Google for "IBA 48V 12V supply" and you will get the first hit from
Maxim. 48V bus (telecom) or 42V bus (electric vehicle) will be very
popular for IBA converters. VRM (eg: pentium 4/AMD64 power supply
on the motherboard) is drawing power from the 12V bus (used to be
from 5V bus in the Pentium 1 era). 

It is not what you exactly want. Still you may want to look at the forward 
converter design and adapt it to your design. 

http://www.maxim-ic.com/appnotes.cfm/appnote_number/3539/ln/en
"A 50 Watt Internal Bus Architecture (IBA) Power Supply".

Regards,
Xiaofan

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