PopularFX
Home Help Search Login Register
Welcome,Guest. Please login or register.
2020-02-28, 07:12:21
News: Forum TIP:
The SHOUT BOX deletes messages after 3 hours. It is NOT meant to have lengthy conversations in. Use the Chat feature instead.

Pages: 1 2 [3]
Author Topic: Joule Thief - P9901  (Read 40574 times)
Group: Tech
Sr. Member
****

Posts: 291
Thanks ION for these tests.

It could be a few factors that is contributing to the increase in efficiency, including Fo and duty cycle. The important issue to be realized and resolved though, is that the GND connection always seems to yield a better efficiency over all, so we should use that connection when building this configuration of JT.

Are we in Agreement?

.99

Given that we start with a given level of energy to be discharged by the inductor, there are just two paths for the discharging current. If we take the grounded LED path back to the inductor via the supply battery, the level of power dissipated in the very low battery internal resistance will be negligible. If we take the flyback route to the inductor, again the power dissipation is negligible in the circuit wiring, so in theory I cannot see how one path can be so much different to the other. If anything, the return to Vbat should have the edge in efficiency IMO being the shortest path. However, if the battery exhibits high resistance due to sulfation, then this could change the situation. All this ignores the energy taken from the battery whilst the forward voltage of the LED is exceeded during inductor discharge in LED grounded config. This energy dissipates in the load thereby depleting battery capacity and increasing the overall load power dissipation in comparison with the return to Vbat config. I see it as a trade-off between lost battery capacity and reduced power dissipation in the LED load. Take your pick.

Hoppy
   
Group: Elite
Hero Member
******

Posts: 3638
It's turtles all the way down
What we're left with is simply a battery driving a LED, and the power is quite low. Even so, the efficiency should be fairly high, not having as many lossy components.

However this is no longer a JT.  ;)

.99

Actually I would guess the efficiency would be close to 100% and that was the point.

I was trying to make a case that part of the high efficiency is that the battery pre-biases the LED to the threshold of turn on with the Vgnd configuration and this is the unseen extra efficiency, that I believe will diminish when increasing the string of LED's hence the Vdrop.

I am only trying to identify a mechanism for the increased perceived efficiency and am theorizing that part of this higher efficiency is "borrowed" from "normal" battery/LED current.

I'll continue to research this privately, and yield that for a single LED with a Vdrop close to the battery voltage there is a measured increase in efficiency using the Vgnd method, so that is the best method for the JT's under discussion.


---------------------------
"Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy
   

Group: Administrator
Hero Member
*****

Posts: 2906
It's not as complicated as it may seem...
Actually I would guess the efficiency would be close to 100% and that was the point.

I was trying to make a case that part of the high efficiency is that the battery pre-biases the LED to the threshold of turn on with the Vgnd configuration and this is the unseen extra efficiency, that I believe will diminish when increasing the string of LED's hence the Vdrop.

This is easy enough to test in the simulations. I'll let you know my findings.

.99
   

Group: Administrator
Hero Member
*****

Posts: 2906
It's not as complicated as it may seem...
ION,

Here are the results of the tests with a core-type unit (3C90 material). I ran 3 tests; 1LED, 2LEDs, 3LEDs in series. Efficiencies computed in each case with LED(s) terminated at GND and at Vbat. All LED powers added together in cases where there is more than one.


1xLED

GND Connection:

Pbat: 61.3, Pled: 25, n=40.8%

Vbat Connection:

Pbat: 63.7, Pled: 18.08, n=23.38%


2xLED

GND Connection:

Pbat: 75, Pled: 12.5+12.5 n=33%

Vbat Connection:

Pbat: 74, Pled: 10+10, n=27%


3xLED

GND Connection:

Pbat: 79.8, Pled: 8.16+8.16+8.16, n=30.6%

Vbat Connection:

Pbat: 78.1, Pled: 7.07+7.07+7.07, n=27.2%


I suspect this trend will continue while adding LEDs in series, until finally, the two efficiencies will equal out at 0%.

