Joule Thief 101

[sm0ky2]

No in fact the resistance is not that critical in the RLC resonator because it is an active circuit where an external power source keeps the resonator resonating regardless of the inherent resistance in the resonating components.  There is no special balance with regards to the resistance in what is essentially an LC resonator.

MileHigh

Bullshit.

When you alter the resistance in a RLC circuit, you CHANGE the resonant frequency.
This is a self-defined term.
Resistance is an important factor in the equations.


[go ahead and do a search on my name, and see how many times I declare bullshit on someone.......]

[MileHigh]

Bullshit.

When you alter the resistance in a RLC circuit, you CHANGE the resonant frequency.
This is a self-defined term.
Resistance is an important factor in the equations.

The most complete response I can give you to that is yes and no.

Yes in the sense that an electronics expert, the late MarkE, stated that the resistance can affect the self-resonant frequency and I was quite surprised.  I don't remember the details but he clearly stated that the value of the resistance can marginally affect the self-resonant frequency and I am quite certain that this effect came into play for larger resistances.

No in the sense that we are talking about a LC circuit where the resistance is typically very low and will not have any real effect on the self-resonant frequency as defined by "omega = 1/sqrt(LC)."  That is a very familiar formula that most people are aware of.

Here is the Google search link for, "resonance of an rlc circuit:"

https://www.google.ca/?gws_rd=ssl#q=resonance+of+an+rlc+circuit

In the first six links you will see the resonance frequency defined for both serial and parallel RLC circuits as "omega = 1/sqrt(LC)" even when they clearly show resistances in the RLC circuits being discussed.  In other words they are ignoring the value of the resistance because in the majority of cases it can be ignored.

So, we are coming back to reality:  For nearly all practical intents and purposes, the resonant frequency of an RLC circuit is a function of the inductance and capacitance only.  When the only resistances in the circuit are associated with the inductor and capacitor themselves and they are quite low, then it is only a function of the inductance and capacitance.  That is a reasonable answer that covers all the bases.

Resistance is an important factor in the equations.

Really?  Then the floor is yours.  Please go ahead and explain exactly what you mean in detail.  What are the equations?

MileHigh

[tinman]

Really?  Take a look at the attached diagram.  This is an intentionally simplified explanation showing the two principal processes that determine the operating frequency of the Joule Thief that ignores the battery voltage and the positive feedback transistor switching process.

There used to be a good explanation on the operating frequency of a Joule Thief that went into quite a bit of detail on Wikipedia but apparently it was disputed because it has since been removed.  Here is a link that discusses the inductance being a prime factor with some information from the older version of the now-modified Wikipedia page:

http://www.elperfecto.com/2011/01/22/toroidal-inductors-number-of-turns-affects-joule-thief/

Feel free to make your case for a Joule Thief being an RLC circuit.

MileHigh

As soon as you have two conducting wires wound around a core next to each other,then you also have a C value. This is more so pronounced due to the fact that the current through these two conducting wires flows in opposite directions at the same time with the JT circuit. There is also the fact that the transistor it self has Capacitance,and this C value alone also plays a factor in the operating frequency of the circuit. I have shown you before with my cool joule circuit that the Miller effect alone can send the circuit into oscillation without any inductive coupling at all between the two coil's. So to say that the JT has no C value is wrong-very wrong.


Brad

[tinman]

The most complete response I can give you to that is yes and no.



No in the sense that we are talking about a LC circuit where the resistance is typically very low and will not have any real effect on the self-resonant frequency as defined by "omega = 1/sqrt(LC)."  That is a very familiar formula that most people are aware of.

Here is the Google search link for, "resonance of an rlc circuit:"

https://www.google.ca/?gws_rd=ssl#q=resonance+of+an+rlc+circuit

In the first six links you will see the resonance frequency defined for both serial and parallel RLC circuits as "omega = 1/sqrt(LC)" even when they clearly show resistances in the RLC circuits being discussed.  In other words they are ignoring the value of the resistance because in the majority of cases it can be ignored.

So, we are coming back to reality:  For nearly all practical intents and purposes, the resonant frequency of an RLC circuit is a function of the inductance and capacitance only.  When the only resistances in the circuit are associated with the inductor and capacitor themselves and they are quite low, then it is only a function of the inductance and capacitance.  That is a reasonable answer that covers all the bases.

Really?  Then the floor is yours.  Please go ahead and explain exactly what you mean in detail.  What are the equations?

MileHigh

Yes in the sense that an electronics expert, the late MarkE, stated that the resistance can affect the self-resonant frequency and I was quite surprised.  I don't remember the details but he clearly stated that the value of the resistance can marginally affect the self-resonant frequency and I am quite certain that this effect came into play for larger resistances.

MarkE was indeed a great man,but even he had room to learn. Im sure you remember the thread MH (i cant),where i presented my cool joule circuit,and told MarkE that it operated due to the miller capacitance effect. At first he refused to believe that to be true, but then later on came back and confirmed that it was indeed the miller effect that was causing the circuit to oscillate.

There are those that dwell on these forum's that dont have much to say,but there knowledge far exceeds that of those here that often make a stand on what they believe to be true. Vortex1 is one of those extremely well versed in EE,and it's due to experience/bench time. He is also the one that worked out how my cool joule circuit was operating--i had no idea as to how or why it was working at the time,but now-because of Vortex1,i know exactly how it works.

The cool joule circuit operation was found quite by accident. I had one coil on top of the other,and as we would expect,the circuit ran quit fine. But when i went to reach for the soldering iron,i knocked the top coil of the bottom one-but the circuit still kept on oscillating . So i moved the top coil (base/emitter-trigger coil) further away from the drive coil,and still it kept oscillating. After a distance of over 1 meter between the two coils,we can eliminate the fact that any inductive coupling between the two coils was taking place,and so i presented this mystery circuit as the cool joule circuit,as i thought it was pretty cool that it operated without any inductive coupling between the two coils.

Anyway,i think you would be wise to listen to what Smokey has to say,as the JT definitely is an RLC circuit.


Brad

[MileHigh]

As soon as you have two conducting wires wound around a core next to each other,then you also have a C value. This is more so pronounced due to the fact that the current through these two conducting wires flows in opposite directions at the same time with the JT circuit. There is also the fact that the transistor it self has Capacitance,and this C value alone also plays a factor in the operating frequency of the circuit. I have shown you before with my cool joule circuit that the Miller effect alone can send the circuit into oscillation without any inductive coupling at all between the two coil's. So to say that the JT has no C value is wrong-very wrong.

Brad

You are not making a case for a Joule Thief being an RLC circuit.  What that is supposed to mean is that the operating frequency is based on an LC resonant tank frequency and you can show how a Joule Thief is an actual RLC circuit.

What you are saying is that there is stray capacitance in the circuit.  Likewise there is stray inductance in the circuit.  In fact, for any circuit there is stray capacitance and stray inductance.  Sometimes it is significant, but most of the time it is insignificant at the normal operating frequency of the circuit.  Part of learning about electronics is to recognize when something is significant or not.

So I will ask you again, is a Joule Thief an RLC circuit or not?  If you say it is and the operating frequency is determined by an LC resonator, then please show the circuit, show where the resonator is, and describe now it operates.  Your discussion about stray capacitance above does not back up your claim.

MileHigh