Joerg said:
Hello Klaus,
Ferrite is a wonderful material. Remember the old VHF/UHF splitters? The
VHF section usually consisted of a double-hole ferrite balun and is
useful up to 300MHz.
Personally I am just not a great believer in split cores or anything
that relies on adhesives to hold core halves together. At least not for
stuff that ships into fields where handling can be a bit rough.
Regards, Joerg
Hi Joerg,
I've built quite a few planar converters, using a combination of clips
and glue. My last dc-dc converter had a planar xfmr and a planar coupled
inductor, and we've made about 30,000 so far. Some of these get carted
about on the back of large trucks )in theory with air riders, in
practice without), and while there have been problems, the cores have
been OK for 5 years now. Some of the thermosetting epoxies I tested were
far stronger than the core, and the operating temperature rise hardens them.
I prefer thermosetting epoxy to glue the cores together, and some form
of CTE-, tolerance- and vibration-absorbing structure to hold it to the
PCB. its usually a good idea to space the core slightly away from both
sides of the PCB, because the permittivity of MnZn ferrite is so high
Of course the production guys then changed to a rather crappy glue that
softens when it gets hot, because it was easier to apply. It remains to
be seen if this was a wise idea (they no longer do it), but I suspect not
Hi John,
I've seen some papers out of South Africe detailing integrated magnetic
structures, where the ferrite material is formed around the windings. J
D Van Wyk springs to mind, but IMBW.
There have also been a bunch from IIRC Korea about coreless transformers
(spiral windings on FR4) and various uses as gatedrives etc. And some
spinoff papers looking at the effect of placing Cu and/or ferrite plates
on the outside. air core gatedrive transformers sound like a great way
to create mysterious blowups, along with maximising EMI emissions and
susceptibility.
any transformer you can make with an E-core, you can make with a planar
core (E-E or E-I). All they have done is reduce the height and increase
the thickness of the cores. Glued cores can have a lot less permeability
than a single piece of magnetic material (eg toroid, n-holer), unless
they are squeezed very close together. several tens of microns can have
a noticeable effect. very high creepage and clearance can be done, but
is a pain (buried windings, coatings of gunk, fancy bobbins etc)
Cheers
Terry