In all the cases above, a GND connection shows a better efficiency. Unless this simulation is not telling the truth, I'd be inclined to always connect my LEDs to GND, if I was indeed a Joule Thief enthusiast that is.  ;)

.99
   
Group: Elite
Hero Member
******

Posts: 3638
It's turtles all the way down
This confirms some of my suspicions, the Vgnd shows a marked decrease in efficiency about 7% per added LED initially.

There really shouldn't be a decrease in efficiency if indeed the effect of a discharging inductor current source was supplying all the current. This is obviously not the case and the Vgnd configuration yields evidence that a partial voltage source (the battery) is part of the inductor discharge cycle.

Notice for the Vbat connection where the true current source effect of a discharging inductor is the only force at play, the efficiency starts rising about 3.5% per added LED initially as Ohmic losses no longer predominate.

Nevertheless the Vgnd has the added advantage of a jump start in efficiency by pre biasing the LED with the battery voltage source.

At some point the efficiency curves will equalize, at it looks like it will be at the 4 LED scenario.

Thank you for running these tests as they have provided some evidence for what I believe is the mechanism of the higher efficiency of the Vgnd configuration.
« Last Edit: 2011-02-16, 09:55:38 by ION »


---------------------------
"Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy
   
Group: Elite
Hero Member
******

Posts: 3638
It's turtles all the way down
As they say, one picture is worth 1000 words, and three points can show a trend.

Of course this chart is meaningless unless you have been following the thread.
« Last Edit: 2011-02-16, 16:54:04 by ION »


---------------------------
"Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy
   

Group: Administrator
Hero Member
*****

Posts: 2906
It's not as complicated as it may seem...
Just for fun, I've tested this "efficiency issue" out to 25 Volts or so. That is the equivalent of about 8 LEDs in series. I checked 3 points of clamping; 2V, 12V, and 25V.

For this test, I created a "self-controlled switch", i.e. like a diode or LED, made from a Switch part in SPICE. The Switch parameters are as follows:

RON = 40 Ohms
ROFF = 1M Ohm
VON = 2V, 12V, and 25V
VOFF= VON-2V

This switch part produces realistic results compared to the LED part I was previously using, only it is far easier to use than the LED.


Here are the results:

LED: 2VON, 0VOFF
Vbat
BAT:57.4, LED:16.07, n=28%

Gnd
BAT:62.24, LED:34.77, n=55.86%


LED: 12VON, 10VOFF
Vbat
BAT:81.0, LED:22.40, n=27.65%

Gnd
BAT:82.83, LED:24.72, n=29.84%



LED: 25VON, 23VOFF
Vbat
BAT:83.3, LED:22.10, n=26.53%

Gnd
BAT:84.3, LED:23.12, n=27.43%



It would appear that the results support my earlier remark that the efficiencies don't equalize until both are at 0%. These tests, if valid, indicate that for every case (any number of series LEDs) the n will be higher with the GND connection. Wave forms can be posted on request.

Simulation note: When simulating with high threshold voltages (i.e. > 8V) , the "minimum step size" must be set to 3ns or less, in order for the simulation to run properly, otherwise it can not sample the high transients present.

.99
   

Group: Administrator
Hero Member
*****

Posts: 2906
It's not as complicated as it may seem...
ION,

You can implement this self-activating switch in PSpice by selecting the "S" part in the ANALOG library. Connect it as shown, and adjust your switch points as desired. A 2V difference worked well for me.

The two terminals on the left are the "sense", and the two on the right are the "switch".

Double-click the device and set the "RON" value to 20 Ohms, and leave "ROFF" at the 1e6 (1M) value.

Go to the "Edit Simulations Settings" and set the "Maximum Step Size" to 3ns. The runs will take longer, but you should have no convergence problems then.

