Tantalum Vs. Aluminium

[eeka chu]

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.

[Bakmeel]

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....

[DSP_Geek]

Low ESR can get you in trouble if you have power traces long enough to show significant inductance, because then you've created a resonant circuit.

[Stocker]

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.

[lgreen]

Also, Tantalum caps are tough to find spec'd for high voltages. There are plenty at 5V but not so many at 35V.

A lot of people here will say that they are afraid to use tant caps because they tend to have spectacular failures....

[jcx]

tantalum caps are bad for audio

bad for safety

bad for humanity and the environment


http://www6.head-fi.org/forums/showp...15&postcount=4

[Ipanema]

How does the low-K dielectric in ceramic cap helps in supply filtering?

Can anyone pls explain to me which caps best for what application and why is it so?

Thanks.

[Stocker]

Originally posted by Ipanema
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.

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.