C0G caps have no significant capacitance change with voltage?

[Faringdon]

Hi,
https://www.murata.com/en-eu/support/faqs/capacitor/ceramiccapacitor/char/0005

...but please may i confirm that C0G has no appreciable capacitance change with voltage.
We know X7R changes cap'ance majorly with voltage...but C0G is just like film or 'lytics w.r.t. voltage change? (dc bias)

[tggzzz]

Oh. Good. Grief.

Why do you think people here can offer a more authoritative statement than the manufacturer?

Or do you just want to chat and form a mutual support/appreciation society?

[coppice]

Oh. Good. Grief.

Why do you think people here can offer a more authoritative statement than the manufacturer?

Or do you just want to chat and form a mutual support/appreciation society?

I agree. Manufacturers are ALWAYS totally open and honest about all the negative points of their products, and can be trusted at all times to clearly point them out in their literature.

[tggzzz]

Oh. Good. Grief.

Why do you think people here can offer a more authoritative statement than the manufacturer?

Or do you just want to chat and form a mutual support/appreciation society?

I agree. Manufacturers are ALWAYS totally open and honest about all the negative points of their products, and can be trusted at all times to clearly point them out in their literature.

And random people commenting on forums are ALWAYS an accurate source of detailed specifications suitable for  professionals designing commercial products.

Treez faringdon is a professional designing commercial producrs, isn't he?

[coppice]

Oh. Good. Grief.

Why do you think people here can offer a more authoritative statement than the manufacturer?

Or do you just want to chat and form a mutual support/appreciation society?

I agree. Manufacturers are ALWAYS totally open and honest about all the negative points of their products, and can be trusted at all times to clearly point them out in their literature.

And random people commenting on forums are ALWAYS an accurate source of detailed specifications suitable for  professionals designing commercial products.

You can't trust them, but they will often point out things you should look into deeper in the documentation and set you on the path to greater understanding. You never know. If enough people join in you might even flush out a genuine expert.... assuming you can distinguish genuine from fake.

I suspect you may have let the nature of the OP set you on a path of bad argument.

[tggzzz]

Oh. Good. Grief.

Why do you think people here can offer a more authoritative statement than the manufacturer?

Or do you just want to chat and form a mutual support/appreciation society?

I agree. Manufacturers are ALWAYS totally open and honest about all the negative points of their products, and can be trusted at all times to clearly point them out in their literature.

And random people commenting on forums are ALWAYS an accurate source of detailed specifications suitable for  professionals designing commercial products.

You can't trust them, but they will often point out things you should look into deeper in the documentation and set you on the path to greater understanding. You never know. If enough people join in you might even flush out a genuine expert.... assuming you can distinguish genuine from fake.

I suspect you may have let the nature of the OP set you on a path of bad argument.

That point doesn't stand up in the context of the original post, viz

Hi,
https://www.murata.com/en-eu/support/faqs/capacitor/ceramiccapacitor/char/0005

...but please may i confirm that C0G has no appreciable capacitance change with voltage.
We know X7R changes cap'ance majorly with voltage...but C0G is just like film or 'lytics w.r.t. voltage change? (dc bias)

[Zero999]

C0G/NP0 capacitors don't have a strong voltage vs capacitance characteristic. I suppose fakes exist, which is the case for every other kind of component.

https://www.allaboutcircuits.com/technical-articles/x7r-x5r-c0g...-a-concise-guide-to-ceramic-capacitor-types/

[Terry Bites]

Oh my days.....!

[Nominal Animal]

Hey, the question does have merit.  NP0=C0G dielectrics are defined by having capacitance basically independent of temperature (temperature coefficient α within ±0.00003 per degree Kelvin or Celsius), and no aging effects, but the voltage-capacitance relationship is somewhat separate.

As I discovered different types of dielectrics and their properties, I encountered the Temp and voltage variation of ceramic caps article at EDN (and a variant at analog.com).
That shows that even for X7R and X5R dielectrics, the dependency varies depending on the voltage rating, but also on the capacitor physical size.  The information was taken from public information provided by two different reputable manufacturers (Murata and TDK), so it is credible.

I did not find any curves, but all capacitor manufacturers do claim that C0G (aka NP0) capacitors have basically no voltage dependency in their capacitance, within the maximum voltage the capacitor is rated for.

