[Amps] Equalising resistors with HV diodes

[Radio WC6W]

On Mon, 20 Sep 2004 12:39:52 -0700 R. Measures <r at somis.org> writes:
> 

Hi Rich,

<snip>

> >    Without the R's, a string of unmatched and/or non-avalanche rated
> > diodes might, or might not, exhibit a higher reverse breakdown 
> > capability
> 
>   The avalanche characteristic is built-in at the time of epitaxy.

   Are your pet diodes (1N5408) characterized in avalanche?

> > but, this figure would wander around with temperature as it effects
> > leakage resistance.  One diode in the string (likely the best, lowest
> > leakage, unit!) would be the most stressed and prone to early
failure.
> 
> Stress is caused by reverse current.  If the reverse currents are 
> equal, how can one diode be stressed more.
    
   Yes, the currents are equal in an unequalized string of diodes but,
"stress" in avalanche is the power product of reverse voltage & current. 
Therefore, the diode experiencing the highest reverse voltage will be
subjected to the highest stress.

    What is the avalanche rating of a 1N5408?   

<snip>

> 
> Why wouldn't a C-filter store the rectified energy from a 
> transient.

  The output filter will indeed store the energy from the "event" from
whichever parts of the rectifier assembly are forward biased but, sans
equalization C's, the instantaneous voltage across individual diodes
which are reverse biased, during the impulse, will vary inversely with
their respective intrinsic capacitances.  

> >
> >
> Richard L. Measures, AG6K, 805.386.3734.  www.somis.org
> 
> 

73 & Good afternoon,
   Marv  WC6W







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