Joule Thief 101

[MileHigh]

I think the problem is that any investigation into a JT circuit should be done in two steps.  The first step should be to understand how it operates in normal mode.  The second step is then to explore any possible self-resonant modes.  However, if it is running in some kind of self-resonant mode, then it is not really a JT any more, it's an oscillator.

Then there is another problem.  If you take a JT circuit and play with component values and turn it into an oscillator, then your claims of it running better and longer than a regular JT circuit would have to be proven on the bench.  A transistor operating in the linear region means that the transistor is acting like a resistor and continuously dissipating power.  Likewise the LED is continuously dissipating power.  One would think that the JT has an advantage here because it is a switching circuit where for most of the duty cycle the LED and transistor are not dissipating power.  Presumably oscillator operation demands that the battery still be capable of outputting some minimum voltage under load, whereas the whole idea behind the JT is that it can operate at very low minimum battery voltages, presumably lower than that of the comparable oscillator.  So the proof has to be in the pudding.

Also to be more accurate, most of the time the transistor is switched ON in a JT circuit and it is energizing the main coil and dissipating power.  However during this time the power consumption of the input side of the transistor is quite low.  Then when the transistor switches OFF the main coil dumps its stored energy though the LED to light it up.   So there is definitely near-continuous power dissipation associated with a JT circuit.

I always thought an interesting comparison would be between a CMOS 555 timer circuit with very carefully selected components lighting an LED and a JT circuit.  The CMOS 555 timer circuit can't operate at the very low voltages of a JT circuit but it probably would have a lower power overhead to keep it operating compared to a JT circuit.  You wonder which circuit would give you better overall performance in the long run.

[Pirate88179]

I think the problem is that any investigation into a JT circuit should be done in two steps.  The first step should be to understand how it operates in normal mode.  The second step is then to explore any possible self-resonant modes.  However, if it is running in some kind of self-resonant mode, then it is not really a JT any more, it's an oscillator.

Then there is another problem.  If you take a JT circuit and play with component values and turn it into an oscillator, then your claims of it running better and longer than a regular JT circuit would have to be proven on the bench.  A transistor operating in the linear region means that the transistor is acting like a resistor and continuously dissipating power.  Likewise the LED is continuously dissipating power.  One would think that the JT has an advantage here because it is a switching circuit where for most of the duty cycle the LED and transistor are not dissipating power.  Presumably oscillator operation demands that the battery still be capable of outputting some minimum voltage under load, whereas the whole idea behind the JT is that it can operate at very low minimum battery voltages, presumably lower than that of the comparable oscillator.  So the proof has to be in the pudding.

Also to be more accurate, most of the time the transistor is switched ON in a JT circuit and it is energizing the main coil and dissipating power.  However during this time the power consumption of the input side of the transistor is quite low.  Then when the transistor switches OFF the main coil dumps its stored energy though the LED to light it up.   So there is definitely near-continuous power dissipation associated with a JT circuit.

I always thought an interesting comparison would be between a CMOS 555 timer circuit with very carefully selected components lighting an LED and a JT circuit.  The CMOS 555 timer circuit can't operate at the very low voltages of a JT circuit but it probably would have a lower power overhead to keep it operating compared to a JT circuit.  You wonder which circuit would give you better overall performance in the long run.

I think a decent JT circuit would win this competition with the 555.  ONLY because it takes some energy to run the 555...and that is the only reason.
There is no magic to the JT BUT, we who experimented with them in the early days were told that conventional electronic theory explained them.  This, of course, is true.  My complaint was, then, why were they not being used in our electronics stuff?  Shortly thereafter, we saw those led garden lights, as well as many other items that actually were using a JT type circuit to its advantages.  Now I am happy.  Now we have chips that do this with minimum input and they are being used in everyday devices.  This answers my question from back then.

Still, no magic, no free lunch, no output more than input...just a good way to use most of the energy in a battery and get more light from leds than you otherwise could.

Damn MH, you and I used to argue about this all of the time and now I have to admit that you were right.  There is no "magic".
Son of a bitch, ha ha.

Bill

I still have not seen anyone else light 400 leds from a 'dead" AA battery like I have done.  No magic there either, just the right circuit for the desired outcome.

[TinselKoala]

http://www.youtube.com/watch?v=wU5x8T2UkuI

[sm0ky2]

Also to be more accurate, most of the time the transistor is switched ON in a JT circuit and it is energizing the main coil and dissipating power. 

You are forgetting the reluctance factor of the inductor in self-resonance.

[MileHigh]

You are forgetting the reluctance factor of the inductor in self-resonance.

I am not sure of what you mean by that.  The more information the better when discussing electronics.