Joule Thief 101

[MileHigh]

Smoky2:

@ MH - I'm glad you learned how to use Google to help you learn things.

Your sarcasm is overwhelming.  There are probably about 20 instances in this discussion where I have pointed out things where you were wrong.  You conveniently ignored all of them.  You can hone your own Google skills right there.

You gave us a big discussion where you invoked damping and the s-plane and got into complex impedances and it all came down to this:

<<< Wo = (sqrt)[1/LC - (R/L)^2] - note that the resistance value (R) is different from the resistance through the primary current path.  >>>

That may or may not be right, I suppose that I could search on it.  I am not going to try to check what you did because I would have to relearn a lot of stuff to do it.  What you are saying may be credible, someone like Verpies would be the one to make that call.

However, what you have not done is this:

1.  Shown how a Joule Thief resonates as some kind of RLC circuit
2.  Shown the actual circuit and/or the equivalent circuit
3.  Shown the timing for the circuit
4.  Several times I have gone over how a Joule Thief is based around two L/R time constants and a switching circuit for the transistor with positive feedback and you have ignored that fact

It's all just talk with no substance to back it up.  What I have said to you is that for a RLC circuit with low resistance then the resistance doesn't factor into the resonant frequency.  That applies to series and parallel RLC circuits.  I was treating that as a separate discussion from a Joule Thief because a Joule Thief is not either type of RLC circuit and it does not resonate.

So if you want to actually show how a Joule Thief is an RLC circuit and resonates then by all means please do.  Because right now it's just a bunch of talk.  For example, you claim that the transistor is operating in its linear region when in a standard Joule Thief the transistor switches ON and OFF.  Like I said before, if you are talking about a hacked Joule Thief acting as an oscillator then it is not a Joule Thief anymore.

So you need to put some substance to what you are saying.

MileHigh

[MileHigh]

Wow, that is a lot more about this circuit than I even knew I did not know.  Thanks.

MH:

I always thought the JT was a tank circuit as I have always tuned mine to either the brightest light, or the lowest mA draw...these were never at the same resistance.  I thought, as Brad and others have said, that a coil has capacitance?  I have several JT's here that I can cut the input power to and the leds will continue to glow for more than a few seconds...not as bright as when the power was on but, certainly bright enough to see clearly so, that tells me the energy had to be "stored" somewhere right?  I had no other caps in the circuits which I am describing.  I always "assumed" that the stored energy was in the inductor and, if a device can store energy than it has capacitance right?

Those that know me know I am no electronics wiz by any means.  I have played and experimented with many variants of these circuits for about 7 years or so now, and I too am convinced that even the most basic JT has capacitance.

Am I wrong here?

Bill

Do you remember about six or seven years ago when people played with car ignition coils and hooked them up backwards so the hot lead from the ignition coil was connected to the earth ground and the ground lead of the ignition coil was connected to the electrical ground of the circuit under test?  Typically the circuit was a gutted CFL driver circuit powered by a battery if I remember correctly.  The net result was the entire setup was bouncing up and down at a fairly high potential with respect to the earth ground potential.  You could touch it anywhere with a neon and the neon would light up.  People would say that was "radiant energy."  More importantly, people would make a connection from the circuit to the earth ground with a wire and observe the CFL get brighter.  They would say, "Oh, power is coming up from the earth ground."  For about two years afterward people would be saying, "power is coming up from the ground."

The "radiant energy" and the "power coming up from the ground" were complete nonsense.  A similar "cult of nonsense" is clearly happening around a Joule Thief operating in its standard mode.

A Joule Thief operating as a Joule Thief normally operates is not a tank circuit.  It doesn't matter that the coil has a capacitance, any coil first and foremost acts like a coil and in a regular Joule Thief the coil acts like a coil.  You note that business is somewhat related to the "cult of a self-resonant coil" also.

There is a good chance that your Joule Thief LEDs glowed for a few seconds after you cut the power because of the stray capacitance in between the two battery leads.  That acted like a small capacitor charged to the battery voltage.  I can't say anything beyond that.  All of the experimenters with the new generation of cheap DSOs are in a great position to look into things like that because they can capture the waveforms.

