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Author Topic: Joule Thief behavior question.  (Read 20293 times)

Offline xee2

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Re: Joule Thief behavior question.
« Reply #15 on: October 27, 2013, 12:45:05 AM »
Something isn't making sense.  You show the collector current of 1.5 amps so if I put two of those in parallel you said that would be cut in half so that would make it 750ma which i not good.


I said each one you add reduces the equivalent collector-emitter resistance (thus more current for a specific Vce). Each additional transistor is another current path and thus each time you add a parallel transistor you increase the current going into the junction of the collectors of all the transistors. The higher the collector current is, the higher the current in the coil will be, and the larger the voltage spike will be when the transistors turn off.

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Re: Joule Thief behavior question.
« Reply #15 on: October 27, 2013, 12:45:05 AM »

Offline Legalizeshemp420

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Re: Joule Thief behavior question.
« Reply #16 on: October 27, 2013, 01:23:35 AM »
Ahhh, yes, to use Ohms Law and since it is less resistance more electrons will flow.

Now I understand I think.  So, in your 1.5Adc ifI had two of those in parallel it would be as if I had 1 transistor with 3.0Adc which makes sense as the current capacity would double but is that really what I am after when my light becomes brighter the more I add?

Thank you.

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Offline xee2

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Re: Joule Thief behavior question.
« Reply #17 on: October 27, 2013, 02:04:36 AM »
Ahhh, yes, to use Ohms Law and since it is less resistance more electrons will flow.

Now I understand I think.  So, in your 1.5Adc ifI had two of those in parallel it would be as if I had 1 transistor with 3.0Adc which makes sense as the current capacity would double but is that really what I am after when my light becomes brighter the more I add?

Thank you.


The higher the collector current is, the higher the current in the coil will be, and the larger the voltage spike will be when the transistors turn off. Bigger voltage spike = brighter LEDs.




Offline Legalizeshemp420

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Re: Joule Thief behavior question.
« Reply #18 on: October 27, 2013, 02:27:36 AM »

The higher the collector current is, the higher the current in the coil will be, and the larger the voltage spike will be when the transistors turn off. Bigger voltage spike = brighter LEDs.




That makes sense, of course, but I read that as 1.5A dc max before POOF not that is what is making it go brighter as opposed to simply allowing it to go brighter.

Take for instance 13003 vs BC337-25.  Collector current is 1A for the 13003 and 800ma for the BC337-25 YET the 13003 is dimmer than the BC337-25 so there is more to it than just this.


Offline xee2

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Re: Joule Thief behavior question.
« Reply #19 on: October 27, 2013, 02:42:12 AM »
That makes sense, of course, but I read that as 1.5A dc max before POOF not that is what is making it go brighter as opposed to simply allowing it to go brighter.

Take for instance 13003 vs BC337-25.  Collector current is 1A for the 13003 and 800ma for the BC337-25 YET the 13003 is dimmer than the BC337-25 so there is more to it than just this.



 ??? Ic max is the maximum current the transistor will take before burning up. Just having a transistor with a large Ic max does not mean you are going to magically get that current when you use it. Yes, there is a lot more to it. I think you need to review how transistors work. The collector current is dependent on many variables. Primarily Ic equals base current times the transistors gain. Thus you can change Ic by increasing and decreasing the base current.




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Re: Joule Thief behavior question.
« Reply #19 on: October 27, 2013, 02:42:12 AM »
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Offline Legalizeshemp420

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Re: Joule Thief behavior question.
« Reply #20 on: October 27, 2013, 02:51:02 AM »



??? Ic max is the maximum current the transistor will take before burning up. Just having a transistor with a large Ic max does not mean you are going to magically get that current when you use it. Yes, there is a lot more to it. I think you need to review how transistors work. The collector current is dependent on many variables.
I know there are a lot of things and my question was a simple question "is there anyway to determine what 2 transistors are doing to create the new imaginary third transistor" and I was just told about the collector current which is not what would be what I asked for.  All it would do is allow more current to flow before the transistor would POP/FRY/EXPLODE/BURN UP, etc...

So, I know what the stats on a transistor means I just never played with magically creating a new imaginary transistor with the stats of the 2 I would put together.  That is what my question was about not about adding to the current capacity of the circuit since even one transistor was enough for my purposes but by adding more and more the LED grew brighter.

