Hello,

I have several of Ceramic capacitors which the company did not mentioned anything about their tolerance. They are 33PF ,472 , 104. what's the reason?

Besides, Can you let me know which kind of capacitors are the best choice at high frequencies?

 

You should be able to find a tolerance specification from the maker; If you can't find a tolerance, find a new maker. I'm gonna shoot in the dark that small value ceramics are in the neighborhood of 5-10%

Define high frequency and your intended use. There are many types of capacitors, and choosing one appropriate for your application depends on the application.

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I believe generic grade ceramics usually run 20% but 10% are available. When buying ceramics it is important to buy only X5R or X7R types. The ones labeled Z5U and Y5F are absolute garbage. They have horrible tempcos and only deliver about 1/5 of rated capacitance if used near their voltage rating.

 

High frequency means FM frequency.
Are mica caps good/best at high frequencies?

 

Do you mean FM broadcast band? That's 88MHz to 108MHz.

 

You forgot to mention that the best ceramic caps are marked NPO or COG. The others you mentioned have lower grade (X7R) and lowest grade (Z5U) dielectric materials.

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-=VA7KOR=- My Solar System Includes Pluto.

 

I didn't forget. I don't recommend NPO/COG for general use because they are physically larger and much more expensive than X5R caps, also they are not available in larger sizes. They are justified in cases where caps have to be dead stable (like a precision timer or clock) but 99% of the time they are not required. Their claim to fame is zero tempco (stable over temp changes). X5R caps are pretty good for this, I think they stay within a 10 - 15% envelope over -40 to 150C range of temp. X5R and X7R are best for most uses. Z5U and Y5F really are junk that isn't adequate for ANY use.

 

I think you'll find that the proper notation originally was not NPO, but NP0, as in Negative/Positive-zero.

I agree with Bob that the NP0 caps are the best -- for their usual application in high-frequency circuits where tempco is an issue, such as with caps that are determining oscillator and filter frequencies. Otherwise, silver mica types are good for that as well. Because of their preferred uses, values of NP0 types do not usually run in excess of 1000pF.

I also find that the usual "crap" grade of disc ceramic caps tend to run high in value, especially if they have the "Z" tolerance code (which would make sense). These caps are usually used as bulk capacitance (decoupling circuits for example) and value is rarely an issue as long as it has a minimum value limit.

As far as decoding those tolerance codes, check this out:

Twisted Pair Forum / Capacitor Nomenclature

Dean

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Dean Huster, Electronics Curmudgeon
Contributing Editor emeritus, "Q & A", of the former "Poptronics" magazine (formerly "Popular Electronics" and "Electronics Now" magazines).

R.I.P.

 

I should post a sticky titled:

"Y5F, Z5U and Why They Are Absolutely Worthless"

The real problem is this:

1) Z5U/Y5F caps of a given voltage rating/capacitance value are smaller and cheaper than X7R/X5R. So, they are a better buy... right?

WRONG, because the Z5U specs are pure baloney. They only apply at 25C temperature with less than 10% of rated voltage applied to the capacitor. Anythng else and the capacitance vanishes quickly.


EXAMPLE:

A "10uF/10V" Z5U cap is only 10uF as long as you only apply about 1V or less..... as the voltage increases, the capacitance falls off a cliff. In fact, at the quoted (rated) voltage, Z5U/Y5F capacitance is only about 30% of the spec. So, the spec is pure BS. Of course, you could get a Z5U cap which hold most of it's capacitance at 10V by buying a "50V" Z5U cap... which (what a surprise) is as big and expensive as a 10uF/10V X7R cap.


AS FOR TEMPCO:

Another Z5U/Y5F ripoff. An X7R cap's capacitance will stay within about 20% of quoted spec over the temp range of about -55C to +125C. Pretty good capacitance value.

The tempco on a Z5U looks exactly like an umbrella centered at 25C, dropping about 50% down at the -20C and +80C temp limits. Again, Z5U caps suck.

In reality (if you operate a cap at it's rated voltage and temp range) a Z5U/Y5F will deliver about 10% of rated capacitance. An X7R will probably hold at least 70% or more across all effects (worst case). Bottom line, Z5U/Y5F caps are a scam for people who don't read the specs. In terms of actual capacitance, they don't give more for the money, they give less. They just look smaller/cheaper because the specs are bogus.


See below: X7R tempco left, Z5U tempco second. The capacitance change caused by applied voltage for X7R is shown third, Z5U cap change from applied voltage is at far right (last two curves are both for 50V caps).

Z5U/Y5F caps are totally worthless.

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I even do not know what those marks refer to!

 

I just have heard that mika ones are suitable at high frequencies.

So how do you choice which cap to be used at radio or higher freq waves