Author Topic: Joule Thief 101 (Read 940997 times)

Pirate88179 · « **Reply #465 on:** February 25, 2016, 04:59:44 PM »

Quote from: MileHigh on February 25, 2016, 04:39:21 PM

Well, like I stated before, the base resistor in a Joule Thief is not supposed to be varied at all. Rather, it is supposed to be based on the EMF coming from the feedback coil and the amount of base current required to switch the transistor hard ON, which is based on the maximum current that will flow through the main coil. The real way to change the way the Joule Thief operates is to play with the size of the core, and the number of turns in the primary and the secondary. The value of the base resistor "falls out" from those and related parameters. Any astute electronics experimenter should be able to show exactly how the value of the base resistor is determined for a given standard Joule Thief configuration.

For the issue of the LEDs in series, I am close enough. If you build a Joule Thief and you are driving a single LED, and you like the illumination level, and then you try 10 LEDs in series and get the same illumination level in each individual LED, then that is telling you that you can reduce the power going into the single LED by a factor of 10. So if you are a keener and you are up to it, you can challenge yourself to figure out how to do that.

MileHigh

But, as we all found out early on, as the voltage in the battery drops, everything that you had balanced perfectly in the JT circuit starts to drift away...so, if you tuned the base resistor for the brightest light at a battery voltage of 1 volt, as the battery drains down to say, .7 volts, your led will no longer be as bright so, you dial in the base resistance with your vr and, now you are back to having a bright led. You can do this down to where the battery is too low to switch the transistor on. This gives you the maximum light you are ever going to get from that battery using those components.

If you built the optimum JT circuit using the perfect windings and components, and I had one of my "regular" JT circuits and we both started out with a battery of 1 volt, I'll bet that when we got to .7 volts or so, I could make my led much brighter than yours by a simple tune of the base resistor...your circuit was perfect for 1 volt, .7 volts and below...not so much.

Does this make any sense?

We were seeing out nice little circuits drift all over the place as the battery was depleted so being able to adjust the base resistance really helped. Also, adding a decent size cap in series with the led helped a lot too.

Now, with the circuit you have proposed, having "constant" power to the coil would nearly eliminate this issue, or at least make it where you didn't even notice any difference in the led operation as that battery would not be allowed to go down to say .4 volts or so.

I guess what I am saying is that we learned, or think we learned, that the "best" set-up for a simple JT was a moving target that you could only "hit" in a certain range unless you could adjust your circuit along the way as the battery drained.

Bill

PS I look forward to seeing what Lidmotor does with your circuit.

MileHigh · « **Reply #466 on:** February 25, 2016, 05:14:55 PM »

Quote from: tinman on February 25, 2016, 02:34:21 AM

You are so funny some times MH.
Throughout this thread,you have been stuck on one circuit that you deem to be !the! JT circuit.
Now your posting different circuit's,and telling everyone to !think outside the bloody box! lol

Fact is MH,most of us here have been doing that all along,while !you! where stuck in the box.

Brad.

Well you are wrong again Brad. A Joule Thief circuit is a blocking oscillator, and the heart of a blocking oscillator is based on energizing an inductor and then "blocking" the the inductor discharge. This is done using digital switching so that the discharge gets rerouted through an LED. The circuit that I posted has the fundamental trait of having an inductor energized and then the discharge goes through an LED and it also uses digital switching. It will not outperform a Joule Thief with respect to LED illumination time or how low a battery voltage it can work at, but it does have an architecture based around the fundamental concepts of energizing and discharging an inductor, and digital switching. That's in contrast to some kind of feedback oscillator that can also drain a battery but it has nothing to do with a blocking oscillator, energizing and then discharging an inductor, or digital switching.

You talk about being "stuck in the box," take a look at the attached image. I am willing to bet you that the issue of the potential inefficiencies in the decaying voltage/current waveform through the LED when driven by a standard Joule Thief have never been discussed by a lot of people on the forums. It's possible that I am the first person to ever raise this issue. Yet many experimenters, probably you included, have stared at this waveform blankly and never even mentioned it. Talk about being "stuck in a box" when something is staring you in the face.

