Re: [EE] Tantalum capacitors?

I remember the computer company I worked for receiving a new dot matrix
printer. It was DOA, and the engineer looking into why pulled the
electronics out and was leaning over it looking for anything obvious that
might be the reason for it being DOA. But the problem was he had forgotten
to remove the power before opening it up, and while his head was bent over
looking for distressed items a tear drop tantalum went ping past his ear
lobe. He was lucky it didn't hit him in the eye.

But ceramics are not a total panacea to replacing tantalums. First you need
to have components that are rated well above (2 or more times the
operational voltage) or else you loose a considerable percentage of the
capacitance - Microchip have good graphs on this in their recommendations
on Vcap components in some of their datasheets, so be careful if the
capacitance value is important and you are operating close to rated voltage.

Also I had one fail in a catastrophic manner - we had a minicomputer arrive
and had it soak testing before handing over to a customer. I got a page to
get down to the customer site pronto as the machine had smoke coming out of
it. At least the operators on site had the sense to power off the machine
when they saw the smoke. When I got there and investigated one of the Vcc
bypass ceramics on the memory board had evidently decided to be a resistor
today, and drew lots of current. The power supply was a 5V 300A switchmode
and as there were hardly any cards it was quite lightly loaded, was quite
happy to supply as much current as the capacitor now resistor wanted to
consume. The result was a hole about an inch and a half burnt through the
PCB. The capacitor had been a ubiquitous (for the time) 0.1uF 25V epoxy
coated type on leads.






On Thu, 24 Oct 2024 at 16:07, RussellMc <[email protected]> wrote:

> On Fri, 25 Oct 2024 at 02:41, Clint Jay <[email protected]> wrote:
>
> > Given all the negatives which have been discussed here, what are the
> > advantages, use cases and why are they still made if they're so bad?
> >
>
> Largely what Chuck said - compact physically and low ESR - but usually not
> so low that they do not suit LDO output capacitor use.
> On a rail where it can be ***GUARANTEED*** (that's yelling in bold with
> emphasis :-) ) that spikes or and other voltage excursions will NEVER
> exceed rated voltage then they can be a good solution. This was far more
> true in the past as ceramic capacitors of high capacitance are now made.
> The other desirable feature is a supply that has limited energy available.
> Those two requirements tend to rather limit the application area.
>
> One reason to use them is the sheer joy of experiencing a capacitor
> sequentially:smell, smoke, shriek, noisily emit flame and then explode.
> I've only seen that happen once but it was very satisfying. The more so
> because it was not in my equipment :-).
>
>
>          Russell McMahon
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