Akula eternal lantern 4

[hartiberlin]

@Void,  you dont get this center pulse with your setup ?

Regarding the 2 and 5 Volts/div differences in ths slope rising , do you have your scope grounded and if yes at which points ?
Maybe it is a groundloop inductance charging or something like this..
Maybe the input amplifier is more snsible to ground loops with inductances in cables
or something like this ??

[Void]

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

Thanks for confirming that Itsu.
Yes, it could be just due to having an economy scope, and there may well be a quirk there.
Yes, I have been noticing the same thing regarding the power supply. What I found is that
I can operate OK at lower frequencies as long as I keep the duty cycle quite low, but as soon as
reached a certain width in the duty cycle the power supply regulator really starts acting up and
my core can really start chattering if I have a small gap in it.

[itsu]

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 was just testing this    , but i do, see screenshot.
Also here the pulse is there smack in the middle of the drain window.
The trick is to lower the gate input voltage to just opening the MOSFET (4V in my case).

This also worked for the MJE13005 transistor, allthought i thought that it should be fully open above 0.7V, but the same effect was seen (pulse)
with a base voltage between 0.7 and 4V.   Going higher made the pulse disappear.

Probably the low collector voltage (3V) has an influence in this effect?

Regards Itsu 

[Void]

@Void,  you dont get this center pulse with your setup ?

Regarding the 2 and 5 Volts/div differences in ths slope rising , do you have your scope grounded and if yes at which points ?
Maybe it is a groundloop inductance charging or something like this..
Maybe the input amplifier is more snsible to ground loops with inductances in cables
or something like this ??

Hi Stefan. No, I don't get the center pulse with a MOSFET, but see my recent post in which I
showed the odd Collector waveform I get when I tried a TIP31C NPN transistor. If I set about a
1.5mm gap in the torroid core, I get the Collector transistioning back to high right in the
center of the base pulse. Whether a center pulse occurs may depend on the exact transistor being used,
but I don't get any center pulses using a MOSFET (so far anyway).
All the best...


To make sure that I didn't have a ground loop to my power supply circuitry, I have the scope isolated from ground.

[Void]

I was just testing this    , but i do, see screenshot.
Also here the pulse is there smack in the middle of the drain window.
The trick is to lower the gate input voltage to just opening the MOSFET (4V in my case).

This also worked for the MJE13005 transistor, allthought i thought that it should be fully open above 0.7V, but the same effect was seen (pulse)
with a base voltage between 0.7 and 4V.   Going higher made the pulse disappear.

Probably the low collector voltage (3V) has an influence in this effect?

Regards Itsu

Ah OK, thanks for that Itsu. My pulse driver board does not allow me to adjust the
Gate pulse voltage. I will have to wait until I get my new function generator, which has been
delayed and probably won't get here for quite some time yet, or until I fix my old function generator.
That's a nice looking center pulse you got with your MOSFET...
All the best...