The underlying question, then, is whether this is true, or if it is a common misconception stemming from their neglible temperature coefficient.

As I am only a hobbyist in electronics, and a scientist, to me an experiment with a few different C0G caps would nicely resolve the question: measure the capacitance of the caps at different bias voltages.  (Can one DC-bias only one leg of a Wien bridge?)

Any suggestions for such a circuit, measuring the capacitance of a DC-biased capacitor?

[mawyatt]

Hey, the question does have merit.  NP0=C0G dielectrics are defined by having capacitance basically independent of temperature (temperature coefficient α within ±0.00003 per degree Kelvin or Celsius), and no aging effects, but the voltage-capacitance relationship is somewhat separate.

As I discovered different types of dielectrics and their properties, I encountered the Temp and voltage variation of ceramic caps article at EDN (and a variant at analog.com).
That shows that even for X7R and X5R dielectrics, the dependency varies depending on the voltage rating, but also on the capacitor physical size.  The information was taken from public information provided by two different reputable manufacturers (Murata and TDK), so it is credible.

I did not find any curves, but all capacitor manufacturers do claim that C0G (aka NP0) capacitors have basically no voltage dependency in their capacitance, within the maximum voltage the capacitor is rated for.

The underlying question, then, is whether this is true, or if it is a common misconception stemming from their neglible temperature coefficient.

As I am only a hobbyist in electronics, and a scientist, to me an experiment with a few different C0G caps would nicely resolve the question: measure the capacitance of the caps at different bias voltages.  (Can one DC-bias only one leg of a Wien bridge?)

Any suggestions for such a circuit, measuring the capacitance of a DC-biased capacitor?

We did develop a DC Bias adapter for our bench LCR meters for this reason (one of which), to evaluate the various aspects of ceramic capacitors DC voltage bias effects. This confirmed the high voltage bias variability of X7R and X5R dielectrics which we already knew, but also provided a means to evaluate some new "questionable" sources for various ceramic capacitors. The NP0/C0G ceramics we've evaluate from Venkel are stable with voltage, temperature and time as we've learned.

https://www.eevblog.com/forum/projects/bias-network-for-lcr-meter/
https://www.eevblog.com/forum/testgear/lcr-meter-plot-software/msg4810088/#msg4810088

We've learned over the many years to not trust just every OEM for, components, test equipment and so on, and some newer ones without a history with us needed to be evaluated. This is especially true today with the counterfeit components lurking from the questionable OEMs and distributors. Over 50 years ago we suffered from a local main distributor of passive components, they were eventually caught and prosecuted for selling counterfeit components. Our case involved counterfeit 0.1% RN55 and 60 "E" type resistors, they were hand selected from remarked 1% RN55 and 60 "C" and "D" components. These were utilized in various critical measurement equipment we developed and sold, and we had no way of knowing if/what product these counterfeit components ended up in, so we had to recall various products, embarrassing indeed 

Ever since we've been somewhat cautious about "unknown" to us sources, and try to evaluate before blindly using such in valued applications/products/recommendations.

Best,

[T3sl4co1l]

FWIW, my tests have shown very little distortion at 200V AC applied to 630V C0G chips.  Gapped ferrite is certainly more.

Tim

[coppice]

Ever since we've been somewhat cautious about "unknown" to us sources, and try to evaluate before blindly using such in valued applications/products/recommendations.

Capacitors and dielectric materials are a minefield when you care about details of capacitive performance. For example kapton is often used as a dielectric for capacitive touch pads. Try various sources of apparently similar kapton tapes. A quick touch is never a problem. However, with some if you hold a finger on the pad for a minute or two, and then lift your finger, the capacitance reading goes straight back to its pre-touched value. Try another similar material and polarisation effects mean the capacitance drops to a substantially different value, and can take a minute or two to drift back to its pre-touched value. That's a lot of fun when a new production batch suddenly starts failing because the software calibration process can't cope with this.

[T3sl4co1l]

Ever since we've been somewhat cautious about "unknown" to us sources, and try to evaluate before blindly using such in valued applications/products/recommendations.

