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Author Topic: Joule Thief - P9901  (Read 50585 times)
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Joule Thief - P9901 « on: 2011-02-12, 23:16:47 »

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It's not as complicated as it may seem...
I built another JT, this time air-core.

The inductors are only about 3uH each. I used #28 AWG, and a rubber (packing) facet washer as my former.

Fo is about 1.1MHz!  >:-)

There is no secondary. The LED is powered like the standard JT off the collector, and goes to GND through a 1 Ohm for current measurement. The emitter has it's own 1 Ohm as well.

It's only about 25% efficient, unless my two power measurements aren't telling the whole story. Note also the strangeness with the negative current and positive voltage; p(t) is zero rather than negative. ???

I used a bit of averaging (4) to clean up the traces a little.

I'll post a schematic later. I suspect this answers the core/saturation question guys. ;)

.99


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"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
   
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Re: Joule Thief - P9901 « Reply #1 on: 2011-02-12, 23:47:21 »
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Poynt,

I still have a nagging feeling about those negative current measurements and the scope channel.  Even if the LEDs when reverse-biased are leaky like you say.

For example, lets take a look at output_view.png.  At about 1.7 main divisions from the left of the capture, the current transitions through zero and starts to change direction.  However, the corresponding voltage is still positive, about +2.0 volts, and is sloping downwards.  Why should the current change direction at this point in time?  It doesn't make sense to me.  You see the same thing on most of your captures.

In this particular case you show negative current but zero power.  What that suggests to me is that the current is zero, and the data for the channel internal to the scope is correct, and the mathematics are correct, but for some reason when that data for that particular channel is given to the module that has to massage it and generate the display, that module is adding a negative offset to the displayed data.

Of course, when the LED is not forward biased enough, the current should be nearly zero, not negative.

If you have any doubts yourself, you might consider simply swapping the channels and doing the same capture.  Will the math be the same?  Will the displayed channels be the same or will you see an offset migrate to the channel that is now displaying the voltage?  I will restate the simple test I stated before, just reverse bias an LED in series with the resistor (like the LTJT secondary setup) with your DC power supply and measure the leakage with your best multimeter and see if it is in agreement with the DSO.

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Re: Joule Thief - P9901 « Reply #2 on: 2011-02-13, 00:32:34 »

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It's not as complicated as it may seem...
Yes, MH I agree. There is something going on here, and at this frequency I am not too surprised.

Maybe that LED is not leaking that much. Could this be a probe problem? The skew looks ok, but there is a DC offset in the current reading.

The scope is also ignoring the fact that the current is negative, because the resulting power trace stays at zero, indicating that the current should be zero.

My simulation also corresponds quite well with this unit, except for that negative current. I am going to try my good 500MHz probes and see if there is a difference. I'll post the results if they look any different.

.99


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"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
   
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Re: Joule Thief - P9901 « Reply #3 on: 2011-02-13, 01:41:10 »

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It's not as complicated as it may seem...
OK, found the problem causing the offset in CH2 in the OUTPUT scope.

Have a look at the scope shot... C.C

.99  >:-)


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"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
   
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Re: Joule Thief - P9901 « Reply #4 on: 2011-02-13, 02:11:23 »
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Ha! Ha! Ha!  It happens to the best (of us) also!
« Last Edit: 2011-02-13, 04:49:34 by MileHigh »
   
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Re: Joule Thief - P9901 « Reply #5 on: 2011-02-13, 02:48:08 »

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

I've been posting all kinds of shots with this setting....you guys missed it too!  O0

I've downloaded the latest firmware version for the TDS3012B and installed it on both scopes, now I am going to try and calibrate the high frequency adjustment on the probes. One probe is showing zero current where there is zero, and the other is showing a slight positive current. Hopefully, the HF cal will fix this.

Then we'll be set to do some of these tests over again.  >:( LOL.

.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
   
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Re: Joule Thief - P9901 « Reply #6 on: 2011-02-13, 15:13:22 »

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It's not as complicated as it may seem...
Here is a schematic of this P9901 JT.

It doesn't get more minimalist than this I suspect. Once the two CSR resistors are removed, it's down to 4 components; Q1, Rb, LED, air-core transformer.

.99

PS. I will be re-measuring all these units with my other good probes on the OUTPUT scope.


---------------------------
"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
   
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Re: Joule Thief - P9901 « Reply #7 on: 2011-02-13, 17:10:17 »

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It's not as complicated as it may seem...
The scopes have been updated to latest firmware, OUTPUT scope CH2 coupling changed to "DC", and bad probe eliminated  (two new probes used in their place). The CH2 current in the OUTPUT scope now looks correct.

