Re: A CW TC without a tube + Re: Solid state TC progress ?

To: tesla-at-pupman-dot-com
Subject: Re: A CW TC without a tube + Re: Solid state TC progress ?
From: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
Date: Thu, 06 May 1999 08:10:47 -0600
Approved: twftesla-at-uswest-dot-net
Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

Hi Marco,
           I'm following your results with interest. A note on iron 
powdered cores:

> Original Poster: "Marco Denicolai" <Marco.Denicolai-at-tellabs.fi> 

<snip> 

> P.S. I wrote that at 300VDC 3A my IGBTs stood cool: my 160 uH test inductor
> core
> instead started boiling (its coating) after about 20 seconds. It was a 33 mm
> O.D. iron-powder ferrite toroid with just 40 turns of wire. Core losses
> were too
> big at 50 kHz. It also did change color (from green to gray!). It is still
> working but now its surface is full of bubbles :)

Iron powder is the wrong choice of material for any application which 
has a high ripple current. The cores are designed to be used in 
forward converters and the like where a high DC current is passed 
through the inductor. They are inherently low permeability as they 
have a distributed airgap to handle the high NI present. If they are 
to be used in an application where a large flux *swing* is present in 
the core, they make excellent snubbing components because of the high 
AC power loss. That may have contributed somewhat to the clean 
characteristics of your circuit operation.

Malcolm