Ceramic Capacitor Behavior - Page 1
Forum section: electronics / projects

author: mawyatt
author_rank: Super Contributor
timestamp: June 08, 2024, 08:17:53 pm
content: There's been some discussions on the bad behavior of ceramic capacitors and specifically how the high dielectric types have a strong bias voltage dependance.Here's an example of how one might use a simple RC Low Pass Filter for PWM, Bandwidth Limit, or Noise Filter application. This LPF is a 1K resistor with a shunt 0.1uF cheap ceramic disc of unknown origin. Three filters were assembled on a Protoboard and two of the filters had the ceramic shunt capacitor biased at 10V and 30VDC, while the first had no DC bias and used as a reference for comparisons.The 1st plot shows the Bode response for 10 to 1MHz without any DC bias applied to any filters, and the three filters behave similar as expected. Magenta(C2) is the 1st LPF, Blue(C3) the 2nd LPF and Green(C4) the 3rd LPF.The 2nd plot shows the 10V DC bias applied to the 2nd filter (Blue) and 30VDC applied to the 3rd filter (Green), note how the low pass corner is pushed out as the DC bias reduces the effective shunt capacitance. The unbiased filter 1st trace (Magneta) has a -3dB corner of ~1.4KHz, while the 2nd (Blue) 10V bias is moved out to ~4KHz. The last plot shows the same result with the cursor moved to the 3rd trace (Green) with 30V bias and a -3dB corner of ~8.3KHz.This shows quite a change in filter performance caused by capacitance dependance wrt to applied DC bias voltage.Best,

author: RoGeorge
author_rank: Super Contributor
timestamp: June 08, 2024, 09:26:28 pm
content: Bad behavior maybe, but I see there a Voltage Controlled Filter for audio.Analog synth musicians should be thrilled by the opportunity.Thanks for posting the measurements!

author: mawyatt
author_rank: Super Contributor
timestamp: June 08, 2024, 09:29:13 pm
content: They (high K Dielectrics) also have really bad hysteresisBest,

author: tggzzz
author_rank: Super Contributor
timestamp: June 08, 2024, 10:47:37 pm
content: I've also been able to eyeball this in the time domain. Not only was an RC risetime dependent on the amplitude, but as the amplitude increased the risetime became visibly non-exponential.Replaced the (small allegedly C0G) capacitor with an air-gap trimcap, and order was restored to the universe.

author: mawyatt
author_rank: Super Contributor
timestamp: June 08, 2024, 11:43:06 pm
content: Doubt that was a C0G you replaced, these are known for their excellent overall characteristics with almost no voltage dependance. They are so good that they are used as the main core integration capacitor in many high resolution leading DMMsBest

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 09, 2024, 04:49:04 am
content: Neat thing about large-signal waveforms here, you can get something more like a linear, or with an inflection point anyway, than an exponential curve on your square wave.Can you do it with a ferrite bead as well? Current bias? That would be of interest for related threads.(Albeit no currently running threads, I think.)Tim

author: Harry_22
author_rank: Frequent Contributor
timestamp: June 09, 2024, 09:18:41 am
content: Good job!Below is some Microcap modeling according to your research.

author: nctnico
author_rank: Super Contributor
timestamp: June 09, 2024, 10:17:21 am
content: It has been known for a long time to not use ceramic capacitors in signal paths where low distortion (for example audio) is critical. Another pitfall with ceramic capacitors is leakage current which can be in the double digit nA range.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 09, 2024, 10:41:28 am
content: Microphonic also; film and tantalum can be preferred for low-frequency signal purposes for these reasons.Tim

author: Harry_22
author_rank: Frequent Contributor
timestamp: June 09, 2024, 11:17:44 am
content: Ceramic is used in some places of a guitar tube amplifier to color the sound.

author: mawyatt
author_rank: Super Contributor
timestamp: June 09, 2024, 12:50:24 pm
content: Quote from: Harry_22 on June 09, 2024, 09:18:41 amNice work yourself with theses modelsThe phase effects as shown with your L R model is due to the setup and not actually due to capacitor, sloppy setup using long leads and a Protoboard, good enough to show the DC Bias effects tho!!Edit: Grabbed one of the cheap caps and our LCR Meter DC Bias Adapter with some custom plotting software using a TH2830 LCR Meter, SDP3303X Supply and AG34401A DMM to sweep Capacitor DC Voltage (need to work on the plotting routines, our software skills are not that good!!!)https://www.eevblog.com/forum/projects/bias-network-for-lcr-meter/https://www.eevblog.com/forum/testgear/lcr-meter-plot-software/Best,

