Searching for low tolerances unpolarized capacitor

Did you check. Available components in any of the shops?

Hi,

for this I use the selection tools of distributors.

Klaus

I don't see a whole lot of capacitors out there in high-C-precision
grades.

Many capacitors also have pretty bad voltco, ruining any initial
accuracy proposition.

I might suggest you order a quantity of loose capacitors, find
a credible C-meter and "select at test" for best values in the
pile.

Or, you might "plug and chug" one by one until you find the
"magic value" (which might or might not be a nice round
"1.000000uF").

Or, you might make the "capacitor" a parallel sum, a big one
that gets you to (say) 82% of target, at whatever coarseness,
and then pick the "trimmer" (fixed or variable) one to make the
exact right answer.

You should be able to find some film capacitors with low tolerance, but they tend to be physically large for a 1 µF capacity.
Metalized types would be the smallest film capacitors.
Would size be a problem?

Hi,

Farnell lists 58 types of 1uF film capacitors <= 5% on stock.

Klaus

Only film / foil types can meet high precision - an internet search will garner the makers for these

traditionally close tolerance caps have been hard to get in fixed values - generally you have to buy a whole bunch and measure them at your factory to sort into groups.

A careful read of the data sheets is needed to determine variation over temp - and with volts ( lesser )

of course the losses vary with applied freq and volts and this can fool some measuring devices ( & engineers ) to think the cap is changing - when in fact it isn't - just the total parallel Z is changing ...

One way to get pretty close with least effort, would be to use a couple of 0.47uF film capacitors in parallel.
That will leave you 60nF short.
Then add a third capacitor maybe 56nF or 68nF or whatever is needed.

Dominik Przyborowski said:

Did you check. Available components in any of the shops?

Click to expand...

No indeed I had no experience from where I can check or order, in the past I was always finding the components I need in the lab but now it is the first time that I have to order it myself

KlausST said:

Hi,

for this I use the selection tools of distributors.

Klaus

Click to expand...

Could you please refer me to some distributer where I can make this search

KlausST said:

Hi,

for this I use the selection tools of distributors.

Klaus

Click to expand...

Could you please refer me to some distributer where I can make this search

dick_freebird said:

I don't see a whole lot of capacitors out there in high-C-precision
grades.

Many capacitors also have pretty bad voltco, ruining any initial
accuracy proposition.

I might suggest you order a quantity of loose capacitors, find
a credible C-meter and "select at test" for best values in the
pile.

Or, you might "plug and chug" one by one until you find the
"magic value" (which might or might not be a nice round
"1.000000uF").

Or, you might make the "capacitor" a parallel sum, a big one
that gets you to (say) 82% of target, at whatever coarseness,
and then pick the "trimmer" (fixed or variable) one to make the
exact right answer.

Click to expand...

Actually it is not important for me to have exact 1 µF, even less like 0.5 µF would work for me, the problem I don't know from where I can search it and it should be with the through hole technology for my board

Hi,

Junus2012 said:

Could you please refer me to some distributer where I can make this search

Click to expand...

See post #6.

I´m sure many other distributors are similar.

Klaus

crutschow said:

You should be able to find some film capacitors with low tolerance, but they tend to be physically large for a 1 µF capacity.
Metalized types would be the smallest film capacitors.
Would size be a problem?

Click to expand...

size is not too much a problem and I can go for small capacitor values, the important thing is to be polarized and with low tolerances of maximum 5 % and support through-hole mounting technology

I am using the capacitor for AC coupling, is film capacitor is ok?

Thank you every body reacted to my post,

I can understand from you that fim/mitelized film and foil capacitor can give me this value,
As I lake to this practical experience, would the material type effect my application for AC coupling the circuit?
I read somewhere else that it is recommended to avoid using the Ceramic capacitor because it will introduce a non linearity distortion.

Thank you for suggesting me the film capacitor and when I read it the data sheet it looks like a perfect solution for the AC coupling

Thank you every body reacted to my post,

I can understand from you that fim/mitelized film and foil capacitor can give me this value,
As I lake to this practical experience, would the material type effect my application for AC coupling the circuit?
I read somewhere else that it is recommended to avoid using the Ceramic capacitor because it will introduce a non linearity distortion.

Thank you for suggesting me the film capacitor and when I read it the data sheet it looks like a perfect solution for the AC coupling

So again it will be useful for me if you suggest me better cap material for my application and also the the voltage rating,

In my application I have a maximum voltage of 8 V, if I find cap with 50 V rating should be a problem?

and what about Mica cap?

Warpspeed said:

One way to get pretty close with least effort, would be to use a couple of 0.47uF film capacitors in parallel.
That will leave you 60nF short.
Then add a third capacitor maybe 56nF or 68nF or whatever is needed.

Click to expand...

Huh? If you parallel 2 capacitors with 10% tolerance you’ve still got 10% tolerance.

Sure, if they are both out by 10% in the same direction, it just means the third "select on test" capacitor needs to be carefully chosen to correct for the 10% difference.

What is wrong with you guys ?

Warpspeed said:

Sure, if they are both out by 10% in the same direction, it just means the third "select on test" capacitor needs to be carefully chosen to correct for the 10% difference.

What is wrong with you guys ?

Click to expand...

So, you think that adding two capacitors and then selecting a third is somehow better than selecting a single capacitor? Cost, reliability and PCB real estate don’t matter? You’re going to have to accurately measure three capacitors instead of one.

You’re not going to end up “60 nF short”. You might end up 34nF high. Or 154 nF short.

Hi,

And in addition to Barry:
Tolerance is not only fix production tolerance, but also includes drift with time, applied voltage, temperature, and so on. It can't be compensated with an additional fix capacitor.
--> choose a suitable one. If farnell has more than 50 different types on stock it should not be the problem.

Klaus

Dear All,

I dop appreciate your nice discussion and reaction to my post,
The issue of tolerance is clear for me as well as how to search for a distributor, like Klaus suggested from farnell

Remaining two practical issues are not clear yet for me,
When I search for the capacitor I can find diffferent options of materials, mainly Mica, Film metalized film, foil and ceramic

Should I consider the material type for my selection or it is only size/cap criteria?

Also about the voltage rating, for example I found many option for my cap with the required value and tolerance but the voltage rating of these cap are far above my need, example of 100 V while I nead max of 5 to 10 V, will this has an effect on the performance?

Thank you once again
Regards

Voltage will affect capacitance; how much depends on the material.

And, yes, the type of material used depends on the application. Plastic capacitors are low distortion, but physically large. Mica is generally more stable than, say ceramic, but I don’t think you’ll find a 1 uF. And there are several types of ceramics with different properties: X5R, NPO, X7R, etc. You can search the web for more detailed information.

Hi,

Voltage: Don´t worry when the capacitor rating is higher than you need.

Material: I go with Crutschow and EasyPeasy: use a film/foil capacitor.

Klaus

KlausST said:

Hi,

Voltage: Don´t worry when the capacitor rating is higher than you need.

Material: I go with Crutschow and EasyPeasy: use a film/foil capacitor.

Klaus

Click to expand...

Here's a document that discusses capacitance change vs. voltage. https://www.maximintegrated.com/en/design/technical-documents/tutorials/5/5527.html

I'm sure that with you should find 1uF NP0 2% through-hole capacitors, maybe they're only in SMD packages, though. But 2% NP0 is a typical option. PPS are stable/respectable runner-up choice to NP0, I think usually 5% unfortunately, not sure if 1uF typical. Silver mica are supposed to be very stable but are costly, and 1uF would be bigger than a 4,700uF electrolytic capacitor maybe(!), looking at the 4,700pF one I have - it's huge...