diode in primary side of transformer which help dissipate energy from leakage inducatance of the primary should be fast reverse recovery my question is what if slow what will happen
and second question what is the different between force revese recovery and reverse recovery in FET OR IGBT

 

diode in primary side of transformer which help dissipate energy from leakage inducatance of the primary should be fast reverse recovery my question is what if slow what will happen?

The diode will act like a short circuit, as "standard" diodes turn on fast enough, but are very slow to turn off. This leads to high power dissipation, and diodes popping like popcorn.

 

Where is the diode in a standard flyback converter on the primary side of the transformer, if not as part of a RCD snubber as I posted in your other thread?