Re: another strange idea
- From: Terry Given <my_name@xxxxxxxx>
- Date: Thu, 04 May 2006 03:59:29 +1200
Joerg wrote:
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
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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