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Author Topic: LTJT - poynt99 Tests #2  (Read 89554 times)
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I'm pretty sure that it's the leveling off in the current rise that causes the transistor to switch off, not the absolute amount of current flow.  It's the change in the rate of change of the current that determines when the transistor starts to switch off.  So that's the second derivative (the "accelerated acceleration") of the current with respect to time that is the determining factor.

MileHigh

I concur.  The only thing I would add is the "slam" condition begins when reasonable second derivative < 0. 
   

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It's not as complicated as it may seem...
No time to perform the tests properly tonight.

Unless something unexpected happens, I'll properly attend to these tests tomorrow night ;)

.99
   
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no worries p99,  life takes precedence.

In the mean time let me pontificate a bit more  :P



Ok,  if the information provided on the toroid is accurate, the following can be calculated approximatly:


N  =  sqrt( 830uH/1.48uH) = 23 turns in the primary coil   (rounded down)    (is this close p99?  can you count the turns?)

H_max  = (23 turns * 0.1 amps max) / (2 * pi * 0.02 m) = 18 A/m    (these are rough estimates of max current from graph, and effective radius of toroid from picture)


Now look at the B-H curve below, for the 3C90 material composing the core, and notice they only show the nonlinear saturating region, and right where the chart begins, H is around 18 A/m at 25 deg temp, basicaly, this is where saturation starts.   The curve below what's shown on the chart would look pretty much like vertical lines (or high u values) which I'm sure some of you have seen.   So, what do you know, saturation begins at about the same number I calculated !  

Guys, you can belive me or not, but the saturation characteristics of the core is what dictates the end of the ON cycle.  Yes, a bit of this and that do play a part, but by far it's the saturation characteristics of the core.  

EM

P.S.  Don't be confused by the B (mT) values on the graph,  the zero value corresponds to the onset of saturation and this is a relative value, referenced to B_sat, not specified explicitly.
« Last Edit: 2011-02-10, 04:45:23 by EMdevices »
   

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no worries p99,  life takes precedence.

In the mean time let me pontificate a bit more  :P

...

Guys, you can believe me or not, but the saturation characteristics of the core is what dictates the end of the ON cycle.  Yes, a bit of this and that do play a part, but by far it's the saturation characteristics of the core. 

EM
...


This variation of the Blocking Oscillator is sometimes referred
to as a "flyback converter" or a "ringing choke converter."

"It is a blocking oscillator in which the recovery time is governed
by an L/R time constant rather than the more familiar RC time
constant used in circuits formally designated as blocking
oscillators.  The transformer core of the flyback converter does
not saturate.  However, in some designs core saturation does
occur.  In either case the diode in the secondary circuit isolates
the converter from the load as the current ramp is developing
in the primary winding during the transistor on time.  This current
ramp eventually terminates regeneratively when the transistor can
no longer supply the demanded current (or, in alternate designs,
when core saturation occurs.)  The collapsing field then induces
secondary current that, because of its polarity, is delivered to the
load.  A unique feature of this circuit is that the peak voltage exceeds
that corresponding to the transformer turns ratio - ordinarily by a
factor of three or four, but sometimes by as much as eight." 

Irving M. Gottlieb
Power Supplies, Switching Regulators, Inverters & Converters
1976, 1977, 1984    Tab Books Inc.




Whether or not the core saturates magnetically is dependent
upon circuit design.  Core saturation is not necessary and is
most often not desired.


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It can be argued that one can learn more about the Joule Thief around here than one can on the nine-hundred and eighty-six pages of Joule Thief discussion somewhere else!   lol
   

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

Thanks for the pontification.  ;D

I've listed two core types on my diagram; one blue, one white. These are two core types that I have on hand, and I used the blue one to construct my unit.

Unfortunately the blue core is not a Ferroxcube part, but I've seen elsewhere that the material is similar to 3E4 (as noted on my diagram "Like 3E4 material, probably Hi u"). This is a SANLIN part, and I was not able to find any good specs on it.

The white core I have is a Ferroxcube part, but I have not tried it yet. It is a smaller core.

