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



Hi Malcolm.

A few more info about that toroid story.

The toroid and its windings were simulating the transformer primary. In my SMPS
topology it receives pulses of opposite polarity so there is no DC and
degaussing is ensured. Its permeability was 90.

What I couldn't find from the Philips databook (it was a Philips part) were the
high-frequency losses figures: good to hear from you that they have got high
ones.

I received today a sample of a Siemens U93/76/30 core (U-U couple): that is the
biggest from Siemens! The problem is that the material is N27, which has
reasonable losses up to 25 kHz (I use 50 kHz). Boy, that has got a Ve of 297000
mm3 and an Ae of 840 mm2! Great size but not optimal material...

Therefore I'll stick with the Philips parts (U100/57/25) and wait to receive
their U-core samples (otherwise I should make new bobbins with a different
size).

During the past week I have spent my time reducing noise and ground glitches on
the SMPS controller (from 300 mV to 20 mV): still, a PCB would be the best
solution, expecially a 2-layer one.





Tesla List <tesla-at-pupman-dot-com> on 06.05.99 17:10:47

To:   tesla-at-pupman-dot-com
cc:    (bcc: Marco Denicolai/MARTIS)
Subject:  Re: A CW TC without a tube + Re: Solid state TC progress ?




Original Poster: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>

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