Help with Buck Converter Charge circuit
Your driver is not the best for the job, that 470 Ohm resistance is too much and the gate voltage will charge smoothly, thus keeping the MOS too long in the linear region. Here's a quick'n'dirty change that can rectify that:



I have made certain assumptions in there, about the supply voltage and the output load, but it shows what I mean. Can you spot the differences? If not, here's a plot of the instantaneous power dissipations of both MOSes (yours is the black trace):



This is for the first `ma of the simulation, so it's right in the beginning of the transient, but relevant, nonetheless. The average readings are 12.515W (black) and 2.512 (red). Nothing calculated, just a quick example.

Note, however, that what I did tries to maximize both the rise and fall times, so it's up to you to decide which and how by adding appropiate series resistors.