I've just finished doing my first off-line flyback, which proved a success. A simple block diagram is as follows:
I know this topology seems common now, for example it is used in Apple USB Charger wall bricks (that video discusses cheap-knock offs, but the principal is still the same).
The problem is, flybacks are very complex beasts to tame. So I started thinking why isn't the following topology just used instead more commonly:
For the record, I have never designed a power supply using this method (particularly, using a high-voltage buck). But on paper I can't seem to see any problem with it.
Is there any reason one might be preferred over the other?
Both provide the same level of isolation, and depending on the parts used, potentially the same efficiency.
From the block diagram you can say the first process has "less steps", but that doesn't necessarily mean less parts, lower cost, or easier to design by any means.