Is joule thief circuit gets overunity?

[poynt99]

In other words, what is being measured as 'output current' under such conditions is actually mainly electrical noise that is being picked up by the circuit and probe. This will in all likelihood greatly skew the output current measurement and give you a meaningless measurement result. The actual output current that is passing through the output LED at this low input voltage setting on the joule thief circuit (for example at 328mV) is most likely in the very low microamps range, probably somewhere in the vicinity of 20uA or so. Also, such a low current is likely well below the minimum amplitude that my scope can measure with any degree of accuracy.
- void -

Seriously?

That noise signal on your trace is not going to greatly skew the current measurement at all. Even if it was 20uA (it's probably much lower), this is about 1/1000th the current in the circuit when it is running.

[Void]

Seriously?
That noise signal on your trace is not going to greatly skew the current measurement at all. Even if it was 20uA (it's probably much lower), this is about 1/1000th the current in the circuit when it is running.

Sorry Poynt99. What you just said doesn't make any sense at all to me. I think I have explained it all quite clearly. The approx. 20uA I am referring to is the approx. actual current flowing through the LED under those operating conditions, not the resulting average or RMS current that the scope is measuring due to the electrical noise pickup at that measurement point. There is also likely a fair bit of measurement error introduced due to the current magnitudes being well down below the very minimum limit the scope can measure with any accuracy. If I take the measured output current sample data points logged in the spreadsheet for the output current measurement (mainly noise) and take the average, it comes out to 240uA average current, but this is just the average of what is mainly electrical noise! This can clearly be seen by comparing the output current waveform scope shot to the noise waveform scope shot with the power supply switched off. Again, for roughly that brightness on the LED, I would estimate the actual current through the LED to be very roughly about 20uA. I am basing this LED current estimate on the current that flows through my LED when it is set to just light very dimly when connecting the LED directly to my DC power supply and measuring the DC current using a multimeter. The LED on Lawrence's board is a different type than my LED, so its actual current at that very dim brightness might be a bit different, but Lawrences's LED seems to perform similarly to my LED in the joule thief circuit, so it is probably similar to my LED in performance. It is just an estimate, but it is probably ballpark.

[poynt99]

I see now.

With only 0.328V input, your voltage across the LED CSR is only about 1.2uVp according to my sim.

On the 2mV/DIV scale, you can only resolve about 8uV.

[Void]

I see now.
With only 0.328V input, your voltage across the LED CSR is only about 1.2uVp according to my sim.
On the 2mV/DIV scale, you can only resolve about 8uV.

Yes, and the noise level picked up by the scope probe is much higher than that, and I believe it is the noise which is the main cause of the error in the output current measurement, based on the magnitude range of the samples and the average of the output current data samples.

Just in case anyone has any doubts about a LED being able to light up dimly with only 20uA of current passing through it (it no doubt depends on what exact type of LED you have however), I connected the LED I have been using in my joule thief circuit directly to my adjustable DC power supply with my multimeter connected in series to measure the LED current, and adjusted the DC power supply voltage so that the LED was just turning on and glowing dimly, very roughly similar in brightness to the LED on board 119 that I ran these last power measurements on. My LED is a yellow LED and Lawrence's LED on board 119 is a white LED, so Lawrence's LED may have a bit different current versus brightness relationship than my LED, but I adjusted my LED close to around the point where the LED is just lighting up, similar to how I had the LED adjusted on board 119 when I did these last power measurements. I would have to disconnect one of Lawrence's LEDs from one of his boards to do this same test on the same type of LED that Lawrence uses on his boards, but I think this test with my yellow LED does show that a LED with somewhat similar performance characteristics to the LEDs used on Lawrence's boards light dimly with current in the very low uA range. I am not certain what actual current was flowing in the LED on board 119 in my last test, but I would guess that somewhere in the range of 15uA to 50uA or so would not be far off from actual. Lawrence, if you want, I can remove a LED from one of your boards which is not working and do this same test.

Pictures of LED brightness with LED current set to a DC current of about 20uA and 42uA are attached below. (My multimeter is probably not super accurate at these current levels, but it is probably at least ballpark), but I didn't have the camera directly facing the top of the LED in these snapshots and it is hard to judge LED brightness in a picture anyway, and although it is also not very accurate to judge LED brightness with the eye, the LED appeared a bit brighter at 42uA than it was at 20uA although this doesn't show up in the attached pictures very well.

