Any advantage of electrolytics over ceramics? - Page 1
Forum section: electronics / general

author: cksa
author_rank: Regular Contributor
timestamp: July 28, 2010, 01:05:09 pm
content: Other than cost, are there any performance drawbacks of using ceramic capacitors over their electrolytic counterparts?I have a datasheet that specifies a 100nF ceramic in parallel with a 10uF electrolytic capacitor for decoupling the power supply. Can I replace the 10uF electrolytic with a 10uF ceramic?

author: david77
author_rank: Frequent Contributor
timestamp: July 28, 2010, 01:11:53 pm
content: I won't say a 10µf ceramic doesn't exist, but I highly doubt it.One of the advantages of electrolytic caps is that there are high values available.You would be hard pressed to find an off-the-shelf ceramic >1µf.Just use the electrolytic or a tantalum, you won't have much choice there.

author: cksa
author_rank: Regular Contributor
timestamp: July 28, 2010, 01:15:04 pm
content: I've got a whole bunch right at my deskHeaps of them at farnell at least. -->http://au.farnell.com/taiyo-yuden/lmk316b7106kl-t/capacitor-ceramic-10uf-10v-x7r/dp/1683680

author: david77
author_rank: Frequent Contributor
timestamp: July 28, 2010, 01:18:00 pm
content: Wow. I bow my head in shameand shut up...Never seen 10uf ceramics before....But nevertheless I'd use a electrolytic and a ceramic in parallel, don't ask me why though... microphonics?

author: Time
author_rank: Frequent Contributor
timestamp: July 28, 2010, 01:19:36 pm
content: I was always under the impression that electrolytics have larger capacitances for their size and ceramics are faster (Maybe due to lower ESR?) so they are better at handling transients.I know someone on this forum will have a much better more complete answer for you.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 28, 2010, 01:39:49 pm
content: Depends on the type of ceramic - Y5V types have poor capacitance vs. temperature and voltage characteristics, but X7 types should be superior to elects in all respects.Ceramics have come long way in the last few years - you can get 10uf down to 0603 , and values up to 100uf at a price. Prices seem to rise steeply above 10uf, but for 10uf and below, ceramics are typically cheaper and better performing than electrolytics nowadays.

author: Zero999
author_rank: Super Contributor
timestamp: July 28, 2010, 02:18:58 pm
content: As manufacturing processes have improved the maximum size of a ceramic capacitor has increased over the years.Ceramic capacitors have a lower ESR, are non-polarised and are more reliable than electrolytics but they're much more expensive than electrolytics.The larger ceramic capacitors are also made of a piezoelectric material which means they're microphonic: they generate an electrical signal in response to vibration, they also have a poor temperature coefficient and distortion characteristics but electrolytics aren't much better so it's a non-issue.What's the maximum voltage on the circuit? You do know that the ceramic capacitors you've linked to only have a maximum rating of 10V; much less than most 10µF electrolytics.

author: migsantiago
author_rank: Frequent Contributor
timestamp: July 28, 2010, 03:32:46 pm
content: If you can't find any 10uF ceramic cap, you can put 10 x 1uF ceramic ones in parallel.

author: Strube09
author_rank: Regular Contributor
timestamp: July 28, 2010, 05:18:28 pm
content: The main drawback of a ceramic will be the farad and voltage rating of the ceramics are limited. While you can find a 10uF ceramic it will be fairly expensive and usually have a low voltage rating.Ceramics have a lower ESR than the Electros and are commonly paralled together in switching supplies output filters. This gives the large farad value of the electro at a lower cost why gaining the low ESR performance of the ceramic (Think of the two ESRs of the capacitors in parallel thus reducing the total ESR of the network). This helps reduce the output voltage ripple of the SMPS and is cheaper than slapping in expensive large ceramics.Also to note as in the other post that ceramics are microphonic and can produce a small voltage due to vibration, but they also observe the characteristics of magnetostriction that is the opposite. Basically the voltage ripple across the capacitor can generate a small magnetic field that vibrates the plates of the capacitor. This can cause a annoying and audible noise from the SMPS. This is also (and usually mostly) observed on the inductor/transformers of the SMPS as well.Hope this helps.

author: Time
author_rank: Frequent Contributor
timestamp: July 28, 2010, 05:43:00 pm
content: @cksaIn case you were wondering, ESR is equivalent series resistance.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 28, 2010, 11:02:10 pm
content: QuoteLast time I bought 10uf 35V ceramics I think they were about GBP0.07 each, although this was a full reel. Lower voltage 10ufs are pennies.One thing to bear in mind with the cheaper 5 series dielectrics is the the capacitance decreases with applied voltage, so you should generally use the next step up the voltage scale (6.3, 10,16,25v) than you would with an electrolytic.Higher values are howeversomewhat pricyWhat's really annoying is many of the manufacturers of these nice caps have a ridiculous price hike for sub-reel quantities - the above example the small qty price is 4x the reel price - someone is really taking the piss here...Another interesting capacitor type I've discovered recently is aluminium polymer, which have insanely low ESR (a few milliohms) in small packages - I've found these perform better than an equivalent value bunch of ceramics in a high current DC-DC conveter application. Still quite expensive, but quite a bit cheaper than equivalent value ceramics.

