Akula eternal lantern 4

[itsu]

Ok Void,   

thanks, i got it.

I also changed to an IRF740 MOSFET, so had to crank up the pulse signal to 8V, but needed to add a TVS to the drain/source to limit the severall hundreds volt peak on the drain.

That showed a similar picture as yours, but both at the 2V/div and 5V/div settings the blue (drain) trace is the same.
So probably a glitch in your (and AKULA's?) scope.

I do notice that when increasing the duty cycle from the 3% shown in the screenshot to about 8% my bench PS goes into current limiting (even when set at 10A  ) and starts to make noises (also the core goes humming).

Regards itsu

[hartiberlin]

The question is now , if these exponential rising flanks are really there or not....hmm..

Itsu,  also strange to hear from you that this center spike is still there without the core ??

I guess these exponentially rising slopes only occur , when the pulse is so short that it also affects the basis pulse as shown by you Itsu...when you made the pulse duration very short...

[hartiberlin]

@Void and Itsu, just use an LC lowpassfilter after your power supply , so your Powersupply will basically just see a DC load and will not be affected.. an 1 Henry and 10.000 uF lowpassfilter should do it...

[Void]

Itsu, regarding whether I get those strange pulses that you are seeing on your collector,
I do not see them at all when using a MOSFET for the driver. I suspect that may be why Akula
used a KT805 transistor to do his initial testing to look for the pulses. Those pulses may not appear
when you are using a MOSFET as the driver. This might explain why Akula used the KT805 transistor
first, and then planned to switch to his MOSFET later after determining what sort of pulse width and
frequency he needed. If you have a MOSFET you can try, I would be interested to see if you still get 
those pulses when using a MOSFET.

As a quick test of this concept, I used the Gate drive pulse signal on my MOSFET pulser circuit to drive a
TIP31C NPN power transistor I had available. I had a 1K resistor going from the base to ground.
The base drive pulses were not very clean, as it seems the pulse driver was getting loaded down,
but nevertheless I did see the collector going high while the base pulse was still On, but I didn't get
a pulse like you are getting. It may be dependent somewhat on which specific transistor you are using,
and the pulses going to my base were maybe lacking a bit in drive current. I'll need to repeat this test
when I have the chance. My old function generator stopped working a while back, so I am waiting for a new
one to come, but it is coming from China and has been delayed as well, so it will likely take a while...   

I got nothing unusual on the Collector of my TIP31C transistor when there was no gap I my toroid core,
but saw the unusual switching back to high in the Collector waveform when I had a 1.5mm gap in the toroid core.
Varying the gap in the core, changed the point in time that the Collector switched to High.

[Void]

I had the same problems years ago with my analog Hameg scope HM 312 when I researched the Newman machine pulses and back current spikes from the back EMF...
In the lower volts/div settings I always had bigger spikes and flanks than in the higher volts/div scale...
But it also happened on another scope , so I am not sure , what it exactly is... Maybe a different bandwidth of the input amplifier or changing the input impedance or something like that ?

Would be good to find out the cause of it. I used a 100x scopehead...

Thanks for the feedback on this. I have some X100 scope probes I can try.
I will give that a try as soon as I have the chance, to see if that makes any difference at all...