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Author Topic: LTJT - poynt99 Tests #2  (Read 89552 times)

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It's not as complicated as it may seem...
For this second run, I wanted to bring the frequency up to the range Lawrence is using.

I used a Dremmel tool to carefully cut a slice out of the core to bring down the core u. Now the Fo is about 52kHz.

05.png is showing an average INPUT POWER of 24.64mW (very close to the previous 6kHz test).

07.png shows that the OUTPUT POWER is at 51.27mW (again very close to the 6kHz test), but this must be divided by 10 to take into account the value of the CSR is 10 Ohms, not 1 Ohm. Therefore, the OUTPUT POWER is about 5.13mW.

.99
   
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Poynt:

My congratulations again on this one.  It's important to state that the traces all make sense now.  The traces you show are indeed what they are supposed to look like, and what you expect them to look like.  Nice sweeping curves showing the LTJT circuit charging and discharging the toroidal inductor, etc.

The math trace also looks like what it is supposed to look like.  This shows convergence between the recorded data and what you expect that data to look like, indicating that you have valid data.  Overall, an excellent job.

Note that if you were to increase the power buy using a larger toroid, and using higher voltages, the curves would look the same but the relative noise levels would start to decrease.  The scope traces would become clean and noise-free.  The operating frequency would also decrease.   But the bottom line is that a "big brother" LTJT circuit would operate in the same manner, and show similar efficiencies.  Scaling it up will NOT get you over unity.

Thank you so much for your efforts.

MileHigh
   

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It's not as complicated as it may seem...
You're welcome of course, and thanks.

I hope that with the help of Lawrence and maybe the professor, we can determine why there is such a large discrepancy in my results so far, and those shown by him and the professor. I have an idea, but I am going to wait on revealing that for a little while.

It will also be interesting to see how the device I build from the parts Lawrence is sending me performs in comparison.

.99
   
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Poynt, stop being cheap.  Get a good battery man.  ;D
   
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Poynt,

Just one question on the L3 secondary output graphs.  The blue trace is the current and you can see it dips below zero.  Is that due to the leakage current through the reverse-biased diode or is that possibly related to the calibration sequence for that channel?  If I recall correctly the diode reverse-bias leakage current should be negligible.  So it looks a bit fishy to me.  You could double-check the reverse-bias current with a multimeter if need be.  At the end of the toroid discharge cycle you can see how the voltage drops until the polarity-reversal happens (2.2 main divisions from the left on the TEK00006.PNG graph).

At the tail end of that discharge cycle the power goes negative and that doesn't make any sense.  So it looks to me like the current waveform is negatively offset.

Assuming that I am correct and the current waveform needs to be offset upwards, it is likely going to marginally decrease the output power calculations for both trials.  That's because you are showing positive power when the diode is reverse-biased, when in fact there is no power.  This false-positive power is much larger in area than the false-negative power at the end of the discharge cycle.  Of course the main power stroke will also be higher in level too.

MileHigh
   

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It's not as complicated as it may seem...
MH,

The reverse breakdown of most LED's is on the order of 5V, so assuming that inductive kickback is present, this might well account for that negative current.

This is why it is important to either find a good LED model, or use a 5V zener when attempting to simulate this circuit in SPICE. I strung several 1N4148's together in my first attempt, but it will not work because this represents a diode with a VBr of about 500V.

In my simulation I will try a 5V zener, or perhaps 5x 1V zeners in series, then I will have roughly the 3V forward voltage of these super-bight LEDs, and the required 5V reverse breakdown parameter. Harvey, you may want to try this in Protel as well.

Note that when the power trace dips below zero (indicating some reactive power is present), that represents power going back out of the load, and this is why we can't use Pave=VRMS x IRMS to calculate the average power.

.99
   
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The reverse breakdown of most LED's is on the order of 5V, so assuming that inductive kickback is present, this might well account for that negative current.

This is why it is important to either find a good LED model, or use a 5V zener when attempting to simulate this circuit in SPICE. I strung several 1N4148's together in my first attempt, but it will not work because this represents a diode with a VBr of about 500V.

