Is joule thief circuit gets overunity?

[ltseung888]

The Atten may not be too bad after all.  The Offset problem may be due to not enough warm up time.

[Void]

@Void,

With the previous post diagrams and analysis, one can see that the use Vrms for analysis could be totally wrong.  For example, the COP calculated from
Output (Ch1 Vrms * Ch2 Vrms)/ Input (Ch1 Vrms *Ch2 Vrms) = 1.27.

The COP from EXCEL gives COP = -19.54.  The negative sign came from Input.

*** If you have a DC Power Supply, lower the Input Voltage to around 0.4V and see if you can observe the crossing of the 0 ref line and/or the spikes on both sides of the 0 ref line for Input Current.  If you do not have a DC Power Supply, find and drain a rechargeable AA battery to around that voltage and observe the waveform.

Ok, that is interesting. However, something doesn't look right with your input current waveform. It is showing as mostly negative when it should be positive current pulses, at least for the most part. That could be where the problem is. Can you confirm that you had channel 2 set to DC coupling? It looks like the coupling was set to AC?

I believe the RMS readings will not be useable if your waveform is not completely positive (pulsating DC) or if the waveform has both positive and negative swings and the positive and negative swings are not very symmetrical. In the scope shots you posted it looks like you didn't have your channel 2 probe set to DC coupling when you measured the input current. If the current waveform were showing as pulsating DC (all positive), I think the RMS reading would provide you with a quite different result.

I did a quick test with the input voltage set at 0.4V, and I do not get much noticeable negative swing on the input or output current waveforms. The output current is starting to get down fairly close to the noise level at this input voltage however. I also tried setting the input voltage to 0.36V, and although my LED still glows dimly at this input voltage, the output current is just barely detectable as very tiny blips on the scope trace, so the output current is unmeasurable on my scope at this input voltage. The output current is right in the scope's noise level at this input voltage.

[Void]

The Atten may not be too bad after all.  The Offset problem may be due to not enough warm up time.

Yes, if you find that letting your scope warm up for 20 minutes gives less offset then that is probably a good idea. After your scope has warmed up for twenty minutes you can then maybe try running the scope's self-calibration routine and see how everything looks then. You should connect each of your scope probe tips to your scope's ground lug connection when running your scope's self-calibration function.

[TinselKoala]

Well, chalk that up to another item of scoposcopy that is as basic as using the "ON" switch to turn it on.

Allowing sufficient warmup time --- usually arbitrarily defined as at least 30 minutes  --- is a basic operational requirement for any instrumental measurements. We haven't mentioned it here before -- except that .99 did -- because it is so basic a concept. But in every text about making measurements, and in every scope manual I have ever seen (with the exception of the Atten) the proper warm-up time interval is mentioned, before making quantitative measurements or internal scope calibrations.

And "note bene"..... it was Rosemary Ainslie's practice, throughout her long series of measurements, to turn on her oscilloscope, make a quick measurement as soon as it booted up, then turn the scope off again, until she was ready to make another measurement.

[Void]

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