Rosemary Ainslie circuit demonstration on Saturday March 12th 2011

[atomicX]

Congratulation Rose... Sorry I'm late.

[rensseak]

I have found interesting bit of information about parasitic oscillations of MOSFETs in PARALLEL (the condition is to have more than one!):
www.microsemi.com/micnotes/APT0402.pdf

PETT oscillations, PETT = P lasma E xtraction  T ransit  T ime.

http://www.mourick.com/parasitic_oscillations.html

[nul-points]

The problem is that the circuit isn't workig.  I think it's the functions generator.  If it is - then I can only test this on Monday because that's the only time I can get another cable.
...
Rosemary

hi Rosemary

i was reading the PDF on parasitic oscillations linked by kEhYo77 and wondered if the following excerpt might be reason for the circuit not working at the moment

  "Such an oscillation condition...can cause over-voltage transients on the gate...and can even lead to uncontrolled, sustained oscillation and destruction of one or more devices"

is it possible that one or more of the MOSFETs has died and is stopping the correct switching action of the remainder?

just an idea

regards
np

<<EDIT #1>>
interesting, also, that rensseak's link to PETT describes the parasitic oscillation as a negative resistance event!  (although i don't recall it clarifying whether it's negative differential resistance, or the real thing)

<<EDIT #2>>
i've been a bit concerned about the suggestions to generate the parasitic oscillations by just connecting a negative voltage across the gate - the driving waveform from the SigGen is after all a dynamic waveform, not just a collection of two DC levels - ie., it also contains transients

so we shouldn't overlook the possibility that the parasitic oscillation is 'triggered' by a transient, before being able to sustain during a suitable state of the input (ie. the negative level)

this possibility seems to be supported by some of the info in the links mentioned above (eg., example oscillations are shown to follow either the 'ON' or the 'OFF' signal transient, or both, at the gate, depending on gate input resistance, production characteristics of the MOSFET die, and/or parasitic inductances in the circuit under test)


http://docsfreelunch.blogspot.com

[neptune]

@Poynt99 .What I actually said in my post was ,"If we want to be pedantic" . I did not specifically say you were pedantic . You ask , how was my post helpful in any way . I was hoping to encourage people to think outside the box , and see things in a new perspective . So I still say there is nothing magical about the battery terminals . I did not say there is anything wrong with measuring there . So please , lets avoid flame wars and leave it at that
@nul-points . You say that applying a constant negative voltage at the gate may not work because there are no transients and you could be right . Harti makes the point that it might be necessary to disconnect and reconnect the 9 volt battery a few times to start the oscillation . And HE could be right . And for less than $5 we could find out the truth .     

[nul-points]

@nul-points . You say that applying a constant negative voltage at the gate may not work because there are no transients and you could be right . Harti makes the point that it might be necessary to disconnect and reconnect the 9 volt battery a few times to start the oscillation . And HE could be right . And for less than $5 we could find out the truth .     

hi Neptune, greetings from the sunny south of England!

i agree

my point is that in electronics (as in so many things), the history of how something reached a state can be as germaine as the state itself

i'm not saying that we shouldn't try a DC negative gate drive setup - or that it is mistaken

i'm saying that the 'low' state of a SigGen output is only half the picture of what happened immediately prior to the start of the parasitic oscillations - and that we should bear that in mind when we try to understand what is happening on Rosemary's experiment

my EDIT #2 above gave some supporting evidence from those links that such oscillations *can* be caused by transitions (in either direction)

our job as 'ou investigators' should be to discover what is 'necessary and sufficient' to recreate unusual energy phenomena

in this case, a negative gate drive may well be 'necessary' - but not 'sufficient'


i didn't mean to be contentious - just thorough

there seems to be an abundance of woolly-thinking in the OU field - and i've certainly contributed my share! 


kind regards
np


PS in your quote above, it appears that Harti & i are essentially saying the same thing - just using a 9V DC gate drive on its own may not be sufficient to start the oscillations - it may be necssary also to add transitions to the steady DC condition

Harti quite rightly suggests that this could be achieved by simply disconnecting & reconnecting the 9V DC a few times

of course, in a circuit with plenty of reactance, we shouldn't ignore the possibility of frequency playing a part, either - so it *could* turn out that just the addition of a few transitions is not sufficient to trigger the oscillations - this could bring us back possibly to a SigGen being necessary to provide frequent/regular transitions!

who said 'breaking the stranglehold' of Classical scientific dogma was going to be easy?!? 


http://docsfreelunch.blogspot.com