Joule Thief 101

[Pirate88179]

Well, like I stated before, the base resistor in a Joule Thief is not supposed to be varied at all.  Rather, it is supposed to be based on the EMF coming from the feedback coil and the amount of base current required to switch the transistor hard ON, which is based on the maximum current that will flow through the main coil.  The real way to change the way the Joule Thief operates is to play with the size of the core, and the number of turns in the primary and the secondary.  The value of the base resistor "falls out" from those and related parameters.  Any astute electronics experimenter should be able to show exactly how the value of the base resistor is determined for a given standard Joule Thief configuration.

For the issue of the LEDs in series, I am close enough.  If you build a Joule Thief and you are driving a single LED, and you like the illumination level, and then you try 10 LEDs in series and get the same illumination level in each individual LED, then that is telling you that you can reduce the power going into the single LED by a factor of 10.  So if you are a keener and you are up to it, you can challenge yourself to figure out how to do that.

MileHigh

But, as we all found out early on, as the voltage in the battery drops, everything that you had balanced perfectly in the JT circuit starts to drift away...so, if you tuned the base resistor for the brightest light at a battery voltage of 1 volt, as the battery drains down to say, .7 volts, your led will no longer be as bright so, you dial in the base resistance with your vr and, now you are back to having a bright led.  You can do this down to where the battery is too low to switch the transistor on.  This gives you the maximum light you are ever going to get from that battery using those components.


If you built the optimum JT circuit using the perfect windings and components, and I had one of my "regular" JT circuits and we both started out with a battery of 1 volt, I'll bet that when we got to .7 volts or so, I could make my led much brighter than yours by a simple tune of the base resistor...your circuit was perfect for 1 volt, .7 volts and below...not so much.


Does this make any sense?


We were seeing out nice little circuits drift all over the place as the battery was depleted so being able to adjust the base resistance really helped.  Also, adding a decent size cap in series with the led helped a lot too.


Now, with the circuit you have proposed, having "constant" power to the coil would nearly eliminate this issue, or at least make it where you didn't even notice any difference in the led operation as that battery would not be allowed to go down to say .4 volts or so.


I guess what I am saying is that we learned, or think we learned, that the "best" set-up for a simple JT was a moving target that you could only "hit" in a certain range unless you could adjust your circuit along the way as the battery drained.


Bill


PS  I look forward to seeing what Lidmotor does with your circuit.

[MileHigh]

You are so funny some times MH.
Throughout this thread,you have been stuck on one circuit that you deem to be !the! JT circuit.
Now your posting different circuit's,and telling everyone to !think outside the bloody box! lol

Fact is MH,most of us here have been doing that all along,while !you! where stuck in the box.

Brad.

Well you are wrong again Brad.  A Joule Thief circuit is a blocking oscillator, and the heart of a blocking oscillator is based on energizing an inductor and then "blocking" the the inductor discharge.  This is done using digital switching so that the discharge gets rerouted through an LED.  The circuit that I posted has the fundamental trait of having an inductor energized and then the discharge goes through an LED and it also uses digital switching.  It will not outperform a Joule Thief with respect to LED illumination time or how low a battery voltage it can work at, but it does have an architecture based around the fundamental concepts of energizing and discharging an inductor, and digital switching.  That's in contrast to some kind of feedback oscillator that can also drain a battery but it has nothing to do with a blocking oscillator, energizing and then discharging an inductor, or digital switching.

You talk about being "stuck in the box," take a look at the attached image.  I am willing to bet you that the issue of the potential inefficiencies in the decaying voltage/current waveform through the LED when driven by a standard Joule Thief have never been discussed by a lot of people on the forums.  It's possible that I am the first person to ever raise this issue.  Yet many experimenters, probably you included, have stared at this waveform blankly and never even mentioned it.  Talk about being "stuck in a box" when something is staring you in the face.

So for you and others who know who they are, don't give me this bullshit that I am "stuck in a box" or "I don't do experiments" or, "I only know what is in books."  I have posted several times that I estimated once that I have about 3500 hours of bench work under my belt and I assume that you are aware of that.  The whining about me is just a cop-out.

