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another strange idea

J

John Larkin

Jan 1, 1970
0
Has anybody made RF transmission-line transformers out of multilayer
PC boards? I've seen switching magnetics integrated into a board, with
traces for the windings and a few strategic holes for mounting an
e-core.

John
 
J

Joerg

Jan 1, 1970
0
Hello John,

Has anybody made RF transmission-line transformers out of multilayer
PC boards? I've seen switching magnetics integrated into a board, with
traces for the windings and a few strategic holes for mounting an
e-core.

The UHF section of all those VHF/UHF 4:1 splitters had "phenolic
transformers". Not exactly transmission line but close. At least all the
ones I mounted in my teenage days were that way. Lower end or higher
frequency reflectometer bridges (SWR meters) often contain directional
coupler strips made from FR-4.

The E-core thing, well, I am not a fan of that. Seen to many come apart
on those desert truck rides. I do it with double-holers.

I see no reason why multi-layer couldn't do it. Except that FR-4's RF
properties are, as Archie Bunker would put it, lousay.

Regards, Joerg
 
M

Mikko Kiviranta

Jan 1, 1970
0
John said:
Has anybody made RF transmission-line transformers out of multilayer
PC boards?

I have designed one on an integrated chip, which is more or
less the same thing, just in a smaller scale

Regards,
Mikko
 
J

Joerg

Jan 1, 1970
0
Hello Klaus,
I can mention several papers if you are interested. None however for
ferrite planar transformers (but wont that be very lossy due to the
limitations of the ferrite?)

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
 
T

Terry Given

Jan 1, 1970
0
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
 
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