Buck converter, mosfet choise

MrAl:
You should really specify your input and output voltage too, and i guess you mean it is not synchronous.

The input voltage of BUCK is 80 volts and output is variable between 0 till 80 volts.
The maximum current is about 5 Amps.

MrAl:
What are you using to control the MOSFET?

I want to use it to control speed of Brushless DC Motor.
tnx.