From: jeroen@nospam.please   
      
   On 2021-08-25 23:21, Phil Allison wrote:   
   > Jeroen Belleman wrote:   
   > ==================   
   >>>>   
   >>>>> ** Typical iron core transformers intended for 50/60 Hz can be used to   
   20kHz and beyond with no such issue.   
   >>>>> As the operating frequency rises, core magnetisation falls cancelling   
   any rise in losses.   
   >>>> Why isn't laminated iron good for RF transformer cores then?   
   >>>   
   >>> ** You have misunderstood my post.   
   >>>   
   >>   
   >> It's true I assumed constant Bmax. I should have said so.   
   >> Constant voltage, as you assumed, is indeed more natural.   
   >>   
   >   ** Well, I deal  lot with audio transformers  - from mic input to hundreds   
   of watts.   
   >   
   >   
   >> I measured the frequency response of a few iron core   
   >> transformers: A 75VA rectangular-core worked well up   
   >> to 40kHz,   
   >   
   > **  Yep.  Audio output types go to about 60kHz or more.   
   >   
   >   
   >> while a similar sized toroid went up to only   
   >> about 10kHz (-3dB), measured between the two independent   
   >> 15V windings of each.   
   >   
   > ** That is odd,  toroidals are usually the best with -3dB responses to   
   100kHz.   
   >     Just the fact the secondary is wound all over the primary does the trick.   
   >   
   > What cannot be done is having a tiny laminated iron core running at 100kHz   
   and high power.   
   >   
   > As well as ferrite there are "powdered iron" cores and toroids that will.   
   > Another material is  "amorphous steel" which as very low losses.   
   >   
   >   
   > ......   Phil   
   >   
   >   
   >   
      
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