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OverUnity Research > Electrical / Electronic Theory and Learning Center > Joule Thief Circuits > Lawrence Tseung sent a Prototype to test... any comments?
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Author Topic: Lawrence Tseung sent a Prototype to test... any comments?  (Read 342750 times)
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img  ltseung888
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #300 on: 2011-01-20, 22:32:16 »
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More notes on the poynt99 schematics

I added the exact position of the oscilloscope probes.

As I mentioned before, when I send out the prototypes, I include a prayer.  I am doing the same here.

May God Guide you in your replication efforts.  Amen.
   
img  itzon
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #301 on: 2011-01-20, 22:43:19 »
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Quote from: ltseung888 on 2011-01-20, 22:32:16
More notes on the poynt99 schematics

I added the exact position of the oscilloscope probes.

As I mentioned before, when I send out the prototypes, I include a prayer.  I am doing the same here.

May God Guide you in your replication efforts.  Amen.

Are you isolating the scope from ground, ie no ground prong on the power cord, when connecting scope probe ground to  B2 & B4?

Itzon
   
img  ltseung888
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #302 on: 2011-01-20, 22:58:29 »
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Quote from: itzon on 2011-01-20, 22:43:19
Are you isolating the scope from ground, ie no ground prong on the power cord, when connecting scope probe ground to  B2 & B4?

Itzon

In the China-made oscilloscopes (Atten), they already have a power ground.  In addition the Channel 1 and Channel 2 are common grounded internally.  Thus Instantaneous Voltage measured at Channel 1 and Instantaneous Current measured at Channel 2 are timed simultaneously.  I hope that the US made oscilloscopes have same or similar feature.

You can get more information on the China-made scope on-line.  Just do a google search on Atten oscilloscopes.
   
img  PhysicsProf
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #303 on: 2011-01-20, 23:14:25 »
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 And I'm back.  Your schematic is helpful, .99 -- a few corrections:  the start-points on the toroid windings need to be reversed (so left dot is down, right dot is up);  The start-point on T3 is UP (recognizing that I may have made a mistake, but I did double-check.)

  Below, I juxtapose your schematic with one from OU today, showing a Joule Ringer schematic.  One can see interesting similarities.  This schematic replaces the lone transistor typical of JT circuits with a Darlington pair -- worth trying in the Tseung mod also.  Lawrence has referred to a cap across the resistor feeding the base of the transistor, which is shown in the J-Ringer schematic.

« Last Edit: 2011-01-20, 23:42:12 by PhysicsProf »
   
img  PhysicsProf
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #304 on: 2011-01-20, 23:41:31 »
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   Several things we have learned in the past couple days of testing:

1.  Probe calibration and matching is VERY important. 
2.  Leads with alligator clips connecting components can generate erroneous readings on the scope, due I think to inductive pick-up.   See the TK video above.  The joule-thief circuit emits RF typically.
3.  We found that the FREQUENCY of the Tseung-device is sensitive to:

  a.  Input voltage.  As Vin goes down, the frequency goes up (data given in an earlier post) sharply.
  b.  A 50 nF capacitor across the 1Kohm resistor leading to the base of the transistor DECREASES the frequency.  Today, on prototype A, adding the cap reduced the frequency from 61 KHz to 27 KHz.  The FLEET index also went down (from about 1 to 0.6).
  c.  Changing the temperature of the toroid from roughly 50 to 70 to 80 F had no noticeable affect on the frequency or FLEET index.
  d.  Replacing the output LED with a simple diode reduced f (from 61 to 30 KHz), and reduced the FLEET index also about half.
  e.  Increasing R on the input resistor to the transistor base from 1Kohm to 5Kohm dropped the frequency (from 753 to 270 KHz with one build).  There was little change in the FLEET index in this instance.
  f.   The frequency of the oscillations in the JT circuit depends strongly on the toroid used in the circuit; we have not yet attempted to correlate frequency with number of windings etc.