Capacitors and dielectric materials are a minefield when you care about details of capacitive performance. For example kapton is often used as a dielectric for capacitive touch pads. Try various sources of apparently similar kapton tapes. A quick touch is never a problem. However, with some if you hold a finger on the pad for a minute or two, and then lift your finger, the capacitance reading goes straight back to its pre-touched value. Try another similar material and polarisation effects mean the capacitance drops to a substantially different value, and can take a minute or two to drift back to its pre-touched value. That's a lot of fun when a new production batch suddenly starts failing because the software calibration process can't cope with this.

Not to mention humidity from the finger; polyimide (Kapton(R) is the brand name) is an effective humidity sensor.

Tim

[mawyatt]

Should mention that some C0G/N0P ceramic caps are so good, that some high end DMMs use them as the main integration capacitor. That should hint at just how good they can be!! I'm sure there are some "fake" C0G/N0P caps around, but those should be easy to find with a simple bias voltage test. Maybe some questionable OEM brands, altho the Venkel C0Gs we have and use as internal "reference" devices to check and confirm proper operation of our LCR Meters, they are that stable.

Best,

[coppice]

Ever since we've been somewhat cautious about "unknown" to us sources, and try to evaluate before blindly using such in valued applications/products/recommendations.

Capacitors and dielectric materials are a minefield when you care about details of capacitive performance. For example kapton is often used as a dielectric for capacitive touch pads. Try various sources of apparently similar kapton tapes. A quick touch is never a problem. However, with some if you hold a finger on the pad for a minute or two, and then lift your finger, the capacitance reading goes straight back to its pre-touched value. Try another similar material and polarisation effects mean the capacitance drops to a substantially different value, and can take a minute or two to drift back to its pre-touched value. That's a lot of fun when a new production batch suddenly starts failing because the software calibration process can't cope with this.

Not to mention humidity from the finger; polyimide (Kapton(R) is the brand name) is an effective humidity sensor.

Tim

Its rare in a touch setup that moisture from the finger could reach the kapton. You could consider warming by the finger too. That doesn't seem to have much effect. As far as I know its basically a polarisation effect. It comes up in dielectric issues all over the place.

[Nominal Animal]

Polyimide is also triboelectric, making it a particularly odd choice for a capacitive touch dielectric material.

[coppice]

Polyimide is also triboelectric, making it a particularly odd choice for a capacitive touch dielectric material.

That makes it an odd choice for a lot of places its widely used, like flexible PCBs. Its really the flexible PCB use of kapton that leads it to be used for touch applications.

[dmills]

The only real trap with MLCC C0G is dielectric absorption, which can sometimes be a bit higher then good film part in PP or PPS, but 'higher' is not the same as particularly bad, and they are just fine in most applications for such things.

Not sure I would use them in an application that wanted a self healing part, they are obviously not designed or specified for that.

For general HF coupling, filtering, timing they do just fine. Integrators, well, do sums based on application to decide if you can live with the dielectric absorption effects, you usually can but you need to check.

Pick a vendor with good data and ideally a decent reputation, I tend to default to Murata but there are plenty of others, the good data being the selling point, and look for the long form data not the one page cut sheet, then read the docs and maybe do some experiments to see how things really shake out. 

[T3sl4co1l]

Not sure I would use them in an application that wanted a self healing part, they are obviously not designed or specified for that.

That said, there are SMT Y caps:
https://www.digikey.com/short/mtm37z0n
Use at your own risk, I suppose.

Not to doubt their value, just that the footprint area is comparable to a THT and it's probably a somewhat specialized application that 1. has low enough vibration to accommodate ceramics reliably and 2. is specialized enough to swallow the cost of these things.

Tim

[mawyatt]

Polyimide is also triboelectric, making it a particularly odd choice for a capacitive touch dielectric material.

That makes it an odd choice for a lot of places its widely used, like flexible PCBs. Its really the flexible PCB use of kapton that leads it to be used for touch applications.

And on some semiconductors as passivation.

Best,

[gnuarm]

Oh. Good. Grief.

Why do you think people here can offer a more authoritative statement than the manufacturer?

Or do you just want to chat and form a mutual support/appreciation society?

I agree. Manufacturers are ALWAYS totally open and honest about all the negative points of their products, and can be trusted at all times to clearly point them out in their literature.

I can't tell if you are being sarcastic or not.  Capacitor makers, especially, do not publish every detail you would want to know.  The link provided by the OP talks about voltage variation of capacitance in the "high" dielectric caps, but not in the temperature compensated caps.  Or did I miss that?

