[Amps] Equalising resistors with HV diodes

[R.Measures]

On Sep 19, 2004, at 3:51 PM, Radio WC6W wrote:

>
> On Sat, 18 Sep 2004 17:55:33 +0200 (CEST) Roger B <f6fer at yahoo.fr>
> writes:
>> Hello to all
>> I am designing a 2kV PSU for a 1kW amp (bridge not
>> doubler).
>> About equalising resistors and capacitors with HV
>> diodes, some says it is absolutely necessary. Others
>> say it is a waste of time with modern diodes.
>> Any comment will be appreciated. 73 Roger
>
> Hi Roger,
>    Depends on which diodes... and how reliable you wish the resulting
> unit to be...

- Indeed   But do "equalizing" resistors increase or decrease 
reliability?  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.  Since excessive 
reverse-current is what typically causes rectifier failure, not having 
more reverse current in any one rectifier is desirable.  Although 
"equalizing" resistors equalize reverse voltages, they often 
un-equalize reverse currents. Thus, unless the measured PIVs of the 
rectifiers are identical, removing equalizing resistors should increase 
reliability.
>
>
>
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org