  I need to add -- early readings of higher FLEET indices (over 3) have not maintained as have decreased the length of various lead wires, moved some components around, etc.    We have looked at five different toroids to date. 
   
img  MileHigh
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #305 on: 2011-01-21, 00:41:46 »
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Quote
a.  Input voltage.  As Vin goes down, the frequency goes up (data given in an earlier post) sharply.

Seeing the schematic makes it easier to suggest a possible explanation for this phenomenon.

As a reminder the Wikipedia article states the following:

Quote
Frequency of oscillation is approximately equal to:  V_battery x R_battery_output_impedance / Transformer_mutual_inductance

At very low excitation voltages the overall voltages and currents in the JT circuit will go down.  This includes the voltages and currents in the secondary winding.  So it's possible that the LED diode's forward voltage in the secondary winding starts to choke off the flow of current.  This starts to make the secondary winding partially "disappear" from the circuit.  The net result of this will be a reduction in the effective transformer mutual inductance.  The rate of reduction in transformer mutual inductance will be faster than the rate that the excitation voltage drops causing the oscillation frequency to increase.

The root cause behind the frequency determination is the standard time constant for an inductor-resistor configuration which is L/R.  Therefore the associated frequency related to the time constant is the inverse of this, R/L.  You can see the similarity with the formula for the approximate oscillation frequency for a standard Joule Thief.

MileHigh
   
img  MileHigh
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #306 on: 2011-01-21, 01:04:58 »
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If for the sake of argument what I just said in my last posting is correct, then there is a moral to that story.  The moral of that story is that every single observation that you make when you experiment with Lawrence's Joule Thief circuit is just "Mother Nature" doing exactly what she is supposed to be doing.  No matter how "unusual" a phenomenon you think you are seeing might appear to be, in fact it's "usual" and perfectly normal.

The worst trap any experimenter can fall into is to go in with a set of biases and preconceived notions that may not have any basis in fact.  Taking a random hypothetical example with no connection to the circuit, someone might say, "Increased resistance must decrease the frequency" and they actually find that increasing the resistance increases the frequency.  If the experimenter then says, "I have found something unusual and non-standard about my circuit" then they are making the gravest of errors.  You can't forget that the Joule Thief will do exactly what it is supposed to do, irregardless of whatever preconceived notions or biases or educated or uneducated opinions you might have.  There will be a reason for every observed change in the operation of the circuit and if you see something that you didn't expect, it's up to you to decide if you want to try to figure out why the circuit is behaving like that.

MileHigh
   
img  ltseung888
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #307 on: 2011-01-21, 01:39:47 »
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Quote from: PhysicsProf on 2011-01-20, 23:14:25
And I'm back.  Your schematic is helpful, .99 -- a few corrections:  the start-points on the toroid windings need to be reversed (so left dot is down, right dot is up);  The start-point on T3 is UP (recognizing that I may have made a mistake, but I did double-check.)

  Below, I juxtapose your schematic with one from OU today, showing a Joule Ringer schematic.  One can see interesting similarities.  This schematic replaces the lone transistor typical of JT circuits with a Darlington pair -- worth trying in the Tseung mod also.  Lawrence has referred to a cap across the resistor feeding the base of the transistor, which is shown in the J-Ringer schematic.



Dear PhysicsProf,

Thank you for making the comparison with J-Ringer.  They indeed have similarities. 

We all look forward to your driving the 140 miles return trip to your esteemed University and test the Prototypes.  Please take your time and make sure the roads are safe before the journey.  Do not let the pressure from the posts here stress you.

If possible, please consider doing the 4 tuning fork experiment at the same time.  That should not take long and will save you an additional trip.

Thank you in advance,

Lawrence
   
img  itzon
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #308 on: 2011-01-21, 01:40:46 »
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Quote from: ltseung888 on 2011-01-20, 22:58:29
In the China-made oscilloscopes (Atten), they already have a power ground.  In addition the Channel 1 and Channel 2 are common grounded internally.  Thus Instantaneous Voltage measured at Channel 1 and Instantaneous Current measured at Channel 2 are timed simultaneously.  I hope that the US made oscilloscopes have same or similar feature.

