Joule Thief 101

[tinman]

Very nice! I wish I could grow peas that big in my garden!

I wonder how small your circuit would be if you put it on a circuit board, with input and output connectors so you could use 2 or 3 LEDs in series and run them off of assorted dead button cells without soldering anything.

Somewhere I drew up the circuits using two different types of chips from garden lights but I can't find them at the moment, I have so many different JT circuits in various places on this computer. It's getting hard to remember where I put stuff.

Well the LED is just a 5mm LED,and the pea was from a frozen packet of pea's--nothing large at all-well no here any way.

I doubt very much that the small garden light chip would drive 3 LED's as bright as you have yours going there though.

Your circuits seem to be as well organized on your computer as mine are--all over the place,burried in many different files/folders


Brad

[sm0ky2]

Smoky2:

For starters, I sometimes agonize about the concept of an inductor in self-resonance.  In the real world of electronics, that just means that the inductor is crapping out and failing to function as an inductor at the self-resonant frequency.  It's something that an electronics designer wants to avoid, not "take advantage of."  I also agonize about my comment about the inductor acting like a series LC circuit at self-resonance and having minimum AC impedance.  My first intuitive sense is that the model for an inductor is like a parallel LC circuit as shown in the attached diagram.  That means it has maximum impedance at self-resonance.

The irony of this situation, is that you defend your position by quoting said indoctrinated sources....
"electronics designer wants to avoid",.. hmm why is that? do you think? Is it because the results become unpredictable by normal circuit analysis? and "data" as we consider it to be becomes useless or unstable? Thinking of ways to take advantage of this, is exactly what we SHOULD be doing in energy research.

Impedance is a purely electrical function, and at SRF the inductor has a purely capacitive response.
"impedance" through the magnetic portion of the circuit, as you would call it, peaks at a maximum at one half of one half of the waveform (1/4 wave). exactly the opposite occurs when the field collapses, and these two balance each other out perfectly. Hence the term resonance.

Reluctance, on the other hand, which is a purely magnetic function, and at 90-degrees to the electric, this has a value of 0 at SRF, allows the field of the coil to induce a flux in the field of the core material, as a natural response to the resonations within the core itself.
Not as a current-driven forced event.

This is the most important point to get, if nothing else I have stated sinks in.

So I am unsure about this discussion and the answer is ultimately to be found in an actual circuit under test on the bench.  I will just repeat that it is essentially impossible to have a hypothetical discussion like we are having with no circuit, no explanation for how it operates, no schematic, and no timing diagrams.

Now, going back to the basic Joule Thief model, you seem to be implying that if it was operating in some kind of self-resonant mode of the main inductor that forms the transformer core of the device, then it would outperform a comparable Joule Thief operating in its normal mode at a given operating frequency as a switching device.  I have no data at all about that, but my instincts are telling me that that is highly unlikely.

I hereby give your instincts a challenge. Test this for yourself.
Not just by some arbitrary value like "longer run times",. but by measuring the current draw through the battery or source of the circuit, and compare this to the scope image of the coil across the inductor,
then compare this to the output of a secondary coil around the core.

A transistor in linear mode acts like its comparable diode-tube counterpart.
in fact the transistor could be replaced by a triode or something similar.
or dare I mention using something like a self-oscillating quartz resonator used in certain german watches back in the 80s.....

Note that a Joule Thief when operating normally has nothing to do with resonance, which I assume you would agree.  It is just a switching device operating at a given frequency based on component values.

"operating normally" is a vague term when it comes to a device that has been re-engineered in over 100 renditions since Bruce cracked the code on the Steven Marks device....

If you consider a "normally operating joule thief" to be a copy of the one on the Instructables Video
Then yes, I agree it is just a switching device that is most likely oscillating at a frequency incoherent to any SRF of the circuit.

This is because the step-by-step instructions do not include a background of knowledge and education required to understand the true operation of the device. What is given, is a tutorial to build a minimalist version of the oscillator, that is non-self-resonant.

Going back to a Joule Thief operating in some kind of "self-resonant mode" there are lots of issues to ponder about that.  For starters, the transistor can only draw current through the main coil in one direction, but resonance means that current is supposed to flow in two directions, so that is somewhat of a paradox.   If the transistor is operating in its linear region, then that means within the signal there is a DC current drain from the battery through the main coil through the transistor to ground.  So that can't be good for the efficiency of the JT overall because the coil and the transistor are both acting like dumb resistors and producing heat.  Also, in true resonance, there is no magnetic field collapse that outputs energy into a useful load like the LED.  Instead, the magnetic field collapse goes back into the electric field inside the coil.

