QUOTE=Flyback;1131536]laptop = 100w+?
Thus not likely a flyback.
I think they are usually half bridges?
or 2TFC's
And vin = 400V not 310...unless it USA mains , as PFC output is ~310v there.[/QUOTE]
All of the laptop adapters that I have worked on have been flybacks. But I will admit, that three pieces are hardly a representative sample. As for a saying that supply greater than 100 watts cannot be a flyback. Well, I have a 120 watt (15V @ 8A) supply on my bench right now that is a flyback. I also have a netbook (which I still consider to be a laptop) that runs on a 40 Watt adapter (19V @ 2.1A)
And why would a PFC output be 310v in USA? All of the PFC supplies I've seen here have been ~385 to match the world wide standard. Even if an engineer were to design a PFC supply for use only in the USA, and wanted a low DC rail voltage, he would likely use something around 190 volts. (120v x 1.414 plus a bit)
Now, back to the Op's question.
You should start with defining the output power you need, and the input voltage you have.
- Then choose a topology, and design a circuit to fill that need.
- Then see what the requirements of the transformer are, and see if you can match it to the characteristics of the transformer you have from your adapter.