Re: caps (was: 8250LP....)

From: Francesco Messineo <>
Date: Mon, 21 Aug 2017 20:46:07 +0200
Message-ID: <>
On Mon, Aug 21, 2017 at 8:32 PM,  <> wrote:
>> On 2017-08-21, at 18:38, Francesco Messineo <> wrote:

>> Tantalum don't leak, but have some other problems (sometimes they
>> explode or burn for example,
> This might happen quickly when you "overdrive" them or put them the wrong way but exploding (to a degree) and burning is certainly a domain of leaking aluminium ones, even if used correctly :-)

hell, no. I've seen far too many tantalum capacitor start burning or
just go "BANG" after decades
of use, and yes, they were all installed correctly.
One day I was fixing a C64 (or it was a VIC-20, can't really remember)
with my TEK 475 (from the '70s) when suddendly the scope turned off
(well, actually some supplies collapsed).
I've then opened it and started to check for shorts in the supply
rails and sure enough, the +15V showed a dead short. I could trace it
with a 4 probe multimeter to a tantalum electrolytic that measured
less than 1 mohm. I then replaced it and the scope is still working
well since that day.
I'm happy that Tektronix knew how to make a proper power supply
current limit, if not, that capacitor would be scattered everywhere
inside the scope and probably some parts of the power supply
regulation circuit would be dead too (it happened on
less-carefully-designed power supplies).

>> and cost more than the MLCCs) and their
>> ESR is usually quite different from the same capacity aluminum
>> electrolytic. So you can't just replace a tantalum capacitor for a
>> regular aluminum one unless you understand that ESR/ESL don't matter
>> in that application, but when you understand that, then MLCCs are
>> cheaper and smaller :)
> Unless you need the capacitances to match the bigger electrolytic ones. Especially at higher voltages. For (relatively small) bypasses they're obviously the best choice but I wouldn't be so sure to recommend ceramics as a general replacement for electrolytic caps. For (your) example if we talk about the bigger ones like those used as board power rails filters then you can quickly need to get into mF range. I just checked with a big supplier here and the biggest MLCC I can get is 22µF and is almost twice the price of a 1000µF tantalum and only about 30% cheaper than the 470µF tantalum-polymer one.

I routinely use MLCC up to 100 uF (they're on for example)
and you can find them up to 680uF (last time I've checked). But I
agree, I would never replace the big electrolytics with them. We
started this thread talking about small leaking capacitor with a small
Why one would drift to 1000 uF? They aren't small in any sense.

Frank IZ8DWF

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Received on 2017-08-21 19:03:43

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