You can get more information on the China-made scope on-line.  Just do a google search on Atten oscilloscopes.

All modern, probably even ancient scopes have the probe ground connected to the "earth power ground" on the power cord.

You can isolate the probe grounds(and scope chassis) from "earth ground" by not having the power cord ground connected to "earth ground", thereby having the probe grounds floating, ie...your scope probe gnd is at whatever potential your circuit is at and minimizing the scopes interference of the circuit being probed.  Some circuits won't work at all when scope probe gnd grounds the point at which it's connected.

My point was, the schematic as shown does not show points B2 & B4 as being grounded.  

Connecting the probe gnd at those points makes them grounded through the scope.

Is the schematic wrong?

Edit...Oops, I just remembered the circuit being probed is running off of battery power, so never mind the "earth ground" stuff.

Itzon
   
img  aetherevarising
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #309 on: 2011-01-21, 01:54:43 »
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Quote from: itzon on 2011-01-21, 01:40:46
All modern, probably even ancient scopes have the probe ground connected to the "earth power ground" on the power cord.

You can isolate the probe grounds(and scope chassis) from "earth ground" by not having the power cord ground connected to "earth ground", thereby having the probe grounds floating, ie...your scope probe gnd is at whatever potential your circuit is at and minimizing the scopes interference of the circuit being probed.  Some circuits won't work at all when scope probe gnd grounds the point at which it's connected.

My point was, the schematic as shown does not show points B2 & B4 as being grounded.  

Connecting the probe gnd at those points makes them grounded through the scope.

Is the schematic wrong?

Edit...Oops, I just remembered the circuit being probed is running off of battery power, so never mind the "earth ground" stuff.

Itzon

Itzon - Professor - Poynty - someone.  What is the signifance here?  Stefan Hartman went to some trouble to tell me that we may be getting our power through the ground pin of our plugs.  Since the only ground is from our scopes and from the functions generator - then the assumption is that we are getting our extra energy from that point.  Is this somehow obviated as Itzon mentions - when we use a battery as our supply?  I'm trying to understand how the energy could come from the ground in the first instance - let alone to our circuit.  Or indeed - if this is a valid concern.

Be glad of some advice here guys.

Rosemary
   
img  poynt99
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #310 on: 2011-01-21, 02:11:07 »

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Quote from: aetherevarising on 2011-01-21, 01:54:43
Itzon - Professor - Poynty - someone.  What is the signifance here?  Stefan Hartman went to some trouble to tell me that we may be getting our power through the ground pin of our plugs.  Since the only ground is from our scopes and from the functions generator - then the assumption is that we are getting our extra energy from that point.  Is this somehow obviated as Itzon mentions - when we use a battery as our supply?  I'm trying to understand how the energy could come from the ground in the first instance - let alone to our circuit.  Or indeed - if this is a valid concern.

Be glad of some advice here guys.

Rosemary

If Stefan was hinting that you might be somehow sucking energy from the earth ground through the scope probes, he would be incorrect.

I think perhaps he was referring to something else, that being when two single-ended scope probes are used, their grounds must be tied to the same point. Further to that, the probe gnd leads themselves are troublesome in high frequency measurement in that they can cause ringing in the scope trace; "ringing" that isn't actually present in the circuit. The problem being, that the probe capacitance and gnd lead inductance form a resonant tank circuit that rings due to induced currents in the gnd lead. That's why you want the gnd lead to be as short as possible.

.99


---------------------------
"Some scientists claim that hydrogen, because it is so plentiful, is the basic building block of the universe. I dispute that. I say there is more stupidity than hydrogen, and that is the basic building block of the universe." Frank Zappa
   
img  aetherevarising
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #311 on: 2011-01-21, 02:40:10 »
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Quote from: poynt99 on 2011-01-21, 02:11:07
If Stefan was hinting that you might be somehow sucking energy from the earth ground through the scope probes, he would be incorrect.

