Why are electrolytic capacitors still in production?

Question

What are the advantages of using electrolytic capacitors?

I know in the past electrolytic capacitors would have more capacitance, but with Multi-layer ceramic capacitors (MLCC) they seem completely obsolete. The MLCCs also can have high capacitances, but they have lower equivalent series resistance (ESR), lower Equivalent series Inductance (ESL), and are much smaller physically. I'm just very curious as to why lower-value electrolytics are in production.

Could someone explain why someone would use a high-value electrolytic over a high-value ceramic capacitor?

Answer 1

Voltage rating would be the biggest difference as electrolytics are much cheaper if you need a higher voltage rating in the same value. But there are many different factors to compare and there are really no hard and fast rules.

For example, if you need a 10 μF cap with a 63 V voltage rating a ceramic capacitor can be several times more in cost.

Ceramic caps have better ratings because the leads are smaller, leads and metal have inductance which leads to a lower ESL spec. So electrolytics will have a higher ESL rating usually.

Source: https://www.johansondielectrics.com/basics-of-ceramic-chip-capacitors

Source: http://en.wikipedia.org

Answer 2

What are the advantages of using electrolytics?

• Available with about 3 orders of magnitude higher capacitance at the same voltage rating
• Capacitance is stable under DC bias, whereas most (Class 2) MLCCs are not

Essentially they give a lot more capacitance and that capacitance is much more stable, especially above a few volts DC.

I'm just very curious as to why lower value electrolytics are in production.

Skimming Digi-Key, not very many lower value electrolytics appear to be in production. Most are higher value/voltage parts you couldn't get in MLCC. Lower values are still useful though, especially for things like audio amplifiers, where you very often don't want the capacitor value to change with voltage.

Answer 3

Your average Al electrolytic has a wonderful ESR-capacitance product in order to double as a snubber against nasty ringing at the MHz ballpark. This is cool because such ringing can easily appear due to usual voltage regulator bandwidths and MLCC loads. This can be simulated below by either disconnecting Cel (regulator oscillates), setting it as a MLCC (10 mΩ ESR, oscillates) or having it there as an electrolytic (stable).

^{simulate this circuit – Schematic created using CircuitLab}

Of course one could emulate this behavior with an MLCC and series resistance, but one would need unusual resistor values on stock such as 33 mΩ or 330 mΩ and one would need a different resistor for different capacitance.

Another disadvantage of larger ceramics is that they are said to be prone to cracking in packages larger than ~1210. So you need loads of small caps to achieve something like 100 μF at 12 V, which is trivial with a single Al electrolytic and saving costs.

Answer 4

The MLCC caps can be microphonic which may not be acceptable .If the value is high then a metal film could be too big and /or too expensive. Also MLCC caps have supply problems so some designers place an electro in paralell with several MLCC caps .

Answer 5

What are the advantages of using electrolytic capacitors?

That they exist, whereas equivalent MLCCs are figments of imagination.

with Multi-layer ceramic capacitors (MLCC) they seem completely obsolete

This does not represent reality at all.

Find us a 650uF 400VDC MLCC capacitor. Plenty of applications exist for such capacitors. Your PC's power supply likely got a few of them.

Try and come up with a MLCC equivalent and tell us how much it will cost, how reliable will it be, etc.

Yeah, it's pure fantasy that MLCCs make electrolytics obsolete. It's not even close!

Answer 6

Tangential economics - electrolytic capacitors are still made because they can be made cheap.

The physical equipment/plant still exists and has long-since paid for itself. The incremental cost to continue operating the line is low, so as long as the part can be sold for a profit, the production line can continue to run until catastrophic failure, or wear produces non-functional parts.

We see this with all manner of items - a bicycle freewheel costs $10 whereas the arguably-simpler cassette costs more. Same goes for plastic injection moulds and parts.

Are these components the best? No, but if the final assembly has a lower BOM with the same overall functionality, then the accountants are happier.

Answer 7

Let's not forget the Inductance of all the foil wrapped into the final shape. I have seen circuits damaged by substituting 'modern' capacitors, only to have a transformer winding fail. That inductance is current limiting, and a replacement transformer for a 1963 'scope is no longer available. When you work on old equipment you need old-style parts.