In my simulation I will try a 5V zener, or perhaps 5x 1V zeners in series, then I will have roughly the 3V forward voltage of these super-bight LEDs, and the required 5V reverse breakdown parameter. Harvey, you may want to try this in Protel as well.

Note that when the power trace dips below zero (indicating some reactive power is present), that represents power going back out of the load, and this is why we can't use Pave=VRMS x IRMS to calculate the average power.

I assume that you agree that when the transistor is on, the LED in the L3 output loop is reverse-biased.  If you scope probe is 1:1 then the reverse-bias voltage is only around 2 volts so no current should be flowing.  I really can't account for the current going negative at the tail end of the core discharge cycle.  You are showing about -24 mV across a 10-ohm resistor when the reverse-bias voltage is about -2 volts.  So the reverse current is about 2.4 milliamps.  That seems off to me.  If you could double-check that with a multimeter that would be appreciated.

It's hard to be sure, but it looks like the discharge through the collector LED is during a brief 1 uS pulse just after the transistor switches off.  You notice in the 04.PNG graphic that the current levels off to horizontal for about 1 uS at the end of the ramp-up.  That's where the core is discharging through the collector LED just like in a conventional Joule Thief.  The L3 loop is also discharging energy during this 1 uS period but most of the energy goes through the collector LED and one-ohm resistor because the impedance in that path is much lower.

After this 1 uS rapid discharge most of the energy stored in the core has been expended and the collector LED forward-bias voltage shuts off any further energy discharge through this path.  Then the rest of the energy is discharged through the L3 loop because it can generate higher EMF than the L2 loop.  So the discharge cycle shown in the 06.PNG graph represents the remainder of the core energy being dissipated through the L3 loop.

That's what I think is happening with the disclaimer that I am not on the bench and I am a bit rusty with all of this stuff.

MileHigh
   
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Poynt:

It just occurred to me that there is something subtle going on with respect to your average input power calculation that probably has to be accounted for.

Let's assume for the sake of argument that I am correct, and that there is a big energy discharge through the collector LED for about one microsecond.  You could easily confirm this by looking at the potential on the 1K base input resistor.  If the potential snaps low about 1 microsecond before the current trace in the 04.PNG graphic stops, that would confirm my speculation in the previous posting.

So that means that during that one microsecond pulse, you are recording an energy discharge that comes from two sources; 1) the voltage times the current supplied by the battery, and 2) the voltage times the current supplied by the discharging L2 coil.

I also noticed that the current during this 1 uS discharge cycle is about 80 milliamps.  I'm pretty sure that that's a huge amount of current for a typical LED and that high current times the voltage across the collector LED should (I think) represent a significant amount of the energy storage capacity of the toroid  (not forgetting that some of that energy is coming from the battery itself).

The energy coming from the L2 coil is stored energy that was already accounted for during the current ramp-up.  Therefore you have to subtract that energy from the input energy calculation.  If you don't you are double-counting some of the energy supplied by the battery per cycle.  That almost makes me queasy and reminds me of a luminary!  lol

Of course with your uber awesome DSO you could do a high-bandwidth capture of the voltage pulse across the collector LED itself.

MileHigh
   

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It's not as complicated as it may seem...
Poynt:

The energy coming from the L2 coil is stored energy that was already accounted for during the current ramp-up.  Therefore you have to subtract that energy from the input energy calculation.  If you don't you are double-counting some of the energy supplied by the battery per cycle.  That almost makes me queasy and reminds me of a luminary!  lol

Of course with your uber awesome DSO you could do a high-bandwidth capture of the voltage pulse across the collector LED itself.

MileHigh

MH,

I think it might be better to place the INPUT CSR directly in series with the battery, that way we can be certain that the current acquisition is correct. I will try that tonight...in the negative leg of the battery. The 1 Ohm in the emitter will be shorted for this test.