Here are the test results once again after the "cleanup":

input_mean_2nd.png indicates an average INPUT power of 41.84mW.

output_mean_2nd.png indicates an average OUTPUT power of 22.3mW.

n=53.3%

.99


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"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
   
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Re: Joule Thief - P9901 « Reply #8 on: 2011-02-13, 21:17:52 »

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Quote from: poynt99 on 2011-02-13, 15:13:22
Here is a schematic of this P9901 JT.

It doesn't get more minimalist than this I suspect. Once the two CSR resistors are removed, it's down to 4 components; Q1, Rb, LED, air-core transformer.

.99

PS. I will be re-measuring all these units with my other good probes on the OUTPUT scope.



Would not the "load" LED and series resistor be better
isolated from the "source" if placed directly across the
primary winding?



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Re: Joule Thief - P9901 « Reply #9 on: 2011-02-13, 21:48:13 »
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Quote from: Dumped on 2011-02-13, 21:17:52


Would not the "load" LED and series resistor be better
isolated from the "source" if placed directly across the
primary winding?



When driven with a 1.5 volt battery or less, there is no need to worry as the forward drop is at least 2.0 volts for a standard red led and higher for other types.

You are correct for higher source voltages as this can flow into the led during the off state of the transistor. I like to keep the load current circulating around the inductor of use, as that is most efficient, and prevents transients from rocking the supply. You will see on my bench most of the circuits I use are drawn and tested that way.

CSR1 should really be moved to the negative leg of the battery, and the emitter grounded. This way you can watch current flowing out of the battery, and during the inductor charge and discharge cycles, including any current that might flow back into the battery (as some may claim).

The resistor CSR1 in the emitter is the worst possible place as it is a potential degenerative element, and does not let you see the whole picture. Also it should be a fraction of an ohm (0.1) to optimize efficiency.
« Last Edit: 2011-02-14, 13:12:39 by ION »


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Re: Joule Thief - P9901 « Reply #10 on: 2011-02-13, 21:54:16 »

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It's not as complicated as it may seem...
Quote from: Dumped on 2011-02-13, 21:17:52


Would not the "load" LED and series resistor be better
isolated from the "source" if placed directly across the
primary winding?

The LED load can be "discharged" through to ground or Vbat, it works both ways. However, there is more power delivered to the LED when it is connected to ground, which is why all the schematics show it this way.

Do you know why more power is delivered to the LED when it goes to ground?

.99


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"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
   
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Re: Joule Thief - P9901 « Reply #11 on: 2011-02-13, 22:08:47 »
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Quote from: poynt99 on 2011-02-13, 21:54:16
The LED load can be "discharged" through to ground or Vbat, it works both ways. However, there is more power delivered to the LED when it is connected to ground, which is why all the schematics show it this way.

Do you know why more power is delivered to the LED when it goes to ground?

.99

Are you referring to "more power" as in "greater efficiency" or more power through current leakage from the source supply through the inductor?


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Re: Joule Thief - P9901 « Reply #12 on: 2011-02-13, 22:29:25 »

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It's not as complicated as it may seem...
Quote from: ION on 2011-02-13, 22:08:47
Are you referring to "more power" as in "greater efficiency" or more power through current leakage from the source supply through the inductor?

What I mean by "more power" is not only more power delivered to the LED, along with more power used from the supply, but higher efficiency as well.

.99


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"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
   
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Re: Joule Thief - P9901 « Reply #13 on: 2011-02-13, 22:40:26 »
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Quote from: poynt99 on 2011-02-13, 22:29:25
What I mean by "more power" is not only more power delivered to the LED, along with more power used from the supply, but higher efficiency as well.

.99

I'd like to hear of this. Are you stating a truth for all JT's of this topology?


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Re: Joule Thief - P9901 « Reply #14 on: 2011-02-14, 01:31:01 »

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Quote from: ION on 2011-02-13, 22:40:26
I'd like to hear of this. Are you stating a truth for all JT's of this topology?

It seems to hold true for both air-core and core-type versions of this configuration. However, in the simulations at least, there is a bigger difference with the air-core version. But in both cases, more power is dissipated in the LED when it is grounded vs. connected to the battery.

In sims with the core, the Pin did not go up at all, but the efficiency went up 12% when the LED was grounded vs. connected to Vbat. The more current we can get through the LED, the brighter it will be and the more power it will dissipate. When the LED is pulsed by IK into the Vbat terminal, there is a lower potential difference seen by the inductor.

Try it yourself ION with your BO unit. Which way produces higher intensity in the LED? Is there any difference in Pin?

