[Amps] Equalising resistors with HV diodes

[DF3KV]

----- Original Message -----
From: <peter.chadwick at Zarlink.Com>
Subject: Re: [Amps] Equalising resistors with HV diodes


> >Please explain why equalizing resistors have merit.
>
> Because if the reverse leakage differs between diodes, the reverse
voltage
> distribution also differs. The one with the least leakage ends up
with the
> highest voltage across it, which could exceed the breakdown volts.
With
> resistors, the voltage distribution across the diodes is fixed by
the
> resistor ratios.
>
> If the capacitances aren't matched, that will also affect the
voltage
> distribution. That's one reason why it is not wise to mix diodes of
the
> same nominal type from different manufacturers without some
equalisation.
> Another is the reverse recovery time.
>
> Experience also suggests that for best reliability, buy diodes from
> reputable manufacturers - some of the far Eastern ones are
distinctly dodgy
> froma reliability viewpoint.

Hi Peter,

If that theory is solid, all fullwave bridge rectifiers should have
equalising resistors connected across the diodes, but no manufacture
suggests that.
I always used triple safety on Vrrm when I used diodes in HV rectifier
stacks and never experienced failed diodes (most BY255)

73
Peter