.99
   
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Poynt:

I just noticed that in your computer graphic schematic for the circuit you show the collector LED being directly across the CE of the transistor.  In your hand drawing of the circuit you show the collector LED being across the collector and ground.  I was basing my thoughts on the computer graphic of the schematic.

Anyway, I hope that I gave you some food for thought!

MileHigh
   
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Me again,

I think that I have to retract my statement about the double energy counting from the discharging L2 inductor.

I was looking at the graphical diagram of the circuit, "poynt99 schematic 1.jpg" that indeed shows show the collector LED being directly across the CE of the transistor.  With this arrangement the one-ohm current sensing resistor does a correct job and is in series with the battery.

Where I screwed up was in the alleged "double counting" of the discharge from L2 after the transistor switches off.  It's true that during the current ramp-up when the transistor is on energy is stored that eventually is discharged through L2.  However, when L2 discharges after the transistor switches off, you are still only recording the voltage from the battery, and the current from the battery during this phase. I referred to this energy component two postings ago also.

This effectively means that the energy discharge from L2 after the transistor switches off is not seen a second time.  Rather, it's more like the energy discharge from L2 is discharged across the collector LED only, and the current through the one-ohm CSR and the battery voltage accounts for the energy supplied by the battery.  There is a voltage bump-up across the collector LED when L2 discharges, buy this is not seen because it is internal to the circuit.

In other words, indeed there is energy that is stored in the core and then released by the core via L2 in a full cycle, but the energy per cycle derived from recording the battery voltage and the current through the CSR only sees this once, not twice.

Sorry, I got lost there and simply had to go back to basics.

MileHigh
   

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It's not as complicated as it may seem...
Good catch though MH, as I am pretty sure I built it as per my hand drawn schematic (which is incorrect). I will make the change when I get home tonight and see if the LED directly across C-E has any significant effect on the wave forms and results. In the simulation, it doesn't.

.99
   

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It's not as complicated as it may seem...
Here are the results and scope shots with the circuit corrected (LED directly across transistor C-E). I've also included an updated drawing and notes.

09.png indicates an average INPUT power of 39.8mW (prior test was 24.64mW, ~61% increase in power).

11.png indicates an average OUTPUT power of 52.09mW/10 = 5.21mW (very close to the prior test).

These results compared to the previous run (when the LED was at ground), would indicate that the previous INPUT power measurement was incorrect.

Note the triangle wave shape of current now.

.99
   

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It's not as complicated as it may seem...
Alright, I didn't like what resulted above, so it was time to clip that energy-sucking collector LED out of the circuit, and prove that the output will indeed go up significantly without it.

013.png is indicating an average INPUT power of 32.88mW (a decrease from the last run).

015.png is indicating an average OUTPUT power of 228.3mW/10 = 22.8mW (a more than 4-fold increase over previous tests!).

Now the input to output efficiency is at about 69%, and yes, the output LED became much brighter.

Who said that collector LED should not be considered part of the output?  ^-^

.99
   
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Hey Poynt!

Quote
Here are the results and scope shots with the circuit corrected (LED directly across transistor C-E). I've also included an updated drawing and notes.

09.png indicates an average INPUT power of 39.8mW (prior test was 24.64mW, ~61% increase in power).

11.png indicates an average OUTPUT power of 52.09mW/10 = 5.21mW (very close to the prior test).

These results compared to the previous run (when the LED was at ground), would indicate that the previous INPUT power measurement was incorrect.

Note the triangle wave shape of current now.

Ha!  That looks better.  You can see how my theories about the discharge of the collector LED were wrong because I was looking at the (formerly) wrong schematic and trying to fit the scope traces in with what I thought was the right schematic.  Trying to put a square peg into a round hole.

Now we clearly see that both LEDs have current flowing through them for the full cycle of the energy discharge from the core.  That feels a lot better!!!  lol

Your new numbers reveal something else that's interesting.  We can make a preliminary deduction that there is roughly (39 - 24) = 15 milliwatts of average power being dissipated though the collector LED.  That's significantly higher than the 5.21 milliwatts of power being dissipated in the L3 output loop.

