How to crappify a cap - Page 1
Forum section: electronics / beginners

author: kfitch42
author_rank: Frequent Contributor
timestamp: February 27, 2013, 04:26:06 pm
content: Ran across thishttp://mightyohm.com/blog/2013/02/simple-fix-for-bus-pirate-power-supply-oscillations/The end result of that is he solved a problem by adding a high(er) ESR cap in parallel with a low ESR cap.That got me thinking (Yeah dangerous I know :) ... just for the sake of argument, can I effectively increase the ESR of cap by adding a resistor?Would adding R1 (see attached) be the right way to add 1 Ohm of ESR?

author: c4757p
author_rank: Super Contributor
timestamp: February 27, 2013, 04:40:49 pm
content: Yes.Except "in" and "out" should be the same node.

author: kfitch42
author_rank: Frequent Contributor
timestamp: February 27, 2013, 04:51:00 pm
content: Ahhh, think I have it now.Would it matter if I put the resistor on the other side of the cap?

author: c4757p
author_rank: Super Contributor
timestamp: February 27, 2013, 04:53:33 pm
content: It is not uncommon to see discrete analog circuits stabilize capacitors like this with separate resistors from a couple ohms to a couple tens of ohms.Quote from: kfitch42 on February 27, 2013, 04:51:00 pmNot one bit.

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 27, 2013, 04:57:25 pm
content: Interesting that on the blog he paralleled the already existing cap with another one.Not sure what the net effect is but it will not increase the ESR.

author: c4757p
author_rank: Super Contributor
timestamp: February 27, 2013, 05:02:42 pm
content: Good point, I misunderstood the blog entry. I thought he was saying that the cap he replaced was parallel to another one, like how large electrolytics are often bypassed with small ceramics, and that he changed the larger one and kept it parallel to the smaller one. Not sure what's going on here.

author: mariush
author_rank: Super Contributor
timestamp: February 27, 2013, 05:44:33 pm
content: That's what they get for not respecting what datasheets say and for trying to be cheap.They could have used a 22-33uF 10v electrolytic from the start and still be fine, just the initial output voltage will ramp up a bit slower. And such electrolytic would have high enough esr to not be an issue.

author: jimmc
author_rank: Frequent Contributor
timestamp: February 27, 2013, 07:08:14 pm
content: As well as causing stability problems with the voltage regulator, a low ESR ceramic decoupling capacitor can form a high Q resonant circuit with the inductance of the power supply tracks and make matters worse at certain frequencies.Connecting a suitable low value resistor across the ceramic cap will damp out this resonance but will also short out the supply!Adding a capacitor in series with the resistor will prevent the supply short.Using a capacitor with a poor ESR is equivalent to a good capacitor with a series resistor so no additional resistor is required.Jim

author: DavidDLC
author_rank: Frequent Contributor
timestamp: February 27, 2013, 07:12:34 pm
content: I just checked my Bus Pirate v4.0 and it has the same problem on the 3.3 V power supply rail.I need to make the fix.David.

author: gotwood
author_rank: Contributor
timestamp: February 27, 2013, 07:26:42 pm
content: can I asked what you used to draw your schematic? freeware?

author: kfitch42
author_rank: Frequent Contributor
timestamp: February 27, 2013, 07:31:09 pm
content: Quote from: gotwood on February 27, 2013, 07:26:42 pmLTSpice ("free as in beer" ware)... windows only, unfortunately. One of these days I will have to see how well it runs under Wine.I drew it in LTSpice, hit "Print Screen", pasted into MS Paint, cropped, saved as .png.

author: tld
author_rank: Regular Contributor
timestamp: February 27, 2013, 10:48:01 pm
content: Quote from: kfitch42 on February 27, 2013, 07:31:09 pmI'm using LTSpice under Wine, on OS X.tld

author: c4757p
author_rank: Super Contributor
timestamp: February 27, 2013, 11:00:15 pm
content: Running perfectly under Wine on Debian for me.

