Is diode needed across current sense transformer primary of SMPS?

[treez]

Yes, the resetting of the magnetizing flux in the secondary only needs 8V across the secondary.
That means 0.08V across the primary, which is not enough to forward bias the diode across the primary.

 

[Anna Conda]

I can see the point about the poorly wound toroid CT with the main wire thru the centre, having more leakage than a carefully wound (distributed) one, however the energy stored in the CT core is very low, a small snubber across the fets will likely take care of this, More important is the layout of the two switch forward and the turn on speeds of the main diodes on the pri side, current in the wiring inductance (pcb) at turn off is likely to give rise to Vds spikes 10x or more greater than any CT contribution.
Add the wiring inductance to the model and see....