I think perhaps he was referring to something else, that being when two single-ended scope probes are used, their grounds must be tied to the same point. Further to that, the probe gnd leads themselves are troublesome in high frequency measurement in that they can cause ringing in the scope trace; "ringing" that isn't actually present in the circuit. The problem being, that the probe capacitance and gnd lead inductance form a resonant tank circuit that rings due to induced currents in the gnd lead. That's why you want the gnd lead to be as short as possible.

.99

Ta muchly Poynty. 

The fact is that I also asked Stefan if I could publish our report there.  I'll check out my emails -  in case I misunderstood him.  He categorically assured me that his primary concern was that we  were getting our energy from ground and through the grid.  And my thought was to disconnect the ground pin.  On discussion with some experts on this - I was assured that there was a campus that actually addressed this by disconnecting the ground.  In as much as it was ever addressed - I thought there was a valid concern. 

So Poynty.  Can I quote you on this?  Is this absolutely correct?  In which case I'll rest easy.

Take care
Rosie
   
img  poynt99
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #312 on: 2011-01-21, 03:03:35 »

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It's not as complicated as it may seem...
Without seeing the actual emails from Stefan, I am only speculating as to what he may have meant.

Regarding the fact that you could not draw power through the scope probes if the scope is connected to earth ground (as it should be), yes I believe that to be true, and also quite true and well known in the art, are the pitfalls with using passive single-ended probes in high frequency measurement, as described above and partly what I've been emphasizing for what seems an eternity.

.99


---------------------------
"Some scientists claim that hydrogen, because it is so plentiful, is the basic building block of the universe. I dispute that. I say there is more stupidity than hydrogen, and that is the basic building block of the universe." Frank Zappa
   
img  ltseung888
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #313 on: 2011-01-21, 03:16:15 »
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Let us look at the hot topic at Overunity.com which is similar to my FLEET prototype.

Reply 130 in the Joule-Ringer! thread
http://www.overunity.com/index.php?topic=10179.msg271488#msg271488

The first picture is their test set-up.  Their scopes have the multiply function and they should be able to get the Input Instantaneous Power Curve easily.  If they also use the mean function as recommended by poynt99, they should get the running mean Input Power.

The second picture is my modification to their set-up.  The second oscilloscope will measure the Output Instantaneous Power.  Channel A +ve will be connected to B1.  Channel A –ve will be connected to B2.  That will measure the Instantaneous Output Voltage.  Channel B +ve will be connected to B3.  Channel B –ve will be connected to B4.  That will measure the Instantaneous Output Current across the 1 ohm resistor.  They can compare the Output Mean Power with the Input Mean Power to get a true COP.

I am sure that they will find a COP value greater than 1 with some playing around.  Since they use 12 V Input to start and use the double transistor technique, they should get a much higher actual Output Wattage.  Lead-out energy is responsible in both prototypes in providing the extra energy.  It is a matter of how efficient the actual device is!

God has revealed the Truth in more than one Open Forum.  Blessed is His Name.
   
img  aetherevarising
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #314 on: 2011-01-21, 03:30:54 »
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Quote from: poynt99 on 2011-01-21, 03:03:35
Without seeing the actual emails from Stefan, I am only speculating as to what he may have meant.

Regarding the fact that you could not draw power through the scope probes if the scope is connected to earth ground (as it should be), yes I believe that to be true, and also quite true and well known in the art, are the pitfalls with using passive single-ended probes in high frequency measurement, as described above and partly what I've been emphasizing for what seems an eternity.