author: amspire
author_rank: Super Contributor
timestamp: February 27, 2013, 11:46:55 pm
content: Quote from: PA0PBZ on February 27, 2013, 04:57:25 pmYes it will.Sounds wrong - how can a resistor in parallel with zero ohms increase the resistance?The reason is the ESRs of the two caps are not directly in parallel.If you had a perfect 1uF cap with zero ESR and put a 1uF electro with 1 ohm ESR in parallel, you will end up with a net 2uF capacitance with ESR. The point is at lower frequencies, half the current is flowing through the second cap, and that current is seeing ESR. Some resistive power is being dissipated and hence you have ESR.Obviously if the frequency goes well above the f = 1/(2*pi*Resr*C) frequency, more of the current will start to go through the perfect zero ESR cap and so the net ESR will disappear.You can actually guess the approximate value of the ESR of the 1uF electro used to snub the oscillations: it would have to add a zero at 15Khz or a bit under. A zero at 15KHz would be 10 ohms ESR using the equation above, so the 1uF electro he picked probably had an ESR roughly in the 5 to 10 ohms range. Above that or below that, it would probably not have stopped the oscillation.

author: PA4TIM
author_rank: Super Contributor
timestamp: February 28, 2013, 12:11:05 am
content: Quote from: jimmc on February 27, 2013, 07:08:14 pmYes and no, the effect is the same but it is ( in some cases) better to dissipate the power in a external resistor as in the ESR of the capacitor because dissipation is heating, and heat is the one thing caps do not like.

author: The Electrician
author_rank: Frequent Contributor
timestamp: February 28, 2013, 12:49:42 am
content: Quote from: PA0PBZ on February 27, 2013, 04:57:25 pmThis seems to be a common misunderstanding. If a couple of caps are parelleled, the ESR of the parallel combination will be greater than the ESR of the cap with the smallest ESR, if the frequency is less than:Sqrt[(C2*R2 - R1*(2*C1 + C2))/(4*C1^2*C2*Pi^2*(R1^3 + R1^2*R2))]which is around 12 MHz or so. At two orders of magnitude or so below this frequency, the ESR of the parallel combination will be fairly well approximated by:ESR~(C1^2*R1 + C2^2*R2)/(C1 + C2)^2which is the case here.I took a high quality 1 uF film cap in place of the ceramic cap mentioned in the first post and measured its ESR versus frequency. I did the same for a 10 uF electrolytic. The ESR of the electrolytic is much higher than that of the film cap.Without a full analysis, one might think that the ESR of paralleled caps must behave like the resistance of a pair of resistors--the paralleled result should be less than either resistance before paralleling. But, the mysteries of complex arithmetic don't give this result for the paralleled caps.The first image gives a mathematical analysis:Here are the sweeps of the caps on the impedance analyzer. The second image shows the ESR of the 1 uF film cap which I'm using in place of a 1 uF ceramic cap. The third image shows the ESR of the 10 uF electrolytic. The fourth image shows the individual cap ESRs plus the ESR of the parallel connection of the two caps. The middle curve is the ESR of the combination.Note that the ESR of the combination is much greater than the ESR of the 1 uF cap by itself, and the value is essentially what is predicted by the mathematical analysis.This is not unexpected if we think about the law of conservation of energy. Putting the cap with the high ESR in parallel must dissipate some additional power in its ESR, and that additional loss will show up as an increase in the ESR of the combination. Edit: This sounds good, but it isn't always true. See my later post.

author: PA0PBZ
author_rank: Super Contributor
timestamp: February 28, 2013, 11:21:58 am
content: I sort of see what you mean, but I'm still confused. Using 2 equal caps gives me half the ESR, but the frequency formula turns negative so I'm not sure what to do in that case. (Both caps 1uF, ESR 0.01 gives ESRparr 0,005 but a maximum frequency of Sqrt[-2.5E14])I probably have to draw the complex vectors to see what happens here...

author: AlfBaz
author_rank: Super Contributor
timestamp: February 28, 2013, 02:31:06 pm
content: Quote from: The Electrician on February 28, 2013, 12:49:42 amJust testing latex...Look about right?

author: AlfBaz
author_rank: Super Contributor
timestamp: February 28, 2013, 03:20:46 pm
content: I'm curious Leco, in that first image you saylet z1=r1 + Xc1. Is it because you are using the complex reactance that we dont need to do the sum of squares... ie 1/j = -j, which takes the 90deg phase shift and direction into account?

