High Voltage - PWM StepDown application

my end goal is 50 volts at 12 amps for a class-D audio application

I would like avoid any heavy Iron and Copper in the whole design.

so I was thinking of using one of Vicors FARM modules that cleanly filter the AC in and
( possibly are doing sync rectification )
but anyway they put out a 400 volts DC at 700 watts
and give a logic out for "power good"


My plan was to use a standard old Intersil IC as the PWM controller and
zener power it after the VICOR starts it up via a standard SCR

and either:
A) using a very low on resistance PFET with a gate transformer

or

B) using a Gate driver IC with an optimal N-FET


can I get some feed back on my ideas

I have simulated the basics using the XFMR and an IRF4905
and believe I can get my desired 600 watts at a cost of 100 to 200 watts

yeah I know I know thats gonna start to kill the VICOR FARM
but this is for initial testing of this DC to DC

I do plan to do a PFC with a lower output voltage than 400 volts
making things cush



Ed
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The transformer circuit doesn't work as drawn, AC coupling at the primary and possibly DC level restoring at the secondary
side is needed. Also it must be expected to give bad gate voltage waveforms and slow switching.

so how much faith can one put in their simulator
because with SImetrix
this does function

Thank you
I will try your suggestions and run the simulations
the PFETS were ordered yesterday and the rest of the circuit is benched

with feedback held at ground just to scope the waveforms at the transformer

Ed