NPO ceramic vs polypropylene

NPO ceramic vs polypropylene

There was a little side discussion on JL?s LC tuning thread. When I look ed at this ~2 years ago I found that ceramics were a tad better than the ?good? poly-pro?s. (I used them in a low freq LCR circuit.. Q~35 so the cap type didn?t make that much of a difference.) (The poly pro?s I have are from Panasonic. low dissipation 2% caps. I can dig up a part number if it?s important, I?m not sure they are made anymore.) So these are both 10nF caps. I first measured them on an SRS720. at 10 and 100kHz.

10kHz 100kHz type C R D R D NPO 10.17 0.6 0.0004 0.006 0.00003 poly 10.16 0.23 0.00013 0.086 0.0056

The R/D numbers are so low I don?t really believe them. So I stuck the C?s in the (original) LCR circuit. So I list peak frequen cy, Vin and Vout. (As measured on a ?scope (digital w/average))

type freq. Vin Vout NPO 6.08kHz 159mV 6.40V poly 6.13kHz 159mV 6.36V

(again no real difference to talk about.) I pulled out a different L...

type freq. Vin Vout NPO 157kHz 91.2mV 7.36V poly 158.5kHz 92.8mV 7.24V

Finally a bit of difference I can believe. Vin dropped because the series L C was loading down the function gen.

So for those who think film are better, you might want to look again at NPO ceramics. They've improved a lot*. Of course this says nothing about the DA of the caps. (How does one go about measuring that?) George H.

*you need to get the new little ones.. the old larger npo ceramics with the dull brown coating are not nearly as good.
Reply to
George Herold
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It's NP0 and not NPO, although that's the way it's pronounced. It is the numeral "oh."

Reply to
bloggs.fredbloggs.fred

That's why they came up with COG, so we don't have to worry about that anymore. :)

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John Devereux
Reply to
John Devereux

Thanks, George, for an excellent response! I would be interested in the part numbers but your numbers are certainly compelling for the NP0s. If nothing else to make sure that we're not comparing a new-generation NP0 with an older-generation metalized polypropylene. I've used the Panasonic ECW series parts- the current web info is a bit confusing (a "built-in fuse function" (deliberately added resistance?); not requiring "a significant amount of pulse current" yet suitable for "high current circuits" ?.

An application that can make DA really stand out is with a sample-hold. For example, charge a capacitor to some voltage and keep it there for some time; then "short to ground" for a much shorter interval. Release the "short" and watch the capacitor voltage (presumably with some extremely-low-bias-current follower). In my tests (done a long time ago now - data long gone) the met-polypros were the best of the lot for DA.

Reply to
Frank Miles

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Yeah sure.. I hope digikey part numbers are OK.

poly was P3103-ND (ECQ series now discontinued.) and ceramic 445-4750-ND I think that was just the cheapest on the DK site... also lots of stock whi ch is always a good sign.

I haven't looked at any others. We've got a few products with a high Q sec tion somewhere in the signal chain and as the polypro's go away I've been r eplacing with ceramics.

I kinda wonder when ceramics became so good. Was there a breakthrough, or just incremental improvement?

George H.

Reply to
George Herold

YUP, no kidding! I have been making servo amps for about 10 years, and used PP film caps in the output filters. Had some problems with them getting hot when the amp was run near 50% duty cycle for a while. I originally tried to find affordable ceramic caps and couldn't find anything less than several $ each. Now, I re-engineered it to use ceramic NPO SMT caps that are about $0.35 each, and they run completely cold under the same condition. That condition is 100 V approximately sine wave at 50 KHz. So, I have changed both the output filter caps and the snubber caps to NPO ceramic. The film caps couldn't stand the IR reflow, so they used to be hand-soldered later. So, I have eliminated several manual processes as a bonus.

Jon

Reply to
Jon Elson

Is that Charlie Oscar Golf, or Charlie Zero Golf?

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Tim Wescott 
Wescott Design Services 
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Reply to
Tim Wescott

I _think_ that the dissipation angle is the arctan of the resistance divided by the reactive impedance (or the arcsine of resistance divided by the total impedance -- your choice).

So it's pretty much just another way of expressing Q -- or maybe it's a convenient way of telling if the cap will roast, I dunno.

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Tim Wescott 
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Reply to
Tim Wescott

C0G has always been C0G (except when it was called NP0, but you know..). It's basically straight... titanium dioxide, or strontium titanate or something? I forget. Once it was discovered, the material properties remain constant, there's just variations in formulation and manufacturing process. Most notably the multilayer process.