[gnuarm]

Oh. Good. Grief.

Why do you think people here can offer a more authoritative statement than the manufacturer?

Or do you just want to chat and form a mutual support/appreciation society?

I agree. Manufacturers are ALWAYS totally open and honest about all the negative points of their products, and can be trusted at all times to clearly point them out in their literature.

And random people commenting on forums are ALWAYS an accurate source of detailed specifications suitable for  professionals designing commercial products.

Treez faringdon is a professional designing commercial producrs, isn't he?

Then there are the people who offer nothing in answering the question, but rag about the question being stupid.  Why don't you let others reply? 

[T3sl4co1l]

Oh. Good. Grief.

Why do you think people here can offer a more authoritative statement than the manufacturer?

Or do you just want to chat and form a mutual support/appreciation society?

I agree. Manufacturers are ALWAYS totally open and honest about all the negative points of their products, and can be trusted at all times to clearly point them out in their literature.

I can't tell if you are being sarcastic or not.  Capacitor makers, especially, do not publish every detail you would want to know.  The link provided by the OP talks about voltage variation of capacitance in the "high" dielectric caps, but not in the temperature compensated caps.  Or did I miss that?

Is coppice ever not sarcastic?

Tim

[DavidAlfa]

They're very stable in all circunstamces but also have low capacitances, so rarely useful except for tuned circuits.

[gnuarm]

They're very stable in all circunstamces but also have low capacitances, so rarely useful except for tuned circuits.

Not really accurate.  Tuned circuits are not the only type where C0G caps are useful.  And "low" is a subjective term.  It means nothing really.  I know people who regularly use 1 pF caps.  Yeah, really.

[TimFox]

I have used C0G SMT capacitors up to 100 nF in critical analog circuits (integrators), but they were in large packages that scare people who think 1206 is large.
I often use 10 nF TH capacitors in regular audio circuits.
Note that NP0 is a military specification for the same material as C0G commercial specification.
If a vendor makes a part that does not meet that spec, he shall not call it C0G.

[Zero999]

They're very stable in all circunstamces but also have low capacitances, so rarely useful except for tuned circuits.

Not really accurate.  Tuned circuits are not the only type where C0G caps are useful.  And "low" is a subjective term.  It means nothing really.  I know people who regularly use 1 pF caps.  Yeah, really.

I think he meant low energy density. Film capacitors are generally a better choice for values over 10nF or so.

[DavidAlfa]

I mean, they're 10-20x more expensive than X7Rs, unless for very specific RF uses, why use them?
For decoupling, value is not critical, use a value large enough that will be good enough at any degrade level.
Of course in any tuned LC/ RC circuit stability is a must, to me it seems like almost the only scenario to justify using C0Gs.
Though I'm only at the average level and might learn something 

[TimFox]

In critical analog circuits, a voltage-variable capacitance will distort the signal, when there is a substantial signal voltage across the capacitor.  This can include coupling as well as filtering.
For bypassing the power on a digital chip, just make sure you have sufficient capacitance at the applied DC voltage.

[coppice]

I mean, they're 10-20x more expensive than X7Rs, unless for very specific RF uses, why use them?
For decoupling, value is not critical, use a value large enough that will be good enough at any degrade level.
Of course in any tuned LC/ RC circuit stability is a must, to me it seems like almost the only scenario to justify using C0Gs.
Though I'm only at the average level and might learn something 

Anywhere a capacitor is used as a source of capacitance (e.g. filters), rather than bulk energy storage (e.g. decoupling) a non-linear capacitor is a source of distortion.

[DavidAlfa]

Yeah that's also what I was refering to.
Tuned circuits include filters
I checked them last week out of curiosity when buying at lcsc, I think the largest C0G fast 1nF or so.

[TimFox]

Mouser has 100 nF 100 V C0G capacitors in 1210 and 1206 packages, along with higher voltage (larger package) and lower voltages.

[Nominal Animal]

Well, Murata GRM3195C1H104JA05D is a 50V 100nF ±5% C0G in 1206 that costs 0.167€ per cap in lots of ten at Mouser, with plenty in stock as of 2023-07-28.  Murata says its capacitance varies by less than 0.3% = 0.3nF between 25°C and 100°C, with operating range -55°C to 125°C, and that its capacitance change with respect to bias DC voltage is neglible (Murata product details page).

