High frequency capacitor selection

[ZeroResistance]

This is a 1nF capacitor with R=10mOhm, L=10nH, source is 0/100V square wave (100Vp-p) of 10MHz with 1ns r/f edges and internal resistance of 10mOhm.
The current is ~1200Ap-p.

That's an awesome plot "imo", If the cap is operating in resonant mode can we expect the same levels of current, or would they be lower?

Ballpark speaking, the RMS current rating is usually 1/5 to 1/100 the pulse rating.  If a pulse or dV/dt rating is provided at all.

RMS current limit is thermal, obviously.  It can be worse at higher frequencies, due to skin effect and such; CDE 940C caps for example are quite prominent in this way (rated for lots of peak amps, but not very much RMS at 100kHz, and even less at 400kHz -- I know, I've melted them before).

Mind that ceramic chip caps aren't very conductive (they aren't made of Al2O3, or much metal!), so they can't handle the same power level that a chip resistor (typically Al2O3 or metal body) of the same size would.

I have plans to build an induction heater with C0Gs; it'll take about qty 300, wired in parallel.  It's a pretty good bit of reactive power handling, though: 100 VA each (30kVA total) isn't bad at all for parts so small!

Tim

Agreed, at 1Mhz skin depth of copper is around 65microns and Aluminium 82 microns. I was looking at film-foil capacitors and not the metalilized types? So if we want to get a 1nF cap running at 1Mhz and higher. Considering the Xc of 160 ohm, and keeping voltage as 250VAC rms would it mean that
Wider foil with around the 80 micron thichness to give a  cross sectional area for passing the desired continuous current should do the job? A Wider foil might obviously affect other parameters, or would it not??

I understand that film-foil capacitors construction is such that it can handle large currents, how do these COG type ceramics handle the same levels of current?

[T3sl4co1l]

That's an awesome plot "imo", If the cap is operating in resonant mode can we expect the same levels of current, or would they be lower?

Good question.  How could we predict such things?

I understand that film-foil capacitors construction is such that it can handle large currents, how do these COG type ceramics handle the same levels of current?

TLDR: find ESR (or loss tangent, which is ~= 1/Q) and solve for power dissipation.

Tim