.99

Poynty.  We use probes on both our LeCroy and our Tektronix that are rated to operate at a given maximum frequency.  We never exceed that maximum.  THEN.  We can get the circuit to resonate at frequencies as slow as 50Hz - and get the same recorded benefits albeit at a required higher applied voltage from our supply.   At no point does the measurement accuracy become 'stressed' or 'suspect' due to high frequency.  There is a point at which it becomes absurd to insist that 'stray' and 'hidden' voltages are 'skewing' our results.  If so - then they skew ALL results everywhere.  Which means that NO RESULTS can ever be relied on.  Then we're flirting with a range of possibilities that exceed any kind of scientific assessment.  Surely?

Your concerns regarding the accuracy of the probes is valid.  What is not valid is to infer or imply that we're operating beyond it's rating and thereby getting inaccurate results.  We do not.

But that aside.  Thanks for your comments regarding the ground pin leaking in extra energy.  I saw it as a possibility - in as much as the Joule Thief circuits seem to make good use of this.  I was therefore concerned that his point was valid.  I'll look for Harti's email on this and forward it to you.

Regards,
Rosie
   
img  GibbsHelmholtz
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #315 on: 2011-01-21, 03:35:58 »
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This enormous current drain on the battery reduces the battery's output voltage to the point where it can no longer forward bias the Base-Emitter junction of the transistor. (This Thévenin-equivalent resistance of the source is actually a requirement for oscillation). When this happens, the transistor goes into the cutoff region (and opens the collector-emitter "switch").

I was skeptical about this part so I reasoned if I use a separate source of voltage for the feedback (another battery), then it wouldn't oscillate (not meeting requirement).  It oscillated.  ???
   
img  poynt99
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #316 on: 2011-01-21, 04:12:04 »

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Quote from: aetherevarising on 2011-01-21, 03:30:54
Poynty.  We use probes on both our LeCroy and our Tektronix that are rated to operate at a given maximum frequency.  We never exceed that maximum.
This issues being discussed have little to do with exceeding the frequency limit of the probes. I'm relatively certain that you won't find any references made by me in that regard. btw, in order to actually use these standard 500MHz probes near their frequency limit, requires extreme care regarding very short gnd leads (actually no lead at all, use the spring accessory as humbugger mentioned), and restricting the measurement to sine waves only. And at 500MHz, not only will the amplitude be down by 3 decibels, but the probe will have already shifted the phase of the signal by a substantial amount.

Quote
THEN.  We can get the circuit to resonate at frequencies as slow as 50Hz - and get the same recorded benefits albeit at a required higher applied voltage from our supply.   At no point does the measurement accuracy become 'stressed' or 'suspect' due to high frequency.
Incorrect assumption again. If there are switching transients, and I am certain there are, then there are high frequency currents present in the circuitry, regardless of how low the switching and resonant frequency are.

Quote
Your concerns regarding the accuracy of the probes is valid.  What is not valid is to infer or imply that we're operating beyond it's rating and thereby getting inaccurate results.  We do not.
Again, see my response above regarding switching transients and the presence of the resulting high frequencies.

.99


---------------------------
"Some scientists claim that hydrogen, because it is so plentiful, is the basic building block of the universe. I dispute that. I say there is more stupidity than hydrogen, and that is the basic building block of the universe." Frank Zappa
   
img  humbugger
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #317 on: 2011-01-21, 04:16:11 »
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Quote from: PhysicsProf on 2011-01-20, 23:14:25
And I'm back.  Your schematic is helpful, .99 -- a few corrections:  the start-points on the toroid windings need to be reversed (so left dot is down, right dot is up);  The start-point on T3 is UP (recognizing that I may have made a mistake, but I did double-check.)

Classically, Professor, the dots on the windings of transformers shown on schematics have nothing to do with how the winding was started or finished.  They are simply relative indicators to show polarity between windings.  In other words, when the dot end of the primary is drven positive, all secondaries will also be positive at their dot ends (AC waveform assumed).