Note also, that the inductance specs given at the top of my diagram were measured before I cut into the core to introduce a significant gap in order to lower the permeability. I succeeded and managed to increase the Fo by a factor of 9 or so.

Once I receive that part kit from Lawrence, I will try to determine an "AL" spec for his core and my two core types as well. I am certain that my cores are much higher u than his. The white TN16/9.6/6.3 3C90 cores are supposed to have an AL of about 1480nH, but as I've mentioned, I have not yet built one using this core.

.99
   
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Hi  .99,

I am aware of a very helpful program on calculating AL and u values of unknown toroidal cores. All what would be needed is to have an L meter and measure a 10 (or any preferred) turns of coil inductance wound onto the unknown core.

Here is the link, it is free and small:  http://dl5swb.de/html/mini_ring_core_calculator.htm  

Check its Tools in the upper Menu line, the first item in Tools is AL and permeability: these are calculated by the program from the measured L of known turns and the measured mechanical sizes (OD, ID, h).

I have found this very useful.  In case you are already aware of this program, then sorry, perhaps others here may find also useful.

Gyula
   

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It's not as complicated as it may seem...
Thanks gyula.  :)

I was going to wind 10 turns on the core and measure the inductance, then divide by 10. That should give me "AL".

This looks like it could be a handy tool though. ;)

.99
   
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I am actually a little puzzled here about the frequency increase.  If you have a core where the number of turns in L1 and L2 are constant, and then you make a cut in the core, you are reducing it's cross-sectional area.  Won't that make the the core saturate sooner but not affect the value of the inductance associated with L1 and L2?  But it is apparent that cutting the core is decreasing L and therefore increasing Fo.  I am having some trouble visualizing this because the current waveforms show a linear rise (see below), indicating core saturation is not a factor here.


Think core saturation at a certain absolute B.

The B in equation B=uH is relative B.

L is reflected upon the relative B.

When Poynt cut the core to reduced mu, he's altering relative B.
   
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It's turtles all the way down
Adding cuts or gaps in a core allows higher values of current before saturation is induced. It also helps to discharge remnant magnetism between charge cycles, allowing operation at higher duty cycles.

Then there is the subject of non-linear gapping, but that is for another chapter in the saga.


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the AL value of the core is inductance per turns ^2 , so this is the applicable equation we need to use.

L = AL * N^2

Note:   If the inductance is measured with a meter, who cares what the AL value is,  this spec is given so we can approximatley calculate the inductance easily and quickly, but the measured value is the final word, unless of course we want to re-engineer and discover what materials we are dealing with.


I should say that cutting gaps into the toroid, as in breaking the magnetic path, will invalidate some calculations, but no matter what we do to the toroid will not affect the B_sat value, this is a material property.  However, cutting up the toroid will affect what magnetic intensity we can generate given number of turns and current flow because this is dependent on the geometry, however reducing the height of the torroid does not affect the magnetic intensity like I've mentioned, but cutting gaps into the toroid, i.e. breaking up the flux path will most definitley affect the magnetic intensity since the reluctance has changed.
« Last Edit: 2011-02-10, 18:05:48 by EMdevices »
   

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It's not as complicated as it may seem...
I'll be doing some testing hopefully over the next couple of hours after I solder some leads on to the assembled unit Lawrence was kind enough to send me via FedEx.

Other good news, the parts kit that Lawrence put in the mail finally arrived today!  :) Thanks Lawrence.

It's going to be a fun weekend folks.  O0

.99
   

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It's not as complicated as it may seem...
OK, now having the OUTPUT scope issues taken car of, I wanted to retest my original circuit build. The first test is the same as where this circuit left off, with the collector LED clipped, and the only output taken from the secondary output LED.

secout_input_mean.PNG indicates an average INPUT power of 33.44mW.

secout_output_mean.PNG indicates an average OUTPUT power of 230.3mW/10 = 23.0mW.

n=68.8%

.99
   

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It's not as complicated as it may seem...
Now let's look at the case where the secondary output circuit is cut open circuit, and the collector LED re-connected as the only load. Note that the LED goes through the 1 Ohm to ground.

colout_input_mean.PNG indicates an average INPUT power of 41.53mW.

colout_output_mean.PNG indicates an average OUTPUT power of 37.1mW.

n=89.3%

As you can see, it is far more efficient to load the JT from the collector than from a secondary winding with 110 Ohms series resistance.