Note that NP0 is a military specification for the same material as C0G commercial specification.

Not exactly: NP0 and C0G encode the same capacitance temperature coefficient α using different notations.  The US military prefers the former, but the latter is what US industry came up with (specifically, Electronics Industries Alliance standard EIA-RS-198).

For example:
 P100 = M7G (α = 100±30 ppm/K)
 NP0 = C0G (α = 0±30 ppm/K)
 N750 = U2J (α = -750±120 ppm/K)

EIA uses a weird encoding of letters and numbers, whereas the non-EIA name is simply Nppm, NP0, or Pppm for ppm ppm/K, with tolerance ±30 ppm/K for |ppm| ≤ 100, ±60 ppm/K for 100 ≤ |ppm| ≤ 500, ±120 ppm/K for 500 ≤ |ppm| < 1000, and ±250 ppm/K for |ppm| ≥ 1000 (if I've understood the naming correctly).  Very straightforward and easy to remember.

Neither of these namings consider anything other than the temperature dependence of the capacitance.

[TimFox]

That is what I wrote about NP0 and C0G.  EIA is a commercial spec.
In the military notation, there are also controlled temperature co-efficient dielectrics such as N750 (-750 ppm/K), which are sometimes seen in non-temperature contexts due to their higher dielectric constant.

[T3sl4co1l]

I mean, they're 10-20x more expensive than X7Rs, unless for very specific RF uses, why use them?
For decoupling, value is not critical, use a value large enough that will be good enough at any degrade level.
Of course in any tuned LC/ RC circuit stability is a must, to me it seems like almost the only scenario to justify using C0Gs.
Though I'm only at the average level and might learn something 

I would say the bigger issue for decoupling is their losses are so goddamned low (Q > 3000 is not unheard of).  You put two in parallel, side by side, and they oscillate together.  Even larger values like 10nF (1206).  An effective PDN using just them, requires resistors EVERYWHERE to keep the Q down!

They have many redeeming qualities.  They're about as ideal a capacitor as you can find.  They're small and dense.  They have the energy density of electrolytics, when higher voltages are considered (>200V or so).  The main downsides are the low loss (when you sometimes want high!), the small values (particularly at low voltages), and the high cost.  And, the brittleness when applicable (but that's true of ceramics in general).

The low-voltage low-value thing, and the high-voltage density, go hand-in-hand: the dielectric strength is excellent, so, layers simply can't be made thin enough (100s nm?) with high yield to make low voltage high capacity parts.  Think of them as better suited to high voltages: a typical 1210 X7R runs out of steam to the tune of 10-30nF at 250V (no matter if you buy a "47nF" or "470nF" part!); meanwhile a 1210 C0G might go up to 47 or 68nF, while still boasting a 630V rating!

Note that high voltage type 2's can have much higher C(rated V)/C(0) ratios, because the same argument applies: thicker layers, and fewer of them, mean better quality dielectric, means freedom from breakdown guaranteed to higher voltages.  To reiterate: type 2 capacitors are only rated for capacitance at zero bias, and the value at rating will always be some amount less. How much, you cannot know besides looking up the characteristics.

I've been working on an LLC SMPS project for a bit and find the 10s nF 630V C0Gs (1206 and 1210) are better in both cost and PCB/layout area than film capacitors; or if not strictly on relative cost, then the absolute cost is certainly acceptable for the few parts needed in an LLC.

X7R have modest to low losses (like, low enough they can resonate together, but not nearly low enough to use for AC purposes at switching frequencies), making them efficient bypass caps for high-ripple application, and they're small and cheap enough for general purpose use.  They fall out of favor in large sizes (physically and electrically, especially at >= 100V), where film or electrolytic take over (depending on voltage and ripple requirements).

Tim

[gnuarm]

I mean, they're 10-20x more expensive than X7Rs, unless for very specific RF uses, why use them?
For decoupling, value is not critical, use a value large enough that will be good enough at any degrade level.
Of course in any tuned LC/ RC circuit stability is a must, to me it seems like almost the only scenario to justify using C0Gs.
Though I'm only at the average level and might learn something 

Power supply decoupling of sensitive analog circuits is a very good place to use C0G caps.  X7R parts can be microphonic adding noise to the supply rail. 

