Joule Thief 101

[tinman]

 



In these recent captures, there is no evidence that the base voltage is exceeding the Vbe breakdown voltage (I believe Tinman measured his 2N3055's as breaking down around 20 volts)

PW

To quote post 1219
The Breakdown voltage of the 2n3055s i use is 15.3 volt's.

Exceeding the base-emitter reverse breakdown voltage of Q1 does not turn on the collector-emitter junction.

Correct.
I am not sure why MH is talking about collector/base junction breakdown.

The spike seen in the recent "death spike" capture looks more like a Miller current spike than as being due to Vbe breakdown current.

That is also correct !some what! PW.
If we look at the scope shots below,even though the voltage is above the 15.3 volt breakdown voltage,current continues to flow below the 15.3 volt threshold. But i believe that the bulk of this! so called! current flow is happening around the breakdown voltage limit.

The first scope shot is across the base/emitter junction,and shows a voltage value peak of about 20 volt's.
The second scope shot is from across the 1k base resistor,and you can see that current is (apparently ) still flowing well below the 15.3 volt junction breakdown threshold.

!BUT! there is something odd with this !so called! current flow--but i am still looking into that.


Brad

[picowatt]

Tinman,

As you change the scope ground connection point, different portions of the circuit become dynamic with respect to stray capacitance (mainly to your bench top or nearby equip).  This can produce some "not really there" spikes or other anomalies as the strays are charge/discharged.

Consider using a short and neat circuit layout and placing the entire circuit on a piece of glass/plexiglass elevated above your bench by insulators. 

PW

[picowatt]

If we look at the scope shots below,even though the voltage is above the 15.3 volt breakdown voltage,current continues to flow below the 15.3 volt threshold. But i believe that the bulk of this! so called! current flow is happening around the breakdown voltage limit.

The first scope shot is across the base/emitter junction,and shows a voltage value peak of about 20 volt's.
The second scope shot is from across the 1k base resistor,and you can see that current is (apparently ) still flowing well below the 15.3 volt junction breakdown threshold.

!BUT! there is something odd with this !so called! current flow--but i am still looking into that.

It is becoming difficult, if not impossible impossible, to keep track of what the scope captures are depicting.  This has become more of a problem as the scope ground is also being relocated in different captures.

Consider posting a schematic of test probe locations with each of your captures as test points change.

A schematic of test point locations for this last set of captures would be handy.

PW

[MileHigh]

Brad:

Whats not suprising, is that you dont know that voltage appears across an inductor,before current flows through it. If you did,you wouldnt be asking as to why the two time basses are different.

Why do you say such nonsensical trash talk idiocy like the comments about voltage leading current?  Why do you lower yourself into the gutter and make such a fool of yourself like that?  It just destroys your credibility and why should anybody trust you for anything when you play ridiculous mind games like that?  It feels like a crank call from a 12-year-old sometimes.

I never said anything about the time bases being different.  Brain ricochet!  I asked you why the periods are different and you did not offer up any kind of real explanation.

I am getting exhausted with the stream-of-consciousness/churning spaghetti/brain-ricochet talk from you.  It's like you need a bloody Google translator just for you.  Throw in the ridiculous immature trash talk that is embarrassing and you are left with Dr. Brainfry on overload.  Perhaps later I will try to deal with it but not now.  I get a headache just thinking about it.

MileHigh

[SeaMonkey]

I am getting exhausted with the stream-of-consciousness/churning spaghetti/brain-ricochet talk from you.  It's like you need a bloody Google translator just for you.  Throw in the ridiculous immature trash talk that is embarrassing and you are left with Dr. Brainfry on overload.  Perhaps later I will try to deal with it but not now.  I get a headache just thinking about it.

Gosh Miles!

That sort of a response is troubling indeed!

Let us hope that you're not going into a "breakdown"
mode and that perhaps a little rest might restore your
vitality and sense of reason?

The Tin Man makes perfect sense to me.