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I've recently run into a number of consumer-grade devices that use 50v, 0.22uF electrolytic capacitors, as well as other similarly rated parts, all below about 10uF. In use, the voltages on them are far less than the rating, usually around ~15-25V maximum, and they seem to be used in op-amp filters or as rail bypass caps.

My question is this: Why on earth would you ever want to use an electrolytic in that kind of a situation? I get that ceramics de-rate as the voltage increases, but surely a 1uF 50-250V ceramic would be better for device lifetime and would be cheaper to boot?

(And yes, I have read Ceramic caps vs electrolytic. What are the tangible differences in use?, but it doesn't quite answer my question.)

MadHatter
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ZetaSyanthis
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    How old are the devices you talking about (or, more to the point, the design?) Ceramic capacitors above 100nF weren't always around - and they were unreliable as they first became available. – JRE Jun 09 '19 at 10:41
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    Stability may be an issue - you should have come across this : https://electronics.stackexchange.com/q/65749/152903 – Solar Mike Jun 09 '19 at 10:57
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    Even today, ceramic capacitors over a few hundred nF tend to have some undesirable characteristics for certain uses; MLCCs are infamous for how their capacitance is a function of applied voltage. – Hearth Jun 09 '19 at 22:02
  • Okay, so it sounds like stability, especially due to the applied DC voltage threshold, is the real key. (Fragility notwithstanding in this application.) – ZetaSyanthis Jun 10 '19 at 11:24
  • @JRE Say 2010 vintage? That rating were definitely available then. – ZetaSyanthis Jun 10 '19 at 11:25
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    That's why I asked. I had problems with 300nF ceramic capacitors in the early 1990s. They liked to develop cracks and change from capacitors to resistors. That was reason to avoid "large" value ceramics at the time. – JRE Jun 10 '19 at 11:28

1 Answers1

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Both of your examples commonly care about ESL and ESR of a capacitor. Along with many other examples like LDO output stability etc. I have done designs like this using Tantalum instead of ceramics for the exact reason. Stuff from China will most likely use Electrolytic ones to save money.

There are still applications where the higher ESL and ESR of an Electrolytic capacitor is hard to replicate.

An incomplete list of applications that still may prefer Electrolytic or Tantalum over Ceramics

  • Linear Regulator output (for stability of the control loop).
  • Bulk input capacitors (to reduce inrush and inductive spikes that come with it).
  • Filters designed a long time ago...
  • Audio DC blocking (Due to lack of capacitance shift with applied voltage).
MadHatter
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    Interesting. I must not have done enough work with these kinds of applications, because I've never run into a situation where you /want/ ESR and ESL. (Or at least never understood it in those terms.) – ZetaSyanthis Jun 10 '19 at 11:26
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    Look up linear regulators and read the output capacitor section. Only in recent years do they now say ceramics are ok. Historically they even had charts for ESR of the capacitor and what what acceptable. – MadHatter Jun 10 '19 at 11:57