author: PA4TIM
author_rank: Super Contributor
timestamp: February 28, 2013, 05:51:59 pm
content: QuoteCan you explain that ? It think you are forgetting something. If the Current is 1 A, then all current goes in that cap through the ESR of the cap. If you take two caps, you still have 1A total current. But now divided over 2 caps. So less current per cap and less current through each ESRThe problem is you have DC behaviour and AC behaviour.For DC the inrush current is dictated by the capacitance and limitted by the ESR ( the RC time) once the inrush current is passed and the voltage over the cap is max only the ESR dictates the ripple current dissipation. So both caps will supply current to the circuit ( buffer), only limmited by there stored energy and ESR.A small capacitance with low ESR will be empty during a surge while the big one still is delivering current, but if the small one is empty the big one has to supply the extra. Total current draw stays the same, dissipation can alter for good or worse. If the big one has lower ESR the dissipation will become lower if the smal one is empty. Because all current now goes through a lower ESR.But at AC ( what you measure) the current through a cap is dictated by the reactance and ESR. If the high ESR cap has a low reactance at that frequency, most current will flow through that cap because of the much lower reactance and a small part through the second cap with low esr and high reactance.So the dissipation has to be calculated per frequency and per cap. And in this case will be higher if only one cap was used.( all current then goes through the high ESR)If the low reactance cap has a low esr and the other a high esr and high reactance the dissipation will be lower as in the first example but total dissipation wil be less because only a small part of the current goes through the high esr cap.If frequency goes up, reactance of both becomes so small, the ESR is going to dominate and in that case they behave as two parallel resistors.In your plot you see this happen. The ESR dives down at the end.Today I took 4 MKT caps parallel. The ESR of one single cap was much higher as the 4 parallel.1 philips 10 % 250V MKT 2.2 uF, measures 0.371 Ohm at 1KHz and 0.078 Ohm at 100 KHz.The 4 caps parallel including extra copper to connect them, so extra ESR :At 1 KHz i measure 0.097 Ohm ( if you correct for the extra copper 1/4th of the ESR)At 100 KHz i measure 0.020 Ohm, ( again about 1/4th of the ESR of one cap)Edit: hope it now makes more sense.

author: The Electrician
author_rank: Frequent Contributor
timestamp: February 28, 2013, 06:35:20 pm
content: Quote from: PA0PBZ on February 28, 2013, 11:21:58 amThe behavior of the ESR of a pair of paralleled caps is somewhat counterintuitive, to say the least! The result depends on just how different the ESR of one cap is from the other, and the difference in the capacitances too.Further investigation shows that the frequency formula you're referring to only gives a useful result if the ESR of C1 is less than (C2*R2)/(2*C1+C2). To understand this see the attached images. In these images and in the formulas, R1 is the ESR of C1 and R2 is the ESR of C2.In the first image, the red horizontal line is the value of the ESR of C1. The ESR of C1 is less than (C2*R2)/(2*C1+C2) in this case. The blue curve is the ESR of the parallel combination of the two caps. Just above the graphs is listed the values of the capacitances and the ESRs. Note that at low frequencies, the ESR of the combination is GREATER than the smallest ESR, but there is a crossover frequency, above which the combination ESR is LOWER than the smallest ESR. The frequency formula is giving that crossover frequency.In the second image the ESR of C1 is greater than (C2*R2)/(2*C1+C2). In this case, there is no crossover of the parallel ESR with the ESR of C1; the parallel ESR is less that the ESR of C1 for all frequencies and the frequency formula fails.The lesson here is that paralleling a good cap with a crappy cap doesn't always crappify the good cap, even at low frequencies. You just have to be sure that the crappy cap is enough crappier than the other one, and the crossover frequency is high enough for your purpose. I did not realize this myself; this shows the value of a proper analysis.

author: The Electrician
author_rank: Frequent Contributor
timestamp: February 28, 2013, 06:45:41 pm
content: Quote from: AlfBaz on February 28, 2013, 03:20:46 pmThe answer is yes. i find the arithmetic much easier if the computations are done with complex numbers. I also find that doing things this way avoids mistakes.For this particular problem, we specifically wanted the real part of the impedance (that's what ESR is), and doing all the computations with complex numbers made it easy to extract the real part.

author: The Electrician
author_rank: Frequent Contributor
timestamp: February 28, 2013, 07:31:03 pm
content: Quote from: PA4TIM on February 28, 2013, 05:51:59 pmIt isn't dictated by the reactance alone; what about the ESR? I know you are aware that the ESR is involved, but in this sentence you forgot to include it. This statement makes it sound like the reactance alone dictates the current.Quote from: PA4TIM on February 28, 2013, 05:51:59 pmIn the first part of the first sentence you refer to "the high ESR cap" as though the other cap will NOT be a "high ESR cap", but then later in the sentence you are apparently referring to the second cap, and you call it "the cap with high esr". I find this confusing.I am aware that English is not your native language. With all due respect, and with no intention to be insulting, I must say that sometimes your sentence structure is not clear, and you seem to be saying (or not saying) things that you don't intend to say, or you fail to say what you really intend to say.I have visited your web site, and I'm impressed by (and envious of) your collection of instruments. You have obviously spent a lot of time experimenting with measurements of capacitors and inductors, and I enjoy reading your results. I hope you post more, but sometimes I have difficulty understanding what you're saying.Sometimes I disagree with what you say, but sometimes when I appear to disagree, the reason is that I'm trying to clarify something you have said that wan't clear.These results are an example of what I find unclear. I think they would have been better presented in the form of a chart.Quote from: PA4TIM on February 28, 2013, 05:51:59 pmAt any rate, in my post above, I extend my analysis and show fully how the ESR of the parallel combination depends on frequency and on the relative values of the ESR and capacitance of the two capacitors.

