Testing the TK Tar Baby

[TinselKoala]

Here's the scopeshot from RA's blog post #50. Note the high current even at the relatively low positive gate signal. In this shot the Q1 mosfet is working ( or the Q2s... who really knows what schematic she was using then). Contrast this with the last shot from 118, for example.

NOTE: Here is another example of HIGH HEAT MODE with a 48 volt battery pack. Why is she removing a battery for these high heat mode experiments? I think I know.

[TinselKoala]

It should be quite similar.  The biasing loop has the 50-ohm resistor so it will always contribute less current.

MileHigh

If you take a 0.25 ohm resistor and hook it between two nine-volt batteries, so that the negative of one is hooked to the negative of the other through the resistor, what voltage will you read between the two positive terminals?

[TinselKoala]

In the days leading up to the demo video, she was posting some strange looking scopeshots. Is her FG just not keeping up at the high pulsation frequencies in these trials?
Note that third one, SCRN0226. This is the last screenshot in her blog, before the first one (SCRN0253, the fourth below) that doesn't show current when a +10 volt signal is on the gate of Q1.

[MileHigh]

TK:

The voltage read between the two positive terminals will be zero volts.  I am not sure how that applies but the switched-on MOSFET will pull the voltage at the drain low enough such that the bias voltage source and the main voltage source (both at same potential) will output some current.  As we know, each current influences the other current and the two currents arrive at a quiescent point.

IS this the main current providing the heat in the load? Could the current path heating the load be helped by the OTHER path, not the drain-to-source path in Q2, but going through the zener of "off" Q1 when the oscillations are happening on Q2.

I think that's possible but it would have to be verified with careful measurements.  Here is the point:  Assuming we are getting the current reversal because the Q2 array capacitance is discharging (Q1's capacitance is also discharging BTW) then once the capacitors have fully discharged, wouldn't you know it, you have energy stored in the inductance of the wires again.  That would keep the current flowing counter-clockwise, and it would flow through the zener diode in Q1.  So it's in theory possible that the diode in Q1 comes into play to "kill the LC resonator" made up of the wire inductance and the MOSFET drain-to-source capacitance.

Of course, every thing I am saying is speculative.  I keep on thinking about the main battery supply and how it may "drown out" these effects.

But in looking at the attached reference schematic, you can at least envision the possibility of something interesting.  When the Q2 array switches back on and the current starts to flow clockwise again, it's possible that the "tail end" of the inductive discharge from the energy stored in the wiring will indeed flow through the Q1 zener diode.

That would be pretty cool if it could be captured on the scope - clockwise current going through the main loop with the Q2 array, and at the same time, a little bit of remaining counter-clockwise current flowing through the Q1 zener diode.  If my speculations are even correct.

MileHigh

[MileHigh]

TK:

Note that third one, SCRN0226. This is the last screenshot in her blog, before the first one (SCRN0253, the fourth below) that doesn't show current when a +10 volt signal is on the gate of Q1.

The cyan is the gate voltage, correct?  Roughly 20 uSec "high" and 20 uSec "low" with the superimposed oscillations.  The "high" is really bad and resembles an exponential decay.  I am at a loss to explain that.

The gate voltage in this capture is pretty gross.  20 uSec is a relatively long time so you wonder what is going on during the "high" phase.

Honestly, in seeing that weird gate waveform I would have investigated it further.  I am assuming that Rosemary and the NERDs just stared at the screen and made the capture and did nothing beyond that.

I can't really venture an explanation for what is going on there beyond stating that we know that when the gate voltage is high we should see current flow.  When we don't see current flow we should assume that something is amiss.  I think that "kindest as always" Rosie Posie did battle with PW over that one.  That was an irrational fight, poor Posie Posie should have simply acknowledged the issue.

MileHigh