Joule Thief 101

[picowatt]

I have not seen a post from PW that states i am wrong

Because I never said you were wrong.  I only stated that up until then you did not actually measure the increase in base current but were making assumptions based on proxies.  What I will state is that it is very possible that either or both of Vce and Ic are likely changing as you decrease the resistance seen at the base.

But again, you need to measure that to be able to state that for sure.  Vce is fairly easy.  Put a scope probe on the Q1 collector and change the base resistor between the two values.  Crank up the VPD so you are using the full screen and note the collector voltage during the on time.

The Q1 collector current is a bit more difficult if the diff measurements are a problem.  The CSR in the emitter leg may be the only option at this point.  Using as small a value as possible will reduce degeneration.  Try the 10R first, you can always change it to 1R later.

PW

[tinman]

Yes that doesn't surprise me.  However, I believe there is a possibility that you can get avalanche effects, so perhaps a few nanoseconds could get the ball rolling.  Or the transistor is old and beaten up and not meeting spec any more.

My first impression was that there was a breakdown in the transistor itself, so perhaps you will get to the bottom of it and find out one way or another.  It looks very jarring to see that negative pulse of current.

MileHigh

The transistor is brand new,i bought 10 of them last week.
I can how ever change it out for another,as i have had new faulty transistors before.

I am hoping Mag's will carry out the same test,as i am interested to see if he gets the same result's.

I have found the video that touches on the miller capacitance effect that was linked to me by a fellow researcher when we were looking into the operation of the cool joule circuit.
Maybe this will help explain thing's?.

https://www.youtube.com/watch?v=Op_I3Ke7px0

Brad

[MileHigh]

Brad:

I have found the video that touches on the miller capacitance effect that was linked to me by a fellow researcher when we were looking into the operation of the cool joule circuit.
Maybe this will help explain thing's?.

Pointing at somebody else's clip for a different circuit is total BS.  You want to explain how a Cool Joule works?  Do an exercise just like you see in that clip for your own circuit.  A "drive by" "throw spaghetti against the wall" "explanation" will not cut it, period.

MileHigh

[picowatt]

The transistor is brand new,i bought 10 of them last week.
I can how ever change it out for another,as i have had new faulty transistors before.

I am hoping Mag's will carry out the same test,as i am interested to see if he gets the same result's.

I have found the video that touches on the miller capacitance effect that was linked to me by a fellow researcher when we were looking into the operation of the cool joule circuit.
Maybe this will help explain thing's?.

https://www.youtube.com/watch?v=Op_I3Ke7px0

Brad

I use FET/bipolar cascode circuits every day in low noise/low THD amplifiers designed to reduce Miller effect. 

Regarding the V_EB breakdown issue, I am a bit perplexed as to how you are able to produce a waveform on the base that exceeds -8.5VDC or so.  I think we have seen up to -16V or so on your base waveforms (correct me if I am wrong).

My breakdown test was with the collector open.  I have since applied 20VDC to Vce while applying the negative voltage to  Vbe with no change in the Vbe breakdown voltage, which was again -8.6V. 

You might try measuring the Vbe breakdown voltage of your flavor of 2N3055.  Set your supply to its lowest current setting or put a several K resistor in series with the base (I did both using 4K resistor).  Connect the supply so that it applies a negative voltage between the base and emitter while measuring across the base and emitter.  See where the voltage gets clamped (similar action to that of a zener).  You can of course ground the base and apply a positive voltage to the emitter, its all relative (making the emitter ground and the base negative allowed me to apply a positive voltage between the collector and emitter as well)

PW

[MileHigh]

Brad:

How on earth can any of that happen if the two coils fields cancel each other out?

Did anybody say that they completely cancel each other out?  Presumably you have a large current in L1 and a comparatively smaller current in L2, for both a high and low base resistance.  That means that the current flowing in L2 takes a slice out of the magnetic energy built up by the current flowing in L1, but does not completely cancel it out by any means.

Even better, look at a toroid and the winding directions and the direction of the current flow for the two coils that make up the Joule Thief transformer and figure it out for YOURSELF.  Don't just blindly assume that you are right.  Blind assumption gives you a 50-50 chance of being right and you are wrong.

In post #1202 PW is mistakenly referencing a different subject.

Does current flow in L2 reduce the magnitude of the magnetic energy stored in the toroid that was built up by the current flow in L1?  The answer to that is yes, and TK and PW also stated that.  Go find the references yourself.

MileHigh