So for you and others who know who they are, don't give me this bullshit that I am "stuck in a box" or "I don't do experiments" or, "I only know what is in books." I have posted several times that I estimated once that I have about 3500 hours of bench work under my belt and I assume that you are aware of that. The whining about me is just a cop-out.

The simple truth is that the kind of basic electronics stuff that you do around here, I haven't done in more than 30 years, and yet I can still whip most of your asses with one hand tied behind my back. Even now, I could literally spin circles around you on a bench and I don't even really like electronics. And to put everything in a proper context, people like Verpies and Picowatt and Poynt99 can easily spin circles around me on a bench. I am no hard-core low-level-details electronics or electromagnetics guy at all, I don't even like it particularly and I was glad that I walked away from working on a bench. I threw all my TTL and CMOS chips and components and power supplies away more than 20 years ago.

So stop your "you only know books" or "you're stuck in a box" or "you don't do real experiments" nonsense. It's just used as a fake talking point "weapon" or as a diversionary tactic when things aren't going the way you thought they were supposed to be going or you or others want to try to hurt my credibility because I am talking straight.

This would be a typical example: "Show me how you started a car with a dead battery." Response: "You don't do experiments." It's pure nonsense.

MileHigh

MileHigh · « **Reply #467 on:** February 25, 2016, 05:42:36 PM »

Bill:

In the whole discussion below I am talking about a normally operating Joule Thief. I am not talking about what happens at very low voltages where the Joule Thief goes into some kind of high frequency oscillation mode.

Quote

But, as we all found out early on, as the voltage in the battery drops, everything that you had balanced perfectly in the JT circuit starts to drift away...so, if you tuned the base resistor for the brightest light at a battery voltage of 1 volt, as the battery drains down to say, .7 volts, your led will no longer be as bright so, you dial in the base resistance with your vr and, now you are back to having a bright led. You can do this down to where the battery is too low to switch the transistor on. This gives you the maximum light you are ever going to get from that battery using those components.

If you built the optimum JT circuit using the perfect windings and components, and I had one of my "regular" JT circuits and we both started out with a battery of 1 volt, I'll bet that when we got to .7 volts or so, I could make my led much brighter than yours by a simple tune of the base resistor...your circuit was perfect for 1 volt, .7 volts and below...not so much.

Does this make any sense?

It makes perfect sense and there are two schools of thought here and a fundamental concept.

The fundamental concept is this: The base resistor is supposed to be a value that ensures that the digital switching operates normally. There may be a "best" base resistor value when the battery voltage is 1.5 volts and a "best" base resistor value when the battery is 0.4 volts. In both cases you have to have proper digital switching taking place and the real variable at play is how much power you burn off in the base resistor and what value helps you minimize this waste power.

However, suppose the battery is 1.5 volts and you get a very bright LED at say a low base resistor value. The Joule Thief may not be switching properly here, the whole mechanism is out of whack and it's also drawing a lot of battery current. You don't want to do that, you don't want to throw the whole circuit out of whack.

The first school of thought goes like this: Design a Joule Thief for mass production with a fixed base resistor. In that case you pick the right "compromise" base resistor value that will work well for a battery voltage range from 0.3 to 1.5 volts. The assumption is that the switching is always normal during the full battery voltage range. Yes, the LED gets dimmer as the battery voltage gets low, that's life.

The second school of thought is that you might indeed get better illumination performance if the base resistor is adjusted at low battery voltage. In theory you would be getting better timing where you energize the coil longer before the switching occurs. The caveat is that the Joule Thief circuit is still switching normally. I am purely speculating here though, and some testing would have to be done to confirm this. Can changing the base resistor value at low voltages change the timing so that the LED gets brighter but the circuit is still switching properly, or, are you getting a brighter LED because the whole circuit is out of whack and sucking power like crazy? I don't know the answer to this.

