TPS40210: TPS40210

I have three power supplies a boost, SEPIC, and a flyback converters using the TPS40210 controller. The operating frequency is 100 KHz for the Boost and the Flyback, and for the SEPIC it is 600KHz. The Boost goes from 24 V to 200 V dc at a maximum load current of 500mA. The flyback goes from 200V at 600 mA to 24 Volts at 4 A. Both of these converters cannot work at higher load currents. The Boost can only output 200 mA, and the Flyback can output only 2.0 A. Beyond these output currents the MOSFET gets very hot. I an thinking of using a Multiphase design for the Boost (maybe 4 phases in parallel with each phase outputting 0.125 mA at 200 Volts each). For the Flyback I am thinking of using a Full Bridge, using the UCC28950PW etc chip. My environment temperature is an oil well at 165C. These regulators have to survive these temperatures for extended periosd of time, so they have to run cool. The SEPIC I haven't tested as yet, and I think I will have trouble with it too. I can use different chip if possible. Any suggestions. I may have to have NDA in place to send schematics.

Sagoo