.99
« Last Edit: 2011-02-17, 02:19:16 by poynt99 »
   
Group: Guest
I wrote up a blog on my experiences with air core coils and JT efficiency.

http://watsonseblog.blogspot.com/2011/02/2011-feb-9-air-core-coil-and-jt.html

One question I have about the schematic. It says 2N2222 for the transistor.  Does this have a plastic case or metal case?  If it's metal then it can be a 2N2222, but if it's plastic, it should say PN2222 or MPS2222 or similar on the case.  Without the true part number, it's impossible to replicate the circuit.

Thanks.
   
Group: Elite
Hero Member
******

Posts: 3638
It's turtles all the way down
Thenks POYNT, tried the switch and it works fine. I'll have to ask a few questions later regarding the switching point vs what I see in the sims.

acmefixer:

Although I have not studied the data sheets that closely, the plastic case should be the same electrically, but temperature ratings and MTBF's may differ. Some data sheets show Ic of 1 amp others 800 mA and thermal resistance junction to case may differ.

Regarding JT utility and efficiency, there is no one size fits all for JT's. Best to define the goal or application, then proceed to make make a best fit. Highest frequency is not always the best and may waste unnecessary power in the switch and in radiation. Depends on the degree of miniaturization, weight, allowable EMI, input voltage, load characteristics and other factors.


---------------------------
"Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy
   

Group: Tinkerer
Hero Member
*****

Posts: 1618
...

One question I have about the schematic. It says 2N2222 for the transistor.  Does this have a plastic case or metal case?  If it's metal then it can be a 2N2222, but if it's plastic, it should say PN2222 or MPS2222 or similar on the case.  Without the true part number, it's impossible to replicate the circuit.

Thanks.


There are a number of transistor types which work well
for this project.  Any of the "2222" packages may be
used - just be aware that some of them may perform better
than others because of slightly different characteristics.

The new family of Low Vce(sat) or BISS transistors work
very well too.  They have higher current rating capability
with equally high Beta within a the smaller SOT package.

One that I like is the NSS60601 (6 Amperes/60 Volts)
in the SOT223.  Other similar types are available from
other manufacturers at Mouser or DigiKey etc...

The transistor type used is not nearly as important as
how well the circuit is "tweaked" or "tuned" for optimum
efficiency.


---------------------------
The animal mind ALWAYS reacts to what it does not understand. This is what sets dogs barking. If you are going to tell the truth, you are going to have to be okay with barking dogs, because they will harry your passage until you pass through town.
Les Visible - 27 February 2020
   

Group: Administrator
Hero Member
*****

Posts: 2906
It's not as complicated as it may seem...
Thenks POYNT, tried the switch and it works fine. I'll have to ask a few questions later regarding the switching point vs what I see in the sims.

Certainly ION. If you have any questions, either post them here or send me a PM. ;)

.99
   

Group: Administrator
Hero Member
*****

Posts: 2906
It's not as complicated as it may seem...
Here is a corrected update as to the proper CSR setup for measuring the INPUT and OUTPUT power for the general JT configuration. This is now in agreement with ION's diagram.

I will try to redo the measurements for the air-core P9901 JT today. I will try to include the CSR1 and CSR2 dissipation as well.

.99
   

Group: Administrator
Hero Member
*****

Posts: 2906
It's not as complicated as it may seem...
I've done a test using the above circuit, and I've realized a much better and simpler way to obtain the actual battery power and actual LED power, than what I proposed here. The power dissipation in the CSR resistors is also easily obtained.  O0

Quote
Notes:

1) P11= probe, scope 1, CH1. P12= probe, scope 1, CH2. P21= probe, scope 2, CH1. P22= probe, scope 2, CH2.

2) INPUT power is obtained as follows:
2.1) Use the scope MATH to produce MEAN[(V1*V2)]. This is the total power of Vbat and CSR1 together. We will call it Pitotal.
2.2) Use the scope MATH to produce MEAN[(V2*V2)]. This is the power of CSR1 alone. We will call this Pcsr1.
2.3)  Pvbat is computed by: Pitotal - Pcsr1.