In my junk box, I have some monster NP0s from '60s TV sets. 100pF is a one inch disc! Purity and, more importantly, density probably weren't so great back then, so they had to use excess thickness to guarantee dielectric strength (they might actually handle 5kV.. who knows?).

MLCCs must be using high density formulations, or finer grained material, or something, which allows them to make micron thick layers. Then they just make a lot of layers. Then they make a lot of caps. Millions of caps. Billions. High speed production does its thing, the market responds, and prices get where they are now.

Tim

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Seven Transistor Labs 
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Reply to
Tim Williams

For DF

0.1), but that only matters to polarized caps (and analogously, powdered iron core chokes).

Tim

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Seven Transistor Labs 
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Reply to
Tim Williams

I think he's talking about dielectric absorption when he mentions DA?

Reply to
JM

In RF slang it's "cog", southern RF slang "caoag".

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Are you sure about the numbers? Where did you get the material or caps from? My experience is more along the lines of these numbers:

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Interestingly, we just had a discussion about this very stuff in a meeting this morning. C0G is good, but it isn't quite this good. I had my comeuppance in that respect as a teenager. I had completed a 1.2kW RF amp for my ham radio station (before anyone bristles, that was legal in Germany back then). For operation on 14MHz I was short one capacitor. Found a nice big ceramic RF cap with low tempco, which must have been C0G. Tuned it up, cranked up the power to the hilt ... *KABLAMMO* ... and cap was gone. Literally, except for the wires. I found a few bits and pieces and they had turned from white ceramic into bubbly green glass. So the loss tangent must have been not too great.

What new little ones?

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Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

PS film is better than PP film or C0G ceramics for DA, but they're not very common.

--sp

Reply to
Spehro Pefhany

Yeah I think about it as 1/Q (there may be a factor of two in there.. no n ever mind I'm confusing it with the damping factor.) Anyway looking at the numbers that are spit out by the srs lcr meter the dissipation factor is ' kinda' independent of the frequency. While what they call R depends on the frequency. Which is pretty weird if you ask me. I'd expect the resistanc e to be roughly constant... Dang am I actually going ot have to read the ma nual?

OK D is 1/Q and R is the ESR. For the cermaic cap ESR (in ohms) (as measur ed by srs) is 2.3(1kHz) 0.65(10kHz) and 0.02(100kHz) Whereas D = 0.0001(

1kHz), 0.0004(10kHz), 0.0001(100kHz) OK as you said D is the ratio of the impedances. So now the question is.... Why does the ESR change with frequency? Where does it come from?

Hey I did find that the srs720 has a set of optional tweezers!

George H.

Reply to
George Herold

Grin.. well that's what the srs meter spat out. Roughly confirmed by a LC Q measurment, (but I'd really need a better big low loss inductor.... oh I could dig one out..)

Hmm well these TDK ceramics look better than that. They don't quote a DF spec though.

Well the new multilayer guys versus the old bulky brown ones. (I sent cass a digikey number.) I noticed that TDK also list some high Q smd varieties.. they might have a quoted spec. I didn't check.

George H.

Reply to
George Herold

Ah, you mean polystyrene? They are good, but their low melting point makes them a non-starter in almost all circumstances.

Reply to
Frank Miles

[snip]

Nice chart! This is also closer to my (old) measurements, including the mica having unexpectedly horrible DA.

Reply to
Frank Miles

In the amps you shipped me you were using polyesters.

Reply to
Frank Miles

ured by srs) is 2.3(1kHz) 0.65(10kHz) and 0.02(100kHz) Whereas D = 0.000

1(1kHz), 0.0004(10kHz), 0.0001(100kHz) OK as you said D is the ratio of th e impedances. So now the question is....

So what's the source of the dissipation factor. If wiki is to be believed,

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Then there are two sources of loss. Conduction electron loss or dipole rel axation. And wiki finds the DF from conduction loss should go as 1/f. (f = frequen cy)

Which is not what I saw. (DF looks kinda constant for the ceramics.) And this is a nice link for film caps,

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apacitorsappguide.pdf

Which I would describe as ~constant DF for Polyester. (above 10kHz) DF increases as ~f for Polyprop. (above 10kHz) and PPS may also increase as ~f, but it's hard to tell because of the linear-log graph. (people doing spec sheets should know how to grap h.)

None of which fits the wiki model?

George H.

Reply to
George Herold

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