Re: overcharging a ceramic cap

Rene Tschaggelar wrote:

> John Larkin wrote:
>
>> Supposed we had a hi-K ceramic cap, say 10 uF at 10 volts, and we
>> charge it from a smallish, say 10 uA, current source. I know that at
>> some voltage past 10, it will start to conduct and limit terminal
>> voltage, sort of like a very sloppy zener, so it won't punch through
>> like, say, a film cap would. But is there a longterm damage mode?
>
> John,
> the involved 10V sound small, but considering the
> tiny distances between conductors, the field strength
> is rather big. I wouldn't be surprised if it reached
> MV/m. And then depending on the "arc-ing" mechanism,
> the stored power is rather big to created damage.
>
>>
>> Oh, and of I use a jfet as a super-low leakage diode, and zenered the
>> gate at that same 10 uA, would the junction be affected in the long
>> term?
>
> Again here the microscopic "arc-ing" mechanism
> defines the possible damage. Is is just a tunnel
> current through some potential barrier, or does
> it involve local ionization, oxidation, ...
> There may be microscopic conducting channels that
> overheat and change their doping.
>
> Rene
Yes, returning to OP topic, yes they will break down, and at successively
lower voltages. They will arc around the grains of the ceramic material,
and the 10 uF will certainly store enough energy to see to the eventual
total destruction of the capacitor. If you are (un)lucky enough the cap
may explode on its first breakdown.
--
JosephKK

.

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