Quote from: TinselKoala on May 20, 2012, 11:17:56 AM
So.... Do The Math (tm RA). We find that 0.0208 Joules have been dissipated in 0.0025 seconds, for a REAL average power of 0.0208/0.0025 == about 8.3 Watts _positive_, that is "flowing out" of the  capacitor. Did I do that right?

Yes, looks right to me, and the TRUE average power trace agrees when you look at t=2.5ms.

MH said,

QuoteThe DSO "doesn't lie" or does it?

The DSO reports what it sees and what it calculates from what it sees. The more better the oscilloscope the more better and different ways it has to look at what it sees.

But if you show it garbage and then tell it to calculate the wrong parameters from the garbage, you will get a very nicely packaged precise report of what the garbage looks like to the scope, and then it allows you to do with that whatever you will.

The DSO is, like any weapon of mass instruction, only as good as the person pulling (or setting) the trigger, and it only can see what it is pointed at and it can only calculate what you ask it to calculate. There is no "idiot user compensation" setting on most oscilloscopes. Perhaps there should be, though. Something like the interlock they put on a DWI driver's car: she can't start it unless she blows a zero first. The scope should require the user to complete a short quiz before it will boot.

QuoteWhat is the difference between Energy and Power?
a. They are the same, the terms are interchangeable
b. One is a measure of Work (a quantity), the other is a measure of How Fast Work Is Done (a rate)
c. Power is in Watts or Joules per Second,  W = J/s
d. Energy is in Joules or Watt-seconds,  J = W x s
e. All of the above except a.

And if you get more than 0 wrong, you have to start over with a new random question.

This is indeed a strange one. The more I look at this one the weirder it seems. Look at the blue signal, presumably the gate drive signal. Compare to when the oscillations start.

Is this the "bad" function generator doing this? How can it deliver a negative polarity without starting the oscillations, even if it isn't working properly?

Do they perhaps have it set to a ramp instead of a square wave, then offsetting the ramp?
72 volts, a positive gate signal for at least part of the time, and no current during the gate HI... weirdness time? And spindle envelopes instead of nice rectangular ones?

I would really like to know "Just what is happening here but you don't know what it is ....do you... Mr. Jones."

http://www.youtube.com/watch?v=-y0mvdkyUPc

TK:

Yeah that one looks very high-strung or something.  One could imagine the ground connection for the DSO was disconnected.

Anyway, those capacitor simulations spell.....

http://www.youtube.com/watch?v=NmZRDUO1wGQ

Tar Baby Turnips.

Top trace is VBatt @ 50v/div, baseline in the usual place.
Bottom is Gate signal from FG @ 5v/div, ditto.

The FG is set to make a ramp (fast up and slow down) or a sawtooth or tilted triangle wave, however you want to call it,  and then this is offset to put most of it below the zero baseline. In the mode shown I don't get much total current on the inline DMM.... but if I offset the ramp only slightly upwards from where it is now, the peaks turn on Q1 and I can get big currents fast: 1.8 amps with seemingly not very much of the ramp peak sticking up past 4 V.