I made the mistake once of using a CP Clare telephony part for a POTS interface.  It had 0dB of supply rejection ratio.   That's right!  0dB!!!  This was not in the data sheet and adding larger X7R caps got rid of the supply noise which was directly coupled onto the phone line.  But it added microphonics which picked up fan noise by the bushel! 

C0G was not an option for this particular circuit, so a whopping 100 uF electrolytic (I hate using them) was shoehorned into the circuit.  Actually, I think it was added on the connector this board plugged into, as there was no space on the board for it. 

I probably could have added a small cap in series with the CODEC power with as large an C0G as would fit.  I never used another CP Clare part either.

[temperance]

I would say the bigger issue for decoupling is their losses are so goddamned low (Q > 3000 is not unheard of).  You put two in parallel, side by side, and they oscillate together.  Even larger values like 10nF (1206).  An effective PDN using just them, requires resistors EVERYWHERE to keep the Q down!

The same can happen with low ESR capacitors. About 20 years ago I made a PFC with two 470µF capacitors in parallel and every time I unplugged the thing I could hear some whining. At first I thought the under voltage lockout isn't working. After some probing around, nothing could be seen. In the end I made horn from paper (you don't want to stick your years next to capacitors charged to 390V) to locate the sound. Somehow charge was being transferred between those two capacitors while the voltage was declining.

About the ceramic caps in an LLC instead of film caps. I'm doing the same thing for a 600W supply. Perhaps of interest:
https://www.psma.com/sites/default/files/uploads/tech-forums-capacitor/presentations/is94-quantifying-allowable-ac-parameters-dc-rated-ceramic-capacitors.pdf

Film capacitors able to handle 250Vpp > 10nF are almost non existent. (app notes from several manufacturers contain capacitors which are not suitable. Yes, Infineon. TI seems to prefer capacitors with lousy data sheets, probably not a match for the application) With film caps you are forced to limit your choice to a bunch of 4.7...6.8nF 1000Vdc caps in parallel if you don't want to limit your choice to one or two suppliers. I then had the idea to look for C0G capacitors, thinking they would be very expensive. Surprise, not expensive at all and they can handle over 400Vpp up 500kHz with an ESR well below 20mOhm. Try to find a film cap able to outperform a 630V 22nF 1206 C0G capacitor. The best you will find will be at least 6x18mm in size.

Did I mention the decrease in loop size using those small capacitors? An other advantage when you care about how much your supply radiates. Now the loop size is dominated by creepage/clearance requirements instead of large capacitors.

Just my two cents on C0G capacitors for anyone cramming an LLC converter into a small space.

[Kleinstein]

The usual C0G capacitor behave very well.  From the dielectric absorption / loss they are comparable to PP or PS film capacitors.  The nice thing is that C0G are also available as SMD parts, while the low loss film types are usually THT only, as they are limited in temperature. With modern MLCCs they also tend to be smaller than film types.
At least for the smaller values like < 25 nF they may even be cheaper than film types.

[T3sl4co1l]

The same can happen with low ESR capacitors. About 20 years ago I made a PFC with two 470µF capacitors in parallel and every time I unplugged the thing I could hear some whining. At first I thought the under voltage lockout isn't working. After some probing around, nothing could be seen. In the end I made horn from paper (you don't want to stick your years next to capacitors charged to 390V) to locate the sound. Somehow charge was being transferred between those two capacitors while the voltage was declining.

You can make almost any oscillate, of course; just add enough inductance.  That's somewhat of a hazard with large lumped values -- in large packages, the links between them can have relatively high inductance.

Hm. Unless those were connected with long cables somehow, it wouldn't make sense for that case to be audible -- 235uF (capacitors act in series in their loop) resonates with say 1uH (~1m apart) at 10kHz.  But with a control loop nearby, who knows, I guess?  (But I'm guessing you probed that and found nothing suspicious?  Or, you have truly magnificent hearing: 30kHz would be from a more reasonable 120nH, and it's not unheard of for some humans to hear this high.  Or, even more speculative, there could be some sort of hetrodyning, against the switching frequency let's say, but... *shrug*?!)

