Diode Strings

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Original poster: "Richard W." <potluckutk-at-comcast-dot-net> 


Hi all,

I have 200 1000V 6A diodes (6A10). Recovery time is ~2.5uS

<http://pdf.searchdatasheets-dot-com/pdf/266/266448.pdf>http://pdf.searchdatasheets-dot-com/pdf/266/266448.pdf 


I hope to use 30 in each leg of a bridge to rectify 14.4Kv from a pig.

6A10s are general purpose diodes so I doubt they're manufactured with 
comparatively tight tolerances. Seaching the mailing list I've read 
something that the first diode to turn off can take the full applied 
voltage and could cause failure if the diodes used aren't at least close to 
being matched.  This seems plausible if the diode turned off at the peak of 
the AC voltage swing but that doesn't seem likely. If the diodes begin to 
turn off relatively close to zero crossing then I don't see that it would 
matter so much. Say I have 30 1000PIV diodes in a string with 15Kv applied. 
Close to zero crossing the the collective voltage drops shouldn't even be 
close to individual diode PIV. I know there are many that have had success 
using 1N4007s but I'm just curious and maybe a bit cautious.

So, am I missing something or is my logic in error?
I've also read about pros and cons using voltage balancing resistors so 
that's on my mind too.
And how does recovery time figure into a diode string operating at 60Hz or 
is 60Hz too slow to even worry about?

I prefer to ask first than use the "powerup/duck" method.


Thanks!

Rick W.
Salt Lake City