Joule Thief 101

[MileHigh]

Back in the old JT topic area, we learned early on that using a base vr was beneficial in several ways.  Yes, it could help maintain the brightness of the led as the battery voltage dropped but, as the battery "died" down to around .4 volts, this would cause the frequency of the circuit, which had previously been high enough that the human eye could not see the on/off switching of the led, to dip low enough that the led would appear to flash on/off.  A little tweak of the base vr and...Bob's your Uncle...the led would now once again appear to be on constantly.

So, I do know from experience that it is useful to use a vr on the base rather than choosing a fixed resistor that is a poor compromise over the entire range of the battery voltage.  There is no single fixed resistance that can give you the longevity of non-flashing, bright light from the led across this range.

Just my 2 cents from having built many of these circuits over the years.  Once you get to where the output from your AA battery JT is over 300 volts, other things become more important to consider as well. (Like not getting zapped!)  As I mentioned early on here, it all depends upon your goal...brightest light possible or longevity of the light from your "dead" battery.

Bill

Firstly, as you have previously stated, the majority of your group's earlier explorations with the Joule Thief circuit were anecdotal observations.  You never seriously analyzed scope traces to figure out exactly what was happening with your Joule Thief replications.

Secondly, let's say you can split the battery voltage response into two ranges.  Let's say that the normal battery voltage range is 1.5 volts to 350 millivolts. In this range the Joule Thief will work just fine with a fixed base resistor and switch properly.  It's in this normal range where if you change the value of the base resistor then the transistor will keep switching normally and the Joule Thief LED will look pretty much the same.  Naturally, common sense is telling you that you can change the value of the base resistor within certain reasonable limits, and if you exceed those reasonable limits in either direction then the Joule Thief will cease to operate normally.

Then let's say that there is another voltage range, and that voltage range is between 350 and 200 millivolts.  In this range the Joule Thief does not act as a normal switching device and all bets are off.  Playing with the base resistor will do something including increasing the brightness of the LED.  But I will stress again that the Joule Thief is not acting like a standard switching device at this very low voltage range.

Needless to say, all of my discussion in my previous posting applies to a standard Joule Thief operating voltage range of somewhere between 1.5 volts and say 350 millivolts.

MileHigh

[tinman]

Firstly, as you have previously stated, the majority of your group's earlier explorations with the Joule Thief circuit were anecdotal observations.  You never seriously analyzed scope traces to figure out exactly what was happening with your Joule Thief replications.

Secondly, let's say you can split the battery voltage response into two ranges.  Let's say that the normal battery voltage range is 1.5 volts to 350 millivolts. In this range the Joule Thief will work just fine with a fixed base resistor and switch properly.  It's in this normal range where if you change the value of the base resistor then the transistor will keep switching normally and the Joule Thief LED will look pretty much the same.  Naturally, common sense is telling you that you can change the value of the base resistor within certain reasonable limits, and if you exceed those reasonable limits in either direction then the Joule Thief will cease to operate normally.

Then let's say that there is another voltage range, and that voltage range is between 350 and 200 millivolts.  In this range the Joule Thief does not act as a normal switching device and all bets are off.  Playing with the base resistor will do something including increasing the brightness of the LED.  But I will stress again that the Joule Thief is not acting like a standard switching device at this very low voltage range.

Needless to say, all of my discussion in my previous posting applies to a standard Joule Thief operating voltage range of somewhere between 1.5 volts and say 350 millivolts.

MileHigh

Ah yes-some back peddling taking place here, along with more bullshit.


Brad

[MileHigh]

Brad:

Do you need an answer to understand the need for a variable base resistor MH?-or will your batteries simply remain at the rated voltage of 1.5 volt's?.
That was a bit of a silly statement by your self MH.

One more time, the answer to your statement above is a resounding NO!  I have made my case and in exploring this issue in greater detail, surprise surprise, it was revealed that you have a ton of misunderstandings and misconceptions about how a standard Joule Thief circuit operates. 

If you want to be in a better position to discuss a hypothetical "resonant Joule Thief" with your peers, I would suggest to you that you would want to understand how a regular Joule Thief works first.  That way you can build up your knowledge on a solid foundation.  I gave you a TON of information about a Joule Thief and that should be a good launching pad for getting it all clear for your own understanding and benefit.  Is every single thing I said going to be 100% right?  Of course not but the vast vast majority of what I said is correct.

If I had a bench setup and was truly motivated to dissect and analyze a Joule Thief then you would be shocked at the amount of good data that I could generate.

MileHigh

[MileHigh]

Ah yes-some back peddling taking place here, along with more bullshit.

Brad

No back pedaling and thanks to me you now understand a Joule Thief better than you have ever understood one before in your life.

[EMJunkie]

This is a very interesting resonance Experiment: Oscillating Neural Network Demonstration


   Chris Sykes
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