For some reason I cannot view the video it is marked as private.
I agree to a large degree with Smudge's analysis.
If you still have your current probe handy, move it to the base drive and instead of looking at base voltage, look at base current.
I'm beginning to think the SG cannot supply enough current to keep the transistor saturated and at the peak point on the waveform, base current from the SG is insufficient to keep the ramp rising, so it turns off, then goes to the maximum current that the transistor can supply (it is now a current source limiting current to the level shown that is somewhat less than the peak current).
The current gain of the MJE13005 is a min of 10, max of 60. That is rather low, and if we consider that it may be as low as 10 then your SG must supply greater than 40 mA drive current to keep the transistor saturated. I suspect the SG is current limited to less than 40 mA output and the gain of the transistor may be a little higher than 10.
The transistor will certainly turn off or limit at some value when base current times transistor gain is exceeded by collector current.
At the low frequency you are driving, the core probably has insufficient inductance and is drawing a lot of current at the peak point on the current waveform.
A much higher gain transistor or higher inductance core would remove some limitations. If you must keep the present inductance, you could also go much higher with drive frequency, at least twice but three times f should remove the problem entirely.
I don't know if I have explained it clearly, but your transistor cannot supply any arbitrary current and stay saturated, it's collector current will be limited by base drive capability (multiplied by current gain) and exceeding that, it will become a current source and limit current at the collector.
« Last Edit: 2014-08-10, 14:11:24 by ION »
Just because it has a patent application or is patented does not always mean it really works.