author: mawyatt
author_rank: Super Contributor
timestamp: June 11, 2024, 05:59:05 pm
content: More bad ceramic capacitor behavior. Plot generated with TH2830 LCR, SPD3303X and SDM3065X for temperature reading. Heating source is ceramic resistor, see below for details.https://www.eevblog.com/forum/projects/lcr-lab-grade-parameter-plotting-fixture/Edit: 0.01uF STE Blue Disc Ceramic, 10nF Green Mylar Film and Yellow 0.1uF added, note the better Mylar performance, especially the popular Yellow Rectangular type. Also a 10nF Mica as a reference for stability.Best,

author: coppice
author_rank: Super Contributor
timestamp: June 11, 2024, 06:16:12 pm
content: Quote from: mawyatt on June 11, 2024, 05:59:05 pmI've seen people do temperature tests on their new design, get widely varying results across the temperature range, and then try to blame every part of the design except the capacitors.People keep talking about the variation of capacitance of these capacitors with DC, but it varies with AC too. The capacitance can vary through each cycle of the signal, leading to some interesting non-linearities in the outcome.

author: harerod
author_rank: Frequent Contributor
timestamp: June 11, 2024, 06:29:14 pm
content: Quote from: T3sl4co1l on June 09, 2024, 04:49:04 amThanks for the cue, I was going to post this link:http://harerod.de/applications_eng.html#EmiFilTestThis contains a "test protocol with pictures" for download, which I attached to this post. I think I put that online, after one of our discussions about current bias of ferrite beads.These little boards are really helpful to check real life performance against datasheets. The first board shown can be used to voltage bias a capacitor or current bias an inductor. More examples are in the pdf. I have several more that are not shown online.

author: mawyatt
author_rank: Super Contributor
timestamp: June 11, 2024, 11:32:38 pm
content: Quote from: coppice on June 11, 2024, 06:16:12 pmCapacitors are far from ideal under almost all conditions, and folks should pay close attention to their application.Since the problem with voltage sensitivity applies to the voltageacrossthe capacitor (differentially), for a given value capacitance lower frequencies become more problematic as the capacitive impedance is higher and usually a larger signal differential voltage across the cap for the volt dependent non-linear effects to work with. Whereas at higher signal frequencies the capacitive impedance is lower and less differential signal voltage, however now ESR and ESL become more problematic.So there seems to be no "Sweet Spot" frequency-wise for general capacitor use, and likely why we have so many different types!!Best,

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 12, 2024, 12:02:53 am
content: I always found it funny that, many people in audio circles, malign for example, the use of electrolytic capacitors in the signal path (coupling, filtering); no, they're not particularly good components, at all, but that's exactly the point, you use a low enough cutoff frequency in the coupling network thatyou don't care...Of course, that was also when I realized some people will form beliefs about things, independent of any rational argument for or against those thingsTim

author: mawyatt
author_rank: Super Contributor
timestamp: June 12, 2024, 12:17:05 am
content: Some of the electroyltics we've tested aren't too bad as long as the peak signal voltage doesn't venture so far as to reverse the instantaneous voltage across the cap to much, and most behave better than the ultra-high K ceramic types wrt to signal/bias voltage and temperature effects.Agree, the "audio" stuff sometimes seems "magic" to certain folks and defies common senseMaybe we can sell some of these negative noise resistors and anti-distortion capacitors that suck out the signal noise and distortionBest,

author: TimFox
author_rank: Super Contributor
timestamp: June 12, 2024, 02:26:57 am
content: Quote from: nctnico on June 09, 2024, 10:17:21 amThat opinion in audio circles is based on capacitors other than C0G/NP0.Only recently have relatively large values (> 100 nF) been readily available in C0G/NP0, so film capacitors (PS or PP) were the appropriate choice.

author: Smokey
author_rank: Super Contributor
timestamp: September 08, 2024, 02:57:46 am
content: I finally got an LCR that can measure DC Bias and threw in the 16V, 47uF ceramics I've been using as DC-DC converter 5V output caps...https://search.murata.co.jp/Ceramy/image/img/A01X/G101/ENG/GRM32EC81C476KE15-01.pdfFunny that in the data sheet they give this generic "Example" plot that shows capacitance change at 5V being negligible (or even positive?).But the actual product page shows the real plot for this specific part....https://www.murata.com/en-us/products/productdetail?partno=GRM32EC81C476KE15%23capacitance change of -42% at 5V for a 16V rated part. Measurements confirm essentially this.well... that's bigger than I expected.. I'm actually surprised the converter was stable.

