[Amps] Equalising resistors with HV diodes

[R.Measures]

On Sep 20, 2004, at 5:22 AM, peter.chadwick at Zarlink.Com wrote:

>
>
>
>
> Rich said:
>
>> Without equalizing resistors, and provided that all of
>> the rectifiers in a series-string have similar junction-capacitances,
>> the reverse current is the same in each one.
>
> To a point. IF the diodes all come from the same diffusion batch, it's
> probable, although if the wafer is large, you can see generally see
> differences from one side of the wafer to the other. Don't let anyone 
> try
> telling you that semiconductor manufacture really is well controlled - 
> if
> they do, ask why we need to do 6 sigma design.
>
> When my employer had a diode/thyristor manufacturing line, I asked the 
> guys
> there: they felt that diodes from the same batch should be OK, but if
> you're not sure, the use of equalising resistors has merit.

Please explain why equalizing resistors have merit.  tnx

> Of course, they
> were dealing with 2000piv 250 amp jobs seriesed up for electric trains 
> -
> and I don't mean the model in N gauge!
>
> 73
>
> Peter G3RZP
>
>
>
>
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org