Classical thinking would say that it mattered not a whit which ends of the wires were put on the toroid first and last.  Only on forums like this would one expect to hear arguments about the manufacturing sequence of toroid windings.  What matters iis the relative direction of windings on a finished unit; the dots show this and are completely arbitrary as long as they show polarity correctly.  To say that a schematic is in error because the winding dots must be placed on the end where the first winding was placed on the toroid core is nonsensical in the classic physics understanding of transformer action. I was surprised to hear your statement implying that this was important.

Thank you for pointing out that you consider it to be important (I do not agree but it does no harm) and thank you for showing us the relative polarity of your third winding, which is important if folks are going to be comparing scope traces on different replications..
   
img  humbugger
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #318 on: 2011-01-21, 04:26:24 »
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Rosemary:  Are you talking about your heater circuit when you say "our circuit" or are you building JTs and talking about them here?  I am confused about what context your comments are to be taken in.
   
img  poynt99
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #319 on: 2011-01-21, 04:29:34 »

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Quote from: humbugger on 2011-01-21, 04:26:24
Rosemary:  Are you talking about your heater circuit when you say "our circuit" or are you building JTs and talking about them here?  I am confused about what context your comments are to be taken in.

humbugger,

Rose is talking about her heater apparatus. Perhaps it is time to re-open the Ainslie thread?

.99


---------------------------
"Some scientists claim that hydrogen, because it is so plentiful, is the basic building block of the universe. I dispute that. I say there is more stupidity than hydrogen, and that is the basic building block of the universe." Frank Zappa
   
img  humbugger
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #320 on: 2011-01-21, 04:34:18 »
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Maybe so, but I doubt it would stop her from filling other threads with comments about her circuit, somehow.   C.C

According to her last report, her heater circuit was "in sulk mode" and wasn't working at all, so there wouldn't be much for her to talk about there right now.  Perhaps she is procrastinating (as many of us do) and looking for distraction (as many of us also do when we have come to a temporary impasse on our own pet projects) .
   
img  MileHigh
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #321 on: 2011-01-21, 06:31:28 »
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Quote from: GibbsHelmholtz on 2011-01-21, 03:35:58
I was skeptical about this part so I reasoned if I use a separate source of voltage for the feedback (another battery), then it wouldn't oscillate (not meeting requirement).  It oscillated.  ???

Can you try and explain that in more detail because it's not clear to me.  What's "the feedback?"  Ideally you could annotate the latest schematic and show what modifications you made.  Alternatively call the coil connected to the transistor base L1 and the coil connected to the transistor collector L2 and the coil connected to the extra secondary pick-up winding L3.  With those references and the latest schematic can you describe what you are doing?  (If somebody could annotate the schematic with full component designations it would be appreciated)

With the Joule Thief when the transistor switches on and starts to energize L2, the transformer coupling back to L1 causes L1 to generate potential to switch the transistor on even harder.  That's normally what's considered to be "the feedback."  When L2 is fully energized there is no more transformer coupling back to L1, and you assume that the supply battery voltage is croaking at the same time.  That causes the transistor to switch off, and that creates feedback to L1 to switch the transistor off even harder.  Then the battery voltage comes back and starts to switch on the transistor through L1 and the whole process starts all over again.

Whatever you did, there must be a similar explanation as to why the circuit is oscillating.

Quote
Maybe so, but I doubt it would stop her from filling other threads with comments about her circuit, somehow.

As opposed to "electron drift" I would call that "Rosie drift" and Rosie needs to be conscious of that.

MileHigh
   
img  hartiberlin
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #322 on: 2011-01-21, 12:55:12 »
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Quote from: aetherevarising on 2011-01-21, 02:40:10
Ta muchly Poynty.  

The fact is that I also asked Stefan if I could publish our report there.  I'll check out my emails -  in case I misunderstood him.  He categorically assured me that his primary concern was that we  were getting our energy from ground and through the grid.  And my thought was to disconnect the ground pin.  On discussion with some experts on this - I was assured that there was a campus that actually addressed this by disconnecting the ground.  In as much as it was ever addressed - I thought there was a valid concern.  