author: ArdWar
author_rank: Frequent Contributor
timestamp: September 08, 2024, 04:02:44 am
content: You shouldn't take charts in whole family template datasheet like that as anything more than showing "yes,aC-V chart looks like this".All (almost?) the bigger capacitor manufacturers do have their own online detailed parametric charts for each P/N. Use that instead if you have to.: Idk if they all got one. I'm only familiar with those from KEMET, Samsung, Murata and TDK.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 08, 2024, 04:05:24 am
content: Quote from: Smokey on September 08, 2024, 02:57:46 amYeah, a lot of people misinterpret this. I forget if it's Murata or someone else, but another datasheet shows several colored curves, which one might understand as including the linked part in question. Nevermind that in both cases, you're looking at thefamily datasheet, mostly dull junk about packaging, specifications and methods, quality and so on.This one at least is specific that it's the "Sample: X7R(R7) Characteristics 0.1μF, Rated Voltage 50VDC" part, clearly not just anything in the family.It would probably be better if they didn't have a curve at all and just had verbiage to the effect of "characteristics vary with temperature and voltage; consult the characteristics database at xxx for more information" -- or, you know, they actually generated the fucking datasheets per-part with curves. They can, Samsung does (sometimes..), but most still do not.Quote from: ArdWar on September 08, 2024, 04:02:44 amI would consider AVX pretty big. Venkel perhaps as well. Neither offers characteristics on anything last I checked. Their loss; I've no problem buying their film caps or whatever, but type 2 ceramics are a strict no-no for me.Tim

author: Smokey
author_rank: Super Contributor
timestamp: September 08, 2024, 07:28:54 am
content: This brings up an interesting question....For all you DC-DC converter designers, what is your process for selecting specific part numbers for input and output capacitors?.. How much work do you do up front scrutinizing datasheets .... vs buying some caps and characterizing them yourself on their own .... vs putting them in circuit and seeing how the converter works and going from there?

author: Someone
author_rank: Super Contributor
timestamp: September 08, 2024, 07:43:25 am
content: Quote from: Smokey on September 08, 2024, 07:28:54 amWhere models/parameters/characteristics are available online you can usually get it right in simulation and have no surprises on the first hardware revision.

author: Smokey
author_rank: Super Contributor
timestamp: September 08, 2024, 08:02:12 am
content: Quote from: Someone on September 08, 2024, 07:43:25 amSo you simulate with specific part numbers and matching specific manufacturer models for all the caps? That still leaves the question of your selection criteria for picking caps to try in the simulation.

author: Someone
author_rank: Super Contributor
timestamp: September 08, 2024, 08:25:23 am
content: Quote from: Smokey on September 08, 2024, 08:02:12 amOnce the characteristics of candidate parts are known simulation might be directly on that, or a degraded/toleranced version, or on some worst case of a set of possible caps. Depends on what the time/budget/constraints are.Knowing which parts to look for in the first instance is either experience or time consuming (or somewhere inbetween).

author: ArdWar
author_rank: Frequent Contributor
timestamp: September 08, 2024, 10:11:05 am
content: For non price/performance constrained design it's usually easier to simply design with enough margin that any typical capacitor is sufficient (aka the jellybean method). Personally I also rarely stray too far from using my selection of proven good design unless necessary. In this case characterization is more like verification, especially for EMI and other unintended interactions.

author: Siwastaja
author_rank: Super Contributor
timestamp: September 08, 2024, 11:27:43 am
content: Quote from: ArdWar on September 08, 2024, 04:02:44 amYeah. It'sunderstandablethey use a (dynamic) web page instead of a PDF document, but why the f*** can't they just say they do. It took meyearsto realize that the data is available, just not on the datasheet. Why not print "for more data, go to our website at qwerty.com <insert QR code here>" on the document? Or stop producing the half-assed PDF datasheets completely and ask the distributor to link to their website instead? Nowadays reading this forum it seems many people still don't realize the data is available on the manufacturer's websites.

author: tggzzz
author_rank: Super Contributor
timestamp: September 08, 2024, 01:01:20 pm
content: Quote from: Siwastaja on September 08, 2024, 11:27:43 am“But theplansdatasheets were on display…”“On display? I eventually had to go down to the cellar to find them.”“That’s the display department.”“With a flashlight.”“Ah, well, the lights had probably gone.”“So had the stairs.”“But look, you found the notice, didn’t you?”“Yes,” said Arthur, “yes I did. It was on display in the bottom of a locked filing cabinet stuck in a disused lavatory with a sign on the door saying ‘Beware of the Leopard.”― Douglas Adams, The Hitchhiker’s Guide to the Galaxy,1978Yes, almost half a century ago. Plus ça change, plus c'est la même chose