Edit: To check how much noise might be affecting these current readings with my multimeter, I connected my multimeter set to the same 2mA DC current range across the one ohm output current sensing resistor on board 119, and the meter measured 0.0000 Amps, so it seems the multimeter when set to measure DC current is nowhere near as sensitive to noise pickup as the scope probe is across the same resistor, but the scope is measuring voltage across the one ohm resistor and the multimeter is measuring actual current through the meter.

[ltseung888]

@Lawrence:
As I have previously explained, as the amplitude of the waveforms being measured fall closer and closer into the noise level amplitude range, the degree of error in the measurements increases accordingly. Also, when making measurements close to the lower measurement limits of the measuring instrument, the degree of error is typically a lot higher than when making measurements that are at higher magnitudes and well within the normal measurement range of the measuring instrument. 

For the input voltage setting you are suggesting here, the input and output current magnitudes are well within the noise level range, especially the output current which is completely within the noise level, and also the current waveform magnitudes are down at the very lower measurement limit of my scope, which will also introduce even further error into the measurements. Regarding the noise, we can't assume that the noise waveforms are always perfectly symmetrical and therefore will average out to about 0 overall, as noise at any instance in time is the sum total of all noise sources affecting your circuit over the measurement period, and although some noise may be fairly symmetrical about the 0 voltage axis, other sources of noise may average out to be more positive or more negative overall, and the noise affecting a circuit can vary a fair bit over time depending on the sources of the noise. The result is that when the magnitude of waveforms being measured are well within the noise level, the noise could very potentially be skewing our measurements quite a bit, and it in all likelihood is. You just simply can't rely on such measurements being at all accurate under such conditions. As I have also mentioned before, you would in the very least need something like a high quality amplified differential probe to attempt such measurements, and you would also want to take steps to minimize noise in your circuit as much as possible. You would also want to be using a good high quality and very well calibrated scope for the measurements as well. Even then, you would still need to be aware of the measurement limitations of the equipment you are using to make your measurements, and be aware of how much error noise may still be introducing into your measurements.

With all the above being understood in regards to the measurement error being much too high to make meaningful measurements at the current waveform magnitudes which result when the input voltage is set very low, I made the following measurements just to show what kind of results you can end up with when attempting to make measurements under such conditions. If a person did not fully understand about measurement instrument limitations, and the effects of noise on measurements when waveform magnitudes are well within the noise level, then a person might make the mistake of thinking that measurements made under such conditions are meaningful. In reality however, it is very likely in the following measurement results that the measured values have a high degree of error due to the current waveforms being measured being well within the noise level. Anyone with an engineering or science background should be well aware of these sorts of measurement limitations and sources of error in measurements.

I used your scope probe connection method for these measurements.
I used a regulated DC power supply only (no super cap in parallel) for the input voltage source.
I made certain that the DC offset for Ch2 (used for current measurements) was calibrated as close to 0V as I was able to get it, before making the measurements.
(Again, these measurements are meaningless due to the current waveforms being measured being well into the noise level.)
Input Voltage: 328mV  (The output LED was lighting dimly at this input voltage setting.)
Input Power:   32.275uW
Output Power: 103.278uW
Efficiency:       319.994% 

Scope screen shots are attached.
Voltage traces are in yellow, current traces are in blue.
Input current waveform is inverted.

@Void,

Thank you for your experiment and the posts. 

At present, I am more interested in whether the "Noise" can help me produce the "forever lighted lamp".  Some groups claimed to have "forever lighted lamp" ON for months and years.  Mr. T S Lau has it ON for weeks.  He thinks that he can pickup the energy from the Power Line a few hundred meters from his window.  Dr. Ting believes an oscillating circuit can be built to efficiently pick up the "electrosmog".  Measurement into the "noise" level is useful if one wants to use the "noise"......

The scope shots from the Atten or similar low cost scopes may not be accurate but they do indicate a possible direction.  Poynt99 has the high end Tektronics and may have time to do a similar experiment like what you have just done.  (I can always wait for results from the Tektronics and skilled team in Hong Kong and Shenzhen.)

Void, you can now do the timing experiment with the capacitors.  Set your DC Power to 1.5 V and turn it ON for 1 minute with 1-4 capacitors.  When the DC Power is switched OFF, see how long each case lasts.  I shall publish my results later so that we can compare them.