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'[PIC]: SMPS Transformer Calculus'
2001\09\16@094852 by Ing. Gustavo Quilosa

picon face
Hi everybody.
       Some have a "how to" calculate a SMPS forward transformer ??

thanks in advance,

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2001\09\17@012430 by Bob Blick

>        Some have a "how to" calculate a SMPS forward transformer ??

Hi Gus,

How about rules of thumb? I find them much more useful, perhaps because
manufacturer's data is required to do exact calculation and my hands-on
experience building SMPS's was as a hobby and using used or undocumented
cores. Now I still hack them together and later check my work with
manufacturer's data to make sure I'm not driving the core too hard. Heat
and efficiency will let you know how well you're doing.

A forward configuration(as an introduction to others who may be listening)
transfers when the transistor is ON, as opposed to flyback types which
store energy in the core and release it when the transistor turns OFF.

This configuration can have one transistor or more. Computer power supplies
are frequently of this type. Perhaps because the smallest core can be used
in a forward converter(because energy is not stored in it), and also the
transistors are exposed to the least voltage(because the flyback is clamped
the way they are connected in computer supplies).

The big drawback is that a substantial output inductor(before the first
output capacitor) is needed. In computer power supplies quite often this is
a toroid with all the outputs wound on it.

Another neat thing about forward converters is that the output voltage(or
rather the input-output transfer) is very linearly related to the turns
ratio and the duty cycle. These circuits rarely "freak out" because of core
saturation so they are easy to hack together without letting the smoke out
of the parts.

Usually I won't build a forward converter under 100 watts because the
smaller core size isn't a benefit, and the extra output inductor and
transistor or snubber makes it more complicated.

As a rule of thumb regarding turns-per-volt, find the right gauge of wire
for your primary and secondary, and wind it. When the core won't take any
more wire, you're done. Seriously.

Cheerful regards,

Bob Blick

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2001\09\17@030440 by Vasile Surducan

Hi Gustavo,
try to find the folowing article:

"The switcher transformer: Designing it in one try for switching power
by Phillip E. Thibodeau

in Electronic Design, september1 1980

Good things does not become older.


On Sun, 16 Sep 2001, Ing. Gustavo Quilosa wrote:

{Quote hidden}

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2001\09\17@073207 by Russell McMahon

picon face
> >        Some have a "how to" calculate a SMPS forward transformer ??

Old but useful -

Philips semiconductors used to publish VERY extensive documentation on all
types of switching power supplies.
I haven't looked recently but I imagine these will be available somewhere on
their site.

There is lopts of other stuff but for immediate relevance try -

-    "Transformer and choke design for forward-converter switched-mode power
        EAB 33 no 3 pages 125 to 147 -

-    "Switched mode power supply transformer design nomograms"
       EAB 33 no 3

-    "Notes on SMPS transformer design nomograms"
      EAB 34 No 3 pp 123 - 136

Year unknown but rather old.
I think EAB is "Electronic Application Bulletin".

       Russell McMahon

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2001\09\17@101033 by Alan B. Pearce

face picon face
>There is lopts of other stuff but for immediate relevance try -
>-    "Transformer and choke design for forward-converter switched-mode
{Quote hidden}

I think I may have copies of these. If I remember correctly they were
published under the Mullard brand name in the 1970's, and the journal was
the Mullard equivalent of the HP Journal that Hewlett Packard used to
publish (do they still do so?).

The articles were published just as colour television was really taking off
in Europe, and this provided the mass market requirement for SMPS, and so a
lot of effort went into developing the cores and other components for them.

To find copies of these it is probably worth checking in a university
library, especially if there is a department involved with electronic
engineering around that time.

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2001\09\17@103934 by Russell McMahon

picon face
{Quote hidden}

I actually have copies of the articles I cited - I can provide them (or the
most appropriate ones) via scanning and email if necessary but it would be
good iot those really interested did a web search to see if these or
something similar or newer was available.

Of course, they could 1st look at


   ALL Philps app notes




I'd guess this may about cover the requirement ... ?

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