The way I think is the from the first school of thought. You can indeed make a wise choice for the value of the base resistor such that the Joule Thief switches normally during the full battery voltage range of 0.3 to 1.5 volts. The fact that the LED gets dimmer as the battery voltage drops is fully expected and it is just a fact of life for a simple Joule Thief circuit.

MileHigh

tinman · « **Reply #468 on:** February 26, 2016, 03:43:45 PM »

Quote from: MileHigh on February 25, 2016, 05:14:55 PM

Well you are wrong again Brad. A Joule Thief circuit is a blocking oscillator, and the heart of a blocking oscillator is based on energizing an inductor and then "blocking" the the inductor discharge. This is done using digital switching so that the discharge gets rerouted through an LED. The circuit that I posted has the fundamental trait of having an inductor energized and then the discharge goes through an LED and it also uses digital switching. It will not outperform a Joule Thief with respect to LED illumination time or how low a battery voltage it can work at, but it does have an architecture based around the fundamental concepts of energizing and discharging an inductor, and digital switching. That's in contrast to some kind of feedback oscillator that can also drain a battery but it has nothing to do with a blocking oscillator, energizing and then discharging an inductor, or digital switching.

You talk about being "stuck in the box," take a look at the attached image. I am willing to bet you that the issue of the potential inefficiencies in the decaying voltage/current waveform through the LED when driven by a standard Joule Thief have never been discussed by a lot of people on the forums. It's possible that I am the first person to ever raise this issue. Yet many experimenters, probably you included, have stared at this waveform blankly and never even mentioned it. Talk about being "stuck in a box" when something is staring you in the face.

So for you and others who know who they are, don't give me this bullshit that I am "stuck in a box" or "I don't do experiments" or, "I only know what is in books." I have posted several times that I estimated once that I have about 3500 hours of bench work under my belt and I assume that you are aware of that. The whining about me is just a cop-out.

The simple truth is that the kind of basic electronics stuff that you do around here, I haven't done in more than 30 years, and yet I can still whip most of your asses with one hand tied behind my back. Even now, I could literally spin circles around you on a bench and I don't even really like electronics. And to put everything in a proper context, people like Verpies and Picowatt and Poynt99 can easily spin circles around me on a bench. I am no hard-core low-level-details electronics or electromagnetics guy at all, I don't even like it particularly and I was glad that I walked away from working on a bench. I threw all my TTL and CMOS chips and components and power supplies away more than 20 years ago.

So stop your "you only know books" or "you're stuck in a box" or "you don't do real experiments" nonsense. It's just used as a fake talking point "weapon" or as a diversionary tactic when things aren't going the way you thought they were supposed to be going or you or others want to try to hurt my credibility because I am talking straight.

This would be a typical example: "Show me how you started a car with a dead battery." Response: "You don't do experiments." It's pure nonsense.

MileHigh

And yet the diamond needle dosnt destroy the soft vinyl record like science says it should.
How is it that the hardest substance on earth dosnt just cut straight through those smale plastic bumps in the vinyl tracks?. Over and over you can play your record's without damage from a material that cuts the hardest of steels.--?one for the books MH.

So many things that good old science has the answers for,and yet never produced. 9 times out of 10,it comes from people that are no ruled by book's. For example-the plane. We all know that it is scientifically possible ,but the science guru's never came up with the plane--powered flight. It cam from a couple of brothers that owned a bicycle shop,that said--yes we can. They were the guys that did the job through experiments,and trial and error--not from book's.
In fact,most great discoveries came from trial and error,and the science to explain it came after.
The good old bumble bee was flying long before science worked out how it could do it--this was after some decided that it was an aerodynamic impossibility-now they know better.

There are many thing's left that science and books are yet to explain,and many of those discoveries will be made by those not ruled by book's,or some one elses science and law's.
Funny thing about scientific laws MH,is that they really are not laws at all--there a !best guess! based around only what we have observed so far. These are man's law's im talking about,not those set by nature it self.

If we are to stick with the book's MH,then there is no stone left unturned. But we here,and on other forums,choose to turn over the stones that are still face down. In the next ten years,i feel that you will see first hand how obsolete your books are,and the new discoveries will once again,be made by those that follow no such rules.