Offline xee2

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Re: Joule Thief behavior question.
« Reply #21 on: October 27, 2013, 03:07:48 AM »
I know there are a lot of things and my question was a simple question "is there anyway to determine what 2 transistors are doing to create the new imaginary third transistor" and I was just told about the collector current which is not what would be what I asked for.  All it would do is allow more current to flow before the transistor would POP/FRY/EXPLODE/BURN UP, etc...

So, I know what the stats on a transistor means I just never played with magically creating a new imaginary transistor with the stats of the 2 I would put together.  That is what my question was about not about adding to the current capacity of the circuit since even one transistor was enough for my purposes but by adding more and more the LED grew brighter.


If you parallel two identical transistors the result will usually be to double the collector current. If the transistors are not identical there is no easy way to tell what will happen.




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Re: Joule Thief behavior question.
« Reply #21 on: October 27, 2013, 03:07:48 AM »
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Offline Legalizeshemp420

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Re: Joule Thief behavior question.
« Reply #22 on: October 27, 2013, 03:11:02 AM »

If you parallel two identical transistors the result will usually be to double the collector current. If the transistors are not identical there is no easy way to tell what will happen.
That can't be all that happens though can it?  I would think the hfe would be effected as well as the other things not just the current.

In my circuit 175ma is being drained from the a 1.23V battery and giving 48ma to the LED so pretty much any transistor would work but by adding the transistors together the LED grew brighter and brighter to a point of 5 transistors and #6 would have been so small of an improvement you might as well not add it.

Offline xee2

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Re: Joule Thief behavior question.
« Reply #23 on: October 27, 2013, 05:12:50 AM »
That can't be all that happens though can it?  I would think the hfe would be effected as well as the other things not just the current.

In my circuit 175ma is being drained from the a 1.23V battery and giving 48ma to the LED so pretty much any transistor would work but by adding the transistors together the LED grew brighter and brighter to a point of 5 transistors and #6 would have been so small of an improvement you might as well not add it.


No that is not all that is happening. Transistors can get very complicated if you want to understand everything. Perhaps someone else can do a better job of helping you. I do not seem to be making much progress.




Offline kooler

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Re: Joule Thief behavior question.
« Reply #24 on: October 27, 2013, 06:13:12 AM »
That can't be all that happens though can it?  I would think the hfe would be effected as well as the other things not just the current.

In my circuit 175ma is being drained from the a 1.23V battery and giving 48ma to the LED so pretty much any transistor would work but by adding the transistors together the LED grew brighter and brighter to a point of 5 transistors and #6 would have been so small of an improvement you might as well not add it.

I may not be able to help you either but it took me a little over a year to understand semiconductors when it comes to transistors or mosfets when you look at the datasheets for each transistors you also need to look at the graphs  and the gains cause there all different.. at different frequency .. and voltages   so for a example is if you had 3 different transistors paralleled you may have 3 different frequencys running into you coil.. some transistors act different with different wave forms to the base and may draw more or less current ... also your coil inductance plays a big role in how much current passes and how much goes out.. ..  it also helps to see about how much resistance and capacitance the transistor has..   hope I could help some how..
 
 
robbie

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Re: Joule Thief behavior question.
« Reply #24 on: October 27, 2013, 06:13:12 AM »
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Offline crowclaw

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Re: Joule Thief behavior question.
« Reply #25 on: October 27, 2013, 04:25:36 PM »

I may not be able to help you either but it took me a little over a year to understand semiconductors when it comes to transistors or mosfets when you look at the datasheets for each transistors you also need to look at the graphs  and the gains cause there all different.. at different frequency .. and voltages   so for a example is if you had 3 different transistors paralleled you may have 3 different frequencys running into you coil.. some transistors act different with different wave forms to the base and may draw more or less current ... also your coil inductance plays a big role in how much current passes and how much goes out.. ..  it also helps to see about how much resistance and capacitance the transistor has..   hope I could help some how..
 
 
robbie
 
I can't add anything extra either, both Xee2 and kooler have given good explanations. When youv'e played about with these circuits as much as we have you will come across many strange occurrences which are not easily explained mainly due to the JT's circuit altering parameters as you add extra devices. 

