Tantalum Vs. Aluminium

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I read in one of National's application notes that you can generally expect a 1uF Tantalum capacitor to provide an equivalent level of performace as a 25uF Aluminium.

I decided to do a bit of looking around and found another site claiming a Tantalum could take the place of an Aluminium roughly ten times it's size.

This, due to their massively lower ESR.

Neither went any futher with the statements.

Tantalums usually have their ESR listed at 100kHz.

So they can supply very high speed pulses. But they usually cost five or ten times more per unit of measurable capacitance.

Would I be right in suspecting that these sources mean they can take the place of electrolytics 25 times their own size only in higher speed filtering, like SMPS outputs? High frequency noise and ripple applications.

At rectified mains frequencies, it's going to more important to have 25 times the measurable capacitance and a higher ESR right? Since the pulses are, by comparison with 100kHz SMPS output noise, slow and deep.
 
The lowered ESR of a Tantalum enables them to provide a higher ripple current capability in general, and maintain their capacitive characteristics into higher frequencies. And yes, they seem to pack more capacity per volume unit.

Aluminium caps will add an inductive parasitic effect at high frequencies (most often modelled in the ESR value), so that is why these are not preferred in SMPS, unless you buy low ESR types.

So if your application is a straightforward mains filter, I'd say you just use aluminium. Maybe you can decide to use a small tantalum paralelled with a 100nF ceramic near the opamp or IC (if you're using any) to kill any noise or EMI picked up in the power rails.

For audio coupling / filtering, well.... there seems to be a discussion there....
 
Also don't forget the tendency of tantalum electrolytics to go short-circuit with a bang, and no visible indication of failure... not so great, especially if there are a lot of them. It was mentioned once that to eliminate the short in a circuit with a lot of tant. caps, they would hook up a high-current supply and there would be a second BANG and no more short circuit.

It would have to be a critical circuit, with audible improvement, to make a good argument to this DIY-er.
 
Ipanema said:
Can anyone pls explain to me which caps best for what application and why is it so?
Thanks.

The short answer is no, and so is the long answer. EVERY application is different, and the garbage going on in power circuits is different from one design to the next. If you want the big picture you have to read lots and lots and lots and then start to know what are the proper questions to ask for ONE application. Sorry. :D

Ask a more specific question if you want to get close to an answer. How's this: big aluminum electrolytics are pretty much useful only for power supply filters. Everything else, you'll go crosseyed studying.
 
diy circuits can usually use today's better Al electros to match or beat 20-30 year old op amp datasheet recommendations of Ta Electrolytics if you search out those decades old parts original specs for esr, esl

polymer electrolyte Al are a effective substitute, may even have too low a esr for optimum damping

only ridiculously high circuit density of cell phones, portable computing devices need the last edge in size and performance and even there the costs of Ta mean many alternatives have been developed
 
IMO, tantalums have no magic properties other than size. Large C in small package. The ESR is low but not super low; it's very consistent so you always know how the circuit will work. Small physical size gives them an inductive (lack of) advantage at high frequencies. Tantalums are fine, but only if used in current limited locations of low dV/dT and only if properly derated. IMO, most people can't/won't spend enough time researching everything you need to know to use them successfully, and shouldn't mess with them. But, properly applied, they're very reliable and you don't have to worry about aging or replacement.

They can successfully be used in audio- Audio Research Corp. used to use a bunch of 'em, including the phono stage input, but they do have non-linearities that will bite you if you don't size them correctly. Basically, if it's large enough that no audio signal appears across it, it can't affect the signal.

All that said, some of the low ESR aluminum electrolytics and polymer caps are so good and quite small, that I can't see most people using expensive tantalums for much of anything. If you really want a shock, check the prices on wet tantalums these days. I've seen what used to be common mil spec parts going for over $200 each!
 
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