I have done for you here a Half Bridge SMPS with vin =310vdc, and vout = 32v and iout = 20A.
I did it in current mode, as current mode with slope compensation does not suffer any instability for a half bridge on the LTspice simulator. Just convert it to voltage mode for use with a voltage mode controller…some of which I sent you earlier.
For the transformer, I have used your ETD44. A Ferroxcube one.
I wound the primary with 24 turns of 2 pieces of 7/0.3 TEX-ELZ triple insulated wire. (2 strands in parallel)
There is a split secondary, and each secondary comprises 10 turns of [5 x 0.5mm] Enammelled copper wire. (5 strands in parallel)
I would sandwich the primary between the two secondaries.
I gave it a Sync FET output, as in the sim and schem.
(attached is the ltspice simulation, schematic, and brief calculation document)
(By the way if you dont have enough input capacitance to keep the vin at 310VDC , and it drops significantly below 310v every 10ms, then it will need to be re-done with the lowest input voltage used as the design input voltage parameter)
for 600-700 watts you need to interleave the Tx wdgs to reduce these HF AC losses ....
Thanks, ...May i ask do you mean the primary interleaved inbetween the two secondaries, as i have done here?
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BTW, the reason you cant do a half bridge in current mode is because the rail splitting input capacitors wont actually be of exactly the same value due to tolerance.....so you will get one charging up more than the other and unbalancing it.