Re: HV Diodes - RVP Fast Recovery Types and Paralleling of ? ? ?

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

Original poster: "robert & june heidlebaugh by way of Terry Fritz <teslalist-at-qwest-dot-net>" <rheidlebaugh-at-desertgate-dot-com>

Having replaced a few diode strings in high-voltage radar power supplies I
feel I should make a comment about how the plates were matched. We neaded 20
series diode plates in parallel so we put 200 volts and a resistor in series
to measure ths diode junction voltage drop of the hole diode plate. we then
selected 20 out of 100 with the same voltage drop to connect in parallel.
The unused plates were saved to use the next time a replacement was neaded.
At a cost of $200,000 per assembly the time required to select matched diode
plates was well worth the effort.
   Robert  H
-- 


 > From: "Tesla list" <tesla-at-pupman-dot-com>
 > Date: Thu, 20 Feb 2003 22:55:58 -0700
 > To: tesla-at-pupman-dot-com
 > Subject: Re: HV Diodes - RVP Fast Recovery Types and Paralleling of ? ? ?
 > Resent-From: tesla-at-pupman-dot-com
 > Resent-Date: Thu, 20 Feb 2003 22:58:08 -0700
 >
 > Original poster: "Malcolm Watts by way of Terry Fritz <teslalist-at-qwest-dot-net>"
 > <m.j.watts-at-massey.ac.nz>
 >
 > Hi Ken,
 >
 > On 20 Feb 2003, at 18:58, Tesla list wrote:
 >
 >> Original poster: "K. C. Herrick by way of Terry Fritz
 > <teslalist-at-qwest-dot-net>" <kchdlh-at-juno-dot-com>
 >>
 >> ...but since diodes have a positive temperature coefficient, will not
 >> paralleled ones tend to share current more or less equally?  The one with
 >> the highest current will get the hottest, thus increase its voltage drop,
 >> & thus finding its current diminished, with the others taking up the
 >> load.
 >
 > Not so unfortunately. The tempco is negative - you can easily do a
 > simple expt. to demonstrate this to your satisfaction. The principle
 > is used to compensate for transistor temperature rise in bipolar
 > amplifiers and takes the form of a sub-circuit known as a Vbe
 > multiplier.
 >
 > Regards,
 > Malcolm
 > <snip>
 >
 >