What is "NPO" in Capacitor Spec?

[dpresley58]

Trying to order from Mouser and was going through the ceramic disk caps. Several of the manufacturers have a listing in the spec like this:

Mallory Disc Ceramic Capacitors 5pF 50V NPO CER

What is NPO? I'm just looking to stock up on some components and this is confusing me.

[Satch12879]

::bump::

[Mark Hammer]

Non polarized.

When it comes to things less than .1uf, it is extremely rare that you find anything polarized, but once you get up over that range they start to indicate whether the cap in question is polarized or not because they can come in both "flavours".  For instance the .22uf tantalum caps that traditionally came in Tube Screamers were polarized (as are all tantalum caps), where ceramic and plastic types are not.

[Peter Snowberg]

NPO refers to the dielectric composition used.

The biggest difference it makes is in temperature coefficient, but the actual values are also closer tolerance to stated values. They're the standard in high precision circuits.

NPO caps are available in small sizes only. The dielectric of X7R is something like 8 times more efficient at accumulating charge than NPO.

The other two main ones you see in ceramic discs are X7R and Y5V. X7R is what you use for the majority of ceramic disc applications. Y5V is the cheap junk- avoid it if you can.

I go for silver-mica myself for small values.... no piezoelectric properties to the dielectric.

[Paul Perry (Frostwave)]

Yeah, it is low (zero) temperature coefficient.
As in, (N)egative coefficient zero, (P)ositive coefficient zero. Hence, NP0.
You can get small value caps in known + or - temp coefficients as well, to balance out coils that are have an opposite coefficient, if you are making RF communications stuff. Of course that is all old hat now that everything is digital........

[Mark Hammer]

N :oops:  P :oops:  O :oops:

My bad.

Thanks for clearing it up.

[Dai H.]

there are different levels of temp. stability ones also. You might see an "N(number)" like "N150", etc. also. And I have some temp. stable monolithic ceramics in larger sizes--maybe 4700nF, but I don't know if they are NPO. Also some are colour colded, like a little purple mark, or orange mark, yellow, etc.

[dpresley58]

NPO refers to the dielectric composition used.

The biggest difference it makes is in temperature coefficient, but the actual values are also closer tolerance to stated values. They're the standard in high precision circuits.

The other two main ones you see in ceramic discs are X7R and Y5V. X7R is what you use for the majority of ceramic disc applications. Y5V is the cheap junk- avoid it if you can.

I go for silver-mica myself for small values.... no piezoelectric properties to the dielectric.

Thanks, Peter (and Paul)... I have the Tab book, "Guide to Understanding Electricity and Electronics". Trouble is, I just don't keep it here at the office where I do my online ordering.  :oops: I was doing a little reading ahead last night and practically dropped the book open to the page that discussed this very topic. (things that make you go, "Oh-hhh")

In a nutshell, my understanding is that NPO (Negative-Positive-Zero) refers to the capacitor's ability to avoid a change in value with regard to temperature. In this case, an NPO hangs pretty close to it's value over a wider range of temperatures.

I drifted off momentarily, trying to envision an application that would -want- a cap's value to fluctuate by means of temperature variation but I'm thinkin' that will take a little more reading.

Great book for a newbie, btw. I highly recommend it if you take the time to slog through the math and get a grip on the concepts. A month or so ago, I -never- thought I'd be hip deep in this world.

[Gladmarr]

COG capacitors are the same thing, by the way.  If you're looking for a cap that is NPO type, COG will work just as well.  I have no idea what COG stands for though, so I'm just trying to be helpful, not necessarily look smart.

:lol:

[Brett Clark]

NP0 or C0G caps have more advantages than just the temperature coefficient. They are FAR more linear than the other ceramic types, as well. They are "less efficient" (larger for the same value), but are much better for most audio purposes than other ceramic types. They also have much less piezoelectric/ microphonic problems.  I never use X7R, etc. in the signal path.

A Certain Brand who Shall Remain Nameless use lots of X7R and Z5U caps in their tube amps. These are often so microphonic that at high volumes the amp will feedback through them like little microphones! I've seen people nearly go crazy thinking that every 12AX7 they could find was microphonic, when actually the noise was coming from the caps near the tube's pins on the PCB. Replacing them all with C0G and/or silver mica is a certain cure. I wonder, though, if the microphonic feedback is deliberate on their part. Is it intended to add "character" to the sound? Or is it just because they're cheap? I don't know, but I prefer my amps without howls and whistles.

[Dai H.]

I think polystyrene is also good for high freqs. and stable if that's what you want. I think a temp. stable ceramic would be more volumetrically efficient (as in the physical space it takes up vs. capacitance)--if space is tight.  

re:using the less temp. stable ceramics in amps, I suppose it could be deliberate. But old amps like Marshalls can have the temp. stable type too. IIRC, I saw a temp. stable ("Nnumber") for a vol. pot bypass cap in my low-end PRS (EG) also. Temp. stable ceramics seem to sound cleaner, subjectively speaking.