I don't understand that comment. Murphy's Law has nothing to do with it
... Ohms Law does. As N6RK said, where high voltage DC is present,
capacitors in series are typically bridged by high value parallel
resistors to make the voltage divider dependent upon the resistors
instead of the much higher (and indeterminate) DC resistance of the
dielectric. For RF, the impedance of the capacitors themselves provides
that same shunting action as far as the bulk resistance of the
dielectric is concerned. Look at any model of a capacitor and you'll
see an ideal capacitor shunted by a high resistance, with bits of series
resistance and inductance that affect Q. Jim and Rick are right ... the
RF voltage will divide among series capacitors almost strictly as a
function of their capacitance.
Besides, you have a similar situation to worry about with parallel
capacitors except the culprit is current instead of voltage. At higher
frequencies where layout (inductance) is an issue, I'd bet unequal
current sharing among paralleled capacitors blows more of them than does
unequal voltage dividing among series capacitors.
All that being said, not many inexpensive RF capacitors handle several
amps very well, so for high power applications we probably end up with
some configuration that includes both series and parallel devices ...
and I'd probably shoot for more margin on the parallel portion than on
the series portion.
73,
Dave AB7E
Bill Turner wrote:
>
>
> Murphy is waiting. :-)
>
> 73, Bill W6WRT
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