.99


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"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
   
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Re: Joule Thief - P9901 « Reply #15 on: 2011-02-14, 12:58:03 »
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Quote from: poynt99 on 2011-02-14, 01:31:01
It seems to hold true for both air-core and core-type versions of this configuration. However, in the simulations at least, there is a bigger difference with the air-core version. But in both cases, more power is dissipated in the LED when it is grounded vs. connected to the battery.

In sims with the core, the Pin did not go up at all, but the efficiency went up 12% when the LED was grounded vs. connected to Vbat. The more current we can get through the LED, the brighter it will be and the more power it will dissipate. When the LED is pulsed by IK into the Vbat terminal, there is a lower potential difference seen by the inductor.

Try it yourself ION with your BO unit. Which way produces higher intensity in the LED? Is there any difference in Pin?

.99

Are you calculating input power over the full cycle or just during the on time of the transistor? With the LED to ground, there is current pumped out of the battery during the inductor discharge cycle because the current loop includes the battery,  but unfortunately is in the wrong direction, and does not have a regenerative effect, just the opposite. Because of this, if you are not calculating power over the full cycle, the circuit will appear to be drawing the same current from the supply yet delivering more power to the LED.

I have simulated this both ways and tested it on the bench. To my observations, the current drain from the battery never reverses, is always in the same direction i.e. out of the battery even during the inductor discharge cycle, although it is about half the inductor charge drain. This must be included in the power calculation.

With the LED connected across the driven winding, it absorbs the energy without forcing the battery to also supply current as current no longer circulates through the battery during the inductor discharge cycle.

I must state again I prefer a 0.1 ohm resistor in the negative lead of the battery as opposed to the 1.0 ohm emitter resistor, as it more accurately allows assessment of battery load effects during both inductor charge and discharge cycles. Also 0.1 Ohm is pretty close to the battery impedance for the sims.
« Last Edit: 2011-02-14, 13:40:34 by ION »


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Re: Joule Thief - P9901 « Reply #16 on: 2011-02-14, 13:43:31 »

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It's not as complicated as it may seem...
I agree, that a smaller CSR placed in series is the best way to go for current sensing.

Regarding this LED placement issue, it is less complicated than what you seem to be looking at ION.

What I'm doing when simulating this, is starting with the basic JT connection just as you showed in your excellent writeup about Testing the Efficiency of Blocking Oscillators.



You show D1 going to Vbat. You will need to replace this diode with a LED that has a VF of at least 2V. Shunting a normal diode to ground will clamp the collector too hard, and it won't oscillate. At least that has been my findings.

While on your bench, try the LED with both connections (i.e. gnd and Vbat); which produces the highest intensity? How does Pin compare in each case?

What I am doing in the simulation is plotting the average power from the battery AND the average power in the LED, for each case. Power transfer efficiency to the LED is greater in the case when it is tied to ground rather than Vbat. Whether the battery power goes up or not seems to depend on the build and whether a core is used. However, that aside, n always seems to increase with the ground connection.

Does this make sense? If not, I will make a diagram and try to explain it.

Btw, I don't believe I have mentioned battery current reversal in this discussion. That is a different issue I believe, but since you mention it, current won't return to the battery in either case of LED connection.

.99


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"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
   
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Re: Joule Thief - P9901 « Reply #17 on: 2011-02-14, 14:10:42 »
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Looking back, I would not have used the emitter resistor, but I wanted the circuit to be somewhat close to the device under discussion.

I needed to use a string of 6 1N5817 Schottky diodes to get above the battery voltage of 1.5 Volts or the circuit would not oscillate.

We agree, there is no current pumped back into the battery with either method. What I'm saying is you will observe a triangle wave current drain using the grounded led technique when measured at the source battery.

The current goes from 140 to 70 mA during the discharge cycle, when it should go from 140 to close to 0 mA when the transistor switches off at the end of the charge cycle. During the "off" period the current ramps from 140mA to 70 mA which is the series current from the power supply through the led not accounted for if only evaluating the charge cycle.


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Re: Joule Thief - P9901 « Reply #18 on: 2011-02-14, 14:55:26 »

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It's not as complicated as it may seem...
Quote from: ION on 2011-02-14, 14:10:42
The current goes from 140 to 70 mA during the discharge cycle, when it should go from 140 to close to 0 mA when the transistor switches off at the end of the charge cycle. During the "off" period the current ramps from 140mA to 70 mA which is the series current from the power supply through the led not accounted for if only evaluating the charge cycle.

I am not evaluating any particular part of the cycles actually.

I trust you have been following along somewhat with the oscilloscope measurements on the LTJT etc? For these tests, the average power both from the battery and to the LED is measured using MEAN[v(t) * i(t) = p(t)]. I am doing precisely the same measurement in the simulation over several (minimum 10) cycles to obtain an accurate measurement. Analysing any particular part of the cycle becomes irrelevant this way. What you get is what you get, an average, and it is accurate. Does this make sense?

