High capacitance ceramics - Page 1
Forum section: electronics / general

author: Stonent
author_rank: Super Contributor
timestamp: November 08, 2013, 01:16:11 am
content: I got to thinking, now that I've been ordering parts for projects things are a little more clear.Typical ceramics seem to top off just under 1uF and that's about where electrolytic capactors start. (I know there are exceptions, I'm just going on most common stuff) Is the polarization in part because the capacitance is so high you can't discharge it fast enough in an oscillating circuit or is it still part of the physics?I was reading an article today that Murata has a 10uF SMD ceramic, but it didn't say if it was polarized or not.Tantalums are a different story I guess, they have a very wide range but are polarized.

author: John Coloccia
author_rank: Super Contributor
timestamp: November 08, 2013, 02:30:57 am
content: Non-polarized electrolytic are just bigger than polarized. Large value ceramics are HUGE, so they're generally unavailable beyond about 1uf. It's just a matter of size. If you really want to use ceramics, you can just put them in parallel. I'm doing this in one of my designs now because I can't tolerate the poor performance of the electrolytic.Tantalum are electrolytic too, and are generally polarized as well. They're VERY exciting when they go into thermal runaway.

author: free_electron
author_rank: Super Contributor
timestamp: November 08, 2013, 02:33:59 am
content: we regularly use 22uf and 33uf in ceramic. but that is about how high they go. those are 1210 footprints ...

author: John Coloccia
author_rank: Super Contributor
timestamp: November 08, 2013, 03:03:07 am
content: Actually, I was saying and typing ceramic, but thinking "film". MLCCs are tiny, indeed

author: nicknails
author_rank: Regular Contributor
timestamp: November 08, 2013, 03:04:21 am
content: Quote from: free_electron on November 08, 2013, 02:33:59 amOut of curiosity, why 1210 footprint?We use 10uF and 2.2uF all the time. Pricing is decent so they can't be that rare.

author: Rufus
author_rank: Super Contributor
timestamp: November 08, 2013, 03:29:36 am
content: Quote from: Stonent on November 08, 2013, 01:16:11 amSmall high value capacitors require very thin dielectric films. It is easy to form thin dielectric films and maintain electrical 'contact' with them by using metal as one plate of the capacitor and a conductive liquid as the other. The liquid is chosen to react electrolytically with the metal to form the dielectric film on its surface. The reaction is somewhat reversible so such capacitors can not stand reverse polarity. The films are self-healing. A hole in the dielectric allowing current to flow grows more dielectric to fill it.Tantalums have the problem that if enough current is available holes in the dielectric can produce catastrophic damage rather than repair.

author: Monkeh
author_rank: Super Contributor
timestamp: November 08, 2013, 04:42:13 am
content: I've got a load of 4u7 ceramics in 1206. They're not terribly hard to find, I don't know where you've been looking..

author: walshms
author_rank: Regular Contributor
timestamp: November 08, 2013, 04:56:18 am
content: More and higher value ceramics will continue to appear, I think. The dielectrics are getting better, and they are getting better at making them.

author: Monkeh
author_rank: Super Contributor
timestamp: November 08, 2013, 09:46:39 am
content: http://uk.farnell.com/avx/st203c227maj10/capacitor-ceramic-220uf-25v-x7r/dp/1829121When you really, really want a ceramic capacitor.

author: Whales
author_rank: Super Contributor
timestamp: November 08, 2013, 09:53:59 am
content: Quote from: Monkeh on November 08, 2013, 09:46:39 amI saw these on Farnell once before and thought about how awesome it would be to be paid to make these. How many actually sell?

author: ovnr
author_rank: Frequent Contributor
timestamp: November 08, 2013, 10:21:36 am
content: Well, a recent project of mine used a47u 6.3v 0805 (X5R)ceramic. Just beware of the usual drop in capacitance - this one is down 80% at rated voltage. Since I'm just using it at 2-3 volts, it's at around 20uF.(And it didn't work out as I had hoped, but that's another story of leaky diodes and shit.)

author: amyk
author_rank: Super Contributor
timestamp: November 08, 2013, 12:20:42 pm
content: Quote from: Monkeh on November 08, 2013, 09:46:39 amAnd it costs more than just buying 10 x 22uf ones...Ceramic caps have a strong voltage-dependence on their actual capacitance:https://www.eevblog.com/forum/projects/t22291/

author: DutchGert
author_rank: Frequent Contributor
timestamp: November 08, 2013, 01:03:41 pm
content: Quote from: amyk on November 08, 2013, 12:20:42 pmBut 10x22uF could screw up your total ESR.....