Efficiency of DC/DC System

I'm in the process of developing a DC/DC converter with an input of 200-350V DC to [email protected] in either a half-brick or 3/4 brick. My original thought was a two switch forward converter that does the entire thing. I had another thought that I could do a two switch forward that converters down to 48V and then a buck that drops it from 48V to 5V. I'm curious if that will allow me to optimize my magnetics better.

Any thoughts would be appreciated.
 
Here is a interesting part.
UCC25640x LLC Resonant Controller
I would think about half bridge, because it reduces the voltages on the transformer to 1/2 right away compared to full bridge or most types.
Here is a design onsemi it is about the right size but too complicated. There are some good ideas. It has active diodes and Power Factor Correction.

Do you need PFC?
Do you want diodes or MOSFETs on the output?
 
Here is a interesting part.
UCC25640x LLC Resonant Controller
I would think about half bridge, because it reduces the voltages on the transformer to 1/2 right away compared to full bridge or most types.
Here is a design onsemi it is about the right size but too complicated. There are some good ideas. It has active diodes and Power Factor Correction.

Do you need PFC?
Do you want diodes or MOSFETs on the output?
I'm not all that familiar with LLC converters. I don't think it would work because I need to operate with an internal fixed frequency of 300kHz, and an external sync frequency of 400kHz.

It's DC in, so no PFC. I am going to be using mosfets on the output.
 
OK so several types of resonant converters will not work, because it need to work at 300 to 400khz.
Use a older style forward, half bridge type PWM.
Hard switching at 400khz will cause some heat problems in the MOSFETs. Look at SiC and GaN MOSFETs, they are faster.
Last time I used MOSFETs as diodes I had a 8-pin IC for each transistor. Worked well. Can not remember the part number.
 
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