Joule Thief 101

[MileHigh]

Here is one of them WTF moments when your fooling around with circuits.
The circuit is as below,but i am now supplying the circuit with a voltage of 1 volt.
Looking at the scope shots,it appears that the transistor is still switched on after the inductive kickback spike starts

Brad

It is another WTF moment but not what you think and the timing shown in your scope shot is most likely unreliable.

This goes out to you and to all Joule Thief experimenters because I have seen this poor practice before:  Why would you put your scope probe right on the base input of the transistor?  There is a very high impedance signal there because the signal source is on the other side of a 1K resistor.  It's the perfect place to put a scope probe to disturb the operation of the device because the base input is the high-gain input of the switching device.

Why don't you put your scope probe on the other side of the 1K resistor, which is the output of the feedback coil L2?  That is a low impedance signal that will not really be affected by the presence of the scope probe.  That will show you the operation of the transformer in action.  You just have to look at the voltage at that point and at the same time to look at the potential of the collector to know precisely whether or not the base-emitter junction of the transistor is conducting or not and if the transistor is ON or OFF.  You need to put your scope probe on the base input of the transistor like a hole in the head.

MileHigh

[tinman]

It is another WTF moment but not what you think and the timing shown in your scope shot is most likely unreliable.

This goes out to you and to all Joule Thief experimenters because I have seen this poor practice before:   It's the perfect place to put a scope probe to disturb the operation of the device because the base input is the high-gain input of the switching device.

Why don't you put your scope probe on the other side of the 1K resistor, which is the output of the feedback coil L2?  That is a low impedance signal that will not really be affected by the presence of the scope probe.  That will show you the operation of the transformer in action.  You just have to look at the voltage at that point and at the same time to look at the potential of the collector to know precisely whether or not the base-emitter junction of the transistor is conducting or not and if the transistor is ON or OFF.  You need to put your scope probe on the base input of the transistor like a hole in the head.

MileHigh

MH
Im done with arguing with you.

You make error after error.
Examples.

Why would you put your scope probe right on the base input of the transistor?  There is a very high impedance signal there because the signal source is on the other side of a 1K resistor.

Because MH,the pot was turned right down to it's lowest resistance,so it would make no difference to which side the scope probe was on.

I am not going to even argue about the two positive-feedback regenerative cycles in a Joule Thief that snap the transistor ON and snap the transistor OFF.  It's a done deal and has been explained properly.

And my scope shot's clearly show you are wrong. Just think about how the coils are wound in your JT circuit MH-->surly you can work it out--you know how transformers work-dont you?.

Your scope shot is clearly not showing a Joule Thief running in it's normal operation mode so I am not going to discuss it right now.  It's just another case of crossed and jumbled up signals coming from you.

More rubbish  MH-->what do you think a JT circuit is designed to do-->thats right,run at low voltages,and be able to light an LED. We are looking at the operation of the JT circuit running at the voltages we want them to run at-->not MH's fully charged battery voltage.


Go back to your book's MH,and leave the experimenting to those that actually experiment.

You do what you want MH,but i will show those that are interested,what actually is happening in JT circuit's when running at the low voltages we want them to.

A competition MH-?. You build your JT based around what you think is going on,and i will build mine using what i believe is going on. We then see who can drain a AA battery down the lowest. Which one of us can design and build a JT circuit that will do the best job of what a JT circuit is designed to do-->drain the most energy from what would otherwise be considered a dead battery.
But we wont stop there MH. After we have done that,then we will see who can get a JT circuit to oscillate without any inductive coupling between the two coils.

So now it's time to put up or shut up MH. I have explained correctly how a(your) JT circuit operates at low voltages(which is what we want a JT circuit to do),and i have explained as to how the cool joule circuit operates without the inductive coupling between the two coils.
Like i said,(and i see you are not brave enough to question or argue with these guy's-1 of whom you sadly cannot),if you disagree with me on that,then take it up with Vortex1, physics Prof, Lidmotor,and a number of other guys that have successfully replicated my cool joule JT. Are you also going to say that MarkE was wrong?--No,i did not think so,you dont have the balls to stand against those guy's-do you.

So thats it MH--take up my challenge,and prove to everyone here that you know better than i ,or shut up.


Brad

[tinman]

@MH'

Think about what is happening with your JT circuit as the magnetic field is increasing in the toroid--L1 induces L2,and this sends more current to the base of the transistor--the transformer effect.
Now think about what happens to the current flowing in L2 when the magnetic field starts to collaps-->The voltage invert's,and the current flows in the opposite direction--unlike L1 where the current keeps flowing in the same direction. This pulls the transistor down/off during the flyback spike MH,not on. We can even place an LED across L2,and watch this happen -for those that do not have a scope.


Brad

[tinman]

Just messing around with the stator from a smart drive washing machine motor.


https://www.youtube.com/watch?v=z3YCpsEliRs


Brad

[MileHigh]

@MH'

Think about what is happening with your JT circuit as the magnetic field is increasing in the toroid--L1 induces L2,and this sends more current to the base of the transistor--the transformer effect.
Now think about what happens to the current flowing in L2 when the magnetic field starts to collaps-->The voltage invert's,and the current flows in the opposite direction--unlike L1 where the current keeps flowing in the same direction. This pulls the transistor down/off during the flyback spike MH,not on. We can even place an LED across L2,and watch this happen -for those that do not have a scope.


Brad

No kidding Brad, you are more or less explaining it properly here but insinuating that I did not say that.  It's just more confusion from you where you are not understanding what I am saying to you and what was said in the videos and explanations that I linked to.   I attached a schematic where I labeled L1 (main coil) and L2 (feedback coil to base resistor) so we can definitively standardize on this labeling for the two coils.

The output from L2 drops in potential first because the rate of change of current in L1 starts to decrease at the end of the energizing cycle.  That starts to turn the transistor off.  That initiates the collapse of the magnetic field in the toroid, which then makes the output from L2 drop even more in potential.  That is the regenerative cycle.

However, the current in L2 does not literally flow in the opposite direction but indeed the transistor is switched OFF.  L2 is simply generating EMF when the transistor is switched OFF.

That's one of the two positive feedback regenerative cycles.

MileHigh