Is joule thief circuit gets overunity?

[TinselKoala]

For comparison with Lawrence's Board 80 Output slide, I have here taken corresponding traces from the PCB JT. Here I am powering it from a partly depleted AA battery that measures 1.304 volts unloaded, on the Simpson digital voltmeter. I don't usually use this much input power, but this is more comparable to Lawrence's input.
The top trace is the Voltage Output at B1, the bottom trace is the Current Output at B3. The top trace is set to 2 volts per division, the bottom trace at 100 mV per division. (The top trace is using the center horizontal graticule line as the baseline, not the line indicated by the number "1" to the right. The lower trace is using the baseline indicated by the "2".)  I am showing only a single pulse to make the point that the waveshapes are the same, except that my "60 MHz" analog scope isn't displaying the spike amplitude.... but I assure you that it is there.

[picowatt]

For comparison with Lawrence's Board 80 Output slide, I have here taken corresponding traces from the PCB JT. Here I am powering it from a partly depleted AA battery that measures 1.304 volts unloaded, on the Simpson digital voltmeter. I don't usually use this much input power, but this is more comparable to Lawrence's input.
The top trace is the Voltage Output at B1, the bottom trace is the Current Output at B3. The top trace is set to 2 volts per division, the bottom trace at 100 mV per division. (The top trace is using the center horizontal graticule line as the baseline, not the line indicated by the number "1" to the right. The lower trace is using the baseline indicated by the "2".)  I am showing only a single pulse to make the point that the waveshapes are the same, except that my "60 MHz" analog scope isn't displaying the spike amplitude.... but I assure you that it is there.

T,

Your Iout trace drops off as a fairly linear ramp.  Board 80's Iout drop looks more exponential.

I don't believe your scope BW is the issue here regarding the "less spikey".  More likely your PCB has less interconnect inductance so the waveforms are more heavily damped.

You don't have the BW limit on do you?  (Just kidding)

PW   

[TinselKoala]

T,

Really, you can't manage A1=Vin, A2=Iin, B1=Vout, B2=Iout with the A3-4 and B3-4 being the scope grounds connected to the bottom of the input CSR?

OK, I'll quit usig them.

Your video shows that the LED is on when the voltage at Vout is hi, which can only happen when Q1 is off.  that is as I stated previously.

Regarding the second part of the video showing the Vin ripples and Vout:

As Q1 turns off, and Vout subsequently goes hi, the current draw on the battery is switched off.  Vin immediately begins to rise as the battery recovers from the load applied when Q1 was turned on.  This battery (Vin) recovery is the rising portion of the "apparent" negative peak during your Vout "hi" time .  The positive most portion of Vin is the maximum recovered battery voltage.  When Q1 turns on again, Vout is pulled lo.  At the same time, currejt is being drawn from Vin which slowly discharges the battery, hence the slow downward ramp on Vin until Q1 again turns off releasing the load on the battery and again allowing it to recover.

Again, if you look at the second part of your video, you will see that Vin begins to drop as soon as Q1 turns on (and Vout goes lo) and immediately begins to recover as Q1 turns off (and Vout goes hi).  So, actually, the poitive going portion of the Vin ripple coincides with Q1 turning off, Vout going hi, and the LED turning on.  The negative going portion of the Vin ripple, which is much slower and drawn out in time, coincides with Q1 being on, Vout being lo, and the LED being off. 


Your waveforms don't look as sharp and "spikey" as Lawrence's.  What do your Vin and Iin traces look like?

PW

One thing you must realize is that those traces were done with the tiny hearing aid battery that is mostly depleted. Here are some traces from this board for comparison to Lawrence's traces, that I just made with an alkaline AA battery that reads 1.304 volts unloaded... that is, it too is fairly well depleted.

I don't usually use this much input power, but this is more comparable to Lawrence's input.

In the first shot, Output, the top trace is the Voltage Output at B1, the bottom trace is the Current Output at B3. The top trace is set to 2 volts per division, the bottom trace at 100 mV per division. (The top trace is using the center horizontal graticule line as the baseline, not the line indicated by the number "1" to the right. The lower trace is using the baseline indicated by the "2".)  I am showing only a single pulse to make the point that the waveshapes are the same, except that my "60 MHz" analog scope isn't displaying the spike amplitude.... but I assure you that it is there. Timebase is at 10 microsec/div and the delay function is used to bring a pulse onto the screen window.

