Different ways of interleave winding an offline Flyback transformer?

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treez

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Hi,
We are doing a 12W Offline Flyback, using an ETD29 core.
We wish to interleave wind. (to reduce leakage L)

Can you confirm there is no difference between…

1…..two series primary coil halves “sandwiching” a single secondary coil.
2….Two paralleled secondary coils “sandwiching” a single primary coil.
 

treez said:
Can you confirm there is no difference between…

1…..two series primary coil halves “sandwiching” a single secondary coil.
2….Two paralleled secondary coils “sandwiching” a single primary coil.
Click to expand...

Off hand, I cannot see a difference between 1 AND 2, but I would prefer 1.

But it actually depends on the number of turns, or rather, turns density. Say you have the primary taking 4 layers on the bobbin, you may go for 1.

I guess the basic idea is to make them physically close. Rest is basic physics!
 
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If it more than 1 layer per pri wdg - if you can put the "quiet" end of the wdg closer to the middle in each case - then you will have less CM switching noise transference to the sec in "2" ...
 
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Thanks, i ended up with a bit more proximity loss by doing it as attached. (6 layers total) I will make sure the quiet half of the primary goes on top, so it shields the rest beneath it. (also changed to a E25/10/6 core)
 

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That is fine - but there will always be a fairly noisy wdg close to the sec side - this is where paralleling allows the quiet +HVDC side to go close to the sec wdgs in each case -
 
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