author: mawyatt
author_rank: Super Contributor
timestamp: September 08, 2024, 02:33:56 pm
content: These are some of the very reasons we've investing in a Hioki IM3536 LCR Meter as well as a Tonghui TH2830 and a bunch of LCR Meter fixtures, some OEM, some modified, some custom!Capacitors are highly complex with all sorts of issues, parameters, features, surprises one must pay close attention too, ceramics seem to lead in all these categoriesIn our case awhile back we had a new project which involved 128 up to 256 (actually could go to 1024) independent AWG channels capable of producing ~ +-100V peak signals with 16 bit resolution 15 bit accuracy, and have direct Bi-Phase waveform modulation with less than 5mv waveform average offset between Bi-Phase polarities with 200Vpp signals. We were recommend for this project by an Advanced Research USG agency based upon our prior career and were not allowed to attend the actual system application testing (no need to know basis), which involved directly controlling a new type Advanced Phased Array Radar based upon Liquid Crystal technology.This project started off right when component availability became scarce due to the Pandemic, and we couldn't find anything in stock anywhere, and had to change the design often to accommodate what was available rather than what we wanted. Frustrating as hell, and scary, as the system had to work first time without our participation with this unknown system defined only by the interface!!With this in mind, and not wanting egg all over our face, we decided to thoroughly test every critical component and not rely on vendors data sheets, especially unfamiliar ones we had to use because of the component situation. So we got a number of KS34465A DMMs, IM3536 and TH2830, all new with Calibration Certifications and set out to check each critical component.Anyway, we were told the overall system was setup inside a large Anechoic Chamber, Target Identified with Coordinates, and Phased Array Beam nailed the Target Spot On, First Time!! So guess this effort paid off as the overall system worked as expected, and we didn't get egg all over our faceThis effort alerted us to the various issues with unknown vendor ceramic capacitors (film types also) and precision resistors. Also created a more conscious review of capacitor data sheets, even from well known vendors, and we began to do more testing with these LCR Meters just to verify device parameters, even from our usual "Go To" vendors.As stated by others even the "Quality" Sources for ceramic caps have details buried in various data sheets, on-line resources and such, which makes it difficult to "extract" what's important for the designer!! Here is where the quality LCR meters can prove worthwhile, allowing one to make measurements with devices "in hand" to establish component confidence, something we've had to do often latelyBest,

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 08, 2024, 07:11:19 pm
content: Quote from: Smokey on September 08, 2024, 07:28:54 amIf the voltage swing is large, on a DC input or output, something's gone terribly wrong with my design -- or it's a wide swing application like a class D amplifier, where linearity has already made the requirement clear. So for most cases, a linearized model suffices. Here's a recent example:The capacitor parameters go into a series RLC model (seehttps://www.seventransistorlabs.com/Modeling/index.html#spiceasimRLCSER.ckt), for convenient representation. The " (xN)" is display only, and the parameters are ESR, ESL and C in order. The inductor is a Coilcraft model. Modeled are 12 and 2 x 1210s, and 3 x electrolytics, for a 12V 800W converter output. Load assumed, wirewound resistor. Resonant, so the rectifier output is reasonably sinusoidal and RMS current is given, and thus output voltage amplitude at/around 2Fsw will be representative, and other frequencies can be eyeballed lower as needed (of course, it's got enough lowpass filtering that harmonics are quickly irrelevant). AC and transient analysis are used, with input and output sources active depending on wiring (I3 is connected to input or output (dangling wire) as needed). Only doing step response for output (step load, see rectifier response). Also, note this is the worst-case assumption, with current driving the rectifier; a resonant supply may well have some impedance there, I hadn't tested that as of this model.In any case, the notes below (and others) survey candidate parts in various ratings, and I put in the total value as needed.Tim

author: Howardlong
author_rank: Super Contributor
timestamp: September 08, 2024, 07:37:53 pm
content: Something else to be aware of that I wasn't until recently is that class II MLCC ceramic caps (e.g. X7R, Y5V, Z5U) degrade over time. Class I (C0G/NP0) aren't affected by this phenomenon.This aging varies significantly not only by dielectric, but also by manufacturer, apparently due to the may the molecular dipoles arrange within crystals in the dielectric.Thankfully most of these caps are used in non-stringent applications such as AC coupling and DC decoupling, but there may be latent failures in waiting in marginal designs. If you're using them for filters or timing with fairly stringent characteristics, you might want to re-think your design.https://youtu.be/yLuWcTo2cb4?si=A9nzO6_W9xLe6vnY

author: floobydust
author_rank: Super Contributor
timestamp: September 08, 2024, 08:01:00 pm
content: For MLCC ceramics, I've mentioned in thread hereGood practice for MLCC power by pass capacitorbefore that they are full of game.MLCC Class II aging in the first few minutes of useis an elephant in the room. Note that soldering heat also resets the crystalline structure wrt aging apparently. Pulling the part to measure it changes its value.The lobbying MLCC cap manufacturers to stop the fake specs, after an automotive product of Continental's failed (LDO oscillating). I have no idea if anything came from that.Even finding voltage-coefficient is difficult, some manufacturers really hide the bad news on their website. I don't use those brands.For electrolytics in the sim, I would include tolerance and any low temp ESR derating if necessary. TheZLJis -20% tolerance and triple ESR at -10°C.