## What does filar mean, with regards to transformers?

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I was looking at these parts: http://www.coilcraft.com/pdfs/he...

and they talk about "One 6-filar winding", "Two trifilar windings", etc.

What does this mean?

Will this help, Michael?

http://en.wiktionary.org/wiki/filum

I think it refers to the number of threads in a winding, or some such..

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Bi-filar is two wires, tri-filar three wires, and so on. They are often twisted together for low-level RF transmission-line transformers.

Leon

Leon Heller G1HSM

leon_heller wrote:
Bi-filar is two wires, tri-filar three wires, and so on. They are often twisted together for low-level RF transmission-line transformers.

Leon

So in the case of a transformer with two trifilar windings, as in the datasheet I linked to, you have two sets of three wires which have been twisted together, then the transformer is wound with these two sets of wires?

How does this change the performance of the transformer?

This "filar" winding process makes the wires function more like transmission lines at high frequencies (say, 1MHz and up). If the transformer is constructed well so that the low frequency behavior matches the high frequency behavior, it works very well as a "broadband" device. Losses tend to be modest and relatively flat over frequency. Input-output voltage ratios, likewise.

Jim

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And normally all wires in a "filament" are coupled
very well, that's the advantage. Unfortunately the
wires in a filament normally are not
well isolated from each other, so the isolation-
breakdown may happen at a low level.

You haven't mentioned what frequency this transformer is working at, but at higher frequencies the current concentrates more on the outside of the wire (skin-effect). Three smaller wires, of the same overall diameter as one larger wire have a greater effective cross-sectional area for the current to flow. Therefore lower losses.

Search Litz wire.

It's pretty common to see bifilar and similar winding configurations used on SMPS transformers these days. 1 other advantage is that bifilar winding can sometimes allow for a nicer transformer winding stack to be made on the bobbin.

oddbudman

davef wrote:
You haven't mentioned what frequency this transformer is working at, but at higher frequencies the current concentrates more on the outside of the wire (skin-effect). Three smaller wires, of the same overall diameter as one larger wire have a greater effective cross-sectional area for the current to flow. Therefore lower losses.

Search Litz wire.

I want a transformer for ~10KHz. But if the filars are all isolated from each other - are there any benefits? And is the mutual inductance between two filars on the same windings as good as between a filar on one winding with a filar on a different winding?

There is no such thing as a "filar", you presumably mean a wire. At 10 kHz it doesn't make much difference how the transformer is wound, unless you need a balanced output or input. In that case a bifilar winding can be useful.

Leon

Leon Heller G1HSM

from:

http://www.datasheetcatalog.org/...

Quote:
Leakage Inductance
Transformer leakage inductance (on either the primary or
secondary) causes a voltage spike to occur after the
output switch (Q1) turn-off. This is increasingly prominent
at higher load currents, where more stored energy
must be dissipated. In some cases a “snubber” circuit will
be required to avoid overvoltage breakdown at the
MOSFET’s drain node. Application Note 19 is a good
reference on snubber design.
A bifilar or similar winding technique is a good way to
minimize troublesome leakage inductances. However,
remember that this will limit the primary-to-secondary
breakdown voltage, so bifilar winding is not always
practical.

Filar has some latin etimology, since in catalan, 'fil' is wire, and in other latin languages, are so similar.

From my ancient memories back to my university time, multifilar windings were used to reduce looses, not only resistive, but also inductive and capacitive, IIRC.

Guillem.
"Common sense is the least common of the senses" Anonymous.

Also, n-filar winding techniques minimize the inductivity differences
between the n individual inductors.

Jörg Wunsch

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leon_heller wrote:
There is no such thing as a "filar", you presumably mean a wire. At 10 kHz it doesn't make much difference how the transformer is wound, unless you need a balanced output or input. In that case a bifilar winding can be useful.

Leon

Surely there is a more precise term than wire. Filum?

A bifilar winding is two wires! What's wrong with that?

Leon

Leon Heller G1HSM

Quote:

Surely there is a more precise term than wire. Filum?