Prev: Root Cause of FDC6303N FET drain and gate short circuit?
Next: Hollywood NetBook ™ Webshop
From: Michael on 30 Jun 2010 11:13
I have a planar transformer primary winding that has 0.2mm x 10mm
cross-section (two windings in parallel, actually, top and bottom of
the PCB; ). It is running at ~450kHz (main harmonic skin depth is
~0.1mm). The thickness of the winding should be well utilized (~50%
duty cycle).
How about the width? How is current distributed across planar
transformer winding (width>>skin_depth)?

Little bit of explanation is probably needed.
The previous version of the same winding was thicker (~1mm) and had
narrow slot cut in the middle (lengthwise) to make the winding look
more Litz-like.
I respun the board to try differentt MOSFETs and changed the winding
size (made it thin) so it may be laser-cut (as opposed to machined).
The efficiency went down by 5% or so. Oooops!
New winding DC resistance is 4mOhm (AC should be higher, but by how
much??) - too thin, oops again. I stacked them up (three in parallel)
- the efficiency did not change appreciably.
From: Tim Williams on 30 Jun 2010 12:05
"Michael" <mk5778(a)yahoo.com> wrote in message news:cff94700-89c6-47e6-88b3-73ea08effb4c(a)i31g2000yqm.googlegroups.com...
>I have a planar transformer primary winding that has 0.2mm x 10mm
> cross-section (two windings in parallel, actually, top and bottom of
> the PCB; ). It is running at ~450kHz (main harmonic skin depth is
> ~0.1mm). The thickness of the winding should be well utilized (~50%
> duty cycle).
> How about the width? How is current distributed across planar
> transformer winding (width>>skin_depth)?

This should give you a clue as to what direction the winding should be narrow.
http://myweb.msoe.edu/williamstm/Images/Induction1401.jpg
All the more reason planar transformers are a bad idea... they're planar in the wrong direction. If you could deposit copper foil edgewise you'd have something pretty handy.

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms
From: Pieyed Piper on 30 Jun 2010 12:22
On Wed, 30 Jun 2010 08:13:25 -0700 (PDT), Michael <mk5778(a)yahoo.com>
wrote:

>I have a planar transformer primary winding that has 0.2mm x 10mm
>cross-section (two windings in parallel, actually, top and bottom of
>the PCB; ). It is running at ~450kHz (main harmonic skin depth is
>~0.1mm). The thickness of the winding should be well utilized (~50%
>duty cycle).
>How about the width? How is current distributed across planar
>transformer winding (width>>skin_depth)?
>
>Little bit of explanation is probably needed.
>The previous version of the same winding was thicker (~1mm) and had
>narrow slot cut in the middle (lengthwise) to make the winding look
>more Litz-like.
>I respun the board to try differentt MOSFETs and changed the winding
>size (made it thin) so it may be laser-cut (as opposed to machined).
>The efficiency went down by 5% or so. Oooops!
>New winding DC resistance is 4mOhm (AC should be higher, but by how
>much??) - too thin, oops again. I stacked them up (three in parallel)
>- the efficiency did not change appreciably.

If Litz like cannot be used due to profile height, then parallel single
mag wire conductors can be used to acquire skin effect based efficiency
gains.

So, like 3 or 4 parallel runs of say #28 will give a better yield than
a flat circuit trace or larger, single wire run would. Even cutting up a
wide circuit trace into several narrower parallel runs increases high
frequency efficiency.

You can also use Litz and smash the winding flat with a jig or fixture
before putting it inside the planar assembly. You can also configure
your own Litz like winding by twisting the three aforementioned mag
wires.
From: Pieyed Piper on 30 Jun 2010 12:24
On Wed, 30 Jun 2010 11:05:51 -0500, "Tim Williams"
<tmoranwms(a)charter.net> wrote:

> If you could deposit copper foil edgewise you'd have something pretty handy.

Makes one wonder if there is not an as yet un-researched technology
using flex circuit mounted "foil" winding laminates.

I have seen a "ribbon" wound transformer core before, but not the
winding itself.
From: Michael on 30 Jun 2010 13:10
On Jun 30, 12:24 pm, Pieyed Piper
<pieyedPi...(a)thebongshopattheendoftheuniverse.org> wrote:
> On Wed, 30 Jun 2010 11:05:51 -0500, "Tim Williams"
>
> <tmoran...(a)charter.net> wrote:
> >  If you could deposit copper foil edgewise you'd have something pretty handy.
>
>   Makes one wonder if there is not an as yet un-researched technology
> using flex circuit mounted "foil" winding laminates.
>
>   I have seen a "ribbon" wound transformer core before, but not the
> winding itself.

"copper foil edgewise" - cutting slot "lengthwise" is the same
"flex circuit mounted "foil" winding laminates is not an option - too
flimsy for almost 100A peak currents.
I still have to find a way of guesstimating what I really need for
copper.
 |  Next  |  Last
Pages: 1 2
Prev: Root Cause of FDC6303N FET drain and gate short circuit?
Next: Hollywood NetBook ™ Webshop