Brad

tinman · « **Reply #469 on:** February 26, 2016, 03:53:19 PM »

author=MileHigh link=topic=8341.msg475491#msg475491 date=1456418556]
Bill:

Quote

The way I think is the from the first school of thought. You can indeed make a wise choice for the value of the base resistor such that the Joule Thief switches normally during the full battery voltage range of 0.3 to 1.5 volts. The fact that the LED gets dimmer as the battery voltage drops is fully expected and it is just a fact of life for a simple Joule Thief circuit.

MileHigh

So show us your smart's MH--design a simple circuit that lowers the base resistance as the voltage in the battery drop's. You pride your self on bench time and knowledge,so show us some of that smarts. You draw up the circuit,and i'll spend the time and money putting it together,and testing it. I'll post the results and video's here.

Brad

Magluvin · « **Reply #470 on:** February 26, 2016, 06:49:22 PM »

Quote from: tinman on February 26, 2016, 03:53:19 PM

author=MileHigh link=topic=8341.msg475491#msg475491 date=1456418556]
Bill:

MileHigh

So show us your smart's MH--design a simple circuit that lowers the base resistance as the voltage in the battery drop's. You pride your self on bench time and knowledge,so show us some of that smarts. You draw up the circuit,and i'll spend the time and money putting it together,and testing it. I'll post the results and video's here.

Brad

While im at work, a lot of the time my mind is on this stuff. You and I are on the same plane it seems. I had thought of the 'exact' same thing.

To have the base control adjust as the batt voltage goes down. Not sure of a self adjusting resistor but using another transistor(circuit) configured to do the job.

Good thought bud.

Mags

Pirate88179 · « **Reply #471 on:** February 26, 2016, 08:43:17 PM »

Quote from: tinman on February 26, 2016, 03:53:19 PM

author=MileHigh link=topic=8341.msg475491#msg475491 date=1456418556]
Bill:

MileHigh

So show us your smart's MH--design a simple circuit that lowers the base resistance as the voltage in the battery drop's. You pride your self on bench time and knowledge,so show us some of that smarts. You draw up the circuit,and i'll spend the time and money putting it together,and testing it. I'll post the results and video's here.

Brad

I had thought about this as well but dismissed it as I "assumed" the resistance adjusting circuit would waste more energy than it was worth. Maybe I was wrong?

Bill

sm0ky2 · « **Reply #472 on:** February 26, 2016, 10:34:15 PM »

Quote from: tinman on February 26, 2016, 03:53:19 PM

MileHigh

So show us your smart's MH--design a simple circuit that lowers the base resistance as the voltage in the battery drop's. You pride your self on bench time and knowledge,so show us some of that smarts. You draw up the circuit,and i'll spend the time and money putting it together,and testing it. I'll post the results and video's here.

Brad

it is a difference in thinking. or perspective, point of view, etc.

in one side, you can preserve the AC wave properties of the inductor.

on the other, you can simply switch digitally, and the whole circuit acts similar to a simple boost converter.

https://en.wikipedia.org/wiki/Boost_converter

while, yes you can test this and it will give some results, (ooh, the LED lights up!!)
it will only give insight on one way of thinking.

to understand how a battery voltage can be increased to light up an LED, you can look for those properties that do so.

To understand what goes on inside a Joule Thief,...
throw the LED out the window..... it causes more problems with analysis than it benefits from the light it produces.
the Joule Thief "does" a lot more things than just boost the voltage from a DC source, to turn on a light emitting diode.

now,- MH may provide us with a circuit to "test".

But let us "test" a JT circuit, with no diode.

and let us test it using a single inductive loop, wrapped around the ferrite (preferably opposite the JT primary coil).
one turn, to the scope.
This gives us a representation of the magnetic waveform through the ferrite.
In this manner, the circuit can be viewed from the perspective of the inductor, while resistance is changed at the base.

