I hope someone can suggest the proper IC / family for the following:

Available DC power ramps up from 0 to 450 VDC at up to 15 AMPS and back down to 0 (SOLAR PANEL ARRAY). 

Intended intermediate load operates from 200 to 400 VDC and may only need 5 or less amps.  Over 400 VDC and poof !

PWM needs to turn on switch (not try to boost or buck) and just pass current <375 VDC.  Droop is ok 

PWM needs to buck as voltage exceeds 375 VDC.

I considered a simple series pass emiiter /  source follower but would rather not burn off 75 volts if a

SMPS can run cooler.   Someone suggested the UC2842 or UC.2843.

External switch can be Nfet, Pfet, or IGBT.  Can supply isolated floating gate drive if needed..

Thank you.