GetDeviceInfo, you are very right, I took some pictures which I will attach here.
Some sweeps get wider with R6.
But it leaves still the question on why they did that.
Rsc is indeed 0,1 ohm, both on the package and measured at several units.
In the beginning, while searching for the reason of these strange patterns in some units, I had recalculated and found 0,1 Ohm to be in compliance with their formula of 0,3/Ipk(switch) .
Where from what I found Ipk(switch) is 2x the output current, so roughly 3A.
So 0,1 Ohm looked OK formulawise.
I like the idea of rising the frequency. In one of the experiments Ct was disconnected accidentally and the thing was swinging in the upper several hundret KHz. No squeeching noise and it was suprisingly not as hot as with the regular schematic.
But others warned me of eddy currents and other things I don't understand, to not go higher, but lower the frequency.
What do you think about their warnings?
From what I have learned so far, it seems that an overcurrent occurs which resets a cycle or so. Would that explain the weird quad pattern in those last graphs?
But why only on that unit, and others have a double or triple pattern, why?
These are the pictures of the same quad unit as pictured in the above link.
These are with the strange R6 in place, showing the stretched ramps as you said:
The first pic is always the main shot followed by zooms.
Timing is 50uS, top curve is Pin 3 (TC) which starts somewhere from 130mV up to 1,4V (the last and highest peak before a longer down ramp starts).
Bottom is junction of R3 and L2.
The "zoom ins" are a 10x magnification of an area from the main, normally in continuation, 5usec per div.
Added after 5 minutes:
And here are the pictures with R6 removed.
The quad pattern, noise and heat all remain, nothing changes in that regard.
The first pic is always the main shot, followed by zooms.
Timing is 50uS, top curve is Pin 3 (TC) which starts somewhere from 130mV up to 1,4V (the last and highest peak before a longer down ramp starts).
Bottom is junction of R3 and L2.
The "zoom ins" are a 10x magnification of an area of intrest from the main, normally in continuation, 5usec per div.
Added after 2 hours 16 minutes:
I tired the 100pF menawhile.
The pulses are shorter but the general pattern of very short bursts (now up to 10) with periods of "silence" remain the same.
And the squeeching and heat is also the same.
I am quite sure that this fast succession of these short pulses are too much for the coil, I just don't know how to prevent them from happening (except the 1.2nF thing mentioned earlier).
I added 100nF directly to the power pins of U1, just in case, no change.