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.manu@gmail.com>
wrote:

> 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 <abraham.manu@gmail.com>
> wrote:
> >
> > 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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