This can be expanded by multiple turns on the secondary winding, to further boost the voltage, and impedance in the load-side of the circuit.
This separates any load, to the output side of the transformer. So only the inductive properties affect the operating frequency.

sm0ky2 · « **Reply #473 on:** February 26, 2016, 11:09:33 PM »

there is only one effective "school of thought".

it is that which is taught in schools

transistors "switching properly"
inductors in the "normal range of operation"

we all have gone over the mathematics of recent days,
we know the circumstances where this "school of thought" explicitly instructs us NOT to go.
Why? What happens when we go there?
capacitors explode, wires burn up, resistors, diodes and transistors fail.
all this happens in circuits that were designed to be well within the tolerances of the components involved.

There are reasons we are taught NOT to do these things.

I will not ignorantly claim these energies to be "overunity" by any definition of the term.
by the contrary, all of the energy involved, we ourselves put into the circuit.

the difference in this "school of thought", is that the normal operation of a circuit,
we throw it all away.

it is our practice to dump everything to circuit ground.

not to loop it back around through itself.

here is one example of a different "school of thought".
this circuit as
proposed by one of our peers, for analysis of the feedback loop.
was presented to me recently.

the effects of this are most prominently demonstrated
as the timing through the feedback loop approaches a phase balance with the input frequency.
the results are quite interesting

[note that this is half-wave AC rectification, and behaves quite differently than its Pulsed DC square wave digital counterpart]

MileHigh · « **Reply #474 on:** February 26, 2016, 11:18:58 PM »

Quote from: tinman on February 26, 2016, 03:53:19 PM

author=MileHigh link=topic=8341.msg475491#msg475491 date=1456418556]
MileHigh

So show us your smart's MH--design a simple circuit that lowers the base resistance as the voltage in the battery drop's. You pride your self on bench time and knowledge,so show us some of that smarts. You draw up the circuit,and i'll spend the time and money putting it together,and testing it. I'll post the results and video's here.

Brad

You have to back up first. Who says that you need a variable resistor for a Joule Thief? I am not aware of that requirement. The only thing that I am aware of is that it was done all the time in the old days of this thread, presumably without any serious circuit analysis or scope work done to see what was happening. It was just an anecdotal observation that the LED changed in intensity when you changed the base resistance.

You are suggesting it so it suggests a question for you: Why do you want to have a variable base resistor in a standard Joule Thief?

With respect to a voltage-controlled resistor, I did what anybody would do. I did a Google search. I saw techniques that used an FET in its linear range which seems reasonable. I saw more sophisticated techniques using operational amplifiers and others using opto-isolators. However, there are going to be constraints and limitations with each one of these techniques, and it's undetermined if one of these methods would plug into a standard Joule Thief. What about power consumption issues?

So for starters, how about backing up. Why do you want to have a variable base resistor in a standard Joule Thief?

MileHigh

sm0ky2 · « **Reply #475 on:** February 26, 2016, 11:35:41 PM »

Quote from: Pirate88179 on February 26, 2016, 08:43:17 PM

I had thought about this as well but dismissed it as I "assumed" the resistance adjusting circuit would waste more energy than it was worth. Maybe I was wrong?

Bill

if the inductance and impedance factors are "just right" within the oscillator,
it does not need to be adjusted very often. (depending on the load).
superbrights seem to give the best light -to- energy ratios, which lead to longer run times.

it seems as though the older LED technology uses a lot more energy to produce the same amount of "light".
if it takes say 6 older LEDs to equal one superbright of the same lumens. then you compare the current draw through all 6 in series, or parallel.
compare to the current draw through the superbright, we get more "light" for our $

I speak of light , lightly.,.. as I am currently experimenting along theories that state there is no quanity of a photon.
since a single photon can diverge, each photon can be represented as an infinite number of photons?
as well as that an electron can emit an infinite number of photons during its' existence.

MileHigh · « **Reply #476 on:** February 26, 2016, 11:49:09 PM »

Quote from: tinman on February 26, 2016, 03:43:45 PM

And yet the diamond needle dosnt destroy the soft vinyl record like science says it should.
How is it that the hardest substance on earth dosnt just cut straight through those smale plastic bumps in the vinyl tracks?. Over and over you can play your record's without damage from a material that cuts the hardest of steels.--?one for the books MH.

