shield winding of flyback transformer

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Hi,
Is the number of shield turns important? I read in a application note that it's better to wind shield so that fill the width of bobbin. So if the turn numbers be one or two turns differ from suggested number of PI expert is it important?
Best Regards.

Yes it is recommended to follow. There is no current flowing in the shield winding so a thin wire gauge is usually used. Multiple strands of the wire gauge can be used in order to fill the bobbin width and to effectively shield the noise being suppressed. You can read some information about shielding on the link below:

https://ac-dc.power.com/sites/default/files/product-docs/an15.pdf

thank you so much for your help.
I read an15 it was useful. If I want to design a flyback transformer without pi expert how can I determine the turns of shield?
And if it's better to fill the bobbin width what is difference between using one strand wire and filling the bobbin width with more turns and using multiple strands with less turns?
Best regards

Hi Zahra,

The shield winding is usually half of the primary winding in a single layer. For example, primary winding is 20 turns in 2 layers. So a single layer of primary winding is 10 turns, therefore, shield winding is 5 turns.

Using a single strand for the shield winding is not convenient as you may need a bigger gauge to fill the bobbin width. It may take a lot of space in your transformer design, so it is recommended to use smaller gauge, multiple strands filling the width to effectively shield the noisy Drain connected to primary half.

Many thanks for your help

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