Rosemary Ainslie circuit demonstration on Saturday March 12th 2011

[fuzzytomcat]

Hi Poynt,

I also found for the electronic students posting in this thread a complete set of the best information available on how a Mosfet works for those whom are not aware on the operation or function, so possibly all posting here is on the same page and something for everyone's reference.

International Rectifier IRFPG50 N-channel MOSFET


http://www.learnabout-electronics.org/fet_01.php  ( JFETs ( Junction Field Effect Transistors )

http://www.learnabout-electronics.org/fet_02.php  ( How a JFET Works )

http://www.learnabout-electronics.org/fet_03.php  ( JFET Animation )

http://www.learnabout-electronics.org/fet_04.php  ( Enhancement Mode MOSFET )

http://www.learnabout-electronics.org/fet_05.php  ( Depletion Mode MOSFET )


Glen

[poynt99]

So.  Your design is good.  Now you'll need to get it to oscillate.  You may need to add 3.3  micro Henries for inductance on the wires.  Maybe help?  Otherwise - all I can say is that ours most certainly works.  Not sure why we can't get it to work on PSpice. 

Kindest
Rosie

It's the inductance present in Q2's Source leg that causes the oscillation, so indeed taking the CSR out kills it in the sim.

Most likely it still works in real life because of the wire inductance still present. Of course in the sim, the inductance is zero unless we put some back in.

I will try re-inserting 200nH inductance there and see what happens.

Rose, what is the voltage swing on the FG for your tests?

.99

[Rosemary Ainslie]

It's the inductance present in Q2's Source leg that causes the oscillation, so indeed taking the CSR out kills it in the sim.

Most likely it still works in real life because of the wire inductance still present. Of course in the sim, the inductance is zero unless we put some back in.

I will try re-inserting 200nH inductance there and see what happens.

Rose, what is the voltage swing on the FG for your tests?

.99

Golly - I nearly missed this.  I assume you mean the voltage that we measure across the gate?  Typically it swings 4 volts in either direction - but negative peak is difficult to determine because of the oscillation.

Hope that helps you Poynty
Kindest regards,
Rosie

[Rosemary Ainslie]

Guys - two points of interest.  The one is that a friend of mine has managed to generate a clean square wave swinging positive to negative - but has NOT found that oscillation.  Interestingly though the cycle mean and mean average voltages are NEGATIVE.  Very intriguing. 

Another friend of mine has simulated this using a 555 applied to the 'Q-ARRAY' as he calls it.  Here detected is a small 'moment' - if that's the right term - where the waveform across the gate allows for a negative triggering that allows for the 'spike' to reverse current flow through the circuit.  Again - none of those PERFECT waveforms that Poynty managed.  But they point to the potentials that we've been seeing. 

We're waiting to hear from some others that are working on more robust software.  Hopefully next week.  And yet others are being canvassed for their own efforts in this regards.  We should get some definitive results during the next week or two.

My report is being held up.  Yet another friend has done a really neat schematic of the circuit configuration - that will satisfy you ALL - AND it has the dubious merit of making it readable for me.  He's promised me an illustration of this soon.  Hopefully by tomorrow I'll be able to post this for you.  I shall also be using that schematic for my 'revised' report.  And I'll also post that up when I've got receipt of it.

So.  We're slowly moving in the right direction here.  Frankly I'm very anxious to see these simulations - precisely because of the advice from our 'esteemed' and 'learned' that simulations of these results are CONCLUSIVE.  And if we can get away from those TEDIOUS experiments - then I'm more than happy.  Not that experimental evidence isn't required.  It's just that it does NOT seem to do much to breach those credibility barriers.   

Kindest regards,
Rosemary



ADDED
BTW - THE NEW SCHEMATIC IS ABSOLUTELY IN LINE WITH THE SCHEMATIC POYNTY'S USED.  NO DIFFERENCES.  DO NOT PANIC.  LOL.  It's just showing the same thing in a slightly different way.

[poynt99]

Please note a correction to my recent statement about the circuit oscillating due to inductance in Q2's Source leg; actually I meant to say the inductance in its Gate leg.

.99