30W offline isolated flyback and use of shield windings.

[chris_leyson]

US7355871B2 https://patents.google.com/patent/US7355871 and US7369026B2 https://patents.google.com/patent/US7369026 from Power Integrations make an interesting read.
US3299384A https://patents.google.com/patent/US3299384 uses a retrogressive neutralizing winding which is interesting.

[ocset]

In an SMPS, is the shield connected to mains earth, or the rectified DC on the primary side?

Rectified DC negative or positive on the primary side. (basically to a "quiet" node as opposed to a switching node)

Here are some shield winding diagrams attached for offline smps.

Strangley, the 2w one has a sheild between primary and primary aux, aswell as between primary and sec (as expected)

[Zero999]

In an SMPS, is the shield connected to mains earth, or the rectified DC on the primary side?

Rectified DC negative or positive on the primary side.

That makes sense.

By the way, be careful if any patents currently apply, especially if you're doing this commercially. I don't see how a simple, basic screened transformer implementation can be patented, as there will be plenty examples of prior art, but it doesn't mean you needn't be careful.

[ocset]

Thanks incidentally, the 70W flyback transformer spec in the post above (#26)  is from a Chinese PSU company....who did the transformer for a UK based company……the spec as you see it there has a serious fault in it, (this fault didn’t occur in the actual unit, so the unit actually worked fine) which of course, we would put down to “human error”.

Its interesting though….how often does this happen?....because without a transformer spec, it means a company/customer cant take the transformer spec elsewhere to get it made……this could be construed as being “convenient” for the supplier.

As the UK gets more into outsourcing its PSU engineering overseas…these "spec errors" could become more prevalent…….its very convenient for a supplier if the customer doesn’t have a proper spec, and  doesn’t know how to do one themselves…because the customer is then bound in to the original supplier, who can then lever the price up, safe in  the knowledge that the customer cant go   elsewhere…or if they do, it will go wrong for them, (because of the “mistake” in the transformer spec) so they will come running back…..many will say the customer just needs an in-house PSU designer to check the specs over….but with PSU design work being increasingly sent overseas…..UK kids aren’t coming into PSU design as a career in such numbers as before.
Slowly but surely, the UK for one, is backing itself into a very deep, sticky corner.