You're better putting one across the fet and one across the transformer, use Ultrafast diodes like Vishay or other manufacturers, search for 5000V reverse voltage..you may have to put two in series..


http://www.futureelectronics.com/en/Search.aspx?dsNav=Ny:True,Ro:0,Nea:True,N:666-4294918011


Mouser only do 1200V...

http://www.mouser.co.uk/ProductDetail/Littelfuse/DUR75120W/?qs=/ha2pyFaduiurbxH0/352xx0BCcNOaYZum6dsFLUPsoX1R22ZiEs0g==

GP02-40-E3/54 has a reverse voltage of 4kV, but forward current is 0.25 A only. Will it work for this purpose?

 

The diode voltage rating should be near or greater than 100V, the current rating should be near the drain current of the power supply

Voltage rating means forward or reverse?

 

The diode voltage rating should be near or greater than 100V, the current rating should be near the drain current of the power supply

Will this 1100 diode work for this purpose?
https://www.fairchildsemi.com/datasheets/SB/SB1100.pdf

 

Voltage rating means forward or reverse?

That would be reverse. That is, how much voltage can the diode block from going in reverse before breaking down.

 

That would be reverse. That is, how much voltage can the diode block from going in reverse before breaking down.

Can I use this diode for this purpose?
http://www.vishay.com/docs/93806/vs-60epu06hn3.pdf
Will the voltage and current ratings be sufficient for my circuit?