The simple truth is that the kind of basic electronics stuff that you do around here, I haven't done in more than 30 years, and yet I can still whip most of your asses with one hand tied behind my back.  Even now, I could literally spin circles around you on a bench and I don't even really like electronics.  And to put everything in a proper context, people like Verpies and Picowatt and Poynt99 can easily spin circles around me on a bench.  I am no hard-core low-level-details electronics or electromagnetics guy at all, I don't even like it particularly and I was glad that I walked away from working on a bench.  I threw all my TTL and CMOS chips and components and power supplies away more than 20 years ago.

So stop your "you only know books" or "you're stuck in a box" or "you don't do real experiments" nonsense.  It's just used as a fake talking point "weapon" or as a diversionary tactic when things aren't going the way you thought they were supposed to be going or you or others want to try to hurt my credibility because I am talking straight.

This would be a typical example:  "Show me how you started a car with a dead battery."  Response:  "You don't do experiments."  It's pure nonsense.

MileHigh

[MileHigh]

Bill:

In the whole discussion below I am talking about a normally operating Joule Thief.  I am not talking about what happens at very low voltages where the Joule Thief goes into some kind of high frequency oscillation mode.

But, as we all found out early on, as the voltage in the battery drops, everything that you had balanced perfectly in the JT circuit starts to drift away...so, if you tuned the base resistor for the brightest light at a battery voltage of 1 volt, as the battery drains down to say, .7 volts, your led will no longer be as bright so, you dial in the base resistance with your vr and, now you are back to having a bright led.  You can do this down to where the battery is too low to switch the transistor on.  This gives you the maximum light you are ever going to get from that battery using those components.


If you built the optimum JT circuit using the perfect windings and components, and I had one of my "regular" JT circuits and we both started out with a battery of 1 volt, I'll bet that when we got to .7 volts or so, I could make my led much brighter than yours by a simple tune of the base resistor...your circuit was perfect for 1 volt, .7 volts and below...not so much.


Does this make any sense?

It makes perfect sense and there are two schools of thought here and a fundamental concept.

The fundamental concept is this:  The base resistor is supposed to be a value that ensures that the digital switching operates normally.  There may be a "best" base resistor value when the battery voltage is 1.5 volts and a "best" base resistor value when the battery is 0.4 volts.  In both cases you have to have proper digital switching taking place and the real variable at play is how much power you burn off in the base resistor and what value helps you minimize this waste power.

However, suppose the battery is 1.5 volts and you get a very bright LED at say a low base resistor value.  The Joule Thief may not be switching properly here, the whole mechanism is out of whack and it's also drawing a lot of battery current.  You don't want to do that, you don't want to throw the whole circuit out of whack.

The first school of thought goes like this:  Design a Joule Thief for mass production with a fixed base resistor.  In that case you pick the right "compromise" base resistor value that will work well for a battery voltage range from 0.3 to 1.5 volts.  The assumption is that the switching is always normal during the full battery voltage range.  Yes, the LED gets dimmer as the battery voltage gets low, that's life.

The second school of thought is that you might indeed get better illumination performance if the base resistor is adjusted at low battery voltage.  In theory you would be getting better timing where you energize the coil longer before the switching occurs.  The caveat is that the Joule Thief circuit is still switching normally.  I am purely speculating here though, and some testing would have to be done to confirm this.  Can changing the base resistor value at low voltages change the timing so that the LED gets brighter but the circuit is still switching properly, or, are you getting a brighter LED because the whole circuit is out of whack and sucking power like crazy?  I don't know the answer to this.

The way I think is the from the first school of thought.  You can indeed make a wise choice for the value of the base resistor such that the Joule Thief switches normally during the full battery voltage range of 0.3 to 1.5 volts.  The fact that the LED gets dimmer as the battery voltage drops is fully expected and it is just a fact of life for a simple Joule Thief circuit.

