion and what you mean by "computer engineer."  I thought that we were talking about Joule Thieves and resonance.  The average computer engineer that designs circuit boards is not concerned with the textbook stuff that you are referring to.  In this day an age the PCB layout and characteristic impedance of the PCB traces are critical and that is a very important issue if that is something you were alluding to.

[Bob Smith]

Smoky
Thanks for your explanations around resonance. It is generally addressed in very limited terms. Your posts are very helpful.
Bob
BTW - guitar builder here - you have my attention.