Re: Diode strings - equalizing resistors

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Gregory Hunter" <ghunter31014-at-yahoo-dot-com> 

I agree. I think back in the bad old days, equalizing
resistors and ceramic disk capacitors were placed in
parallel with every diode on a long string to
compensate for uneven cutoff, swamp out the spikes,
etc. I remember seeing plans and schematics for such
in old ARRL handbooks. Diodes were fragile, expensive,
and not very uniform. That has changed dramatically
over the last 20 years. Diodes are now rugged,
ultra-cheap, and highly uniform. They are priced so
low, it is probably cheaper just to replace a diode
string rather than spend any money protecting it. They
are so uniform, the equalizing components are not much
use anyway. Bulk 1N4007s are practically giveaway now,
at least in hobby quantities. What--3 cents each from
Mouser?

Greg

--- Tesla list <tesla-at-pupman-dot-com> wrote:

 > Original poster: "Richard W."
 > <potluckutk-at-comcast-dot-net>
 >
 > Hi List,
 >
 > I have a question concerning the use of equalizing
 > resistors on diode strings.
 > I've heard it said the reason for the resistors is
 > that if one diode turns
 > off before the others then all voltage may be seen
 > across that one diode.
 > That makes sense if the diode turns off anywhere
 > else but close to zero
 > crossing. But the diode/s won't trun off until the
 > voltage is near or at
 > zero crossing. At that point there really shouldn't
 > be enough voltage
 > anywhere in the string to overwhelm the PIV spec of
 > any one diode if the
 > diodes are rated at 700 vrms or 1000PIV.
 >
 > Is my thinking amiss?
 >
 > Rick W.
 > Salt Lalke
 >
 >
 >
 >


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