Xfmr design for smps

I have a couple questions, one is about identifying smps topology and
the 2nd is about the 3rd winding in an example I found. I need to
design a smps that can take

Vin: 70V to 105V and output 5V at 1A

I've chosen to use the mic9130 http://www.micrel.com/_PDF/mic9130.pdf

On the front page of the datasheet there is a "Typical Application"
schematic, which is not to far off from what I need to do, it's
Vin: 36V to 72V
Vout: 3.3V @ 4A

So, I think I'll copy that design, but now I have to design a
transformer... from the reading I've done about this, looks like one
of the first things I need to know is the topology of my smps.  That's
my question, can anyone tell me the topology of this smps example?
Looks like an isolated synchronous buck converter... or maybe a
forward converter?  Also I don't see how the third winding is
supplying the stead voltage to Vcc, according to the datasheet Vcc
operates between 9V -18V (pg 3) confusingly on pg 8 it says Vcc is
typically 8.5V....

much thanks!

panfilero <panfilero@gmail.com> wrote:

>I have a couple questions, one is about identifying smps topology and
>the 2nd is about the 3rd winding in an example I found. I need to
>design a smps that can take
>
>Vin: 70V to 105V and output 5V at 1A
>
>I've chosen to use the mic9130 http://www.micrel.com/_PDF/mic9130.pdf
>
>On the front page of the datasheet there is a "Typical Application"
>schematic, which is not to far off from what I need to do, it's
>Vin: 36V to 72V
>Vout: 3.3V @ 4A
>
>So, I think I'll copy that design, but now I have to design a
>transformer... from the reading I've done about this, looks like one

Buy an off-the shelf transformer:
http://katalog.we-online.de/kataloge/eisos/index.php?language=en&vw=Uebertrager_fuer_AC_DC_Wandler

>of the first things I need to know is the topology of my smps.  That's
>my question, can anyone tell me the topology of this smps example?
>Looks like an isolated synchronous buck converter... or maybe a
>forward converter?  Also I don't see how the third winding is

Its not forward. It is a flyback.

I'd check this website for a solution: http://www.powerint.com/

-- 
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
--------------------------------------------------------------

On Mar 8, 3:08=A0pm, n...@puntnl.niks (Nico Coesel) wrote:
> panfilero <panfil...@gmail.com> wrote:
> >I have a couple questions, one is about identifying smps topology and
> >the 2nd is about the 3rd winding in an example I found. I need to
> >design a smps that can take
>
> >Vin: 70V to 105V and output 5V at 1A
>
> >I've chosen to use the mic9130http://www.micrel.com/_PDF/mic9130.pdf
>
> >On the front page of the datasheet there is a "Typical Application"
> >schematic, which is not to far off from what I need to do, it's
> >Vin: 36V to 72V
> >Vout: 3.3V @ 4A
>
> >So, I think I'll copy that design, but now I have to design a
> >transformer... from the reading I've done about this, looks like one
>
> Buy an off-the shelf transformer:http://katalog.we-online.de/kataloge/eis=
os/index.php?language=3Den&vw=3DU...
>
> >of the first things I need to know is the topology of my smps. =A0That's
> >my question, can anyone tell me the topology of this smps example?
> >Looks like an isolated synchronous buck converter... or maybe a
> >forward converter? =A0Also I don't see how the third winding is
>
> Its not forward. It is a flyback.
>
> I'd check this website for a solution:http://www.powerint.com/
>
> --
> Failure does not prove something is impossible, failure simply
> indicates you are not using the right tools...
> nico@nctdevpuntnl (punt=3D.)
> --------------------------------------------------------------

why do you say it's a flyback?  it doesn't seem to be based on a buck-
boost topology to me, flyback would mean it could buck and boost the
input voltage, seems like it can only buck....