3-Phase buck power design,pls help me look it ok?

maybe,you suggest me design by stackfet by flyback.sorry,we  need buck.So please help me look it.Give me some idea,get it better. Thanks ALL.

in second picture,as soon as power on,Lnk564 start working,and then mosfet open by Zener diode.after the process,I need a signal to keep the mosfet on,so I want use the BP to do  it.

when Lnk564 on,d&s are on same voltage step,and BP is above 5~6V on it.I use Bp keep the mosfet on.

This is only a idear,we need some suggestion,like about BP's load capable. 

OR!Maybe you  can give a better simple solution.  

Can you give me some additional details about your design? 

Min/Max Input voltage, Output voltage, output current, etc. 

Any other special requirements for your application? 

What is the reason you specifically require a buck topology?

-The Traveler

Vin:42V～420VAC，Vout:12V/0.1A

the reason is that

I don't want transformer and photocoupler  in my design.And the size can be small.

So I want  know whether the idea can work well?3Q 

Peter - 

You can most likely use Link-LP in a buck configuration although it's not supported by our design software.  I would reccomend you switch to LinkSwitch-TN and use PI Expert to start your design.  With the input voltages you're using, you'll need to enter Vmin and Vmax manually into the design spreadsheet.  Overall though, the design should be fairly straight forward.  

A couple words of caution/advice:

For a discontinuous buck reducing 590V down to 12V would require a duty cycle of approximately 2%.  LinkSwitch-TN is going to have a minimum duty cycle of approximately 2.3% when you look at switching frequency and the minimum on time of the MOSFET.  I would make sure you test the design under many different input and output conditions to make sure the design is functioning correctly.

With the 420Vac input, you're going to be close to the Drain BVDSS of the MOSFET.  You might be ok provided there isn't too much ringing from parasitics and if you can ensure input transients won't exceed the max drain voltage of the IC.  Make sure you verify the drain voltage under several different input and output conditions and ensure that there is enough margin between the peak drain voltage and the BVDSS of the MOSFET.

-The Traveler

First,Thanks for your advice!As long as the BP can drive the mosfet,I think using Link-TN is no problem.

I will try it .Thank you again.