Dear Kai,

A big thanks for your patient explanation. Your reply has helped to clear lots of assumptions that I had on this topic.

"But unfortunately, there is always this damned interwinding capacitance of several 100pF between primary winding and secondary winding of mains transformer present, which can make trouble, big trouble!"

Suppose I use a transformer with a shield between the primary and secondary or use a transformer that has a U-I core as opposed to the E-I core what happens to the interwinding capacitance. Why I said a U-I core is that in this case the primary and secondary are on opposite legs and not one on top of each other like in the E-I core.

Wont the above steps help reduce the inetrwinding capacitance ?

Also can you post some links for the kind of ferrite beads that you had recommended in your reply ?

Thanks

Raghu