Rich says:
>True, however the typical 5ua reverse current ability charges the
tiny
>capacitances with aplomb.
Now, where does the 5uA current come from? Only when the diode goes into
reverse leakage, i.e. when the reverse voltage is exceeded. So it appears
that to get your distribution, the 5uA leakage flows in the 101volt diode,
but not the 190 volt diode.
Roll over Kirchoff!
We're leaving the equalised diodes out of this. With equalised diodes, if
you exceed the reverse breakdown voltage of the diode with the lowest
breakdown voltage, you are in trouble. (I think Rich agrees on that one).
The cure for that is correct design and tolerancing.
Where we are arguing about is non-equalised diode strings using diodes that
are not guaranteed to be matched. This is where I say that the dangers
occur, and Rich has to explain:-
a) how the voltage distribution when exceeding the total rated reverse
voltage of the stack does not lead to excess volts across one or more diodes
(and thus leakage current through the diode)
and
b) how the voltage distribution across the stack can be guaranteed to be
such that an individual diode breakdown voltage is not exceeded with the
possible spread of parameters in unmatched diodes (including, but not
limited to trr, Vbr, capacity, and the varying V/I characteristics when in
reverse breakdown).
Don't need insults for this, Rich - I expect everybody is getting bored by
it.
73
Peter G3RZP
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