Joule Thief 101

[MileHigh]

The Google search engine built into this web site works quite well.  I pulled up an old posting I made with my good old mechanical analogy for a Joule Thief.  Many people are aware that a perfect mechanical analogy for an inductor is a flywheel.  So, starting with a flywheel I "constructed" a mechanical analogy for a Joule Thief as an exercise bike:

<<<
Imagine you go to the gym and you find an old-style exercise bicycle.  The type with a seat and pedals and a chain link to a big flywheel, like a regular bicycle.  There is a friction belt that goes around the circumference of the flywheel.  You set the tension on the friction belt to adjust the difficulty level.

Imagine the belt is completely loose.  You pedal for a few seconds and get the flywheel spinning and then you stop pedaling.  Then you add tension to the belt and the flywheel spins down and stops.  Then you loosen the belt and repeat the whole process all over again.

Even when you are completely exhausted, it's still possible for you to pedal and get the flywheel spinning if you pedal slowly and take your time to build up the speed.  Don't forget that the friction strap is loose when you pedal.

That's a Joule Thief.  You are the battery.  The flywheel is the coil.  The friction belt is the LED.

The torque that you put on the flywheel from pedaling is the battery voltage.  The torque that the flywheel puts on the belt during the braking is the coil voltage when it's de-energizing.  The rotational speed of the flywheel is the current through the coil.
>>>

So that might be mysterious for some or make perfect sense for others.   Just about anything that you can do with a coil with respect to energy dynamics and circuit behaviour can be replicated and simulated in the mechanical world with a flywheel.

MileHigh

[sm0ky2]

The Google search engine built into this web site works quite well.  I pulled up an old posting I made with my good old mechanical analogy for a Joule Thief.  Many people are aware that a perfect mechanical analogy for an inductor is a flywheel.  So, starting with a flywheel I "constructed" a mechanical analogy for a Joule Thief as an exercise bike:

<<<
Imagine you go to the gym and you find an old-style exercise bicycle.  The type with a seat and pedals and a chain link to a big flywheel, like a regular bicycle.  There is a friction belt that goes around the circumference of the flywheel.  You set the tension on the friction belt to adjust the difficulty level.

Imagine the belt is completely loose.  You pedal for a few seconds and get the flywheel spinning and then you stop pedaling.  Then you add tension to the belt and the flywheel spins down and stops.  Then you loosen the belt and repeat the whole process all over again.

Even when you are completely exhausted, it's still possible for you to pedal and get the flywheel spinning if you pedal slowly and take your time to build up the speed.  Don't forget that the friction strap is loose when you pedal.

That's a Joule Thief.  You are the battery.  The flywheel is the coil.  The friction belt is the LED.

The torque that you put on the flywheel from pedaling is the battery voltage.  The torque that the flywheel puts on the belt during the braking is the coil voltage when it's de-energizing.  The rotational speed of the flywheel is the current through the coil.
>>>

So that might be mysterious for some or make perfect sense for others.   Just about anything that you can do with a coil with respect to energy dynamics and circuit behaviour can be replicated and simulated in the mechanical world with a flywheel.

MileHigh

Correction

the proper physical analogy to this circuit is a weight on a spring.
when dropped the weight oscillates exactly like the RLC

the inductor acts like a gravity well

resistance is analogous to friction in this case.
The difference is, unlike reluctance, the gravitational gradient is not affected by a change in frequency.
(that is to say at velocities that are far below relativistic terms)

[tinman]

Brad:

You are doing nothing more than playing a bait and switch game again.  It's very frustrating.

I showed you a standard Joule Thief circuit and you said, "That's an RLC circuit."  That's wrong - it's not an RLC circuit.

Now you are pulling off the switch and saying, "Oh no, there are many Joule Thief type circuits and I am talking about other circuits."

The answer to that is no - no bait and switch nonsense is acceptable.

Nor am I convinced that the other circuits will do what you are saying.  If you want to make a case and demonstrate what you are saying then fine, but throwing words at the issue like you are throwing spaghetti against the wall is not going to work and the spaghetti is not sticking.  Electronics simply doesn't work like that and you actually have to put some substance behind what you are saying.

MileHigh

Is the below not !your! JT circuit MH?.
It works quite fine without any inductive coupling between the two coils.
How dose it do this without the C in the LRC circuit MH ?.

Like i said--there is not just one JT circuit,and you clearly stated that the JT circuit is an LR circuit only-long before you posted a diagram of 1 JT circuit. But even that circuit you posted !is! an LRC circuit-otherwise the circuit below would not oscillate.

https://www.google.com.au/search?q=joule+thief+circuits&espv=2&biw=1024&bih=634&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwj1rLj5xPnKAhXMFZQKHbdhDSQQsAQIJA

Brad

[MileHigh]

Correction

the proper physical analogy to this circuit is a weight on a spring.
when dropped the weight oscillates exactly like the RLC

the inductor acts like a gravity well

resistance is analogous to friction in this case.
The difference is, unlike reluctance, the gravitational gradient is not affected by a change in frequency.
(that is to say at velocities that are far below relativistic terms)

Here is the "big surprise":  I described a Joule Thief in its normal operating mode as a pulse circuit.  Note I described the energy dynamics only and I did not make any reference to a timing system.   An exhausted peddler on a exercise bicycle can still muster up enough energy to make the flywheel spin because the belt providing resistance setting is slack.  That is analogous to a nearly dead battery that can still get current to flow through the coil.  It's all about the basic energy dynamics taking place in a Joule Thief:  All that a Joule Thief does is energize an inductor and then releases that stored inductor energy into an LED load.  Since a discharging inductor is a current source it can discharge just as easily through 10 LEDs in series as a single LED.