This is why I said the LED is just an indicator, meant for dummies to know their "JT" is working....
you can throw the LED away, or bypass its drain on the oscillations, by using a capacitor of appropriate value.

The bottom line is this:  I am sure you can mange to hack a JT circuit so that some kind of high frequency oscillation takes place and the LED lights up.  I am not convinced at all that that is related to the self-resonant frequency of the main coil of the JT transformer at all.  I would suspect that any operation at the true self-resonant frequency of the main coil would not really work, the circuit would crap out.  Rather, I suspect that the oscillation is based on some kind of positive feedback between the transistor acting as an amplification device and the JT transformer with some kind of capacitive coupling through a transistor junction being a critical element in the feedback loop.  No matter the case, an investigation into exactly why and how it is oscillating would require some pretty decent electronics smarts and very decent bench skills of which very few on this forum would be in a position to do.  I doubt that I would be able to do it myself unaided but I would be able to follow it and understand it.  It is highly likely that any kind of oscillation mode will light up the JT more efficiently than the JT operating as a simple switching device that energizes an inductor and then discharges it through a LED.

MileHigh

about the circuit crapping out - yes if you take the SRF of most cores and try to run your circuit at that frequency. Better to select a lower resonant node of the cores SRF, which also is an resonant node of the SRF freq. of the LRC of the coil. (and caps if used) - which can be blindly tuned in most cases, by using a variable resistor across the base and carefully observing your oscilloscope.

As for others being able to do this,. yes, read through the JT threads and you see that many are capable of, and do do this.... unfortunately, most of them missed the point, and although they did "tune" into what appeared to be resonant nodes, they usually went right passed them to the nearest peak brightness of the LED, which results in a decay function of the oscillations - more current draw from the source.

This is evident in a few of their scope shots.

sometimes I just feel like im beating my head into the wall... The ones that get it do all sorts of things with this knowledge.. for instance my older brother builds guitar pedals with a JT inside, and never has to worry about replacing the batteries. Most of his house is decked out with LED JT's that have run for years. If he could get one to run his TV hed probably fire the power company.

He's a music major, so he knows all about constructive interference, resonant harmonics, etc...
But even he didn't get it at first. it took me almost 2 years to get him to understand the importance of resonance in this circuit. Once he saw it happen on his scope, it was like a whole world opened up. Now he loves the joule thieves. I go to his house and he has dozens of them, in flashlights, in Altoid Cans, hes taken this further than I ever could. To the point of choosing his own transistors, depending on the waveform he wants, he swears by the old germanium ones. says they work the best.

[Magluvin]

Like in a subwoofer system, a sealed box vs a vented/bass reflex box. The pic below shows the sealed box 3cu ft in yellow and the vented 3cu ft box in green tuned to 30hz.

Just by adding a vent tube of a certain size and certain length to the same box we get a 9db gain at 25hz and nearly 7db at 30 hz. 9db increase is equal to a 3 fold input  power increase. Example  to increase 9db from 500w input would take 4kw. So just by enabling the use of resonance the output is increased.  And in this case there is an increase of some sort across the board of sub listening range.

If so, then why not in an electronic circuit?

Mags

[MileHigh]

Smoky2:

In this response I am going to be somewhat minimalist and not quote you, but I will still respond to what you are saying.  The real arbiter of a lot of the points being made is the bench, and I am not in a position to go onto a bench.

I have been watching some debates on YouTube recently about atheism vs. religion and also some debates about evolution vs. creationism.  I see a real tangible parallel with this debate where I take the atheist/scientist side and you take the religious/mystical side.  I submit to you that you have some ideas that are "out there" about electronics stemming from ignorance and/or false beliefs.  Nor do I claim to be an expert on electronics but I can speak reasonably well on the subject.  It's worth it for any person with an active mind to look up the YouTube debates I mentioned.

All that being said, some rebuttals:

- I strongly object to the use of the term "indoctrinated" when it comes to getting a formal education about electronics.

- Electronics designers put a component in a circuit to perform a specific function.  If the component fails to perform the desired function at the required frequency, then you change the component.  Normally there is no chance of finding "advantage" in a situation like this.

- An inductor does not have a "purely capacitive response" at the SRF.  That is simply not the definition of what happens at the SRF.