author: The Electrician
author_rank: Frequent Contributor
timestamp: February 28, 2013, 07:47:01 pm
content: I was looking at the expression for the parallel ESR of two caps, and decided to see what it becomes at very low frequencies.The attachment show limit formulas for the value of the parallel ESR as the frequency goes lower and lower.The first expression is for different cap and ESR values. The second expression is for identical cap values, but possibly different ESRs.

author: The Electrician
author_rank: Frequent Contributor
timestamp: February 28, 2013, 09:22:44 pm
content: It's always good to have experimental verification of a mathematical result that is counterintuitive.I picked out a couple of mylar capacitors with ESR versus frequency curves as nearly identical as possible. The first image shows three sweeps of the two .47 uF caps. The top two curves are the ESR of the two caps individually. The bottom curve is the ESR of the two caps in parallel.The second image shows the same three sweeps as the first image, plus a sweep of one of the caps with an additional 4 ohm resistor in series with it. The top curve is of the cap with 4 ohms in series.The condition for the existence of a parallel ESR that is greater than the ESR of the better cap is that R1 is less than (C2*R2)/(2*C1+C2). If we set C2=C1, this expression becomes R1<R2/3. So if we have caps with the same capacitance, with ESRs of R1 and R2, R2 must be greater than 3*R1 for a parallel ESR greater than the ESR of the better cap to exist.The experimental results are not quite straightforward because the ESR of these capacitors varies with frequency. But, if we can find a frequency where R2 is greater than 3*R1, we should see the ESR of the parallel combination being greater than the ESR of one cap alone.The third image shows the previous curves plus one new one. The new curve is the ESR of a parallel combination of one of the caps with a 4 ohm resistor in series and the other cap without any additional resistance in series. This is to show the effect of a crappy cap (the one with an additional 4 ohms in series) in parallel with a good (sort of) cap.The ESR of the combination starts out less than the ESR of a single cap, but at about 1.13 kHz, the ESR of the combination becomes greater than the ESR of a single cap, until at about 500 kHz it is again less than the ESR of a single cap.Note that at the frequency of marker A, the ESR of the cap with the 4 ohm resistor in series is about 5.8 ohms. At that same frequency, the ESR of a single cap is about 1.78 ohms. That is about the 3 to 1 ratio the mathematics predicts should be where the crappy cap can cause the parallel ESR to be greater than the ESR of the "good" cap, and indeed that is where the ESR of the combination becomes greater than the ESR of the "better" cap.

author: PA4TIM
author_rank: Super Contributor
timestamp: February 28, 2013, 09:42:24 pm
content: You are right, problem is I must do most typing laying down, do use an ipad. The touchscreen is hard to operate for me. Alltough the screen will not allways react well on the screen i'm glad there are tablets so I can read things like EEV blog. Correcting is even more hard. A text like above took me allmost an hour. Halfway it went wrong and a part dissapeared because i pressed the correction key on the touchscreen so then it became a total mess. Sorry for that.I will correct the text.I noticed your later post and your conclusions are ( i think) in the same direction as what I was trying to write. Placing caps parallel is rather unpredictable if you do not know the parameters. It can be an improvement or make it worse. So the only way is measuring on the frequency of interest. Your meter (or a vna) is a very nice tool to do that. It will show if the combination was a good choise.I made a powersupply for an instrument, used a lot of filtering, inductors, ferite beds and parallel caps. The result was one severe oscillating powerrail. The others stayed stable. Adding a resistor in serie with a MKT cap solved the problem.I have it not at hand here at the moment, but "AC theory" from D. Knight has a lot of math and theory about calculating complex impedances parallel. It is a free download at his site. Very well written and interesting. It goes very deep.For your last test. What if you place the resistor at the other site of the cap?Problem is ESR behaves like a resistor but it is not exact the same, the resistor adds selfinductance, extra copper, thermo electric effects, solder, even maybe some capacitance. The ESR is sort of distributed through the capacitor. So i think the phase ( the type a vna meaures) will behave different. If I'm fit enough I will do some vna tests tommorow for the same experiment. Not that I do not believe you, or think you measure wrong but I find your theory and results very interesting, and maybe a vna gives some additions information.Like in an inductor, what we measure and looks like distributed capacitance, is in real the delay of the signal through the coil. Like the Vf in coax. Combined with real capacitance and inter winding capacitance.So it measures as capacitance but it is not.

