[TCML] comments on Finn's circuits

[DC Cox <resonance@xxxxxxxxxxxx>]

If I'm reading it correct ---- and I say if here because it's hard to see
the scope divisions:

The 5 volt drive signal is getting a 26.3 degree phase shift between voltage
and current at the zero crossover point.

This equates to 1.88 volts off of zero crossover point.

Finn is switching at 26.3 phase angle --- that's nearly 1/3rd of his current
is being switched at the cross over point.

If he is running (guessing here) 30 amps, then thats nearly 10 Amps of
current being switched at the zero cross over point.

Look carefully at Finn's waveforms and you will see that I am right.

am I right or wrong on this so far   ?????   If I'm missing some important
point, hey, I'm open to criticism, not just open to cheap shot personal
attacks that a few members have posted.


The gate drive signal is a square wave rich in harmonics.  If you do a fast
Fourier transform on Finn's data you will see some nasty harmonics that are
coming thru.

Finn does filter out the harmonic using essentially a ham radio "trap"
circuit.  Nothing new here as Chris Craft has been building amateur radio
broadband antennas using this exact same technique
for over 40 years.  I used one as a ham operator back in 1966.

Finn is swamping out the bad harmonic using a trap filter, and, yes, he does
get rid of the overshoot, but the real root of the problem is the gate drive
transformer turns ratios are not correct.  They can not just be
2:1, 3:1, or 4:1 if you want to have a drive without the harmonic
overshoot.  You have to make some minor adjustments to clear up the
overshoot.  Try it on an actual TC gate drive xmfr of an operating coil and
you
can see the changes in overshoot.  Small adjustments of a few turns will
clear up most of the gate drive harmonic problems.

Or, as Finn has done ---- you can use a trap filter circuit.  No problem
with that ---- either one works.

But, as I initially stated this WILL DEFINITELY NOT correct the zero point
crossing problem.

That's all I'm saying   ---- my points are:

(1) using trap filters is nothing new in EE circles  --- been around for 40
yrs.

(2) Finn's circuit will correct for a gate drive mismatch problem.  He is
swamping out the over drive, not correcting for it.

(3) Finn's circuit will NOT correct the zero point crossing problem --- at
least definitely not in the data he has posted.


Thanks for your patience and comments.

Dr. Resonance
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