About the ceramic caps in an LLC instead of film caps. I'm doing the same thing for a 600W supply. Perhaps of interest:
https://www.psma.com/sites/default/files/uploads/tech-forums-capacitor/presentations/is94-quantifying-allowable-ac-parameters-dc-rated-ceramic-capacitors.pdf

Oh man, that had some slide gore... slide 5 apparently says:

Code: [Select]

Ex. Use of X7R (Class II dielectric)
• Provides Cost Savings
• Not Ideal as Series Resonant Capacitor (lack of stability)
• High ESR causes significant efficiency loss in power transition
• Quality Factor is orders of magnitude higher than C0G dielectrics
Design optimization is the important element here, but can come at a price. Therefore,
MLCC suppliers must work closely with design engineers to verify compliance with end
application requirements and ensure proper safety margin is considered while
supporting improvement efforts.

That must be a typo, "orders of magnitude lower" surely.

Also on pp.11-13, curious that they show a micrograph and diagram of CaZrO3, but not BaTiO3; I guess the dipole cartoon is supposed to imply domain wall movement or such, but, it doesn't really do that...

But overall, an informative and useful slide deck.  Am curious what their rationale is for "modeling" ESR, and apparently doubting their instruments (at times?).  That's not covered in the slides, but maybe there was some in the accompanying talk, or questions thereafter.

Film capacitors able to handle 250Vpp > 10nF are almost non existent. (app notes from several manufacturers contain capacitors which are not suitable. Yes, Infineon. TI seems to prefer capacitors with lousy data sheets, probably not a match for the application) With film caps you are forced to limit your choice to a bunch of 4.7...6.8nF 1000Vdc caps in parallel if you don't want to limit your choice to one or two suppliers. I then had the idea to look for C0G capacitors, thinking they would be very expensive. Surprise, not expensive at all and they can handle over 400Vpp up 500kHz with an ESR well below 20mOhm. Try to find a film cap able to outperform a 630V 22nF 1206 C0G capacitor. The best you will find will be at least 6x18mm in size.

...At frequency?  I've definitely ran hundreds of volts on induction heaters, even with commercial capacitors.  (Protip: don't use the super-compact X-type caps; they do work, surprisingly, but they get... warm... )

Conversely, I've had an application where the "DC Link" type MKPs melted.  That's some weird shit... the dielectric expands massively as it melts, carrying the electrodes with; at some point, the bottom seal (epoxy) cracks, contents squirt out, and....... they keep on operating? Sometimes?  Despite the "elephant's foot" eviscerating onto the PCB, they can actually operate that way for some time...  But eventually, enough stretch and shear occurs, electrode separation shrinks, self-healing fails, and it shorts out.

Anyway, trick is to look through high frequency and snubber types.  It's tricky, because a lot of snubbers are shit for HF losses.  CDE 935C for example, probably by way of the schoopage being whole-face (thus shielding the center by skin effect), and the generally thick build, they're good for hardly any Irms at 100kHz.  All peak, no average.  Lots of sifting through datasheets or characteristics to find V(F) or I(F) ratings (or ESR(F) and Pd ratings).

I've been impressed by, let's see, *digs through parts bin*...
Hmm B32632 (EPCOS/TDK) is now obsolete, huh...
Or what is this one, either B32672 or B32642?  Still in production, nice.
There was... B32262 maybe?? I'm sure I'm misremembering, but some 630VDC (250VAC) 0.1uF 15mm (LS) cap I used for my first big induction heating tank capacitor ever.  Rated I think 2.3A/ea at 100kHz or so?  Maybe they're still around (under the correct series).

Illinois Capacitor PPBs are nice, though on the expensive side, and if you need to obey ratings, the RMS is surprisingly not all that high.  They take abuse, at least in my limited experience; do with that what you will.

KEMET (nee Aerovox) R46, R73, etc. have some nice offerings.  Some low ESR and high density X caps, as well as pulse and resonant stuff.

I think 715P ("Orange Drop", CDE, nee Sprague) would be quite excellent if they just didn't make them with steel leads.  Dielectric losses are low and metallization seems adequate otherwise.  Expensive, probably because they're in the audio and repair boutique.

Panasonic have a number of nice dipped PP families too, though it's kind of a pain sifting through their website to find all the data.