author: The Electrician
author_rank: Frequent Contributor
timestamp: February 28, 2013, 11:15:10 pm
content: Quote from: PA4TIM on February 28, 2013, 09:42:24 pmIf you can post the link I would like to download it.Quote from: PA4TIM on February 28, 2013, 09:42:24 pmDo you mean "...the other side of the cap?". By placing the resistor at the other side, do you mean to connect the resistor to the other lead of the capacitor? I suspect that's what you mean, so I did the measurement. The attached image shows the ESR and phase of the capacitor plus resistor with two sweeps superimposed with the scale changed to get maximum resolution, and the resistor connected to first one cap lead, then the other. They appear to be right on top of each other, which is what I would have expected at such low frequencies. I'm only sweeping up to 1 MHz maximum so most of the curve's extent is at lower frequencies than that.The capacitor does have an outside foil of course, and at higher frequencies it might make a difference if the lead connected to the outside foil is the one connected to the resistor (or the other way around), but I don't see any difference in these sweeps.

author: PA4TIM
author_rank: Super Contributor
timestamp: February 28, 2013, 11:44:12 pm
content: What I mean is high side of meter- resistor- cap- low side meterAnd then hi side - cap - resistor - low side meter.And this in parallel with the other cap.But I do not expect it to make a difference, at least not at these frequencies. At high frequency it is very interesting regarding pcb design. Like the inductance of traces, vias, the place of solderislands. There are caps with 4 solder connections in a cross, caps with build in series resistors ( not new, i have a few old micas with resistors in a potted housing) sometimes caps are used and selected to work on the self resonant frequency so impedance for the wanted signal is as minimal as possible. The Agilent impedance measurement handbook has some info on that. Not very deep but interesting.I understand you allready have the book from Hiebel. Do you know the book from Joel Dunsmore, that is great too. I will edit his post to place the link to Knight because I can not switch tabs on this thing without loosing the previous text.Edit :http://www.g3ynh.info/zdocs/AC_theory/AC_theory.pdf

author: BravoV
author_rank: Super Contributor
timestamp: March 01, 2013, 01:02:55 am
content: The Electrician, thanks, learned a lot from your posts here !Looking at your knowledge and that piece of fine gadget, I assume you are a proffesional ? Cause just checked the price of that gear, dropped my jaw real hard here and don't think that is hobbyst grade stuff.

author: The Electrician
author_rank: Frequent Contributor
timestamp: March 01, 2013, 02:02:49 am
content: Quote from: BravoV on March 01, 2013, 01:02:55 amYes, I got my EE decades ago.Have at look at this thread:https://www.eevblog.com/forum/projects/capacitor-measurements-on-an-impedance-analyzer/where I said "...such instruments are usually only available to working engineers; not so much to hobbyists!"If your jaw has any room to drop further, check out this analyzer:http://www.home.agilent.com/en/pd-1000000858%3Aepsg%3Apro-pn-4294A/precision-impedance-analyzer-40-hz-to-110-mhz?nid=-33831.536879654.00&cc=US&lc=eng

author: BravoV
author_rank: Super Contributor
timestamp: March 01, 2013, 02:16:17 am
content: LOL ... much appreciated and had that thread bookmarked already, should you made any interesting measurements again, please update it, pretty sure it is watched & followed closely by many fellows here, again, thanks.Edit : Seems like you could use of that latex site like AlfBaz did, rather that thru the hassles uploading those math formulas in picture, just a thought.

author: AlfBaz
author_rank: Super Contributor
timestamp: March 01, 2013, 02:48:30 am
content: Quote from: BravoV on March 01, 2013, 02:16:17 amThe beauty of that "dynamic" picture link is that if I hit edit post I can edit the formula.Might post a thread explaining how it's done

author: The Electrician
author_rank: Frequent Contributor
timestamp: March 01, 2013, 03:51:00 am
content: AFAIK this forum software can't deal with tex (or latex) directly. Is that true?The latex site you linked still is treated as an image, surrounded by (img)(/img) so in a few years if that site goes away or changes drastically, such links won't work. The images I upload aren't much of a hassle and they will be more or less permanent.