Offline TinselKoala

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Re: Joule Thief behavior question.
« Reply #26 on: November 03, 2013, 05:52:35 AM »
OK.... here's another one.

I always test random transistors in my JT TestBed. This is a basic JT circuit that uses a 13-13 turn toroid, a 1 K base resistor, and has a load bank of 24 white LEDs in a 2S12P arrangement. It has a switch that can put a 70 nF capacitor across (in parallel) with the base resistor. It typically runs on a AAA battery. You all have seen this JT of mine, I'm sure. I even use it as sort of a transistor tester.

It runs on all kinds of NPN transistors, with slight differences or great differences in brightness and the response to switching in the base capacitor. I call the performance with a 2n2222a the "baseline standard".

Now that I have some BC337-25 transistors, I decided to try one in there. It works fine, about like a 2n2222, when it's hooked up properly, and it dims a bit when the base cap is switched in, and is silent.  BUT... when I flip it over, so that C and E connections are swapped, it works with Much Brighter LEDs in both modes and it makes an audible whine. Interesting, yes? Some other transistors will also work "flipped", but by no means all.

I also tried a 2sc4508... and it is _even brighter_ than the BC337, and hardly any dimming with the base cap. But it does not work at all in the "flipped" orientation.

MJE3055: in the standard orientation, very bright, with audible whine. Switching in the base cap causes no change in brightness but a change in pitch of the whine.  Does not work "flipped".

2n2369a: moderate brightness in standard orientation. Switching in the base cap is very interesting. The lights are very dim, but lit, and slowly brighten a bit. No sound. Does not work at all "flipped".

The monster 2sd1877... does not work at all in this JT but I will be trying it in Gnino's dual-incandescent-battery-charge circuit next.

So I'm liking the BC337-25, "flipped", and the 2sc4508. I have not yet scoped these different configurations.





Offline Legalizeshemp420

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Re: Joule Thief behavior question.
« Reply #27 on: November 03, 2013, 09:03:00 AM »
Yes, I stumbled onto the flipped situation with the BC337-25 about 2 weeks ago now.  As I was removing my transistors I noticed it was reversed yet it still worked which is just odd.

Offline ddredar

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Re: Joule Thief behavior question.
« Reply #28 on: November 12, 2013, 09:34:31 AM »
Hi all

I'm a JT noob, and have read through the JT 101 thread, and several others.  All this information is very interesting.  I have not been able to pull myself away from this stuff for hours. :P  I have very basic electronics knowledge from some classes I took in college many years ago.  So I know what this circuit is doing and how, but am amazed at the voltage output.  My first JT worked perfectly the first time.  However. I do have a couple of questions of my own.  hopefully one of you experts can educate me on this.

So my first JT I did with only one LED (3.3v 28ma) using an old AAA battery putting out 1.25v.  I thought the JT was providing close to the 3.3V for the LED.  But then I found a post on how to measure the output using a diode and capacitor.  With the LED in place, I measured the output at 1.8v.  With the LED removed, I was astonished to fine it measure at about 25v.

Now I understand that with the LED in place, it can act as almost a dead short.  Which would account for the difference in my voltage measurements.  But am I really dumping 22+ volts into my single LED?

In addition, I have added up to 80 LEDs in parallel, and they are BRIGHT.  But that would mean I'm drawing 2.24 amps from the circuit. I'm using an NTE293 transistor that's rated at 1A continuous and 1.5A peak.  How is that possible?

Also, can someone tell me if there is a way to measure the amp output of the circuit?  My meter just reads 0.0.  I'm assuming its because it cant keep up with the oscillation speed of the circuit.

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Offline xee2

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Re: Joule Thief behavior question.
« Reply #29 on: November 12, 2013, 04:24:55 PM »
ddredar


The Joule thief only lights the LED for a short time each cycle, most of the time the LED is off. You do not see this because your eyes can not respond fast enough. Thus it is only using power for short periods of time, not continuously. As a result  he average power is very low. An LED is a diode and will always have a fixed forward voltage drop when it is conducting, no matter how much voltage is applied.

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Re: Joule Thief behavior question.
« Reply #29 on: November 12, 2013, 04:24:55 PM »

 

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