Re: Edge response, dynamics, and really ugly time constants

"Ancient_Hacker" <grg@xxxxxxx> wrote in message
news:1140179614.108187.326750@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
I'm really confused. Looking at the waveform envelope it looks like
about 0.3 milliseconds between peaks of the fast ringing, 2
milliseconds (hard to tell, it's so damped) for the slow ringing..
That makes the ringing frequencies about 3 KHz and 500Hz, plus or
minus a lot.

Yeah, you got me there.. I was looking at it later, and I thought, huh, that
slow transient is a *lot* longer than the other... like, six times longer
per wave...

If you're trying to stabilize the average level, you're looking in too
much detail. You need to look at the analog control voltage, not look
at the PWM switching transients.

Not the switching transients- all the class D stuff is out of question,
pretty well set in concrete and hopefully about as reliable.

I didn't capture the input, which would tell gain and bias with respect to
the tank's parameters, but just to take a random look like this, I'm not
real interested in it. You just need to know that it's going up or down,
squarewave-style.

I'll take some more detailed analytic steps later.

But to answer your question, I've had the best luck at stabilizing
these kinds of transients with an ad-hoc 2-minute session with a R/C
substitution box.... Twiddle the knobs for least ringing and read off
the settings. Then wire in that 4.7K and 330pf series capacitor,
backnote the schematic, and nobody will know you didnt do a full
theoretical Laplace and Hamiltinian expansion. Works for me!

Heh heh. I've got the phase lock stabilized, by chucking a 0.1uF cap across
the op-amp's feedback resistor. Voila, integrate the error signal over
about 0.1 second. (Only problem is when the tank signal clipper drops out,
due to insufficient tank voltage capable of switching the comparator, which
causes a discontinuous phase voltage above a certain range. Naturally, this
causes hysteresis and it literally sings as a result..)

Tim

--
Deep Fryer: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms


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