RE: rectifier stack experts? Add protection diode stack

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Original poster: "Mccauley, Daniel H by way of Terry Fritz <twftesla-at-qwest-dot-net>" <daniel.h.mccauley-at-lmco-dot-com>

> I like your simplification of replacing forward biased diodes with wires.
> It helps to see what's happening more clearly.  I probably could have
found
> a better word to use than "potentially".  The engineering book I was
reading
> did not go into much detail as to why the bridge must be rated Vpeak * 2.
I
> assumed it was because the diodes and capacitor tend to act together in a
> fashion similar to how a cascade multiplier works to increase voltage.
> Another reason I didn't question it was that I once rectified the output
of
> a 15kV NST with a full bridge rated for 25kV, 1A continuous, which worked
> fine until I added a capacitor.  After that, it lasted about two minutes.
> Maybe I will do some more research to see if I can find something that
goes
> into more detail.  Maybe you could too and post your findings.  I think it
> would help everyone of us tinkerers to know that we are needlessly
> destroying our diodes when it could be avoided.

An easy way to destroy a bridge in a HV application is to run it charging a
capacitor, then discharge the capacitor in a way that gets some voltage
reversal.  When the cap voltage reverses (or tries to), the bridge is
forward biased, and currents get real high, cooking one or more of the
junctions in your HV rectifier.  Since destroying $50 worth of rectifiers,
I've always run a resistor in series between the bridge and the filter
capacitor.

>>>>>>>>>>>>Not only that.  You should have another series diode stack from
your output
to ground.  This could be a diode stack consisting of say 50 1000V Diodes.
This diode stack
would provide a return path for a voltage reversal condition and are almost
always used in
high voltage power supplies.

Dan