capacitor nonlinearity again

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Isn't capacitor voltage dependence relatively slow physical effect ?

VLV

Should be pretty easy to take the standard nonlinear inductor model and swap out integral(V dt) for integral(I dt).

Everything else is the same, including "core" loss. There should still be a cutoff frequency where losses take over. Let's see, eddy current becomes "eddy voltage", but not "eddy", which implies a parallel loop, it has to be in series now. That would be the voltage dropped across the ESR. Should be easy to estimate from Z plots, as well as ESL.

Anything you can do with a saturable reactor you can do with a saturable cap, obviously. It'll be smaller, but probably comparable loss, given the low Q of type 2 ceramics.

Tim

-- Deep Friar: a very philosophical monk. Website:

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

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Maybe a series connection of a normal capacitor and a behavioral voltage source. Make the voltage of the BV k times an odd power of the voltage across the capacitor.

Jeroen Belleman

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It's fast enough to cause distortion at audio frequencies, but it does seem to be very, very messy.

This guy did a lot of testing...

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This guy assumes capacitor nonlinearity to be static; while it is time dependent effect. That's why his simulations don't match with his own measurements.

I'd model capacitor nonlinearity by gyrator with lowpass in control path. First order approximation would probably be enough for practical purpose.

Vladimir Vassilevsky DSP and Mixed Signal Designs

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Or use a table, as in...

but, as you suggest, add a low-pass "driving" the table.

You could likewise tabularize the dissipation factor.

Wonder how you would go about characterizing the "frequency response"? ...Jim Thompson

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It looks messy enough that it's hardly worth modeling, at least to use in a product. Even if you decide it's safe, the next batch of caps may be worse.

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very nice page there.

mylar wins!

I should send that guy some polypropylene, polycarbonate and polystyrene caps to test.

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G source, output in parallel with the capacitor, output current made a function of both the current thru the capacitor and the voltage across it. ...Jim Thompson

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Except for the horrible DA!

Nominally I would expect a higher voltage would the ceramic to be more compressed and so raise the capacitance. That seems to be in correspondence with mechanical compression used to create voltage (fire starters).

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Here you go...

Published curves directly digitized with my (nearly) favorite tool,

GetData Graph Digitizer...

digitizes anything you already have as a graphical file, or can scan. ...Jim Thompson

of a

that I did

falls off

capacitor based

I was unaware that LTSpice supported two input G sources.

?-)

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PSpice supports input as an Algebraic expression, multiple variables. I think LTspice does also. ...Jim Thompson

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Hit the wrong button...

Date: Mon, 13 May 2013 17:13:33 -0700 Message-ID:

Shows the PSpice solution. ...Jim Thompson

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Do you know if there is a correct term for the hysteresis or recovery of a dielectric in a capacitor? I've never seen it listed on a datasheet other than the "short terminals during shipping and storage" for high voltage film caps.

When I was super super exciteed to wind my own caps, I recall that one particular plastic, (possibly acetate?) was virtually impossible to completey discharge at once. You could draw arcs off the things over and over and over again.

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That's technically also dielectric absorption, just on a long time scale. Electrolytics can recover several per cent of their previous voltage, if discharged briefly. In a film cap, a few per cent of 20KV could still be interesting.

Mylar caps have bad DA in the millisecond time scale. They are nasty for sample-hold, precision integrators, ramp generators, dual-slope ADCs.

Not that anybody uses dual-slope ADCs much any more.

Modeling Dielectric Absorbtion in Capacitors:

gives some subcircuits as an approach.

I took that link out of a book, which is written in German (sorry for that) from Michael Reisch "Elektronische Bauelemente" plus modeling in SPICE. rgds Joerg

I did

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The good old engineering term is 'soakage'.

Cheers

Phil Hobbs