- You talk about a 1/4 wavelength without saying how the fundamental is defined.  Nor do I think that transmission line and antenna type concepts apply here but I would leave that to experts like Verpies and others to comment on.

- You relate "resonance" to a field collapse and 1/4 wavelengths.  Can you define resonance at the most basic level without even discussing frequency or impedance?  it's important to know what it really means.

- Reluctance does not have a value of 0 at SRF and the whole concept is invalid and makes no sense.

- It makes no sense to measure the current craw of a JT and then compare it with the voltage across a coil.  On face value that makes no sense and the units are not comparable and you would have to add to what you are saying for it to make sense.

- There is no real point in comparing a transistor to a tube in the sense that yes indeed they can perform similar functions but so what?  I fail to see any tangible connection between a transistor operating in linear mode and a quartz timing crystal.

- When I say "operating normally" I am referring to a vanilla JT circuit.

- I would say that the LED is the standard load for a standard JT configuration.  If you replace the LED with a capacitor and presumably some kind of useful load is across the capacitor then you have a primitive buck, boost, or buck/boost converter.

- Using a variable base resistor in a JT circuit will change it's operating parameters and everybody does it.  In a way it's a shame because the real exercise is supposed to be to determine the optimum value for the base resistor.  In a standard JT circuit the base resistor by design is not supposed to be varied.

- I agree that a JT can be tuned but it's not in the way that you are thinking.  The real exercise is to experiment with the JT circuit and see how you can change the frequency and energy of the pulse discharge that lights the LED.  There are no "resonant modes" to find.  Rather, the exercise should be to see what you can do in terms of pulse frequency and energy and initial current and relate that back to perceived brightness and associated power draw.  That would be the real exercise in understanding how the JT works as a switching pulse circuit.

- You are simply quoting anecdotal evidence about your brother's experience so far.  Everybody knows that a JT circuit will suck a battery dry and the same thing will eventually happen with your brother's projects - he hasn't "struck magic."

- Naturally I can't really comment on your brother's circuits, I can just reiterate that a standard JT circuit has nothing to do with resonance at all.

If I could summarize this succinctly I would say that things have to be done one step at a time.  If the JT experimenter could master the original JT first, and truly understood all the issues, then they could look at modifying it and start hacking into it and start getting it to resonate in various ways.  However, then it simply wouldn't be a Joule Thief anymore.

Anyway, you can see there is a divide between what I am saying and what you are saying.  I disagree with your quasi-mystical descriptions of what a Joule Thief is all about and is capable of doing.  There is no point in looking for something esoteric without having a basic and complete understanding of how it works first.  The classic example for that is having a JT light a long string of LEDs in series.  People will play with that without understanding why that happens.  If you truly know how a basic JT works first, then there is no surprise or anything special about a JT lighting a long string of LEDs.

MileHigh

[allcanadian]

@MH

I have been watching some debates on YouTube recently about atheism vs. religion and also some debates about evolution vs. creationism.  I see a real tangible parallel with this debate where I take the atheist/scientist side and you take the religious/mystical side.  I submit to you that you have some ideas that are "out there" about electronics stemming from ignorance and/or false beliefs.  Nor do I claim to be an expert on electronics but I can speak reasonably well on the subject.  It's worth it for any person with an active mind to look up the YouTube debates I mentioned.

The innovator's proclaimed we are the future and the critics replied-"you cannot withstand the storm". The innovators responded... "We are the Storm".


Ignorance and false beliefs are subjective and vary in time. They said many technologies were impossible 200 years ago and yet here we are, aren't we?. Thus I can only imagine what is called mystical if not impossible today may become an obvious reality in the future.


I watched those debates on youtube and it was pretty comical. My god that poor old christian soul didn't have a leg to stand on. It reminds me of the good christian soldier who prayed to god each morning then carpet bombed innocent civilians in the afternoon because someone told him to. Uhm... just because someone else told them to and apparently this isn't an issue. Personally, if anyone told me to carpet bomb, maim or torture civilians I would tell them to go fuck themselves but that's just me the Atheist.


In any case I can respect the fact that people are entitled to their own beliefs, I have no issue with that. However they should not expect me to keep a straight face or think they have any credibility when they tell me they believe a bearded man in a white dress created the universe in six days. That wasn't part of the bargain and many seem to confuse the right to believe with the right to be respected for a belief and think it cannot be questioned.


Strange world we live in... never a dull moment.




AC