Hello Sirs,

I made a PI Expert design for a 12V 1A (1.3 peak) output based on a tiny switch III. I have some doubt about the design of the primary shield. Here attached please find the PI expert file converted to xls.

As you can see the mechanical drawing and the electrical drawing agree each other but the winding instructions do not agree with the formers for the primary shield winding.

In my opinion a shield winding realized according to the mechanical drawing do not work correctly. Infact the shield moves in the same way as the outer layer of the primary (but this is useless as they share the same cold point) and in opposition to the secondary winding. On the contrary following the winding instructions the shield seems to work because it moveslike the secondary and in opposition to the primary.

Beside this, in order to improve output diode dissipation, the output diode is on the return leg of the transformer (connected between GND and the not dotted end of the transformer)and following the above consideration I think that, if we leave the dotted end of the secondary on the secondary side, the shield must be realized with the dotted end on the secondary side and connecting the "dotted end" to the primary positive (the dotted end of the shield should be the cold point).

Can you please confirm these considerations ?

Thanks in advance !!