Also of note, comparison of this unit with my P9901 air-core unit, you can see that a ferro-magnetic core is not used to make the device function (via core saturation), but rather to make it much more efficient, i.e. 90% vs. 50%. Q. How does it do that? A. By increasing the inductor Q.

.99
   
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Good work POYNT

So to what do we attribute a turnoff mechanism with an air core?

In the ideal world, with an air core, there would be no turnoff mechanism as the inductor would draw greater current increasing drive and so on. In the practical world with a real battery with a internal resistance of 120 milliohms, there will be a limit to the current drawn by the inductor, allowing for a turnoff mechanism (when current goes steady state, drive disappears)

(edit: I'm also discussing an ideal circuit with no emitter resistor to limit current. If you are testing with the one ohm emitter resistor, that will also act as a current limiter)

Be interesting to simulate the air core version with zero battery impedance and zero winding resistance to check this.
« Last Edit: 2011-02-13, 19:28:26 by ION »


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Poynt:

Thanks for redoing the captures.  If I can make a request it would be to do a set of captures where you also look at the L1 output voltage that drives the base input resistor.  This is the critical signal that's associated with the Joule Thief feedback mechanism that shows when the transistor is switched on and off.  Perhaps doing this for the "standard" LTJT configuration would be informative for your readers.

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 (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

   It just occurred to me to ask --  Did you account for the Power lost in MEASURING the current in the INPUT circuit, using (I presume) a low-ohm resistor?   

That power dissipation in the measuring-resistor may be small, but should IMO be accounted for.  I would use V*V/R to determine the power lost in the measuring-resistor, and subtract this from the "INPUT Power".  Would you check this, please?  (Perhaps you handled this already and I missed it?)
   

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It's not as complicated as it may seem...
   It just occurred to me to ask --  Did you account for the Power lost in MEASURING the current in the INPUT circuit, using (I presume) a low-ohm resistor?   

That power dissipation in the measuring-resistor may be small, but should IMO be accounted for.  I would use V*V/R to determine the power lost in the measuring-resistor, and subtract this from the "INPUT Power".  Would you check this, please?  (Perhaps you handled this already and I missed it?)

Hi Professor.

Yes, you are absolutely correct; the power in the current sensing resistor, and any other resistors in the power loop should have their power dissipation accounted for also.

In this case, the power in the 10 Ohm and 100 Ohm were not accounted for, and so in reality, the efficiency would be higher than the 69%. I would estimate it is actually between 80% to 90% if those two resistors are included. The best way to make the actual measurement, would be to replace the 110 Ohms with a single 1 Ohm as you have done with your tests.

I did not perform this measurement because it was not part of the claim Lawrence is making.

If you wish, I can do this test with a 1 Ohm installed. Let me know.

.99
   
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  Wait -- how did you measure the CURRENT coming from the battery, the current in the "input" or JT circuit -- what resistor did you use there?
Let's start with that. 
   

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It's not as complicated as it may seem...
  Wait -- how did you measure the CURRENT coming from the battery, the current in the "input" or JT circuit -- what resistor did you use there?
Let's start with that. 


The INPUT power was measured as per my diagram on the first page in this thread. Battery voltage and battery current (via the 1 Ohm in series with the transistor emitter) were measured and multiplied in the scope. Mean power was also shown.

This was performed with the collector LED clipped, and thus, not in the circuit. It was therefore not skewing the results.

.99
   
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The INPUT power was measured as per my diagram on the first page in this thread. Battery voltage and battery current (via the 1 Ohm in series with the transistor emitter) were measured and multiplied in the scope. Mean power was also shown.


