variable output buck smps
Hi,
Do you already have a bulk 48V power supply that you intend to use, or do you want to design that part as well? A flyback design will cope easily with the 60 to 70W that you require for your regulator input, these are isolated and a number of reference designs exist for offline PSUs, the efficiency is usually about 70%. This bulk supply PSU MUST use an isolated topology if you are using a non-isolated low voltage regulator such as the buck.
For the regulator the buck design as per your reference design is probably OK, they can be made quite efficient, usually around 80 to 85%. The 555 / 741 at the top is only used as an out of regulation indicator, the Buck part is handled by the TL494 and its associated pass transistors, which handle the voltage regulation and over current limiting. VR1 sets the output voltage and R24 is the current sense resistor as you probably already know.
Regards,
Bob.