So many things that good old science has the answers for,and yet never produced. 9 times out of 10,it comes from people that are no ruled by book's. For example-the plane. We all know that it is scientifically possible ,but the science guru's never came up with the plane--powered flight. It cam from a couple of brothers that owned a bicycle shop,that said--yes we can. They were the guys that did the job through experiments,and trial and error--not from book's.
In fact,most great discoveries came from trial and error,and the science to explain it came after.
The good old bumble bee was flying long before science worked out how it could do it--this was after some decided that it was an aerodynamic impossibility-now they know better.

There are many thing's left that science and books are yet to explain,and many of those discoveries will be made by those not ruled by book's,or some one elses science and law's.
Funny thing about scientific laws MH,is that they really are not laws at all--there a !best guess! based around only what we have observed so far. These are man's law's im talking about,not those set by nature it self.

If we are to stick with the book's MH,then there is no stone left unturned. But we here,and on other forums,choose to turn over the stones that are still face down. In the next ten years,i feel that you will see first hand how obsolete your books are,and the new discoveries will once again,be made by those that follow no such rules.

Brad

These are just a bunch of tired old cliches that aren't true Brad. The needle and the record player? A materials scientist or a mechanical engineer could explain that to you in intimate detail. The most basic fact is that the needle is not sharp and doesn't cut into the vinyl. Clearly the vinyl is strong enough to sustain the typically one gram force of the needle that rides on two tiny spots of vinyl as the groove moves past. You can look it all up in books. The Wright brothers were science gurus and used the scientific method to successfully engineer their airplane. They did serious research and experiments, you are grossly underestimating how they achieved their goal. The bumblebee is just another cliche, and I think that somebody even ran the computational fluid dynamics on a supercomputer to "prove" that the bumblebee could fly. The algorithms and the number crunching simply weren't around to do that decades ago.

Most of the laws really are laws, and they are Nature's laws. The laws that govern how circuits work are basically the same laws of physics that people are familiar with in the physical world. I am just talking basic stuff, not relativistic stuff.

There are also new books being written all the time about new stuff. That's why you can go out and buy an 8-terrabyte hard drive and turn your vast collection of 6000 Blu-Rays and DVDs into files and put them on your hard drive.

Tons of new stuff will be discovered in the future, and new laws may get written and even old laws may be overthrown or tweaked. However, when I spin up a flywheel the laws that govern/describe its operation are not ever going to change. Same thing applies to a coil.

MileHigh

MileHigh · « **Reply #477 on:** February 27, 2016, 12:45:56 AM »

Smoky1:

Quote

in one side, you can preserve the AC wave properties of the inductor.

on the other, you can simply switch digitally, and the whole circuit acts similar to a simple boost converter.

Look at the basic Joule Thief schematic again. If it's not switching then you are suggesting that a certain value of base resistance will keep the transistor partially conducting in some kind of meta-stable oscillation. It would be like when you lean back in your chair and you find yourself at that balance point where you don't know if you are going to fall backwards or not. Your arms and legs start to wiggle around as you struggle in your own uncomfortable state of meta-stability hoping that you fall forward and recover equilibrium and all goes back to normal.

Look at the L1 coil. What's going to happen? The L1 coil is going to be "yanked down" (to ground) by a meta-stable twitching transistor with what looks like a twitching resistance to ground. L1 is going to see what effectively looks like a meta-stable AC "yank down" superimposed on some DC "yank down."

Big deal, the L1 has one side tied to +1.5 volts and the other side of L1 is connected to a twitching transistor. So it will respond to that stimulation like any coil will respond to some kind of signal applied to it. It's not quite a conventional AC impedance response, it's more of a response to a meta-stable wobbling DC with another meta-stable wobbling AC superimposed on it. Or more accurately you can say there is a DC voltage source on one side of the coil and a funky skittish meta-stable variable resistance to ground on the other side of the coil. SO WHAT? A crazy skittish meta-stable resistor is trying to induce current to flow through the L1 coil. Are you expecting the parting of the Red Sea or something?