author: tecman
author_rank: Frequent Contributor
timestamp: July 28, 2010, 11:35:51 pm
content: Electrolytics: lowest cost/uFd, poorer HF capability due to ESR AND ESL, very poor tolerance, average life and aging issues, generally used for larger capacitance, and are physically big, not many under 1 Uf.Ceramic: Among the best HF capability, poor to excellent tolerance and tempco (NPO), long life, large values (>10 uF) not too common or practical, most are physically very small for the rating, very low ESL (suitable for RF apps), no aging issuesIn many digital apps paralleling both can result in good bulk capacitance and good HF response.Paul

author: Zero999
author_rank: Super Contributor
timestamp: July 29, 2010, 12:02:27 am
content: Quote from: mikeselectricstuff on July 28, 2010, 11:02:10 pmWhat supplier did you buy them from?In RS the cheapest 10µF ceramic capacitor is £0.09 but it's only 6.3V, the cheapest electrolytic 10µF capacitor is £0.025 and it's 63V, the cheapest 50V 10µF ceramic capacitor is £4.04 - I think you've go that backwards.http://uk.rs-online.com/web/search/searchBrowseAction.html?method=retrieveTfg&Nso=0&Nr=AND%28avl%3Auk%2CsearchDiscon_uk%3AN%29&N=4294626770+4294626539+4294626334&Ns=I18NPrc1_uk&binCount=2600&No=0http://uk.rs-online.com/web/search/searchBrowseAction.html?method=retrieveTfg&Nr=AND%28avl%3Auk%2CsearchDiscon_uk%3AN%29&N=4294963016+4294626541+4294626334&binCount=4646&Ns=I18NPrc1_uk&Nso=0#resultArrowThe cheapest 10µF 50V tantalum capacitor is £0.796 which is good quality and not too expensive so is ideal as long as you're not bothered about it being polarised.http://uk.rs-online.com/web/search/searchBrowseAction.html?method=retrieveTfg&Ne=4294957704&Nso=0&Nr=AND%28avl%3Auk%2CsearchDiscon_uk%3AN%29&Ns=I18NPrc1_uk&N=4294963016+4294626531+4294626334+4294911276+4294911215&binCount=1591&multiselectParam=4294963016%204294626531%204294626334%204294911276&selectAttribute=63Vdc#breadCrumb

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 29, 2010, 08:38:13 am
content: QuoteDigikeyI'm sure you can find probably better, as Farnell,RS,Digikey etc., are often more expensive than franchised distis once you get to full-reel quantities. Digikey also tend to get newer parts before RS & Farnell.

author: Zero999
author_rank: Super Contributor
timestamp: July 29, 2010, 09:39:44 am
content: Quote from: mikeselectricstuff on July 29, 2010, 08:38:13 amI know RS are expensive but that wasn't my point which was that you had got it the wrong way round, 10µF 35V Electrolytic capacitors are still cheaper at Digikey than the same value ceramics.At Digikey:The cheapest ceramic I could find is £0.038 in large quantities.http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=587-1352-2-NDI could find a 50V 10µF electrolytic capacitor for £0.02 in large quantities:http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=P10393TB-NDIf ceramics were cheaper than electrolytics, they would've started to displace them but they haven't.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: July 29, 2010, 12:59:54 pm
content: QuoteYou're not comparing like with like by comparing a SMD ceramic with through-hole electrolytic. The latter will have additional assembly costs, as well as board space.SMD electrolytics are generally more expensive than through-hole, and take more PCB area, so certainly below 10uf, and possibly a bit higher the overall cost of a ceramic will likely be lower for surface mount.SMD Tantalums at 10u and below have pretty much been obsoleted by ceramics for most applications.

author: Zero999
author_rank: Super Contributor
timestamp: July 29, 2010, 01:14:47 pm
content: That's because you can't compare like with like, SMT ceramic capacitors are cheaper than through hole but SMT electrolytic capacitors are more expensive than through hole.You're right about ceramic being more cost effective than tantalum though.

author: Unknown
author_rank: Unknown
timestamp: July 29, 2010, 06:53:04 pm
content: Lower ESR can be a problem for LDO regulators, lots has been written about it, eg. National semi AN-1482. Unless the datasheet specifically mentions compatibility with ceramic caps (some modern ones do), I wouldn't assume so.It was already mentioned, but don't forget the voltage coefficient of crappy dielectrics like Z5U, see for examplethis datasheet. If you put any signficant amount of DC over the cap, you might have much less capacitance than you'd think. X7R and up are much better.