high freq ETD core transformer winding technique

[sss]

this is my first time winding an ETD type ferrite core (used to work with toroids), so i need some advices with winding techniques...

first , the primary :


as u can see , there are 2 cases :


a- the winding fits the bobbin and everything is ok .
b- the winding cant be fitted into one layer , so second layer is needed and the winding goes in the oposite direction.

first question:
is it ok to wind like that? (example b) it looks to me that the second layer goes in the other direction , but it seems like theres no other choice except connecting the 2 layers in series externally...
what u guys think?

[sss]

one more question
i know that the best way is to sandwitch the primary or the secondary winding . my only problem with this technique is the different lenght in wire for the outer parts of the sendwitch
so , i got an idea :
lets say i need 2 primaries and 2 secondaries (for push pull car smps)




as u can see in the image , i'm thinking to wind the first part of the 2 primaries in bifilar winding ...
then i'm gonna wind the secondary (or the secondaries, didnt want to make the drawing too messy )
and the last part - 2 more primaries in bifillar winding.

now , in usial designs the first and the second part of the primaries are connected in series , i was thinking to connect them in paralell , what do u guys think? will the paralell connection of the outer sides of the sendwitch ruin the "sendwitch effect" and i will gain nothing?


also, as u can see the secondary is wound in the oposite direction , is this is how it should be?

[ifrythings]

For your first question, think about electron flow, if you keep going the same direction (clockwise) you have no problem and the electrones keep moving the same direction around the core,\. but if you go clockwise and get to the end of the bobben, then start going counter-clockwise you'll have problems as the first winding's electrons are going one way and the second part of the winding is going oposite, you get a complete cancilation.

Main thing is pick a direction (clockwise or counter-clockwise) and use that direction the whole way thrue winding.

[darkfenriz]

Originally posted by sss


a- the winding fits the bobbin and everything is ok .
b- the winding cant be fitted into one layer , so second layer is needed and the winding goes in the oposite direction.

first question:
is it ok to wind like that? (example b) it looks to me that the second layer goes in the other direction , but it seems like theres no other choice except connecting the 2 layers in series externally...
what u guys think?

I think, that winding like 'b' causes flux to cancel out itself and then disables magnetic transformation, but I am not sure...

[darkfenriz]

Originally posted by sss
.....

also, as u can see the secondary is wound in the oposite direction , is this is how it should be?

Are you willing keep secondaries and primaries orthogonal? This way you create a communication 'twisted pair', which was invented for minimum crosstalk, which is not the case for a transformer of course.

[zilog]

Adjust the number of parallell wires per secondary to completely fit the coilformer in one layer. I think that I would break the primaries in two separate windings and do the center-tap connection outside of the transformer just to avoid having high voltage swing at adjacent wire turns, causing high winding capacitance and thus lower LC parasitic resonance.

As for the layering order, you should stack the windings pri1-sec1-pri2-sec2 assumed that pri1 and sec1 conduct current at the same time. The reason for this is to keep eddy current losses down, see this link

[sss]

Originally posted by ifrythings
For your first question, think about electron flow, if you keep going the same direction (clockwise) you have no problem and the electrones keep moving the same direction around the core,\. but if you go clockwise and get to the end of the bobben, then start going counter-clockwise you'll have problems as the first winding's electrons are going one way and the second part of the winding is going oposite, you get a complete cancilation.

Main thing is pick a direction (clockwise or counter-clockwise) and use that direction the whole way thrue winding.

and how can u explain all the EI transformers with 200+ primary turns?
u can open any transformer that u got , and see that the coil is wound the way i showed in "b" .

[theChris]

in post1, case b, are you talking about the winding type, clockwise/counterclockwise, or the direction in which the coil is building. if you mean that you are going to spool up the wire to make 1 layer, then continue on back on another layer that is spun in the same way (when viewed from above) that builds a second layer on top of the first one, then you will be fine.

[sss]

Originally posted by theChris
in post1, case b, are you talking about the winding type, clockwise/counterclockwise, or the direction in which the coil is building. if you mean that you are going to spool up the wire to make 1 layer, then continue on back on another layer that is spun in the same way (when viewed from above) that builds a second layer on top of the first one, then you will be fine.

i'm talking about the direction of the coil build up...

[simingx]

The winding doesn't go in "the opposite direction"... it's just as if you started winding it in the same direction from the other end of the core.

As long as all the turns go either clockwise or anti-clockwise when viewed from one end of the former it's OK.

Think about how a spool of thread is wound...