Tim

[Zero999]

I would say the bigger issue for decoupling is their losses are so goddamned low (Q > 3000 is not unheard of).  You put two in parallel, side by side, and they oscillate together.  Even larger values like 10nF (1206).  An effective PDN using just them, requires resistors EVERYWHERE to keep the Q down!

The same can happen with low ESR capacitors. About 20 years ago I made a PFC with two 470µF capacitors in parallel and every time I unplugged the thing I could hear some whining. At first I thought the under voltage lockout isn't working. After some probing around, nothing could be seen. In the end I made horn from paper (you don't want to stick your years next to capacitors charged to 390V) to locate the sound. Somehow charge was being transferred between those two capacitors while the voltage was declining.

What sort of capacitors were they? 470µF 400V are usually aluminium electrolytic which is not piezoelectric.

[TimFox]

to T3sl4co1l:

"I think 715P ("Orange Drop", CDE, nee Sprague) would be quite excellent if they just didn't make them with steel leads.  Dielectric losses are low and metallization seems adequate otherwise.  Expensive, probably because they're in the audio and repair boutique."

Another SBE series 716P uses copper leads:  they are still available from CDE.  The shape of the body is somewhat squashed, compared with 715P, but the specs are the same.
https://www.cde.com/resources/catalogs/716p.pdf

These two series from Sprague are metal film and polypropylene foil, instead of the more common metallized film units that are smaller.

[temperance]

What sort of capacitors were they? 470µF 400V are usually aluminium electrolytic which is not piezoelectric.

Just regular (in that time BC components) 450V 470µF capacitors connected together on a copper plane. Maybe some relic from 20 years ago is still somewhere in box in a shelve between failed attempts at construction a class D amplifier.

What you hear is electrostriction. Of course it wasn't loud and about 10kHz. But clearly audible at a short distance.

T3sl4co1l
...At frequency?  I've definitely ran hundreds of volts on induction heaters, even with commercial capacitors.

100...250kHz, 250Vpp or 88Vrms. I've looked at those from TDK and Kemet.
For example the one you mentioned: B3265x: https://www.tdk-electronics.tdk.com/inf/20/20/db/fc_2009/MKP_B32651_658.pdf

I will stick with the C0G capacitors. It saves a lot of space minimizes loop area and they can be placed with a regular pick and place. Cost, about 10 cent for a 10nF 650V capacitors in quantities. Not bad at all. I don't mind if 8...10 pieces will be required.

The CDE 716P is similar and I would need smaller capacitors in parallel to reach my goal unless reverting to two pieces 2kVdc measuring about 32x11mm each.

Slide gore. I didn't even see that while scanning for other more relevant bits and pieces. Nonetheless, the slide contains some valuable information.

[ballsystemlord]

These might interest readers:
https://www.vishay.com/docs/28536/geninfo-cd-rfi-safcaps.pdf
https://www.raviyp.com/difference-between-x7r-x5r-x8r-z5u-y5v-x7s-c0g-capacitor-dielectrics/

[Weston]

I am surprised that no one has mentioned U2J capacitors yet. Its a (new-ish?) Class I dielectric with not great temperature coefficient compared to C0G and a somewhat lower but still high Q  (seems to be ~250 to >1000) and a higher energy density and lower cost.

Based on the product literature it seems targeted for power applications, both resonant capacitors and high voltage DC decoupling. I have seen it used in a few projects and have it designed in for a LLC converter I am currently working on.

https://www.digikey.com/en/product-highlight/k/kemet/u2j-dielectric-multilayer-ceramic-capacitors

[TimFox]

I am surprised that no one has mentioned U2J capacitors yet. Its a (new-ish?) Class I dielectric with not great temperature coefficient compared to C0G and a somewhat lower but still high Q  (seems to be ~250 to >1000) and a higher energy density and lower cost.

Based on the product literature it seems targeted for power applications, both resonant capacitors and high voltage DC decoupling. I have seen it used in a few projects and have it designed in for a LLC converter I am currently working on.

https://www.digikey.com/en/product-highlight/k/kemet/u2j-dielectric-multilayer-ceramic-capacitors

From the Kemet sheet, that dielectric seems to be the same as “N750” ceramic (military code).  I have used that dielectric in disc capacitors and ceramic trimmers where the higher dielectric constant resulted in a smaller size than NP0, and I could tolerate the higher tempco.