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Author Topic: Akula eternal lantern 4  (Read 278622 times)

hartiberlin

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Re: Akula eternal lantern 4
« Reply #120 on: August 04, 2014, 10:26:30 PM »
@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 ??
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Void

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Re: Akula eternal lantern 4
« Reply #121 on: August 04, 2014, 10:27:14 PM »
Quote from: itsu on August 04, 2014, 10:11:23 PM
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  :o ) 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.


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itsu

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Re: Akula eternal lantern 4
« Reply #122 on: August 04, 2014, 10:30:41 PM »
Quote from: Void on August 04, 2014, 10:16:42 PM
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 
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Void

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Re: Akula eternal lantern 4
« Reply #123 on: August 04, 2014, 10:31:18 PM »
Quote from: hartiberlin on August 04, 2014, 10:26:30 PM
@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.

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Void

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Re: Akula eternal lantern 4
« Reply #124 on: August 04, 2014, 10:34:29 PM »
Quote from: itsu on August 04, 2014, 10:30:41 PM

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...

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itsu

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Re: Akula eternal lantern 4
« Reply #125 on: August 04, 2014, 10:41:58 PM »
Quote from: hartiberlin on August 04, 2014, 10:16:33 PM
@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...

Thanks Stefan,

i was meaning to make something like that because i hate it when the PS does that.

Ok,  so we are back to square 1 i guess.

Perhaps we need a better translation of the video in which Akula explains the effect, i personally had problems following the tekst  :o


Regards Itsu
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Void

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Re: Akula eternal lantern 4
« Reply #126 on: August 04, 2014, 10:44:11 PM »
Quote from: hartiberlin on August 04, 2014, 10:13:28 PM
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...

I suspect that those exponentially rising pulses are not there. It may be due to
some change in capacitance when switching between 2V/div and 5V/div. I think the Atten
scopes have the same insides as my Siglent scope, at least for certain models anyway,
so that might explain why Akula got the same strange looking waveform on his scope.
If the strange looking waveform is just an artifact of the scope, then what was Akula talking about?

Also, yes. If Itsu gets the same odd pulses when using an air core coil, then it seems it is not
related to some characteristic of ferrite. So then, what exactly causes those strange pulses?
Could it be just random short duration noise spikes on the base or gate causing the switching to occur?
Wait, no, I guess not, because the pulses Itsu and Akula are getting seem to be very stable and consistent...


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Void

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Re: Akula eternal lantern 4
« Reply #127 on: August 04, 2014, 10:47:54 PM »
Quote from: hartiberlin on August 04, 2014, 10:16:33 PM
@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...

Yes, I have already tried a large value choke with not much change, but maybe
including the large filter cap as well will help. I have found however that the power supply regulator
is OK at lower pulse frequencies if I keep the pulse widths short.
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itsu

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Re: Akula eternal lantern 4
« Reply #128 on: August 04, 2014, 10:55:05 PM »
Quote from: Void on August 04, 2014, 10:44:11 PM
I suspect that those exponentially rising pulses are not there. It may be due to
some change in capacitance when switching between 2V/div and 5V/div. I think the Atten
scopes have the same insides as my Siglent scope, at least for certain models anyway,
so that might explain why Akula got the same strange looking waveform on his scope.
If the strange looking waveform is just an artifact of the scope, then what was Akula talking about?

Also, yes. If Itsu gets the same odd pulses when using an air core coil, then it seems it is not
related to some characteristic of ferrite. So then, what exactly causes those strange pulses?
Could it be just random short duration noise spikes on the base or gate causing the switching to occur?
Wait, no, I guess not, because the pulses Itsu and Akula are getting seem to be very stable and consistent...

I just used my other scope (200MHz OWON PDS8202), but also there no difference in the drain/collector 2 or 5V/div. settings.


Yes i think its a (false) switching of the transistor/MOSFET due to the low gate/base (well, not really on the base) input signal, allthough my Tektronix scope "sees" no spikes or noise on that gate/base signal.

Regards itsu

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hartiberlin

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Re: Akula eternal lantern 4
« Reply #129 on: August 04, 2014, 10:55:35 PM »
Hi Istu and Void,
Where are you measuring exactly the yellow gate (base) signal ?

Directly at the Function generator output or
directly at the basis of the transistor ?

If you still have 10 Ohms parallel with 10 nF in series at the output of the
FG before going into the base , this RC could really be
Responseable for the sudden switch off or spike in the circuit
As it could ring itsself with its stray inductance by being energized by a pulse...
So please only directly show the signal at the base..
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hartiberlin

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Re: Akula eternal lantern 4
« Reply #130 on: August 04, 2014, 10:58:23 PM »
Quote from: Void on August 04, 2014, 10:47:54 PM
Yes, I have already tried a large value choke with not much change, but maybe
including the large filter cap as well will help. I have found however that the power supply regulator
is OK at lower pulse frequencies if I keep the pulse widths short.

you really need this Filter capacitor otherwise it is no lowpass filter and it will not help
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itsu

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Re: Akula eternal lantern 4
« Reply #131 on: August 04, 2014, 11:01:19 PM »
All my yellow traces are only measured directly on the base/gate.

The purple trace (in some screenshots) is at the input of the circuit, meaning before the 10 Ohm / 10nF RC.

Regards Itsu
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hartiberlin

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Re: Akula eternal lantern 4
« Reply #132 on: August 04, 2014, 11:04:29 PM »
I find it really strange that in theAkula scope shots there is on the yellow base signal
3 different states like high , mid and low...
Why is the base signal going back to mid state after just a few nanoseconds of
 on time ?
 does anybody know , why this happens ?
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hartiberlin

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Re: Akula eternal lantern 4
« Reply #133 on: August 04, 2014, 11:12:59 PM »
Quote from: itsu on August 04, 2014, 11:01:19 PM
All my yellow traces are only measured directly on the base/gate.

The purple trace (in some screenshots) is at the input of the circuit, meaning before the 10 Ohm / 10nF RC.

Regards Itsu

Okay,  I  see then your signal from the drain or collector effects the base signal by some kind of capacitive coupling between the drain and gate capacitor or collector and Base diodes..
 otherwise it is note possible that one could get such a burst on the base signal when pulse width is so low....so the gate or base is affected by the drain or collector...
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Void

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Re: Akula eternal lantern 4
« Reply #134 on: August 04, 2014, 11:59:18 PM »
Quote from: hartiberlin on August 04, 2014, 11:04:29 PM
I find it really strange that in theAkula scope shots there is on the yellow base signal
3 different states like high , mid and low...
Why is the base signal going back to mid state after just a few nanoseconds of
 on time ?
 does anybody know , why this happens ?

Can you post a scope shot. Could what you are calling a high state on the base
be overshoot, and then it falls back to its high pulse level, and the low state is base pulse off?

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