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Tantalum or what? is there a substitute?

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bigal_scorpio

Active Member
Hi everyone,

I am building a small dc to dc buck regulator circuit and the schematic shows either 1 of 330uF Tantalum or 2 parallel 220uF Tantalums.

My problem is that I can't get hold of either locally or even from the suppliers I often use on the net (Rapid)!

I wondered if there was a specific reason why Tantalums were used and if I could substitute another type, say an electrolytic maybe?

The design says the tantalums should be at least 3 volts which is very small in terms of voltage for most other types of caps, so maybe this is a factor in using them?

If anyone has any info or ideas on this I would be very grateful :)

Thanks for looking...........Al :confused:
 
they often spec tant caps because of their low ESR and low inductance.

instead of one cap at 330uf, use three at 100uf?

you can use regular electrolytic, but over-spec them in terms of voltage by at least 2x, so for 3v output, use 10v caps. your efficiency will still suffer. again, use three instead of one, to reduce the ESR
 
You can substitute tantalums with niobium oxide (if you can get them) and probably ceramic (if you can get ones that are large enough and pay a pretty dime for those sizes)- but not electrolytics. Sorry! Tantalums are needed over electrolytics because of their frequency characteristics.

EDIT: I read your post more carefully and 330uF is massive for a tantalum. I'd just go with electrolytics jsut because they're way cheaper for those values. I would maybe (maybe) stick a small ceramic cap closest to the regulator to try and make up for the frqeuency characteristics (all non-idealities of parallel capacitors aside).
 
Last edited:
why not post the schematic, perhaps we can suggest alternatives if we know the design criteria...

vin=?
vout=?
switching frequency=?
inductor=?
max output ripple=?
max load=?
 
Tantalum update with Schematics

Hi again,

Thanks for all the helpful comments and ideas, here is the schematic for anyone who is interested - the circuit is Fig 2. on Page 9.

Thanks again guys...........Al :)
 

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  • MAX1703ese.pdf
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Use low ESR electrolytics, In your application they will work just as well and will be way cheaper!
 
Sanyo OS-CON and Panasonic SP/CB-series ceramic
capacitors offer the lowest ESR. Low-ESR tantalum
capacitors are a good choice and generally offer a
good tradeoff between price and performance. Do not
exceed the ripple current ratings of tantalum capacitors.
Avoid most aluminum-electrolytic capacitors,
because their ESR is often too high.
(emphasis mine)
It doesn't say not to use aluminum electrolytics, just be sure the ESR is low enough and the current rating is high enough. My assessment is that tantalum caps simplify the selection process, but with proper care you don't have to use them.

Some people here have very bad experience with tantalum caps, but that is not my experience.
 
mneary said:
(emphasis mine)
It doesn't say not to use aluminum electrolytics, just be sure the ESR is low enough and the current rating is high enough. My assessment is that tantalum caps simplify the selection process, but with proper care you don't have to use them.

Some people here have very bad experience with tantalum caps, but that is not my experience.

In many decades of troubleshooting I've found as many bad electrolytics as tantalum. I am aware of the bad rep some have of tantalum, but have not seen that personally. It may be a case of too close a voltage rating or a low quality manufacture.

Lefty
 
Tantalum or what update 2

Hi again guys,

I have considered all the excellent advice you have posted and I think I may have found some that will do the job.

The link below is what I think may be suitable, so if anyone can confirm or dismiss these please let me know.

Thanks again............Al :)

**broken link removed**
 
Assuming that the ohms heading is a typo, and the ESR listed is milliohms, I would say those are very good caps. Remember that your ripple current may be greater than your steady state output, so derate accordingly.
 
With caps like Panasonic FM series electrolytics, is there really any reason to use tantalums? FM series has very low ESR and impedance @ 100kHz, but >100kHz is there any reason for an equivalently sized tantalum to have an advantage?
 
speakerguy79 said:
With caps like Panasonic FM series electrolytics, is there really any reason to use tantalums? FM series has very low ESR and impedance @ 100kHz, but >100kHz is there any reason for an equivalently sized tantalum to have an advantage?
One word- bling...and uhhh...planned product obsolecence?

But maybe electrolyte drying or temperature? I also heard that electrolytics form themselves to voltage they are being operated at over time since the exact same thing is done to give them a particular voltage rating in the first place?
 
Leftyretro said:
In many decades of troubleshooting I've found as many bad electrolytics as tantalum. I am aware of the bad rep some have of tantalum, but have not seen that personally. It may be a case of too close a voltage rating or a low quality manufacture.

My experience is the exact opposite, in many decades of servicing I've found tantalums incredibly unreliable. The manufacturers soon realised this though, and they were only used in any quantities for a fairly short period.

Even now, first port of call when repairing something is to have a quick glance round and see if there are any tantalums on the board - if there are, check and see if they are S/C - this cures many faults without any 'skill' required at all! :D

This isn't to say that electrolytics, particularly modern ones, are troublefree - far from it, but they usually go low ESR, and tant's normally go S/C.
 
Nigel's rantings in the past have me paranoid about tantalums and now I only ceramics...and grudingly only use electrolytics when the capacities in ceramic are too expensive (exceeding $2 per ceramic capacitor) or when the capacities don't exist.
 
Where I work, our boards are littered with tantalum caps. I've seen no reliability issues.

But these days if you need low ESR, you can get more for your money with modern electrolytics.
 
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