When are you going to get over this resonance fetish?  It's like trying to jam a square peg into a round hole with you.

As far as your analogy goes, you don't have a sample electrical circuit to base it on so that's not too good.  You have yet to show any Joule Thief operating in "resonance" - it's all just talk and talk is cheap.

The inductor acts like a gravity well?  Are you referring to the spring perhaps in an oblique way?  Nor do you have an equivalent to a battery source in your analogy.

MileHigh

[MileHigh]

Is the below not !your! JT circuit MH?.
It works quite fine without any inductive coupling between the two coils.
How dose it do this without the C in the LRC circuit MH ?.

Like i said--there is not just one JT circuit,and you clearly stated that the JT circuit is an LR circuit only-long before you posted a diagram of 1 JT circuit. But even that circuit you posted !is! an LRC circuit-otherwise the circuit below would not oscillate.

https://www.google.com.au/search?q=joule+thief+circuits&espv=2&biw=1024&bih=634&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwj1rLj5xPnKAhXMFZQKHbdhDSQQsAQIJA

Brad

No, they are not Joule Thief circuits because it looks almost certain that they will not have the same performance as a Joule Thief when it comes to extracting energy from a nearly dead battery that has a low voltage-high impedance output.

All that you are really doing is baiting and switching yourself in a case like this.  You were playing around with Joule Thief circuits and you stumbled across the "Cool Joule" circuit and decided for yourself that it was a "Joule Thief."  It simply does not work like that.

Lidmotor is a great guy and he replicated your circuit for fun, but made no claims and did no serious investigation into how the circuit actually works.  He simply had fun and did a demo clip only.  The same thing applies to the two other clips, they are just demo clips with zero analysis of the circuit and zero explanation of the operation of the circuit.

Neither did you make any attempt at all to explain how your circuit worked.  That's not electronics Brad, it's just show and tell and don't explain.  As TK said many times and I echoed him, you are not doing an experiment, your are just observing and nothing more than that.

Those circuits that you see in the clips and the circuit schematic that you posted are simple oscillators based on amplification and feedback.  They are basically like having a microphone and a PA system and pointing the microphone at the speakers and getting high-pitched feedback.  The base input of the transistor is like a microphone and the input is being "tickled" by the coil.  Sometimes even thermal noise in the circuit is enough to get the feedback going to start the oscillation.  Since the transistor is firing you take advantage of that to energize an inductor and light an LED.

You guys are blindly saying there is no coupling between one coil and the other coil.  Well, I hate to tell you this but there is some kind of coupling taking place somewhere to get the positive feedback oscillation going.  It could be inductive, it could be capacitive, it could be just from coupling in the local interconnect wires in the immediate vicinity of the transistor.  There is absolutely nothing new and nothing special about an amplification stage (the transistor) spontaneously causing a feedback oscillation.  Among other things, I am pretty sure the gain of the transistor itself will affect the frequency - higher gain, higher frequency.

Perhaps the biggest issue is that you yourself have no clue exactly how and why the circuit is oscillating.  It's not necessarily easy either because sometimes just putting a scope probe on the circuit may stop the oscillation.  This is just a "black box" show and tell and you don't know what's inside the black box.

But going back to the standard Joule Thief, I believe that when the battery is even below the switch-on voltage for the base-emitter diode in the transistor, the Joule Thief can still operate and keep switching on the transistor.  That's because the "primary" side of the transformer can still boost the battery voltage before it gets to the transistor base resistor.  The "Cool Joule" is nothing more than an oscillator that takes advantage of the transistor switching to do the old coil-light-an-LED trick, but there are no extra tricks to keep it running when the battery voltage gets very low.  So it's not a Joule Thief because it does not do anything special to extract energy from a very-low-voltage battery.

Like i said--there is not just one JT circuit,and you clearly stated that the JT circuit is an LR circuit only-long before you posted a diagram of 1 JT circuit.

You are not going there Brad.  You have been fully aware of what the standard Joule Thief circuit is for years and you are fully aware that that's exactly what I have been talking about.

But even that circuit you posted !is! an LRC circuit-otherwise the circuit below would not oscillate.

It is absolutely NOT an LRC circuit.  There isn't even a capacitor in the schematic and if hypothetically you could somehow remove all of the stray/parasitic capacitance in the circuit the standard Joule Thief would still operate perfectly.  Time to get real and stop this nonsense talk.

MileHigh