Joule Thief

[Farmhand]

The way I see it a circuit that is provided a signal from a microprocessor to switch the primary, without any feedback for "auto resonance" is not a joule thief. I might be wrong. But to me it would just be a switched transformer. More akin to a solid state Tesla coil if air cored.

I have used different IC's and micros to provide the signal to switch small Tesla coils, they are no Joule thieves. To get resonance the frequency must be varied slightly at times and a load means it or the L/C needs to be changed to keep resonance. For without the resonance the power is much less. Personally I would have thought a mosfet would be the best switch for such a setup.

It would go like this, Microprocessor - mosfet driver - mosfet as a low side switch.

Cheers

[MileHigh]

Farmhand:

It's still arguably a Joule Thief in the sense that it's still sucking the maximum amount of juice out of the main battery.  So in that sense it's still "stealing" Joules so in namesake it still has the "soul" of a Joule Thief.   The system performs the same type of function as a standard Joule Thief.

We had this discussion about resonance and Joule Thieves with TK several months ago.  The standard Joule Thief has an "operating frequency."  That's distinct and different from resonance.  The output power is determined by how long the main coil is energized and the frequency of the pulse train that switches on the transistor and energizes the inductor.

It may sound like resonance but it isn't.  Resonance typically implies some kind of LC oscillator or some sort of tank oscillation where the energy goes back and forth between an L and a C.  In a JT timing is determined more by a resistance and an inductance interacting.  In some ways the oscillating of the JT is similar to how a 555's frequency is determined by your choice of R and C for the timing components.

Perhaps another way of stating it is to say that resonance implies some frequency but an operating frequency does not necessarily imply some form of resonance.

Yes, you can say that they oscillator itself inside the Joule Thief is "resonating" in a generic or lay person's sense, but when you discuss it using technical terms it would be inappropriate to say that it is in resonance.  Operating frequency is the best term that I can think up.  Note there is no "resonant spot" to hit for the main coil of the JT to get the maximum power output.  The power output will be a function of the operating frequency and the transistor on time alone.

MileHigh

[Farmhand]

Well I know from experience that when I excite a transformer with a pulse train signal and switch it with a mosfet, I get the most power out when the secondary is tuned to resonance, just because most joule thieves might not work at resonance or a harmonic doesn't mean they would not work better if they were made to do that.

True a Joule thief is a self oscillating circuit not needing to be in resonance.

But I see the self oscillating feature as a basic part of what makes a joule thief a joule thief.

http://en.wikipedia.org/wiki/Joule_thief

First line on the Wiki.

A joule thief is a minimalist self-oscillating voltage booster that is small, low-cost, and easy-to-build; typically used for driving light loads.

The difference between the radiative and receiver effects between an out of resonance and in resonance small Tesla type transformer/coil is great. With no resonance the fluro held in the hand won't light so well, the voltage at the terminal is much less and when a direct load is placed on the terminal eg. the fluro is touched to the terminal the transformer goes out of tune, if the L/C is adjusted or the frequency adjusted to keep resonance the voltage and power peaks.

Just going near the coil will affect it's tune a bit but actually touching a fluro to the top terminal changes it a lot, and with a manual frequency pulse width adjustment it must be tuned for the load, or tuned to excite a receiver with load, or tuned to just oscillate at resonance with no real load so maximum radiations are forced.

Just because a circuit can use it's battery right down doesn't qualify it as a joule thief to me.

Cheers

P.S. This Armstrong oscillator variant kinda shows that if I touch to the secondary the fluro it lights better than if I touch it to the top terminal because it affects the L/C less.
Towards the end of the video I show some cool patterns in the fluro, which is not new to me I've made a lot better cool patterns in other video's.

It's not a joule thief because it requires over 10 volts to run but it does self oscillate.

So can anyone explain why there are dark and light bands in the fluro ? And why they can move from either end to the middle or from either end to the other end ?
https://www.youtube.com/watch?v=xz_pSsZtUZo


These below are oscillator driven, not self oscillating.

This video shows the power of resonance, at the receiver transformer. Even though the power is low the difference between resonance and no resonance is great. Right at the end of this video clip you can see the neon and hear the "escaping gas" sound it makes when brought close to the transmitter terminal.
https://www.youtube.com/watch?v=jJgHWYTk6_g

Another different freaky fluro pattern
https://www.youtube.com/watch?v=Gr9JX_sIP2I

My self, I prefer oscillator driven (at full frequency, not a harmonic) and manually adjusting the LC and frequency-pulse width ect.  Just my preference. Which is pretty much what your circuit would do wouldn't it.

I have thought about using feedback to a micro, but only so much time to spend.

..

[SeaMonkey]

Joule Thief for the advanced student who
demands the most from the least.

[wings]

source for JT boiled potato battery

http://www.youtube.com/watch?v=36hzlFVgVa8


http://blogs.smithsonianmag.com/ideas/2013/12/a-potato-battery-can-light-up-a-room-for-over-a-month/?utm_source=facebook.com&utm_medium=socialmedia&utm_campaign=12032013&utm_content=innovationspotato