Type of capacitor

Thread Starter

Tobias12

Joined May 25, 2019
24
Hello ! What type of capacitor is a good choice to work at 800 Hz, voltage 12-15V and nominal capacitance around 24 nanofarads ?
 

KeithWalker

Joined Jul 10, 2017
877
Thank you. I have one more question. Ceramic capacitor doesn't work at high frequencies ?
Modern ceramic capacitors work extremely well at high frequencies and as general purpose capacitors in most applications.. Some of the older types like ceramic tubular capacitors and barrier layer capacitors are obsolete today because of their size, parasitic effects or electrical characteristics.
Regards,
Keith
 

Thread Starter

Tobias12

Joined May 25, 2019
24
Modern ceramic capacitors work extremely well at high frequencies and as general purpose capacitors in most applications.. Some of the older types like ceramic tubular capacitors and barrier layer capacitors are obsolete today because of their size, parasitic effects or electrical characteristics.
Regards,
Keith
So, it's good to choose a modern ceramic capacitor for my application ?
 

Analog Ground

Joined Apr 24, 2019
384
There is a gazillion capacitors which meet your criteria (so far). How accurate do you want your output in frequency, linearity for the triangle and over what temperature range? Ceramics will work and NPO dielectric is a good choice as already mentioned. At 800 Hz, you can go with mylar or MKP4 already mentioned, etc. Do you need small size? Leads or surface mount?
 

Analog Ground

Joined Apr 24, 2019
384
A downside of Ceramics, certain types (C sensitivity to its terminal V) -

https://www.murata.com/support/faqs/products/capacitor/mlcc/char/0005

View attachment 205503


Regards, Dana.
This is a very important (bad) characteristic of Z5U and X7R ceramic dielectrics, especially for ramp generators and timing circuits. I believe NPO dielectrics are much, much better. Hence, the recommendations for NPO. It is a great link. I have never seen a clear explanation of why high dielectrics are so bad with this spec. The voltage coefficient of capacitance is very low for polypropylene which makes them good for high accuracy timing.

Edit: I think it is hard to find an NPO capacitor with a value as large as 24 nanofarads. Look to a film type like polypropylene.
 
Last edited:

Janis59

Joined Aug 21, 2017
1,174
I am playing with NanoVNA today and fell in the shock HOW BAD are the most of smd capacitors. All my 0,1 mkF caps turned out to be the good inductors as soon over the 3 MHz when I am using it being the Vcc capacitors. Warmly suggest, if any doubt about a certain capacitor, apply the NanoVNA or at least SA1201, yet the last works only OVER the 137 MHz up to 2700 MHz. There are a drastical price reduction on all e-bay shops for a moment, seemingly because of the pandemy.
 

andrewmm

Joined Feb 25, 2011
304
I am playing with NanoVNA today and fell in the shock HOW BAD are the most of smd capacitors. All my 0,1 mkF caps turned out to be the good inductors as soon over the 3 MHz when I am using it being the Vcc capacitors. Warmly suggest, if any doubt about a certain capacitor, apply the NanoVNA or at least SA1201, yet the last works only OVER the 137 MHz up to 2700 MHz. There are a drastical price reduction on all e-bay shops for a moment, seemingly because of the pandemy.
I would be surprised if a ceramic capacitor was a good induct or at 3 MHz.
I use ceramic capacitors in filters et all well into the 100 MHz range,
I'd suspect your meassurment system, cable length has a huge effect on VNA meassurments above KHz range.
 

Analog Ground

Joined Apr 24, 2019
384
I am playing with NanoVNA today and fell in the shock HOW BAD are the most of smd capacitors. All my 0,1 mkF caps turned out to be the good inductors as soon over the 3 MHz when I am using it being the Vcc capacitors. Warmly suggest, if any doubt about a certain capacitor, apply the NanoVNA or at least SA1201, yet the last works only OVER the 137 MHz up to 2700 MHz. There are a drastical price reduction on all e-bay shops for a moment, seemingly because of the pandemy.
Do you get something like this? 0.1uF ceramic surface mount. Typical bypass capacitor.

capImpedance.jpg
 

Janis59

Joined Aug 21, 2017
1,174
RE: A.Ground. Exact like that. Cap was got from scraped PC, thus I was sure even the GHz will satisfy it. And was shocked the circuit already at 50 MHz cannot stand the battery of 100 such parallel. Now I know why. Cabling of course had an compensational verification in end of cable. VNA have 6 channels to save the verifications for 6 differential cable types.
 
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