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PICList Thread
'[EE] transformer winding direction'
2019\03\17@061649 by Manu Abraham

picon face
Hi,

Looking at a transformer, primary 12T secondary 200T, step-up

The primary is split in two, the secondary in 3, to reduce leakage inductance.

ie,
1. L1. Secondary  50T
2. L2. Primary  6T
3. L3. Secondary  50T
4. L4. Secondary  50T
5. L5. Primary  6T
6. L6. Secondary 50T


L1 and L3 (secondary) are at opposite sides of the secondary.

In which case isn't the direction of the flux changing ?
So, when L1 is wound clockwise, shouldn't L3 be wound in a
counter-clockwise fashion ?

Am I thinking right, or thoughts in the wrong direction ?

Apart from the original questions, any thoughts on a better
methodology to reduce leakage inductance ?

Any thoughts ?

Thanks,
Manu
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2019\03\17@103933 by Manu Abraham

picon face
Replying to my own post,

On second thoughts the interleaved layering would cause an imbalance,
since not all layers are linked withe same amount of flux, which
brings me to:

L #1 100T Sec
L #2 6T Pri
L #3 100T Sec
L #4 6T Pri

That said, 2 questions again:
#1. Should the Primary be in Layer #1, or is it better to start with
the Secondary ?
#2. Both the Primary and Secondary should be would in the Clockwise
direction itself ? (I hope so)

Thanks,
Manu


On Sun, Mar 17, 2019 at 3:45 PM Manu Abraham <spam_OUTabraham.manuTakeThisOuTspamgmail.com> wrote:
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2019\03\17@110249 by Jim

flavicon
face

Typically, transformers are wound with the primary closest to the core. This aids the flux entering the core with the most strength, and
therefore, providing the most coupling between windings and inproving
efficiency.

Also, it depends on the use of the transformer as to which way the
secondaries are wound.  Generally, they are all wound in the same
direction.  However sometimes they are wound counter to the primary, or
each other in some cases.  Usually the start of a winding will have a
dot at thst point on the schematic.
And if it is wound counter, the voltage out will be 180 degrees out of
phase with the primary.

Hope this helps.

Regards,

Jim

> ---{Original Message removed}

2019\03\18@031317 by Sean Breheny

face picon face
Manu,

I am having trouble picturing this transformer. What is the core material
and shape? Are all the windings on the same part of the core, or is it an
E-I core or E-E core and some windings are one one "leg" and others on
another "leg"?

Given the low turns count, I'm guessing that this is a transformer for a
switching power supply. Power transformers in the 10s or 100s of kHz use
very different winding techniques than 50/60Hz transformers. It is very
common to use several layers of turns in parallel for each winding and to
interleave them. The reason is not mainly to get better coupling - it is to
reduce losses. Think of it this way - the principal path which the flux
takes is through the core material, but for a transformer, the flux is
rather small because most of the flux from the primary is cancelled by the
flux from the secondary. The remainder is only what is needed to produce
the voltage across the transformer terminals. So, in the space between the
primary and secondary windings, there is higher flux than elsewhere - each
layer of primary winding increases the flux and then the next layer of
secondary decreases it. If you put all the primary together and THEN all
the secondary, you would have a higher flux in the region where the primary
layers end and the secondary layers begin. This would create larger eddy
currents in the copper of those nearly winding layers (eddy currents in the
copper).

The TI-Unitrode seminars (available online in PDF form) are a very good
guide to this, although I found some technical errors in them. The ones
most relevant to this are the PDFs named:

slup126.pdf
slup171.pdf
slup197.pdf
slup200.pdf
slup205.pdf

You can just search for these filenames and download them directly from TI

Sean


On Sun, Mar 17, 2019 at 10:44 AM Manu Abraham <.....abraham.manuKILLspamspam@spam@gmail.com>
wrote:

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2019\03\18@040306 by Manu Abraham

picon face
Hi Sean,

It is a simple switching ferrite transformer (full bridge, PSFB to be
precise), Primary 12T, Secondary 200T
The core is ETD type, similar to EE but the central section is round,
which makes things slightly more easier, operational frequency is
between 95kHz to 100kHz

The transformer is an interleaved one, the windings interleaved to
improve coupling and to reduce leakage inductance.
As you said, the flux is rather small and I have kept the flux still
smaller, hence the larger no. turns eg: 12T and 200T otherwise it
would've been still lesser. This has been done with the intent, to
reduce core loss, but Cu losses increases inversely. But that is not a
big issue, as the Cu is rated at 2x the current. So, Cu losses is also
somewhat reduced/handled there.

Yes, I agree completely to what you say and hence divided the primary
into 2 parts and the secondary also into 2 parts, for interleaving; 2
exactly, because the flux needs to be balanced between the different
interleaved segments. I have the unitrode documents at hand and have
pondered over them again and again.

One thing that confuses me always is the direction of the winding,
during interleaving. Somehow, this beast seems to keep attacking me
all the time. ;-)
But I think, having the primary closest to the core would be more
ideal as Jim says in a previous post, which makes sense.

Thanks,
Manu


On Mon, Mar 18, 2019 at 12:48 PM Sean Breheny <.....shb7KILLspamspam.....cornell.edu> wrote:
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2019\03\18@051947 by AB Pearce - UKRI STFC

face picon face
Seeing this and searching for those TI app notes brought up this PIclist page ...
https://piclist.mit.narkive.com/2psUD8wg/ee-utterly-superb-ti-magnetic-design-resources

which mentions a large number of them and some others besides.



{Original Message removed}

2019\03\19@024756 by Manu Abraham

picon face
Why post broken links ? Again, as I said, have those documents at hand.
That wasn't my query tho.

> Seeing this and searching for those TI app notes brought up this PIclist page ...
> https://piclist.mit.narkive.com/2psUD8wg/ee-utterly-superb-ti-magnetic-design-resources
>
> which mentions a large number of them and some others besides.
-- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
mailman.mit.edu/mailman/listinfo/piclist
.

2019\03\19@025104 by Manu Abraham

picon face
Hi Jim,

In the process of trials and errors. Thanks for the thought.

Cheers,

Manu

On Sun, Mar 17, 2019 at 8:36 PM Jim <@spam@jimKILLspamspamjpes.com> wrote:
{Quote hidden}

> > ---{Original Message removed}

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