Obviously with a higher input power and the same L3-related output power, the efficiency of your original LTJT unmodified configuration is even lower than before, about 13.1%.

Really big shew!

MileHigh
   
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Alright, I didn't like what resulted above, so it was time to clip that energy-sucking collector LED out of the circuit, and prove that the output will indeed go up significantly without it.

013.png is indicating an average INPUT power of 32.88mW (a decrease from the last run).

015.png is indicating an average OUTPUT power of 228.3mW/10 = 22.8mW (more than 4-fold increase over previous tests!).

Now the input to output efficiency is at about 69%.

Who said that collector LED should not be considered part of the output?  ^-^

.99

It's a whole new ball game!!!  That's starting to sound "about right" to me.  Core losses and wire resistance losses coming into play along with the overhead associated with the CSR at the emitter, the base input resistor, the diode drop at the transistor base input, etc.

Now we just need some Lawrence Tseung magic to get you over the top!

MileHigh
   

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It's not as complicated as it may seem...
When would these be needed?

http://www2.tek.com/cmswpt/psdetails.lotr?ct=PS&ci=13429&cs=psu&lc=EN

Harvey,

Mostly in cases where a current and differential voltage probe need to me time-matched, but would also be desirable when making critical measurements using probes with differing cable lengths, or models.

As I am using 4 probes all the same make, model and cable lengths, it should not be a problem with these tests.

.99
   
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Obviously with a higher input power and the same L3-related output power, the efficiency of your original LTJT unmodified configuration is even lower than before, about 13.1%.



After a long day, I came back and COP dropped to 13%.  The road to OU just went from .8infinity to 1.1infinity.  Thanks >:(

Anyhoo, after several...juxtaposing I found the LED on L3 may have mounted in opposite of the prof's.  Therefore, the conclusion is...this juxtaposing is some good shi...sstuff. :D
   

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It's not as complicated as it may seem...
Good catch though MH, as I am pretty sure I built it as per my hand drawn schematic (which is incorrect). I will make the change when I get home tonight and see if the LED directly across C-E has any significant effect on the wave forms and results. In the simulation, it doesn't.

.99

I must correct my post here.

The change in the simulation does make the same difference as observed with the real circuit. The CSR wave form becomes more triangular vs. sawtooth.

.99
   
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Poynt:

It's the old cliche about how a programmer can only write about 10 lines of clean error-free code per day when you average things out over time.  We both made mistakes and found them and recovered.

It's going to be interesting when the FedEx shipment arrives.

For Lawrence and Poynt:  I believe that there are now two samples in transit, one by FedEx and one by regular mail.  It would be very helpful if you can establish what measurements were made by Lawrence's group in Hong Kong (or China?) for each sample.  Then when Poynt makes his measurements on each sample you will be able to compare the data.

Pictures of the setup and your handwritten notes are also appreciated.

MileHigh
   

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It's not as complicated as it may seem...
MH,

The kit Lawrence shipped via regular mail is not an assembled unit, so there are no measurements of that one yet. As for this latest fully assembled unit, see Lawrence's data he already provided.

I'll post my test results of each one as they become available.

.99
   
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Alright, I didn't like what resulted above, so it was time to clip that energy-sucking collector LED out of the circuit, and prove that the output will indeed go up significantly without it.

013.png is indicating an average INPUT power of 32.88mW (a decrease from the last run).

015.png is indicating an average OUTPUT power of 228.3mW/10 = 22.8mW (a more than 4-fold increase over previous tests!).

Now the input to output efficiency is at about 69%, and yes, the output LED became much brighter.


.99

So you finally cut out that transistor-LED as I suggested -- hurray!  I did that weeks ago.    O0

Quote
"
.99:  Who said that collector LED should not be considered part of the output?  ^-^

NOT ME! At least, not if you understood me correctly (and I don't think you did).   

My next suggestions --
1.  Replace the 10ohm + 100 ohm resistors with a 1-ohm resistor, and take measurements.  (Makes V*I more straightforward also.)

