19 Jan
2012
19 Jan
'12
2:06 a.m.
I wrote:
Actually I don't see anything in that paper that
contradicts my claims
that the oxide breaks down when the capacitor is not used under bias
for a long interval, nor that such an oxide breakdown reduces the
effective working voltage of the capacitor, leading to failure when
used at the original rated voltage.
I've seen other papers from capacitor vendors, possibly including CDE,
that discuss this problem. I don't have those papers handy at the
moment, so I'll have to dig around for them.
Here's a copy of the CDE application guide:
http://www.cde.com/catalogs/AEappGUIDE.pdf
They explain how the oxide formation is done during manufacture (p. 3)
and mention that there is an aging step that does some additional
forming (p. 4). They discuss field-reforming capacitors with high DC
leakage in the "Shelf Life" section (p. 16). They don't directly state
that the reformation process should ramp the voltage relatively slowly,
but that's one effect of their recommended 1K series resistor.
I'm pretty sure I saw some applications information from a capacitor
vendor that had more details on reformation, but I don't recall which
vendor and still can't find it.
Eric