To get 24VDC out at 8.5 amp even the TOP-250 would be marginal unless done as a forward converter.

The on resistance of the TOP-271 is 1.8 ohm worst case at 100C, just over 5 amp capability.

For Vin ave = 280VDC say the ave input current is ~ 0.9A and the peak current ~ 3.6 A in a properly designed flyback. The peak output current is ~ 34 amps, quite a bit.

The dissipation on the TOP-271 would be 4 watts just from conduction losses + switching losses - say another 2W = 6W so good heatsinking required

Also the Tx must be very low leakage to reduce turn off energy on the primary < 1uH, else your turn off snubber will need to handle ~ 5W ( for 1uH Llk )

A forward converter with moderate output L would be the way to go ...

good luck

Thanks,maybe you can give a better choice.hmmmmm,about PQ3220 for 200W?

ETD44 ...

Hi Peter Wang,

You can check in PIXls with link below if you wanted to verify your selected core if it is possible for your design requirement. If your selected core is not in the selection, you can just select custom and enter the specs of your selected core. Hopefully it helps. Thank you.

https://piexpertonline.power.com/pixls/design/index

Thank you very much,Mallora!

Thank you very much,Mallora!

Thank you very much,Mallora!