So Poynty.  Can I quote you on this?  Is this absolutely correct?  In which case I'll rest easy.

Take care
Rosie


Hi Rosie,
I meant the ground current loops that might be flowing between your equipment, that is your scope
and your function generator.

These could induce also currents inside your circuit.
If you ever have seen the trouble musicians go through, when they have a live
Gig and all the amplifiers have a huge hum due to ground current loops
you will know, what I am speaking of.
The same can be true in your several equipment all grounded maybe to different
grid plugs getting ground current loops into your circuit.
Thus it is a must to measure this all floating from earth ground and
disconnect the earth ground from your scope ground and function generator
ground and tie together the scope and function generator ground at the same
location in your circuit.

I hope it gets clearer now.

Regards, Stefan.
   
img  GibbsHelmholtz
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #323 on: 2011-01-21, 13:43:26 »
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Quote from: MileHigh on 2011-01-21, 06:31:28
Can you try and explain that in more detail because it's not clear to me.  What's "the feedback?"  Ideally you could annotate the latest schematic and show what modifications you made.  Alternatively call the coil connected to the transistor base L1 and the coil connected to the transistor collector L2 and the coil connected to the extra secondary pick-up winding L3.  With those references and the latest schematic can you describe what you are doing?  (If somebody could annotate the schematic with full component designations it would be appreciated)

With the Joule Thief when the transistor switches on and starts to energize L2, the transformer coupling back to L1 causes L1 to generate potential to switch the transistor on even harder.  That's normally what's considered to be "the feedback."  When L2 is fully energized there is no more transformer coupling back to L1, and you assume that the supply battery voltage is croaking at the same time.  That causes the transistor to switch off, and that creates feedback to L1 to switch the transistor off even harder.  Then the battery voltage comes back and starts to switch on the transistor through L1 and the whole process starts all over again.

Whatever you did, there must be a similar explanation as to why the circuit is oscillating.


MileHigh

Yes, I see L1, L2, L3 as you described.  The feedback I was refering to is L1 .  Your explaination is pretty much the same as wiki and almost completely described what the JT is doing.  The part I was skeptical about is that Wiki said the reason the transistor initially switches off because it does not have enough voltage from the battery to forward bias the base-emitter.  This can't be the reason because I know a lot of circuit just need a jump start and it self-oscillate. 
   
img  MileHigh
Re: Lawrence Tseung sent a Prototype to test... any comments? « Reply #324 on: 2011-01-21, 14:29:35 »
Group: Guest
Quote from: GibbsHelmholtz on 2011-01-21, 13:43:26
Yes, I see L1, L2, L3 as you described.  The feedback I was refering to is L1 .  Your explaination is pretty much the same as wiki and almost completely described what the JT is doing.  The part I was skeptical about is that Wiki said the reason the transistor initially switches off because it does not have enough voltage from the battery to forward bias the base-emitter.  This can't be the reason because I know a lot of circuit just need a jump start and it self-oscillate.  

Yes I think that this issue merits some further investigation.  Let me suggest three cases worth investigating:

Case 1:  Using an old battery with a relatively high output impedance.  This is where the Joule Thief shines because it soaks up energy from a nearly dead battery.   It will charge up L2 with current flow, and then L2 discharges through one or more LEDs lighting them up.  It can light up 50 or more LEDs in series like this.  So the question is does the output voltage from the battery dip as we expect?  It's highly likely that the answer is yes because of the high output impedance of the battery.

Case 2:  Using a fresh alkaline battery with a relatively low output impedance.  Assuming that the Joule Thief oscillates, does the battery voltage still dip?  If not, what about the potential at the transistor base input?  It's possible that the potential induced across L1 itself is enough to cause the transistor to switch off, without pinching off the battery voltage.

Case 3:  Using a power supply with a very low output impedance.  Here you assume that the transistor cannot pull the power supply voltage low enough to switch off the transistor.  Therefore if there is oscillation you assume that the mechanism works like described in Case 2.

MileHigh
   
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