MileHigh

[tinman]

Well you are wrong again Brad.  A Joule Thief circuit is a blocking oscillator, and the heart of a blocking oscillator is based on energizing an inductor and then "blocking" the the inductor discharge.  This is done using digital switching so that the discharge gets rerouted through an LED.  The circuit that I posted has the fundamental trait of having an inductor energized and then the discharge goes through an LED and it also uses digital switching.  It will not outperform a Joule Thief with respect to LED illumination time or how low a battery voltage it can work at, but it does have an architecture based around the fundamental concepts of energizing and discharging an inductor, and digital switching.  That's in contrast to some kind of feedback oscillator that can also drain a battery but it has nothing to do with a blocking oscillator, energizing and then discharging an inductor, or digital switching.

You talk about being "stuck in the box," take a look at the attached image.  I am willing to bet you that the issue of the potential inefficiencies in the decaying voltage/current waveform through the LED when driven by a standard Joule Thief have never been discussed by a lot of people on the forums.  It's possible that I am the first person to ever raise this issue.  Yet many experimenters, probably you included, have stared at this waveform blankly and never even mentioned it.  Talk about being "stuck in a box" when something is staring you in the face.

So for you and others who know who they are, don't give me this bullshit that I am "stuck in a box" or "I don't do experiments" or, "I only know what is in books."  I have posted several times that I estimated once that I have about 3500 hours of bench work under my belt and I assume that you are aware of that.  The whining about me is just a cop-out.

The simple truth is that the kind of basic electronics stuff that you do around here, I haven't done in more than 30 years, and yet I can still whip most of your asses with one hand tied behind my back.  Even now, I could literally spin circles around you on a bench and I don't even really like electronics.  And to put everything in a proper context, people like Verpies and Picowatt and Poynt99 can easily spin circles around me on a bench.  I am no hard-core low-level-details electronics or electromagnetics guy at all, I don't even like it particularly and I was glad that I walked away from working on a bench.  I threw all my TTL and CMOS chips and components and power supplies away more than 20 years ago.

So stop your "you only know books" or "you're stuck in a box" or "you don't do real experiments" nonsense.  It's just used as a fake talking point "weapon" or as a diversionary tactic when things aren't going the way you thought they were supposed to be going or you or others want to try to hurt my credibility because I am talking straight.

This would be a typical example:  "Show me how you started a car with a dead battery."  Response:  "You don't do experiments."  It's pure nonsense.

MileHigh

And yet the diamond needle dosnt destroy the soft vinyl record like science says it should.
How is it that the hardest substance on earth dosnt just cut straight through those smale plastic bumps in the vinyl tracks?. Over and over you can play your record's without damage from a material that cuts the hardest of steels.--?one for the books MH.

So many things that good old science has the answers for,and yet never produced. 9 times out of 10,it comes from people that are no ruled by book's. For example-the plane. We all know that it is scientifically possible ,but the science guru's never came up with the plane--powered flight. It cam from a couple of brothers that owned a bicycle shop,that said--yes we can. They were the guys that did the job through experiments,and trial and error--not from book's.
In fact,most great discoveries came from trial and error,and the science to explain it came after.
The good old bumble bee was flying long before science worked out how it could do it--this was after some decided that it was an aerodynamic impossibility-now they know better.

There are many thing's left that science and books are yet to explain,and many of those discoveries will be made by those not ruled by book's,or some one elses science and law's.
Funny thing about scientific laws MH,is that they really are not laws at all--there a !best guess! based around only what we have observed so far. These are man's law's im talking about,not those set by nature it self.

If we are to stick with the book's MH,then there is no stone left unturned. But we here,and on other forums,choose to turn over the stones that are still face down. In the next ten years,i feel that you will see first hand how obsolete your books are,and the new discoveries will once again,be made by those that follow no such rules.


Brad

[tinman]

 author=MileHigh link=topic=8341.msg475491#msg475491 date=1456418556]
Bill:

The way I think is the from the first school of thought.  You can indeed make a wise choice for the value of the base resistor such that the Joule Thief switches normally during the full battery voltage range of 0.3 to 1.5 volts.  The fact that the LED gets dimmer as the battery voltage drops is fully expected and it is just a fact of life for a simple Joule Thief circuit.

MileHigh

So show us your smart's MH--design a simple circuit that lowers the base resistance as the voltage in the battery drop's. You pride your self on bench time and knowledge,so show us some of that smarts. You draw up the circuit,and i'll spend the time and money putting it together,and testing it. I'll post the results and video's here.


Brad