Kapanadze Cousin - DALLY FREE ENERGY

[verpies]

You say: "Note, that in this zone both MOSFETs are OFF" but do you not mean "both GATES are OFF"

Yes, I can see you are paying attention.

because i clearly see the yellow MOSFET being ON in that time.

After all these scopeshots, I can say with certainty that during the "gray zone", the MOSFET's drain-source channel is OFF but the MOSFET's body diode is beginning to conduct (ON). 
If you zoom in vertically on the drain voltage during this period I bet you'll find the body diode's forward voltage there -1.2V.

The interesting question is: What would happen if the body diode did not exist?
You can find out by disconnecting the other primary half and scoping the voltage being developed across it during the "gray zone".

You also say: "no energy flows from the power supply nor from snubber capacitors ......."   but be aware we have no snubber capacitors right now, only 54V TVS's.

I know   That's why I was able to write, that "no energy flows from snubber capacitors"

[verpies]

I put up slightly more then 1 cycle @ 8us gate time, both gates.
first screenshot is at current point 2  (current through drain) 
second screenshot is at current point 3 (current through TVS) 

Look, your scope has 5 channels now!
The 5^th channel shows the current flowing through the Drain connected to the OPPOSITE winding.

Anyway, take a look at the currents in the "gray zone".  The TVS current rises rapidly and it decreases slowly (over ~2μs) while the negative drain current is increasing. (negative increase looks like falling visually)

This is an illustration of unusual current sharing between the TVS diode and the MOSFET body diode.  It is unusual because the forward voltage drop of the body diode is 1.2V but the clamping voltage of the TVS diode is 54V, so the diode with the lower voltage drop should bear the majority of the current, but that is not what happens in the "gray zone".

Could the body diode be that slow?

Do you have a 100V Schottky diode that you can put in parallel with the opposite MOSFET's body diode, just to see how much speedup we can get by helping the body diode?

[nul-points]

...so i think you're seeing interaction between both halves of the push-pull arrangement, through the winding, enabled by the inherent body-diode of each device

ie. when one side switches off, flyback current is continuing to flow in from the opposite winding via the body-diode there
...
All the best
np

Lol - please allow me the merest Smirkette, if this gets confirmed as a body-diode issue

...maybe save me one of those Donker Biers?  ;-)

all the best
np

[verpies]

when one side switches off, flyback current is continuing to flow in from the opposite winding via the body-diode there

If you were the first then you deserve the credit for it.
However, there is no continuation of current flow in the opposite winding.  Instead there is the initiation of current flow there, so I would agree with the following revised statement:

When one side switches OFF (while the opposite side is already OFF), current begins to flow in the opposite winding via the MOSFET's body-diode connected to it.

The reality is more complex, however, as evidenced by Itsu's recent scopeshots. 
Namely the current continues to flow in the winding that was switched OFF, through the TVS diode and begins to flow through the MOSFET's body diode connected to the opposite winding. 
These diodes bear the current together albeit unequally - in the beginning the TVS diode bears most of the current and in the end, the body diode does. 
The time evolution of this current sharing, most likely happens because the TVS diode is faster and the body diode has a lower voltage drop in the end...

[nul-points]

heheh - don't mind me - i was just teasing!

np