You say you are already regulating it with the micro. So presumably you are using a fixed duty and kind of relying on that to give you 150V from 300V , (as long as your inductor is in CCM this is OK-ish).
So now you want to do the control with the micro….but presumably you are going to use current mode control?…..(Bucks are generally easier in current mode). So where is your high speed PWM comparator coming in to it?, does the micro have one internally? Remember, even if using voltage mode control, you still need a FET current sense to prevent possible disaster. If I was you I would use a high side NFET for the buck FET and put a current sense transformer up there for the source current sense.
Remember that the upper resistor of your output voltage divider is the input impedance of the error amplifier in your smps control loop…if it is high Ohmic value, then this could make for a slow feedback loop unless you compensate for it elsewhere.
Give me a shout if you want a PCB layout guide for smps…as this can ruin your day, and may well have been why the person wanted you to use an isolation amplifier..because they thought the pcb layout would be bad….in fact, I attach it anyway
- - - Updated - - -
Also, please find an article, which may put you off using a software control loop
- - - Updated - - -
ok, its 1444KB, and it wont upload, its called "the digital power supply revolution" by Dr Ray Ridley