Rosemary Ainslie circuit demonstration on Saturday March 12th 2011

[poynt99]

I've got something slightly better than the above in the works.

Hang on to your chairs, as my friend Professor Lewin would say.

.99

[Pirate88179]

I've got something slightly better than the above in the works.

Hang on to your chairs, as my friend Professor Lewin would say.

.99

Professor Walter Lewin?  He is a great guy and MIT is lucky to have him.

Bill

[poynt99]

From the original "as-built" connections, I've analyzed the circuit and performed a bit of reverse engineering to come up with the underlying circuit and schematic. No function generator is required (similar to the above diagram I posted) for oscillation, only a second DC source capable of adjusting from about 3V to 10V.

In general, only a single MOSFET is required. Q1 is never in conduction and simply provides "negative" feedback via its body diode and channel capacitance for the Gates of Q2-Q5 (or just Q2 as I have shown).

Many questions and objections will be raised to this I'm sure, so I will put together a brief mosaic of diagrams depicting the progression from the original to what you see below.

There is one more final step in the progression, but I'll post that later once everyone has had some time to digest this and the mosaic first.

In the mean time if there are any questions about this, I'll try my best to answer.

.99

[poynt99]

Here is that "mosaic" I promised. This will gradually take you through the progression from the original 5-MOSFET circuit to the single MOSFET equivalent. I opted to omit Q3-Q5 because aside from additional current capability and a lower frequency Fo, the circuit operation remains the same, or "better", depending on your perspective.

Fig1_prog.png illustrates the circuit in the original as-built form.

Fig2_prog.png shows the same circuit but with Q3 - Q5 omitted.

Fig3_prog.png explains why Q1 is always in an OFF state, and why other considerations are required regarding the role it plays in the circuit.

Fig4_prog.png depicts the circuit with Q1 removed and the equivalent functional components (the body diode and channel capacitor in parallel) in its place.

Fig5_prog.png illustrates and explains why we can replace the function generator with a negative DC source of about -5V. The negative DC source is then moved to the right (under the Q2 Source) which allows for a much clearer perspective of how the over-all circuit is functioning.

The final circuit drawing was posted above in the file Q1_schema04_reduced.png.

All questions welcome.

.99

[Rosemary Ainslie]

Golly.  This is a FIRST.  A red letter day.   I wake up to all these interesting variations - and everyone moving forward with ever better designs.  This is just so wonderful.  Tears in the eyes - Poynty Point.  Hopefully and SOON I'll be entirely redundant to this exercise.  Can't wait.  It was where I was hoping to end up with the previous replication - only to discover that I actually had to salvage this from certain destruction.  It needs lateral thinkers and some real skill.  Sorely lacking in it's earlier presentations.

I can't impose your designs here Poynty.  But I'll send all involved a copy of your posts.  I have a sneaking suspicion that they're moving in the same direction.  Thank you for this.  I see how valuable is the use of simulations.  I'm also still blown away that simulators even show a benefit. 

Now Poynty.  If you were to do some marginal editing on your blog - then I believe I could almost retire - and retire happily.  I think I've covered just about everything that I can.  All that's now needed is to try and get our academics to take note.  And there are two such coming early next month.  So.  And HOW NICE IS ALL THIS?!?!

I'll wade through and see if there are any outstanding questions. 

Kindest regards,
Rosie   

ADDED   
and for clarity - it represents an emotional roller-coaster waveform.  One full cycle with an average ending round about here.