.99

Right -- that's what I thought.  Now, did you calculate and subtract the power lost to the input-JT circuit due to power dissipation in this 1 ohm resistor? I would like to know how much power is dissipated in the 1ohm measuring resistor, and how much power is consumed in the remainder of the input circuit. I don't know how to make my question any more clear.
   

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It's not as complicated as it may seem...
Right -- that's what I thought.  Now, did you calculate and subtract the power lost to the input-JT circuit due to power dissipation in this 1 ohm resistor? I would like to know how much power is dissipated in the 1ohm measuring resistor, and how much power is consumed in the remainder of the input circuit. I don't know how to make my question any more clear.

I'm trying my best here Professor.  :)

Hopefully this will help. I didn't include the power in Rb as it is quite small, but it can be measured as well.

.99
   
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I'm trying my best here Professor.  :)

Hopefully this will help. I didn't include the power in Rb as it is quite small, but it can be measured as well.

.99

Yes, the power in Rb is quite small, but needs to be quantified since this resistor is intended only for measurement and is not a necessary part for the circuit to run.  I find that it's presence (or absence) does affect the frequency at which the circuit operates, for example.  And if there were a way around it, one would like to make measurements without perturbing the system.

At present, given the tiny currents in your DUT, it seems the best we can do is to be quantitative in calculating the power dissipated in Rb, and that is what I have asked of you.  I haven't seen any numbers yet, and request (again) that you provide the numbers --
Quote
I would like to know how much power is dissipated in the 1ohm measuring resistor, and how much power is consumed in the remainder of the input circuit.

"Quite small" is a start but is qualitative; a quantitative measurement is what I'm requesting, and you say this "can be measured."  Please do.  The numbers leading up to "Pcore" in your set of measurements would also be enlightening, if you would please share the numbers with us.  Thanks!
   

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It's not as complicated as it may seem...
Yes, the power in Rb is quite small, but needs to be quantified since this resistor is intended only for measurement and is not a necessary part for the circuit to run.  I find that it's presence (or absence) does affect the frequency at which the circuit operates, for example.  And if there were a way around it, one would like to make measurements without perturbing the system.

At present, given the tiny currents in your DUT, it seems the best we can do is to be quantitative in calculating the power dissipated in Rb, and that is what I have asked of you.  I haven't seen any numbers yet, and request (again) that you provide the numbers --
"Quite small" is a start but is qualitative; a quantitative measurement is what I'm requesting, and you say this "can be measured."  Please do.  The numbers leading up to "Pcore" in your set of measurements would also be enlightening, if you would please share the numbers with us.  Thanks!

Professor,

Rb, the 1k base drive resistor exhibits an average power dissipation of only about 0.5mW. This amounts to less than 1% of the total input power, so I have never really been concerned that not including it in the computations would make or break any claims, one way or the other.

It is possible to measure the power in Rb, but it is not all that straight forward. What one needs to do is use two scope probes to measure Vb and the input side of Rb so that we obtain the instantaneous voltage across Rb. We need to use the scope to take the difference between the two probe measurements to obtain VRb (voltage across Rb). The scope would need to square this math function to get VRb2/Rb, and I am not certain many scopes will do this. For less than 1% of the total power, I do not feel this is worth all the effort making this measurement.

I thought you were more interested in the power dissipation in the current sense resistors, CSR1 and CSR2, and I have shown how to make those measurements. I have not made the measurement on these two resistors yet, and that will have to wait for the weekend.

.99
   
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Professor,

I thought you were more interested in the power dissipation in the current sense resistors, CSR1 and CSR2, and I have shown how to make those measurements. I have not made the measurement on these two resistors yet, and that will have to wait for the weekend.

.99

This part is correct, I misunderstood your definition of Rb earlier --  I await your measurements this weekend. 
My question stands:
Quote
Now, did you calculate and subtract the power lost to the input-JT circuit due to power dissipation in this 1 ohm resistor? I would like to know how much power is dissipated in the 1ohm measuring resistor, and how much power is consumed in the remainder of the input circuit. I don't know how to make my question any more clear.
   
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