Joule Thief 101

[hoptoad]

The answer to your question is that the turns ratio in the Joule Thief transformer allows the feedback coil that drives the base resistor to amplify the voltage that is across the main coil that drives the LED.  In your recent setup you used an 8:1 turns ration such that the low battery voltage can be multiplied by eight so that you can still switch on the transistor.

Now that your question has been answered, the floor is yours.

Please explain to the readers exactly how a Joule Thief works.

The problem with your explanation for the specific alternative circuit shown by Tinman, is that , at turn on, no current can flow through the collector junction until the base has been turned on, and by your explanation the base cannot turn on, because no current is induced into the coil that feeds, because no current can flow through the collector coil while the collector junction is open, until the base turns on.

There is no direct source voltage coupling to trigger the base because there is no direct DC connection to the base, only an inductive connection which requires current through the collector coil. A severe case of chicken and egg, unless their is something else in the circuit momentarily allowing the base to initially trigger. That initial trigger mechanism lies in the tiny capacitance in the transistor junction.


Cheers

[MileHigh]

TK:

The 3055 transistor is "kicked" into oscillation in the first place even though the voltage supplied seems too low, by ... wait for it... .stray capacitance. Once it starts oscillating, then it's getting plenty of base voltage because of the 8:1 transformer. Again, this effect may be easier to see with other transistors, which will need more stray capacitance to start oscillating (like by touching the Collector or Emitter lead with a finger or a small cap lead.) And all 2n3055s are not created equal... this is an extremely common transistor to be "faked" by unscrupulous Chinese sources. Performance varies wildly.

Nope, see my previous posting.  The transistor is initially "kicked" on by pure transformer action.  There is a regenerative cycle (positive feedback) to turn the transistor ON, and a regenerative cycle (positive feedback) to turn the transistor OFF.

Brad, the floor is yours.

MileHigh

[tinman]

Brad:

For the sake of completeness, I will respond to this:

Well you missed it in the video:  https://www.youtube.com/watch?v=0GVLnyTdqkg





Now Brad, the floor is yours.

Please explain to the readers exactly how a Joule Thief works.

MileHigh

Starting at 2:45 he says, "An interesting feedback happens during the time the red coil is creating a magnetic field.  That changing magnetic field induces a voltage in the green coil.  What's good is that the voltage is in the right direction to add to the voltage already being provided by the battery."

Once again MH--he is referring to the cascade effect taking place once the transistor starts to conduct. The driven coil can only amplify the base coil once the transistor start to conduct. The battery send a current through the green coil and resistor to the base of the transistor. Before the transistor can switch on,the voltage being supplied must be the minimum required by the transistor. Once the transistor starts to conduct,current starts to flow through the red coil. This increase the current and voltage flowing through the green coil,and so switches the transistor on even harder. No problem at all with this transformer effect MH,but how dose the transistor start to conduct once the battery voltage falls below that of what is required by the transistor to switch on. This is the part you are missing,and how you are doing that is beyond me. I dont see much skill on your behalf MH playing a role here.

The sudden voltage drop at TP2 will be amplified by the turns ratio and become a sudden voltage increase at TP1 switching the transistor ON.

This alone MH shows us that your supplied information and video's are wrong,and is what i have been trying to tell you for the last two pages on this thread.-->the battery is not solely responsible for switching on the transistor-->and only now are you admitting that i was correct.


Brad

[MileHigh]

Brad,

At this point the transistor switching ON has been explained.  So forget about the battery voltage issue and please explain to the readers exactly how a regular Joule Thief circuit works.

Now more stalling, no more conditions.  If you continue with that it's going to look like you are stalling and trying to avoid the request.

It's time for you to explain the big picture of exactly how a Joule Thief works.  The floor is yours.

MileHigh

[tinman]

TK:

Nope, see my previous posting.  The transistor is initially "kicked" on by pure transformer action.  There is a regenerative cycle (positive feedback) to turn the transistor ON, and a regenerative cycle (positive feedback) to turn the transistor OFF.

Brad, the floor is yours.

MileHigh

Dont pull that one MH.
It only took you !how long! to work out that your provided explanations and videos were incorrect,and that i was correct when i said(countless times) that the battery cannot be what is switching on the transistor once the battery voltage falls below that of the required voltage to turn on the transistor.

Great to see you admitting to being incorrect.


Brad