Is joule thief circuit gets overunity?

[ltseung888]

@Lawrence: How can you be absolutely sure that your timer device is not supplying any power at all to your circuit under test? How can you be sure that you have indeed accounted for all power inputs to your circuit? As I've shown, the circuit you and void and I are using is capable of picking up power from the environment very easily, and can produce bright light in the LED without even being connected to anything with any wires at all, if there's sufficient ambient power floating around. And power supplies and instrument probe leads can trick you by supplying power through ground loops and other wiring infecilities.

@TK,

Try to do the Board 116 experiment with a rechargeable AA battery.  The voltage of the battery should run down to approximately 0.4V and then remain there for a few days.  Capture the Input Waveform then and see if your waveforms show the spikes crossing the 0 reference line.

The experiment is simple enough - no capacitors and no twin timers to confuse the issue.



You can then eliminate the various other effect at your site.  If you prefer, I shall be happy to send you two Zhou boards just like with void.  More independent confirmation, the better.

[ltseung888]

Spreadsheet comparison of Board 116 and Board 124.

LED on Board 124 is still very bright even in day time or with other lights on.  Board 116 is dim but is still ON - turn off other lights and the effect is unmistakable.

[Void]

One of the main potential problems I see already when making measurements at low supply input voltages (for example at Vin < 0.5V), is the current magnitudes start to go down much closer into the noise levels. This can no doubt skew measurements and introduce a degree of error into the measurements results. However, it seems you say that you start to see the unusual results at these lower input voltages so we will have to take noise levels into account as best we can.

There is a technique of using a differential probe (or using two matched and calibrated probes) to take more accurate measurements at lower magnitude levels, but I have not used this method before so I am not familiar with the details. That may be a measurement method that might possibly improve measurement accuracy at lower input voltages, so it may be worth looking into. I am not certain that the differential probe measurement method would help here, but I think that it may. However if you are sending your boards to some universities for testing, they would probably be familiar with the differential probe measurement technique, and would likely use that method if it will give more accurate measurements.

- void -

[Void]

Spreadsheet comparison of Board 116 and Board 124.

LED on Board 124 is still very bright even in day time or with other lights on.  Board 116 is dim but is still ON - turn off other lights and the effect is unmistakable.

Those are interesting test results. Definitely worth investigating further, IMO.

- void -

[Void]

@Lawrence. Here's an overview on using a differential oscilloscope probe when making low power measurements with a scope. The author of the article also recommends a current probe for low power current measurements as well.
http://www.edn.com/electronics-blogs/scope-guru-on-signal-integrity/4403528/Low-power-measurement-techniques

However, any testing I am going to do will just be with regular single-ended scope probes, so I will have to work within those limitations with the understanding that the margin of error will be higher. I do have a current probe for my scope, but it is cheaper quality one and it has poor shielding and is very susceptible to EM fields. I don't find it is any much more accurate than my regular scope probes.