The pulse for load dump for 12V applications reach 90V in 10ms, makes a peak at 100V during 10ms and decrease 'slowly' (1/EXP) in 380 ms. So the average voltage isn't exactly 100V during 400ms. It's rather 40 or 50V.

The protection is made by a varactor.
I will add the schematic to my website soon if you want

The power supply I have the schematic under my eyes has 13 passive components front of the switched regulator (diods, capacitors, inductances). It gives you an idea of the protections implemented.


Regards
Stephane