Re: [TCML] DRSSTC Waveforms (updates)

[Michael Twieg <mdt24@xxxxxxxx>]

Justin, I still think you're implementing the phase lead incorrectly.  Steve
mentioned that in his circuit (which I presume you're using unmodified), he
clamps the output of his zero crossing transformer with diodes, no burden
resistor.  That is a very nonlinear load, so implementing predictable phase
shift on the signal with that load won't work well.  To implement phase
shift on the feedback CT, he and I both do something different.  We burden
the CT with a combination of resistance and inductance to give the desired
complex impedance,  then we connect that to the clamping diodes through a
large resistance.  That resistance is very important because it prevents the
nonlinearity of the diodes from screwing with the phase lead network.
Without it, it won't really work at all.  Refer to the schematic Steve
posted.  I've been using a near identical method for the last year, and it
works great.

Also, in you diagram you show the burden resistor and inductors in
parallel.  This can work, though it's easier to put them in series (less
inductance is required).

If you tell me some information about your coil and circuit, I can suggest
some values for the circuit.  I'll need to know:  your operating frequency,
your CT turns ratio, the rough peak primary current, and the desired phase
shift (or lead time) you want to see on your zero crossing.  Also if you
know the magnetizing inductance of your CT output, that might be helpful
(since it can cause phase lead itself).

-Mike

On Fri, Jul 8, 2011 at 11:45 PM, Justin B <boshjack@xxxxxxxxxxx> wrote:

>
> An update from my previous thread, With attempt of inductance and
> resistance.
>
> I decided to just wind my own inductors.  I used barry's inductance
> calculator for air core inductors.  I then made 10 counts of 10uH inductors.
>  I understand its rough estimates.  I hooked the inductor (L) and resistor
> (R) in series.  Which was then in parallel to the CT.  See the figure i
> included below of my hookup. (Fig A)
>
> I took a picture at each inductance level. 1 inductor, 2 inductors, 3
> inductors, 4 inductors, and 5 inductors.
>
> I adjusted the pot, and it didnt shift the waveform till the very end where
> 1 turn shifted it maybe 5mm. so I had fine control over it.  As I adjusted
> it, I was watching the ZOOMED square waveform, right side, ringing.  I
> djusted it until the line was flat, but if i adjusted it more, the thing
> flipped out making very bad waveforms, and required me to adjust back, and
> reset my driver.  I assumed this is proper acting of the driver, because I
> think its switching too early, causing issues.  So, I didnt see this is bad
> operation.  To me it sounds expected.  Anyways, I have a few questions.
>
> First,  Why is it that the top waveform, looks like i have BAD ringing.
>  Yet the zoomed in 2nd-timer waveform, the ringing on the right side of the
> square, looks lovely (for the most part)?  The same spot, in the above wave,
> looks horrible.  What do I beleive? The zoomed in, or the zoomed out?
>
> Second, The ringing on the left side seems fully uncontrollable.  I can
> fully kill it on the right side (comparing to the zoom version), but I have
> NO control over the left side.  Is this the side that requires delay
> triggering?  Such as the resistors I have on my gate of the CM300?
>
> If you think it would make a difference, I CAN try all in parallel. (Fig B)
>
> Figures (A) and (B)
> http://i.imgur.com/HKGVr.png
>
> Waveforms
> http://i.imgur.com/k325x.jpg
>
> As a side note, The CM300 currently has 15 ohms of resistance on each leg.
>  It originally was 5.1 ohms
>
> Any suggestions/ideas are welcomed, I will try other orientations of the
> (L)(R).
>
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