At 04:10 PM 2/6/2007, Dan Zimmerman N3OX wrote:
> > A trap, especially at high power, is not a good place to use any kind
> > of ferrite or powdered iron core. Ferrite is notorious for saturating
> > on current peaks and thereby causing distortion and harmonics.
>
>Yet many of us are using autotuners (which all have powdered iron
>inductors) on pathological matching cases, probably with high
>circulating currents.
I would say it's not so much that ferrites are notorious for
saturating, it's more like it's easy to screw up a ferrite design so
that it will saturate. People build multi tens of kW switching power
supplies with ferrites. There's a ferrite transformer in the output
stage of a 10kW RF power amplifier my officemate was building for a
research project. All a matter of good design.
The problem is that designing magnetic circuits is not easy, nor
intuitive, so a casual approach based on copying another design and
modifying has a high probability of unforeseen effects. For folks
who do it on a day to day basis, it's probably easier, but, to me, it
seems much more a black art than, say, a straightforward triode or
FET power amplifier design. (but the power converter designer might
say the reverse.. he thinks designing magnetics is straightforward,
but wouldn't contemplate taking on a Class AB FET design.)
Jim, W6RMK
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