In your scenario the L2 signal that drives the base resistor is just the inverse of the skittish meta-stable voltage seen at the bottom of the L1 coil. That is effectively the "French tickler feedback" that keeps the transistor in some kind of spastic meta-stability.

The whole "meta-stable transistor in a quivering Joule Thief like some spastic guy permanently balanced on a backward leaning chair" really means nothing. Basic circuit analysis can explain it all. There is no mystery to uncover, no mystique, no "hidden knowledge that 'they don't want to teach you.'"

It's just a spastic Joule Thief tweaked into a meta-stable elliptic seizure because it is being tickled that does nothing special at all. Will the meta-stability get stable and settle down into a "resonance" oscillation frequency. It might do that you never know. But SO WHAT? What's so special about a transistor that is varying at a stable oscillation frequency because of feedback to the base such that it that it effectively energizes an inductor with a regular "yank down" and when the effective resistance of the transistor "oscillates high" some of the energy in the L1 coil gets dumped into the LED to light it up?

Some current will get induced into the L1 coil, and when the spastic transistor is at a temporary high resistance, some of the current from the coil will flow through the LED and light it up. Then the spastic transistor will start to conduct again, the LED will shut off, and more current will be induced into the coil. The process will repeat itself over and over which will effectively pulse the LED ON and OFF at a high frequency. Is there something profound happening here? The answer is no.

MileHigh

MileHigh · « **Reply #478 on:** February 27, 2016, 12:55:36 AM »

Quote

But let us "test" a JT circuit, with no diode.

I will just repeat what I said before: With no diode the L1 coil will simply slam a short pulse of current through the collector-emitter junction of the transistor. There will be a very short high-voltage pulse of current. L1 will force current through the presumably switched-off transistor.

Now, this will presumably mess up the normal timing of the Joule Thief where there is an orderly feedback signal back to L2 during the normal discharge of L1 through the LED. Will it still undergo a normal switching cycle when you remove the LED? I think the switching will stop completely therefore what I said in the first paragraph is probably more academic than real.

MileHigh · « **Reply #479 on:** February 27, 2016, 01:44:39 AM »

Smoky1:

Now I am going to play devil's advocate:

Quote

It's just a spastic Joule Thief tweaked into a meta-stable elliptic seizure because it is being tickled that does nothing special at all. Will the meta-stability get stable and settle down into a "resonance" oscillation frequency. It might do that you never know. But SO WHAT? What's so special about a transistor that is varying at a stable oscillation frequency because of feedback to the base such that it that it effectively energizes an inductor with a regular "yank down" and when the effective resistance of the transistor "oscillates high" some of the energy in the L1 coil gets dumped into the LED to light it up?

So let's assume for the sake of argument that you get better run times for the LED in this stable resonance/oscillation mode. It's a definite possibility, you never know.

So let's go back to something I said: The transistor briefly "oscillates down in resistance" and conducts and when that happens the LED goes off and the coil starts to energize. Then the transistor briefly "oscillates up in resistance" and the coil dumps some energy into the LED to light it up.

So you energize the coil in "small sips" and then the coil dumps those small sips of energy into the LED through "resonance."

When you strip that down to the bare bones, it's just like a DC-to-DC converter that pulses a coil for a very short time at a fairly high frequency and then dumps that energy into an output capacitor. I think a typical pulsing frequency is around 60 kHz and they only pulse the coil for a fraction of a time constant for the maximum efficiency (reducing i-squared-R losses.)

So just like you can buy a small very high efficiency DC-to-DC converter that switches at 60 kHz, you can buy a small very high efficiency DC-to-current converter that switches at a high frequency and the current output can be set to drive an LED.

So perhaps behind all the smoke and mirrors about a "resonant Joule Thief" the basic operating principle is essentially very similar to how a DC-to-DC converter operates. The fundamental principle is better efficiency through very small sips of energy that are then sent to the LED. This reduces resistive losses in the main L1 coil.

MileHigh

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