author: BravoV
author_rank: Super Contributor
timestamp: March 01, 2013, 05:25:24 am
content: Quote from: The Electrician on March 01, 2013, 03:51:00 amThis is even better, glad to know that you're also aware not to rely at external hosting sites, attached pictures or any other infos inside the post still is the best choice until now, they will last as long as this site's life.Really hate and very disappointed when everytime reading an excellent post/thread at forums that all it's picture or other precious infos are gone, not to mention sometimes they turned into those nasty spam advertisings cause the host has changed their business along the time, especially those free ones.

author: mzzj
author_rank: Super Contributor
timestamp: March 01, 2013, 06:13:23 am
content: Quote from: PA0PBZ on February 27, 2013, 04:57:25 pmWill increase ESR as others have shown already but more importantlydecreasessupplyimpedance.

author: AlfBaz
author_rank: Super Contributor
timestamp: March 01, 2013, 07:19:59 am
content: Quote from: The Electrician on March 01, 2013, 03:51:00 amNo this site cant render texQuotePlus BravoV's comments are a good point. Its a bit of a shame but on plus side, typing formulae in ascii has the benefit of being easier to translate into code if needed...

author: PA0PBZ
author_rank: Super Contributor
timestamp: March 01, 2013, 08:13:23 am
content: Quote from: mzzj on March 01, 2013, 06:13:23 amThat is not always the case as you might have noticed reading all the comments

author: GK
author_rank: Super Contributor
timestamp: March 01, 2013, 08:23:48 am
content: The term ESR should only be used to refer to the restive portion of the capacitors total impedance. In large value electrolytic capacitors the ESR can dominate over a wide frequency range. See the plots here:http://www.users.on.net/~glenk/capacitor/capacitor.htmPutting multiple large-value electrolytic capacitors in parallel is an effective and reliable way to lower the net ESR (as well as the total capacitance) and is often done in SMPS design, where just one real large capacitor may not fit the required form factor, or may not have a high enough ripple current rating on it own.

author: PA4TIM
author_rank: Super Contributor
timestamp: March 01, 2013, 08:50:13 am
content: I think you mean, also increase capacitance, not lower capacitance.Those plots can have a problem, the setup with probes. (I do not say they this is the case but it can be) The resonance looks like parallel resonance because of the voltage increase.The pots go to very high frequency, it should be better to solder probeadapters to the pcb and push in 10X probes with sufficient bandwidth.But I agree it is a good way to lower output impedance of a psu and less dissipation caused by ripple current per condensator, what in turn increases the lifetime of the cap.I was testing a dynamic load and reading the appnotes from Williams about that, and he advised to parallel a whole bunch of caps while testing. So I did and that gave me a 1:1 currentresponse on the switching without ringing or other nasty effects. At first I used a good psu to align the load ( i made many adjustment trimmers to peak everything as good as possible) but that gave severe ringing around 50 KHz. But with some beefy caps parallel (50000 uF total) i could adjust everything perfect.( it is a miniload, only to 3A, it is easy to get it to 10A or more, but I allready have a big one, this is a small one for quick checking LM317 or 78XX psu's on ripple and stbility as part of other designs)

author: GK
author_rank: Super Contributor
timestamp: March 01, 2013, 08:55:56 am
content: Yes I meant > capacitance.There isn't anything wrong with the plots or the (200MHz 10:1) probes. The parallel resonances shown are due to the net inductance resonating with the much smaller bypass capacitors capacitance.

author: PA4TIM
author_rank: Super Contributor
timestamp: March 01, 2013, 09:49:54 am
content: The probes are fine, i mean those to huge loop antennas they call groundleads ;-)I will pace two pictures of the efect of such a loop. Williams also gives a lot of examples why this is not the way to probe at high frequencyOriginal signalProbe in probe adapterProbe like you use it

author: GK
author_rank: Super Contributor
timestamp: March 01, 2013, 09:52:37 am
content: CRO probe resonances and funky effects did not kick in until >50 MHz, that's why I limited the measurements to =< 30 MHz

author: The Electrician
author_rank: Frequent Contributor
timestamp: March 02, 2013, 11:05:19 am
content: Quote from: GK on March 01, 2013, 08:23:48 amFollowups to this post would seem to be best continued on your thread:https://www.eevblog.com/forum/projects/bypassing-large-electro%27s-with-smaller-caps/