Replace electrolytic capacitors with ceramic or tantalum capacitors. - Page 1
Forum section: electronics / projects

author: luiHS
author_rank: Frequent Contributor
timestamp: April 13, 2019, 11:22:00 am
content: Hello.Is it possible to replace, in the circuit of a switched power supply, electrolytic input and output capacitors, by ceramic or tantalum capacitors?To assemble with my pick and place machine, it would be better to reduce the size of these components (SMD), but I am not sure if enough that the capacitors are of the same value.Regards

author: MagicSmoker
author_rank: Super Contributor
timestamp: April 13, 2019, 11:38:26 am
content: Quote from: luiHS on April 13, 2019, 11:22:00 amNot something I would do without careful analysis of the circuit because the ESR of the humble aluminum electrolytic can actually be helpful in some situations. For example, the ESR of the input elko reduces ringing/overshoot that can occur when power is suddenly applied while the ESR of the output elko inserts a zero that helps stabilize the control loop.

author: Psi
author_rank: Super Contributor
timestamp: April 13, 2019, 11:46:42 am
content: It's usually ok to do this.But as said above, watch out for things going unstable.Low Dropout linear regs are the worst for this but switchmode regs can also go unstable if you push the ESR very low.Using tantalum's in place of electrolytics is less likely to make things unstable than using ceramics.Because while tantalum's have low ESR ceramics have very low ESR.Downside of tantalum's is price and they have a tendency to fail very easily if you don't respect their voltage rating (including spikes exceeding the rating).

author: Miti
author_rank: Super Contributor
timestamp: April 13, 2019, 12:12:08 pm
content: Check this out if you intend to use smd tantalum caps.http://www.kemet.com/Lists/filestore/Derating%20Guidelings%20for%20Tantalum%202011%20(3).pdf

author: Siwastaja
author_rank: Super Contributor
timestamp: April 13, 2019, 12:26:02 pm
content: Quote from: luiHS on April 13, 2019, 11:22:00 amNot easily. It's a complete redesign wrt capacitors, and requires the full understanding about said capacitor types, in said circuit. This is far from trivial. At least the following apply:* Control loop stability,* Stray LC snubbing, especially related to inrush voltage overshoot and ringing* Surge current ratings (tantalums may catch fire)* Board flex with large ceramics

author: Psi
author_rank: Super Contributor
timestamp: April 13, 2019, 01:14:54 pm
content: Quote from: Siwastaja on April 13, 2019, 12:26:02 pmFor a professional product definitely, no question.For a personal hobby project it's more of a 'try it and see', it's more likely to work than it is to fail

author: Doctorandus_P
author_rank: Super Contributor
timestamp: April 13, 2019, 08:01:56 pm
content: You may also want to think about "conductive polymer capacitors".https://duckduckgo.com/?q=conductyive+polymer+capacitors&t=opera&ia=webThese have lower ESR than electrolytics, which may result in less needed capacitance, but as the other options it would need a carefull review and is not a no-brainer 1:1 replacement.

author: NorthGuy
author_rank: Super Contributor
timestamp: April 13, 2019, 08:35:03 pm
content: When ceramic capacitors are subject to DC bias (such as 9V, for example), their capacitance should be dramatically derated. The smaller the capacitor, the more derating you need. Several manufacturers have apps which let you evaluate the real capacitance under DC bias. Because of the derating, you'll need physically bigger caps or several smaller caps. Most likely, you will not be able to scramble enough capacitance to replace your electrolytics.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 14, 2019, 03:34:47 am
content: From a design standpoint, yes. The issues Siwastaja mentioned need to be considered; simple substitution isn't likely to work out perfectly.Other big concerns are, the amount of space required to replace, say, a 1000uF electrolytic with two dozen 1210 size ceramics; or the cost of doing so, as large ceramics simply aren't cheap, even if your THT assembly isn't!Don't forget that you aren't getting the nominal value, at the rated voltage. You need to check the characteristic sheet to find how much C drops with voltage, and shop accordingly.Of course, SMT electrolytics are PnP-able too, but they are physically smaller than what's available in THT so you need more.Tim

author: Siwastaja
author_rank: Super Contributor
timestamp: April 14, 2019, 03:14:50 pm
content: Quote from: Psi on April 13, 2019, 01:14:54 pmI don't see much difference between a hobbyist or professional approach.In both worlds, projects can be designed by "do random things randomly, and see if it works by luck" approach, and often are! Not saying this is fundamentallywrong.Often, it's a combination of extending your knowledge as far as possible, then resorting to doing random things when you can't get any further.But, capacitor types are one of the difficult areas where blind replacements arequite likely to fail. It doesn't matter whether it's professional of hobbyist; the laws of physics and component properties are the same.For example, a converter designed to accept DC input up to 24V, and using ICs/semiconductors rated to, say, 30-35V,willdie once you replace the electrolytic input caps with ceramics, as the circuit will now see at least 48V input peak in a hotplug situation, almost 100% guaranteed failure.

author: NorthGuy
author_rank: Super Contributor
timestamp: June 23, 2019, 11:14:36 pm
content: Quote from: Siwastaja on April 14, 2019, 03:14:50 pmIf a hobbyist gets 50% yield that's a success. If a professional gets 50% yield that's a disaster.