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Why AN-18 and AN-15 dont state dots to be same end of flyback transformer?

Posted by: treez on

Why is it that Power.com app notes AN15 and AN18 dont state that in flyback transformer, the dotted ends of the coils should be at the same end of the former, for EMC reasons.?

Also, why does these documents not state that the Flyback switching node end of the primary must be the start point of the first-wound primary coil? (so it gets buried and shielded by the other windings to improve EMC performance)

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Submitted by PI-csbabu on 03/18/2021

Hi Treez,
In general flyback back topology drawn with opposite polarity windings to distinct from forward transformer. The dotted ends of the primary and secondary winding at the same end of transformer gives EMI advantage and good for automation point of view but it again depends on secondary layout.
If you notice the transformer construction (for example fig.35 & 38 in AN-15) given in all the application notes, primary winding start is at the bottom of the transformer, which is also a swinging node buried under other windings.