Joule Thief

[TheNOP]

i totally agree with xee2

my resume would be this :

Increasing the base resistor reduces the voltage reaching the transistor base, giving the transistor less time to conduct currents.
because the base coil reverse voltage oppose the voltage at the base more rapidly.

decreasing the base resistor augment the voltage reaching the transistor base, giving the transistor more time to conduct currents
because the base coil reverse voltage has to be greater in order to oppose the base voltage.

this is one of the reasons why i suggested less turns on the base coil.

[jadaro2600]

THEORY OF JOULE THIEF FREQUENCY VS BASE RESISTOR VALUE  by xee2

Increasing the base resistor value reduces the base current. This current flows through the base coil. When the resistor value is high the current is very small. When the base resistor value is low the base current is larger.

When the transistor turns on the current increases slowly in the collector coil (as a result of the inductance of the coil). The changing current in the collector coil induces a current in the base coil that opposes the base current that is already flowing there due to the base resistor. The larger the current change in the collector coil is, the larger the opposing induced current in the base coil will be.

When the transistor turns on the collector coil current builds up very slowly. At some point the increasing current in the collector coil will be large enough that the opposing induced current in the base  coil will be large enough to cancel the current due to the base resistor and then the transistor will turn off. If the base resistor value is small, then the base current will be large and it will take longer for the opposing base coil current to increases to a large enough value to be big enough to cancel the base current flowing due to the resistor. Thus it takes longer for the transistor to be turned back off when the base current is large (small base resistor value) than when the base current is small (large base resistor value).

The frequency is just how often the transistor is turned on and off. With a small base resistor value (large base current) this happens less often during each second due to the longer time it takes the transistor to be turned back off. Thus increasing base resistor value increases frequency and decreasing base resistor value decreases frequency.

So frequency depends on the base resistor value and the collector coil inductance.

I like your explanation.  And TheNOP's as well.

Please then tell me what causes the transistor to heat up?

Wouldn't only partially opening the transistor CE path create resistance in the transistor and thus heat buildup?  Or am I thinking of a transistor acting more like a resistor and/or relay?

[Pirate88179]

Jeanna:

Excellent tests and results.  Thank you for doing them and posting them.  I also want to thank our electronics guys (I know there are more of you out there) TheNOP and Xee2 for taking the time to explain things to us that we "should" have already learned.  The thing I believe is very encouraging is that, the more we as a group study and experiment with the JT, the more we find that it isn't "exactly" what was once thought.  That is good enough for me. I never claimed, nor do I do so now, that this is any type of OU.  I think this is but one of several devices that can't be totally fit into one simple definition.  I believe Tesla, and then Stubblefield, knew this as well.  As our EE guys have said all along..."no magic" and I believe they are correct.  But, as long as we can continue to make this circuit do things that are not now currently being done, then I am happy.

Don't get me wrong here.  I confess to not understanding enough about "conventional" electronics to argue with anyone.  That is not my point.  OK, here is what I am trying to say.  Even though this may be well known and old school, it is not being used in ways it could be and that is what I think we are doing best.

I just read about the Honda Insight produced in 2000. (They stopped production but these cars are sought after)  This vehicle made over 75 mpg!!!!!  Now Honda has began making it again all these years later, and it gets like 50 mpg!!!

I love finding new uses for old things.

Thanks to everyone on here for their participation and contributions.  I have been silent for a while but have been here reading and learning.  Keep it up.  I can't think of anything more fun than this.

Bill

[Pirate88179]

I like your explanation.  And TheNOP's as well.

Please then tell me what causes the transistor to heat up?

Wouldn't only partially opening the transistor CE path create resistance in the transistor and thus heat buildup?  Or am I thinking of a transistor acting more like a resistor and/or relay?

Jadaro:

My understanding, and others that know more can correct me, is that a transistor is either off or on.  No in between.  there is "supposed" to be nothing bleeding through partially either before it switches on, or off.  That is why it is one beautiful invention. (Thank you Mr. Shockley)  Now maybe, given manufacturing tolerances, there is some partial seepage. If so, it would be news to me but then, I am getting used to learning from you folks on here.

Bill

[TheNOP]

My understanding, and others that know more can correct me, is that a transistor is either off or on.  No in between.  there is "supposed" to be nothing bleeding through partially either before it switches on, or off.  That is why it is one beautiful invention. (Thank you Mr. Shockley)  Now maybe, given manufacturing tolerances, there is some partial seepage. If so, it would be news to me but then, I am getting used to learning from you folks on here.

not exactly true.
transistor can be half on, if it wasn't able to be, you could not use it to amplify a signal.
the voltage between the base and emitter of the transistor determine the currents that will pass between the collector and the emitter.

it is true that, in the case of the jt, we are using the transistor as a switch tho.

but nothing is perfect, our transistor switch is not perfectly on or off.
that is why all transistors have a frequency limits, time is needed for them to fully conduct.
some transistor are close to be as fast as a mechanical switch tho, in regard to the time needed before conducting.
they are call fast switching transistors


@jadaro2600
the currents passing trough the transistor create the heat, more current, more heat.
all transistors have internal resistance, just like any semiconductors do.