MileHigh

[MileHigh]

Here is the first clip that I linked to that explains how a Joule Thief works:

https://www.youtube.com/watch?v=0GVLnyTdqkg

Here is another clip doing the same:

https://www.youtube.com/watch?v=Ddzwgxe4Q9o

Here is another clip that is very simplified and does not discuss the timing issues or the transformer action, but it does have a scope waveform which I captured:

https://www.youtube.com/watch?v=OQzA6EwoPlk

What all three clips have in common is that they explain how a Joule Thief is a pulse circuit.  There is no mention of an RLC circuit or resonance.

Look at the captured scope waveform for the LED and for the transistor base input.  That is the waveform of a pulse switching circuit, not a resonant circuit.

MileHigh

[tinman]

Nope, you aren't going to actually show how a Joule Thief is an RLC circuit and show how it operates as an RLC circuit because you can't.  You can't sketch out the circuit or sketch out timing diagrams to back up what you are claiming.  What you are doing is making up a word salad.




MileHigh

What is a JT to you MH? .Do you know why it is called a JT ?.
It was called a joule thief because it can drain a lot of the remaining energy(joules) from a battery that would otherwise be considered dead. There are many variations to the circuit that can achieve this,and not 1 circuit alone can be considered to be !the! joule thief circuit. You have posted the most common and simple circuit that you claim to be !the! JT circuit. You have posted the effect based around a circuit,in stead of a circuit based around an effect. This is like presenting a vehicle that suits tires,in stead of tires that suit the vehicle.

Also, the Joule Thief will not work as a Joule Thief, if it woks at all, without the inductive coupling between the two windings.  Saying it works because of "the C value of the transistor" is just more word salad.

Below is a scope shot of a joule thief working the way you say it will not. The scope is directly across the emitter/collector junction,and the coil that triggers the transistor is inside an old PM DC motor housing,where the coil is placed between the two large magnets within that housing,and eliminates any inductive coupling between the two windings. The supply voltage to the circuit is 1.02 volts,and yet the LED lights quite nicely

The fundamental timing and operation of a Joule Thief is based on L/R time constants and there is no resonance at play at all

Please see second scope shot showing the magnetic field of the driven coil by way of a sniffer coil.


-

the Joule Thief timing and operation is governed by the interaction between inductance and resistance and not capacitance.

It would seem that my JT dose not wish to comply to your rules MH.

Brad

[MileHigh]

Brad:

There are many variations to the circuit that can achieve this,and not 1 circuit alone can be considered to be !the! joule thief circuit. You have posted the most common and simple circuit that you claim to be !the! JT circuit. You have posted the effect based around a circuit,in stead of a circuit based around an effect. This is like presenting a vehicle that suits tires,in stead of tires that suit the vehicle.

With that kind of logic I can throw spaghetti against the wall and claim it is a Joule Thief also.  Sorry, but you are not going to make up the rules as you go along to suit your fancy and make everything you say "right."  Everybody knows what a Joule Thief circuit is.  If you have another circuit that you claim does what a Joule Thief does, then show it.

Below is a scope shot of a joule thief working the way you say it will not. The scope is directly across the emitter/collector junction,and the coil that triggers the transistor is inside an old PM DC motor housing,where the coil is placed between the two large magnets within that housing,and eliminates any inductive coupling between the two windings. The supply voltage to the circuit is 1.02 volts,and yet the LED lights quite nicely

No schematic, no explanation, no timing, no nothing.  Just a bunch of squiggly lines on a scope display that you claim is a "Joule Thief" to suit your fancy.

"The coil is placed between the two large magnets within that housing,and eliminates any inductive coupling between the two windings."   That's just more word salad.  You seemingly just made up a "rule" that a coil placed between two magnets will eliminate any inductive coupling between the two windings of the coil.  It's not true and you are right back at square one showing that you haven't grasped one of the most basic concepts in electronics.  Just make it all up as you go along to suit your fancy and please yourself.  Who cares about those pesky details.

Please see second scope shot showing the magnetic field of the driven coil by way of a sniffer coil.

All that I see is a squiggly line.  It could be a dial tone from a phone for all I know.

If you can't present substantive data to make your point, then it's all just a mushy word salad that means nothing.  Take a look at some of Itsu's clips and postings for his presentation style and reporting of his results and contrast that with what you are doing.

MileHigh