3) OUTPUT power is obtained in much the same manner:
3.1) Use the scope MATH to produce MEAN[(V3*V4)]. This is the total power of LED and CSR2 together. We will call it Pototal.
3.2) Use the scope MATH to produce MEAN[(V4*V4)]. This is the power of CSR2 alone. We will call this Pcsr2.
3.3) Pled is computed by: Pototal - Pcsr2.

4) The efficiency n of the battery power delivered to the LED alone is then: n = 100(Pled / Pvbat).

5) If we were to insert a 1 Ohm CSR resistor in series with the transistor emitter, we could measure and calculate the transistor power dissipation in a similar fashion. We already have the voltage across the transistor, V3, so the other required voltage measurement would be that of a CSR3 resistor labeled "V5". Note, V5 is not the same as V2.

My results for the P9901 circuit are as follows:

Pintotal = 41.2mW
Pcsr1 = 3.39mW
Pvbat = 37.81mW

Pototal = 24.4mW
Pcsr2 = 0.69mW
Pled = 23.71mW

n(vbat to led) = 23.71/37.81 = 62.71%

.99
   
Group: Professor
Hero Member
*****

Posts: 2688
 Thanks, .99, for these test results and the clear explanation of how you obtained them. 

  The "other shoe" is of course the JT with the ferrite core, rather than the air core. 

I'm looking forward to your measurement results using the ferrite core -- same method otherwise.
It was with the ferrite core in an almost identical set-up that I found a surprising (approx) n = 1.3, as I reported last Friday,
http://www.overunityresearch.com/index.php?topic=717.msg11327#msg11327

 so I'm particularly looking forward to your further results with the ferrite core this time.  I may have done something wrong, but would like to compare with your results.  Of course, we are using different toroidal-windings.

   

Group: Administrator
Hero Member
*****

Posts: 2906
It's not as complicated as it may seem...
Coming up soon professor.....I'm heading over to do them right now.

.99
   
Group: Professor
Hero Member
*****

Posts: 2688
  Great, looking forward to the results .99

  A comment about your schematic -- I have the wire from the emitter of the 2n2222 going back to the point you have labeled V2, rather than going to ground.  As it stands, I don't see how you account for this "loss" from the circuit, with emitter output going direct to ground.

  Other than that, and the fact that I used a ferrite core, our circuits look the same.
   

Group: Administrator
Hero Member
*****

Posts: 2906
It's not as complicated as it may seem...
The results are posted professor.

See this post.

Regarding your emitter connection, that needs to be connected as shown on my diagram, where it is going to ground, not directly to the negative battery terminal. All currents going in or out of the battery must go through the supply current-sensing resistor, otherwise your INPUT power measurement will not be correct.

.99
   

Group: Administrator
Hero Member
*****

Posts: 2906
It's not as complicated as it may seem...
OK, I've discovered that Pitotal must be added to Pcsr1, not subtracted. Let's try again:

My corrected test results for the P9901 circuit are as follows:

Pintotal = 41.2mW
Pcsr1 = 3.39mW
Pvbat = 44.59mW

Pototal = 24.4mW
Pcsr2 = 0.69mW
Pled = 23.71mW

n(vbat to led) = 23.71/44.59 = 53.2%

.99
   
Group: Professor
Hero Member
*****

Posts: 2688
OK, I've discovered that Pitotal must be added to Pcsr1, not subtracted. ...
.99

No, I think you were right the first time.  You measure the total input, then SUBTRACT the power dissipated in the measuring resistor.  The power dissipated in the measuring-resistor is not available for the rest of the circuit.
  What would the power be in the input circuit if you reduced CSR1 to 1/2 ohm?  then to 1/4 ohm, etc.

Perhaps the most important aspect of this exercise is getting the measurements right, subtracting when one should subtract, getting the ground connections right, etc.   I'm not sure you/we are there yet.
   
Pages: 1 2 [3]
« previous next »


 

Home Help Search Login Register
Theme © PopularFX | Based on PFX Ideas! | Scripts from iScript4u 2020-02-28, 07:12:21