So, making the average power measurements for BOTH the battery power AND the LED power, the LED always exhibits more power when it is tied to ground, vs. being tied to Vbat. As well, the efficiency is always higher this way. At least that is my finding.

I encourage you to try the experiment on your bench. I will be surprised if you see no improvement in efficiency with the ground connection.



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"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
   
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Re: Joule Thief - P9901 « Reply #19 on: 2011-02-14, 16:50:07 »
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Ok Thanks I'll double check it on the bench.


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Re: Joule Thief - P9901 « Reply #20 on: 2011-02-14, 23:05:11 »
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Referring to P9901 schematic in reply #6 and my statements in the prior posts;

 I double checked the waveforms and my analysis and will now state that the method of sensing current in the emitter resistor CS1 misses a full 1/3 of the power being delivered from the battery during the off cycle of the transistor or discharge cycle of the inductor.

To get the full picture of battery power to the load, you need an independent shunt through which all current during charge and discharge cycles can be seen.

Then, rather than the clean cutoff off of current as seen in the emitter sensing method of CS1, you will see a triangle wave of current across that external shunt and the extra power drawn from the battery during the discharge cycle that has been missing from the calculation.

Continue to look only at current through CS1 as a indication of input power, and you will be missing part of the input power picture.

This is true for all cases where the LED is brought back to the battery for ground and bypasses the current sense resistor CS1. It does not apply where LED current is strictly circulated around the driven inductor as in post #16 above.

 Attached is the corrected method of accounting for all power used from the battery source.
« Last Edit: 2011-02-15, 00:42:27 by ION »


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Re: Joule Thief - P9901 « Reply #21 on: 2011-02-15, 00:40:41 »

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Quote from: ION on 2011-02-14, 23:05:11
...

To get the full picture of battery power to the load, you need an independent shunt through which all current during charge and discharge cycles can be seen.

...

That's my analysis and I'm sticking to it...



Well done!


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Re: Joule Thief - P9901 « Reply #22 on: 2011-02-15, 01:12:49 »

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It's not as complicated as it may seem...
Thank you for straightening out my error ION.

I will retest the P9901 shortly. That should make my 53% efficiency drop somewhat.  :'(

.99

NOTE: All units other than the P9901 were tested as per single CSR method.


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"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
   
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Re: Joule Thief - P9901 « Reply #23 on: 2011-02-15, 03:17:34 »

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It's not as complicated as it may seem...
Here is some simulation data requested by ION regarding my claim about the differences in efficiency with the LED terminated at ground (GND) vs. when terminated at the + terminal of the battery (Vbat). I claim that the efficiency will always be higher when the LED is terminated at GND.

I tested two circuits, one with a core, and one with an air-core. The average power (mW) for each component is listed, and the core loss is determined by the difference between the battery power and the components power. Efficiency n is determined by LED power / Battery power. Rb is the 1k Base resistor, and Rs is the primary DCR.

With Core

GND Connection

BAT:68.7, LED:27.9, Q:12.6, Rb:0.85, Rs:0.30. Components Total: 41.65. Core Loss: 68.7 - 41.65=27.05. n=27.9/68.7=40.6%


Vbat Connection

BAT:69.3, LED:20.8, Q:15.3, Rb:1.04, Rs:0.36. Components Total: 37.5. Core Loss: 69.3 - 37.5=31.8. n=20.8/69.3=30.0%


Air Core

GND Connection

BAT:80.4, LED:49.6, Q:29.8, Rb:0.59, Rs:0.39. Components Total: 80.4.  n=49.6/80.4=61.6%


Vbat Connection

BAT:68.6, LED:32.99, Q:34.3, Rb:0.833, Rs:0.40. Components Total: 68.6.  n=32.99/68.6=48.1%


The two circuit diagrams illustrate the two connections. I hope it is fairly clear from the data which one yields a higher efficiency.

.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
   
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Re: Joule Thief - P9901 « Reply #24 on: 2011-02-15, 04:00:03 »
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Thank you for the testing POYNT. Your numbers tell the story. Looks like your efficiency went up rather than down???

There appear to be two questions:

first, why did the efficiency go up when current drain over the full cycle is considered.(external shunt)

The second question  is: why is the ground connection more efficient than the Vbat connection ?

This is completely counter-intuitive considering in the grounded connection we see current drawn from the battery during the charge and the discharge cycle and there is no mechanism for recycling of power back to the battery.

While in the Vbat connection, the current flow during discharge is isolated from the battery, hence there is no extra drain during the discharge part of the cycle.

I admit I am now at a loss to explain this.

Anyone care to offer an explanation?


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