Claimed OU circuit of Rosemary Ainslie

[Rosemary Ainslie]

Thanks.  What a relief.  I am definitely not equal to such efforts. 

[MileHigh]

.99:

THANK YOU for the PSpice plots in #2560, they are like gold.

I think that we learned a few things here.  The plot for the power dissipated in the MOSFET says a lot.  We know that the coil is on an unstoppable mission to discharge it's energy when the MOSFET starts switching off.  Hence we see the first big spike when the switch-off occurs.  That's the coil forcing it's energy through the closing door of the MOSFET switch.  This shows the MOSFET being "smacked" by the inductor, something that I have been mentioning all along.  After that you are probably just looking at a simple RLC resonator discharging through the 10-ohm resistor, where the capacitance is associated with the drain structure inside the MOSFET.  It's like a little bit of "backwash" because the drain capacitance finds itself at a certain voltage potential after the shut-off and is then staring down that nice spring of an inductive resistor sitting in a pool of chocolate pudding.  Of course in real life there is also stray capacitance at play here, and I assume the stray capacitance and the drain capacitance are comparable in size.

This happens in real life:  You are in the basement of a house shutting off the cold water valve and you notice the valve is at the end of a 50-foot straight length of pipe.  The water is running upstairs and if you shut the valve off too quickly you get the watter hammer effect, a big bang followed by the decaying sound of oscillations in the pipes.  The 50-foot straight length of pipe with water moving through it is the charged inductor, and the water pressure is the voltage.  The valve itself goes up in temperature a touch because it dissipates the energy associated with the moving mass of water.  Just seeing if anybody is capable of switching dimensions and having a Eureka! moment.  lol

When you think of it, if you could shut off the water valve fast enough the water pipe would simply explode.  It sounds like there may be a Darwin Award in there somewhere.

Also, adding the fly-back diode would stop the smacking of the MOSFET and instead the coil-resistor would discharge through the flyback diode and then back into itself.  Here is your famous "recirculating current" but with a sober reality:  There is no "resuse" of energy, rather, you start with a certain fixed amount of inductive energy, and it burns off and becomes heat with a time constant of L/R.  Even if R is very small and L is very large so that it takes 20 minutes such that you can imagine the same current goes around in circles thousands of time, there is no "extra energy" associated with every new loop around the loopy-loop.  You are starting with a FIXED amount of inductive energy, and that slowly is "burned off" and becomes heat energy.  There is no way to "cheat COP" here and "gain COP" out of thin air.

Also thanks for showing the drain voltage.  The "right side up" version of what happens when the coil does it's big POSITIVE spike!  lol

MileHigh

[MileHigh]

.99 and Harvey:

Also, an integration of those for a 1 minute run. I doubt that it is long enough for any thermal modeling to become active, but it is a start to where I am going with this.

1 minute is an eternity in SPICE when dealing with these frequencies. Usually it's not necessary to run that long anyway, which we'll get into when/if we get to that point.

Not wanting to jump the gun here but the thermal modelling issue can be covered fairly quickly.  There is no thermal model in PSpice that I am aware of, but it's pretty trivial.

Just look at the rising exponential curve for the shunt voltage in post #2559.  That could just as easily be a temperature versus time graph for the MOSFET package temperature or the load resistor temperature.  The time constant is longer for more massive objects (thermal capacitance) and longer the more isolated the object is from paths of thermal conduction to the outside world (thermal resistance).

So a thermos is just a thermal capacitor that has a long time constant because the thermal resistance to the outside world is very high.  The temperature inside the thermos follows the same exponential decay curve.  Another Eureka! momment!!!

MileHigh

[MileHigh]

Harvey:

It's Boris the Spider from the Gulag in Siberia.

Как Ð'аши дела?

I don't think we need common grounds for this test as we are checking the current flow in each path at the same time. As long as your probe references are each isolated we should be ok. Otherwise the test becomes meaningless.

It's not really a problem if the grounds are all common as .99 plucked from the manual.  You have four channels, you are in oscilloscope heaven.  Let's use the battery ground as the channel ground, shall we?  Connect Channel 1 across the main load shunt resistor.  Connect Channel 2 to the battery supply voltage near the positive shunt resistor.  Connect Channel 3 to the other side of the positive shunt resistor.  You have all the information that you need to crunch your currents, plus you have a bonus channel!

Connect the bonus channel to check what happens to the potential difference between the two grounds of your two quasi-isolated nodes, or whatever else you want to do.  Perhaps that tempting gate signal?

Suppose Aaron exports that data and you whip up the Excel spreadsheet to plot it.  It would be really cool if both files were hosted on the same freebie hosting web site.

MileHigh

P.S.:  .99:  Can you run an FFT on some of the signals in PSpice?  it woudl be fun, and educational for some of the audience.  We have the technology, we can transform the description of time-based signals into frequency-based signals and go back and forth through these two dimensions or domains and actually see the harmonics!!!

[poynt99]

P.S.:  .99:  Can you run an FFT on some of the signals in PSpice?  it woudl be fun, and educational for some of the audience.  We have the technology, we can transform the description of time-based signals into frequency-based signals and go back and forth through these two dimensions or domains and actually see the harmonics!!!

Of course! 

.99