Re: rectifier stack experts?

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

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, October 19, 2002 3:51 PM
Subject: Re: rectifier stack experts?


> Original poster: "Crow Leader by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<tesla-at-lists.symmetric-dot-net>
>
> The large rectifier stacks that International Rectifer made rated tens to
> hundreds of thousands of kV at AMPERES were somehow compensated. They
don't
> makt that product line anymore and I cannot find data sheets for them.

That's because diode manufacturing has gotten a lot more consistent (6
sigma, and all that), and they make soft fast recovery diodes now...

>
> I've seem many x-ray machine rectifier strings with just diodes. They all
> appear to be rated under 500mA. This is not useful to me.

The same technique works at higher currents...

Check Philips Semiconductors... or a specialty house like Diodes, Inc.



>
> What do people use in large commerial radio transmitters?

Strings of uncompensated diodes. or vacuum tube rectifiers..


Folks, this is one of the areas where the "old standards" aren't applicable
any more... Rotary spark gap technology is pretty much the same for the last
50 or more years, so those WWII reference works are quite applicable.  BUT,
when it comes to semiconductor devices, there's been a LOT of advances in
the last 10-20 years, and techniques that were essential in 1970 just aren't
appropriate any more.

I was cleaning out the garage a while ago and ran across a transistor
ignition (not CD, but points replacement)  made by my father in the 60's...
4 germanium power transistors in series, and all manner of stuff to equalize
them. Today, 1 device, designed especially for ignition duty, with good
avalanche characteristics, etc.

Likewise, the discrete semiconductor manufacturers make diodes specifically
designed to be seriesed up in HV strings.  Don't bother fooling around with
1N400x diodes, unless you are a masochist, or have a really, really good
deal, lots of free time for assembly, and are going to massively overdesign.

I might also point out that if you go to the trouble of putting an R and a C
around each diode, you've tripled your component count, and since diodes and
Rs and C's are all about the same price, why not just use 3 times as many
diodes? (unless you are worried about the total Vf)