Joule Thief 101

[Magluvin]

Ive figured that the shorted winding just causes the inductance of the primary and trigger windings to be much lower than without the shorted winding.

In a normal say 60hz transformer, if we short out a winding it causes the primary to pull lots of current from the source. But here it is different because the operating freq of the JT depends on the reactions in the transformer, and with the shorted winding the drive coils inductance is lowered and the circuit self adjusts to operate at a much higher freq. But with a normal 60hz transformer, the input doesnt change so the input current rises hard.

Got the thing to get up to 2.5mhz but at that point the led is fairly dim. Havnt seen any resonant nodes so far. I tried some caps on the 3rd coil and there seems to be certain band widths that the led jumps to a decent brightness and jumps back down when out of that band width. But nothing brighter than normal running.

Id like to make a new thread to work on JT mods experimenting with resonance, but I dont want it to become a thread like this one has become in the past days. And there are sooo many JT threads that Im not sure another should be made.  Stumped on that idea.  If I title the thread for JT Mods Experimenting with resonance, then there shouldnt be any bickering about resonance because the thread should be about how to get the JT to have resonance. But I dont believe that would be enough to keep the thread on target.

Still fiddling with it.

Mags

[Pirate88179]

Ive figured that the shorted winding just causes the inductance of the primary and trigger windings to be much lower than without the shorted winding.

In a normal say 60hz transformer, if we short out a winding it causes the primary to pull lots of current from the source. But here it is different because the operating freq of the JT depends on the reactions in the transformer, and with the shorted winding the drive coils inductance is lowered and the circuit self adjusts to operate at a much higher freq. But with a normal 60hz transformer, the input doesnt change so the input current rises hard.

Got the thing to get up to 2.5mhz but at that point the led is fairly dim. Havnt seen any resonant nodes so far. I tried some caps on the 3rd coil and there seems to be certain band widths that the led jumps to a decent brightness and jumps back down when out of that band width. But nothing brighter than normal running.

Id like to make a new thread to work on JT mods experimenting with resonance, but I dont want it to become a thread like this one has become in the past days. And there are sooo many JT threads that Im not sure another should be made.  Stumped on that idea.  If I title the thread for JT Mods Experimenting with resonance, then there shouldnt be any bickering about resonance because the thread should be about how to get the JT to have resonance. But I dont believe that would be enough to keep the thread on target.

Still fiddling with it.

Mags

There is no resonance in a JT circuit.


Yes there is.


No, there isn't.


Yes there is.


No, there isn't.


Is too.


Is not!


Too!


Not!




Mags, that is what your topic would look like.


Bill

[tinman]

Ive figured that the shorted winding just causes the inductance of the primary and trigger windings to be much lower than without the shorted winding.

In a normal say 60hz transformer, if we short out a winding it causes the primary to pull lots of current from the source. But here it is different because the operating freq of the JT depends on the reactions in the transformer, and with the shorted winding the drive coils inductance is lowered and the circuit self adjusts to operate at a much higher freq. But with a normal 60hz transformer, the input doesnt change so the input current rises hard.

Got the thing to get up to 2.5mhz but at that point the led is fairly dim. Havnt seen any resonant nodes so far. I tried some caps on the 3rd coil and there seems to be certain band widths that the led jumps to a decent brightness and jumps back down when out of that band width. But nothing brighter than normal running.

Id like to make a new thread to work on JT mods experimenting with resonance, but I dont want it to become a thread like this one has become in the past days. And there are sooo many JT threads that Im not sure another should be made.  Stumped on that idea.  If I title the thread for JT Mods Experimenting with resonance, then there shouldnt be any bickering about resonance because the thread should be about how to get the JT to have resonance. But I dont believe that would be enough to keep the thread on target.

Still fiddling with it.

Mags

Moderate your thread mag's,and just remove the junk.


Brad

[sm0ky2]

The 3055 transistor is "kicked" into oscillation in the first place even though the voltage supplied seems too low, by ... wait for it... .stray capacitance. Once it starts oscillating, then it's getting plenty of base voltage because of the 8:1 transformer. Again, this effect may be easier to see with other transistors, which will need more stray capacitance to start oscillating (like by touching the Collector or Emitter lead with a finger or a small cap lead.) And all 2n3055s are not created equal... this is an extremely common transistor to be "faked" by unscrupulous Chinese sources. Performance varies wildly.

TK:

Nope, see my previous posting.  The transistor is initially "kicked" on by pure transformer action.  There is a regenerative cycle (positive feedback) to turn the transistor ON, and a regenerative cycle (positive feedback) to turn the transistor OFF.

Brad, the floor is yours.

MileHigh

You are both correct from different perspectives, in that the feedback IS related to a stray capacitance value.
And while a "current" cannot be measured prior to the transistor switching on, there IS a voltage induced at the base of the transistor.

[sm0ky2]

unfortunately Bill speaks the wisdom of the ages.

Even if you stated resonance as a prerequisite of experiment,
there would still be those that subject the topic to conjecture, and disinformation.
(I think I may have attempted that at one time, when I was less articulate in discussions of this topic)

I can give you a (generic) set of guidelines, that may vary slightly, depending on the particulars of your design.
That may help identify if your particular circuit is able to converge with resonant nodes of the various parts of the circuit.
an "ideal" situation would be to have every component, and every portion of the circuit at resonance,
however, this is sometimes more difficult that I made it seem in the words of my previous posts.
Mathematically, we can see how this is done, as I have shown.
But in reality, even the tiniest resistances and capacitances from our wiring can change the resultant frequency node, and where it lay on the scale of frequencies the device can operate at.

this is why I recommended using your oscilloscopes

It simplifies the whole ordeal because (provided your scope is of quality) the mathematics are performed for you by the machine.

I recommend starting with the standard setup, (LED in either location), the only modification is the use of a VR instead of the set resistance at the base of the transistor.

1) The first step should be taking the transistor out of digital mode. With a scope across the Emitter and the center tap of the coil,
  adjustments are made to the base resistor until this signal closer resembles a sine-wave, than a sharp peak and long slope.
There is a range in which this occurs, depending on the transistor, this can be a very small range in resistances.
The actual frequency data is available from the manufacturer, labeled: linear mode, or linear freq range, etc.
to give you a guideline of what you are looking for.

2) expand your scope image, so that you can see the fluctuating details within the signal. You don't need to go TOO deep, just enough that the little spikes and whatnot are visible to you on the screen.
   Now, within the range of step 1, so that you don't throw the switch back into digital mode, make adjustments to the base VR,
to attempt to locate nodes that clean up the spikes, a smoothing effect will occur, and you may notice certain of those little spikes getting larger. (this looks like a problem, but let it be, it actually raises the RMS of the total signal amplitude)
What you are doing here, in a sense, is reducing the amount of conflicting feedback, that damages the quality of the signal.
Or as I state it: bringing the system closer to a "total circuit resonance".
or minimizing destructive interference.

3) Pay close attention to the quality of your coils, not just the number of turns, but where the first and last turn begin and end, as well as the straightness of the wire and spacing between coils / slope.
This may seem trivial, but when you examine what this does to the circuit, imperfections create variances in capacitance and inductance along the length of the coil. This can destroy some of the effects of positive feedback.

There are more, most of which I have already gone over last week, so will not regurgitate here.
But an important thing to remember, about resonance:
Your scope is your friend, scoping multiple parts of the circuit and comparing changes in one, to changes in the other.
This will assist in  identifying destructive interference (negative feedback), and otherwise signal disrupting events occurring within the circuit.

Quality is important, not just peak values.
resonance has pure qualities, an inverse or reflection of itself.
anything other than that is disruptive.