Different ways of interleave winding an offline Flyback transformer?

[treez]

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.

 

[c_mitra]

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.

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!

 

[Easy peasy]

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" ...

 

[treez]

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)

 

[Easy peasy]

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 -