The second shot is the Input, the top trace is the Input Battery Voltage at A1 and the lower trace is the Input Current at A4. The top trace is at 500 mV per division and is using the center horizontal graticule marker as its baseline, not the number to the right. The lower trace is at 100 mV per division, is using the numbered graticule line "2" as its baseline, and clearly and repeatably shows values both above and below the baseline. No "invert" is used and the probe is positioned just like Lawrence's is wrt current direction. Timebase is at 50 microsec/div.

So you can presumably see clearly that, if Lawrence's board is OU.... then mine must be too, since it gives the same instrumental readings when powered and probed in the same way that his is..... excepting the appearance of the high-frequency spikes.

And your detailed explanation seems to concur with what I said: the LED turns on at the bottom of the valleys, at the point where the slope reverses, and the power represented by the decreasing voltage slope to that point is the power that is pulsed into the LED.

[picowatt]

One thing you must realize is that those traces were done with the tiny hearing aid battery that is mostly depleted. Here are some traces from this board for comparison to Lawrence's traces, that I just made with an alkaline AA battery that reads 1.304 volts unloaded... that is, it too is fairly well depleted.

I don't usually use this much input power, but this is more comparable to Lawrence's input.

In the first shot, Output, the top trace is the Voltage Output at B1, the bottom trace is the Current Output at B3. The top trace is set to 2 volts per division, the bottom trace at 100 mV per division. (The top trace is using the center horizontal graticule line as the baseline, not the line indicated by the number "1" to the right. The lower trace is using the baseline indicated by the "2".)  I am showing only a single pulse to make the point that the waveshapes are the same, except that my "60 MHz" analog scope isn't displaying the spike amplitude.... but I assure you that it is there. Timebase is at 10 microsec/div and the delay function is used to bring a pulse onto the screen window.

The second shot is the Input, the top trace is the Input Battery Voltage at A1 and the lower trace is the Input Current at A4. The top trace is at 500 mV per division and is using the center horizontal graticule marker as its baseline, not the number to the right. The lower trace is at 100 mV per division, is using the numbered graticule line "2" as its baseline, and clearly and repeatably shows values both above and below the baseline. No "invert" is used and the probe is positioned just like Lawrence's is wrt current direction. Timebase is at 50 microsec/div.

So you can presumably see clearly that, if Lawrence's board is OU.... then mine must be too, since it gives the same instrumental readings when powered and probed in the same way that his is..... excepting the appearance of the high-frequency spikes.

And your detailed explanation seems to concur with what I said: the LED turns on at the bottom of the valleys, at the point where the slope reverses, and the power represented by the decreasing voltage slope to that point is the power that is pulsed into the LED.

TK,

I still think Board 80's waveforms look a bit different than yours.  Not just that the spikes are missing, but the general slopes on the tops of bothe the V and I waveforms appear to have a different rate.

As with regards to your last sentence above, I agree that the LED turns on at the bottom of the input voltage valleys, at the point where the slope reverses, BUT, I would state: the power represented by the decreasing voltage up to that point is the power being drawn from the battery and stored in the toroid (and as well disipated in Q1, the input CSR and the battery's Rint).

The LED turns on when no current is being pulled from the battery (Q1 is off).  As well, if there is any battery recharging from the collapse of the toroid, it is occurring during the rising portion of the Vin waveform from just past the most negative peak when the LED is on.  During that period (whilst the waveform is rising) the LED is on and current must flow thru the LED, output CSR, Input CSR, input battery, and the toroid to complete he circuit.  The collasing toroid acts as an additional battery in series with, and with a voltage higher than, the input battery.  The polarity is such that the current thru the LED and toroid tends to raise the terminal voltage of the input battery slightly during the LED on time.  So, if anything, the battery is actually recovering a bit of its charge when the LED is on.

The internal R of the input battery will affect the amount of ripple seen on Vin, and the amount of battery depletion determines the battery internal R.

What happens to your circuit with a fresh alkaline?

PW

[TinselKoala]

T,

Your Iout trace drops off as a fairly linear ramp.  Board 80's Iout drop looks more exponential.

I don't believe your scope BW is the issue here regarding the "less spikey".  More likely your PCB has less interconnect inductance so the waveforms are more heavily damped.

You don't have the BW limit on do you?  (Just kidding)

PW

You are probably right about the spikes, I withdraw my assurances. I just checked with a higher-bandwidth scope and I can't resolve the spike.
No, no bw limit on.

The I drop difference is probably because of the source battery, I should think. But I'm not so sure it is that different.