Re: Cap C-V test

On Thu, 1 May 2025 22:36:11 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:

On 5/1/25 22:09, john larkin wrote:

 
https://www.dropbox.com/scl/fi/a7425c69k3w8wx8tqjpq5/X110_CV_Test.jpg?rlkey=pc3c0b12ncswv6ajrn148stdk&raw=1
 
 
The DUT is a Venkel 2.2 uF 100v 1812-size ceramic cap. I need to run
it at 48 volts. 0.8 uF is probably OK. I have room on my board so I
guess I'll add another cap in parallel.
 
My AADE cap meter was behaving strangely here, so I measured C by
noting the -3 dB frequency driving the cap from a 50 ohm sine wave
generator.
 

>
I used an old Rohde & Schwarz KARU capacitance meter to match
capacitors. It was really good at that, but sometimes it just
wouldn't work. At some point, I decided to finally figure out
why. It turned out the KARU applied over 300Vpp of AC at tens
of kHz to my little capacitors.
>
Oh.
>
Jeroen Belleman

300v will radically change the value of a ceramic cap.

The fungen+scope can tell you a lot more about a cap than the single
number reported by a c-meter (that you maybe can't trust anyhow.)