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Old 19th October 2007, 12:16 AM   #1
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Join Date: Nov 2005
Default Question about bifilar primary winding

I have determined that I need a bifilar wound primary on an off-line 200W SMPS.

The primary winding would take up 1 layer unifilar wound, and 2 layers bifilar wound.

It then becomes attractive to split the bifilar into 1 unifilar winding in layer 1, and a second unifilar winding, in layer 3, with the secondary sandwiched in layer 2 between them. This would help both with proximity effect, and with leakage inductance.

So the big question: is this arragement (2 physically separated windings in parallel) any different, electrically, from a bifilar wound single winding?
Would there be any side effects to doing this?

Thanks for your help
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Old 19th October 2007, 07:40 PM   #2
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Your best bet is to make a single winding on two layers, series connected. Half on layer one and the other half on layer three.
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Old 19th October 2007, 08:19 PM   #3
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Let me rephrase my question.

In a multifilar winding, does turn 5 of one strand, HAVE to be next to turn 5 of another strand?

What if it's located elswhere on the coil form?

Does that change anything?

Do any of the equations change? Does the transformer model differently if individual strands of multifilar windings are saparated?

Does anyone know?

Thank you kindly
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Old 19th October 2007, 10:16 PM   #4
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If your goal is to reduce leakage inductance and primary skin effect then splitting the primary and parallelling/series connecting the sections will do that. Making the primaries bifilar will only reduce leakage inductance between them, which doesn't make much sense as they are parallelled.

And that multifilar thing, isn't the definition of multifilar that you take all the wires and wind them at the same time? That would cause turn x of each strand to be in close proximity to each other. But making windings multifilar only makes sense when you want to decrease leakage inductance inbetween them, like in a push-pull primary or secondary.

What kind of topology is this, and what voltages?
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