Re: Toroid cores for GDTs

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Ward <steve.ward@xxxxxxxxx>

Herwig,

The only way to know for sure would be to wind a GDT and test it in
circuit with your MOSFET or IGBT as a load.  Generally, if the core
has a fairly sized cross-sectional area, you can get away with as few
as 10 turns (at 15V (30Vp-p) drive) when running 100khz or greater.
If you want to run lower frequency, you may need more turns (say up to
18 turns) to get down to about 20khz.  You really want to keep the
number of turns to a minimum, so that leakage inductance in the GDT
itself is minimized.

Just a tip, you should use wire with plastic insulation to wind the
transformer.  Enamel-based magnet wire often shorts out to the core
from pulling the wire through and scraping the insulation off.  I just
use wire from cat-5 cable.  Be sure to twist all of your wires
together using a drill or something like that.

Oh, and powdered iron toroids are *usually* painted with epoxy, though
i have rarely found one or 2 that were not.

Steve

On 1/23/06, Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: "Herwig Roscher" <herwig.roscher@xxxxxx>
>
>
> List,
>
> I acquired some nondescript and unpainted toroid cores, which I would
> like to use as gate drive transformers for a SSTC project.
>
> Unfortunately I do not know neither the manufacturer nor the mix nor
> the material. The only value I could figure out is the AL factor.
>
> Are there methodes to find out if the cores were made of powdered
> iron or of ferrite? And of course I would like to know the frequency
> range of the cores as well.
>
> Any help is appreciated very much.
>
>
> Bye             Herwig
>
> ----------------------------------------
> Greed is the root of all evil !
> ----------------------------------------
>
>
>