I plan on designing a variable power supply (1-50V, isolated), able to provide a power of about 50W. For efficiency's sake, linear regulation is out of the question. The natural thing would be to design a flyback AC-DC supply, but there are a number of problems raised:
- The fact that it is variable complicates things: for example, the aux winding will not provide a fixed voltage. Also, will the flyback topology be appropriate for a large range of duty cycles ?
- I did not find any off-the-shelf flyback transformer that would be appropriate. Either the output voltage is not right, or the power, or the aux voltage, or they are not in stock anywhere. So I'd certainly have to design my own transformer, but I don't feel confident about this part (neither regarding the core choice, the design, or the DIY construction of this).
- Even the other parts of the flyback supply design seems risky: the snubber across the primary winding (which seems to consume a lot of power, by the way), the optocoupler feedback (which seems to require some tuning), etc ...
On the other hand, I feel confident about designing an appropriate DC-DC buck converter. There are a lot of tools from various manufacturers to help in designing them (TI, Linear Technology, ...), and it seems there are a lot less parameters that could lead to a non-functioning design.
So, I plan on using a simple toroidal transformer (much more easily available) to do the isolation and an initial stepping-down of the AC voltage, then the usual diode bridge + filtering capacitor, and then the appropriate DC-DC conversion step.
Apart from the fact that the transformer will be a lot bigger (and more expensive) than for a flyback design, are there some drawbacks of using this topology ? It seems nobody really does this, but I can't think of any reason that would make this a bad idea. The efficiency should still be pretty high, right ?