2.  Replace the 1 Kohm resistor to the base with 500ohms; take measurements.

 3. Then -- place a capacitor in series with the LED, that is, between the 1ohm R and the remaining LED -- and take measurements again.  This is what I have done after some tinkering, with interesting results.  I use a 100 uF capacitor most of the time.

I realize this is getting rather far from the Tseung circuit as he sent it, but my goal is to see what happens to the circuit when tweaked, to see whether the COP can be boosted up.

4.  I have also wound my own toroid, the JT portion of it anyway, starting with a pre-wound 100 uH toroidal inductor from Jameco as the secondary winding -- again with interesting results.  Jameco 386601, 0.037 ohms, 100 uH.   I did this as a way to improve repeatability from one toroid to the next, hopefully, by starting with a pre-wound toroidal inductor.  More on that later if anyone is interested. 
   

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It's not as complicated as it may seem...
Hi Professor.

Yes, I am interested in trying the 1 Ohm in the output to see if I get the same resulting phase shift you showed. Did you also get a better efficiency with the 1 Ohm in place of the 110 Ohms?

Will you post some input and output shots similar to the ones I posted...with MEAN values instead of RMS?

I'll try your other suggestions as well, as time permits. I suspect I will be receiving the kit from Lawrence very soon though. At the moment I'm more focused on testing a unit that Lawrence feels is worthy of testing, which is why I am looking forward to receiving and testing the fully-assembled unit.

Thanks,
.99
   
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PhysicsProf:

I am going to make a few comments about your suggestions in advance of anyone trying them out.  The purpose of commenting ahead is to hopefully shed some more light on the way the Joule Thief works.

Quote
2.  Replace the 1 Kohm resistor to the base with 500ohms; take measurements.

This can be expected to have a marginal effect on the operation of the circuit.  Lowering the base input resistor will mean that the transistor switches on slightly faster.  Because the JT does a "snap" when the transistor switches on and off, you are talking about changing the timing by a few microseconds at most.  Also lowering the base resistor will increase the power dissipation slightly.  I suspect that lowering the base input resistor will increase the operating frequency of the JT by a very small amount.

I should also state that I am assuming that the 1K resistor is low enough in value to fully switch on the transistor so changing the resistor to 500 ohms will not make much of a difference.  In the unlikely case that the 1K resistor does not not in fact fully switch on the transistor, then things change.  When you make a Joule Thief you want the transistor to act as an ON-OFF switch, you don't want the transistor to work in partial conduction mode.

Quote
1.  Replace the 10ohm + 100 ohm resistors with a 1-ohm resistor, and take measurements.  (Makes V*I more straightforward also.)

In the past I made reference to the JT as a transformer and made reference to changing the load on the secondary affecting the impedance match and the power transfer.  Those statements were incorrect because it's not really a transformer.

The real way of looking at the JT is that it is a circuit that operates in two cycles, first cycle charges the core up with magnetic energy and then the second cycle discharges that energy stored in the core, and then the process starts over again.

The following discussion assumes that the collector LED has been removed and the only output load is on L3.

The key point here is that once the core has been charged up with energy, then you discharge that finite amount of energy.  So if you change the load on the L3 secondary coil, you will be able to affect the rate that the energy discharges, but not the amount of energy itself that's available to discharge into the load.

So with those points in mind, it looks like reducing the load to an LED in series with a one-ohm resistor will speed up the discharge cycle considerably.  This shortened discharge cycle will therefore increase the operating frequency of the JT and as a result increase the average power consumption of the JT.  However, the overall average-power-in to average-power-out efficiency is not likely to change considerably.

The most important thing to learn here is that the amount of energy per individual discharge cycle should not change substantially when you go from a (LED + 110 ohm) load to a (LED + 1 ohm) load.  It all depends on the amount of current flowing through L2 the instant before the transistor switches off.  If the amount of current is the same then the amount of energy stored in the core will be the same.  Thus you are dealing with a fixed amount of energy that is available in the charged-up toroidal core of the Joule Thief.

MileHigh
« Last Edit: 2011-02-08, 20:14:47 by MileHigh »
   
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