Joule Thief 101

[TinselKoala]

Yep, all true, pretty much without additional comment necessary.

I've demonstrated my HVJT lighting up 6 NE-2s in series, spiking to over 800 volts, using a AAA battery for input, or even using my wireless power receiver-transmitter system instead of an onboard battery.


Mostly I want to point out that the two circuits using NPN transistors that Mags posted up above are just about equivalent in terms of light intensity and electrical efficiency, as far as I can tell. They work fine using supercaps, but the input voltage must be kept low or the transistor will saturate and stop oscillating, of course. With no LED load they spike to over 26 volts with less than 1 volt input.

Here's a scopeshot of the  Mags "right" circuit (LED across transformer winding rather than across E-C of the transistor). I made a 6-pad version and used a MPSA18 transistor and a 150 ohm base resistor to keep it consistent with my "standard" 6-pad JT, and I used 2 Max Lumileds in series as the load. Both circuits give an illumination of about 11.5 lux at my standard 43 cm distance in my lightbox.

I don't know what to say about the PNP circuit up above, I've never tried it myself. I have made some PNP JTs... in fact the standard circuit will generally work with a PNP transistor if you reverse E and C connection and battery polarity. (IIRC... I don't have one set up at the moment.)

[TinselKoala]

OK... to do a more valid comparison of the two circuits (Mags's "right" with LED across the coil, and the Standard "wrong" with LED across E-C of transistor) I wound another toroid of 36+36 turns (arbitrarily chosen) and breadboarded the two circuits with the same components each time, to eliminate variations due to component differences. I used a 1000 ohm gate resistor, an MPSA18 transistor, two Max LumiLEDs in series as load, and the toroid, all same components in both cases. I used my lightbox with Extech LT300 lightmeter to check the brightness of the LED load at 18 inches from LEDs to sensor. It's simple to rewire the breadboard from one configuration to the other, just have to change one wire. I used the same depleted AG13  alkaline button cell, which measures 1.27 volts open-circuit (after running the tests).

So, the scopeshots below show the two circuits.
#128 is the "Mags right" circuit, and it produced a reading of 8.5 Lux on the lightmeter.
#129 is the "Standard wrong" circuit, and it produced a reading of 9.8 Lux on the lightmeter.

Later on I'll do an electrical efficiency test by measuring the average input power to the circuits and compare that to the brightness, so I'll get values in Lux per Watt for the two circuits.

[MileHigh]

Smoky2:

To claim that this is not an Armstrong Oscillator, is rather an absurd statement.
Even in its' most simplified form, it still remains such.
The fact that people ignorantly destroy the resonance of the tank, is quite frankly irrelevant.

It is clearly not an Armstrong oscillator and there is no resonant tank.  There is nothing absurd about my statement at all. You simply have to look at a Joule Thief schematic and compare it to the schematics of an Armstrong oscillator.  See attached.

So if you want to make that claim and have it taken seriously then you have to go beyond just posting text.  Right now you are the one making the absurd statement.

What is the effect of discharging a magnetic inductor (current source) through a coil, when the inductor was magnetically charged, with the lowest possible reluctance?

Does the inductor (current source) then discharge with the most energy possible, because losses are minimized?

Why would you intentionally try NOT to do that?

If I understand your question properly, and that's sometimes difficult because you are sparing with your words, when one inductor discharges into another inductor (presumably with no current flowing through it) then you get a near-instantaneous spike of voltage from the first inductor inducing the second inductor to get current flowing though it.  In a very short amount of time both inductors have the same current flowing through them.  The original current flowing in the first inductor takes a step down such that the energy is conserved.

I don't know why you say, "Why would you intentionally try NOT to do that?" because there is seeming no discernible context to whatever point you are trying to get across.

You seriously need to do some research. I can name no less than a dozen people on this forum that have posted videos of a JT running from an earth battery.

The problem is that you did not say "earth battery" you said "earth."  Of course a Joule Thief can run from an earth battery which in reality is just current due to the slow corrosion of a metal like magnesium.

the desk was a woodentop, metal frame desk, upon which sat a lamp, a computer and monitor.
The desk measureably sat at about 43V DC, we assumed because of the electronics sitting on it.
and Yes it powered a JT, because we tried it.

One more time, it's the same issue.  All that you said was "metal frame desk" and you said nothing beyond that.  If you made serious measurements on the "output" of the desk you would quote more than just "43V DC" which is almost meaningless.

These LED's, when powered on, then switched off, take some time to turn off. The light dims gradually.

I'd be more than happy to look at an LED data sheet showing that if you can link to one.

MileHigh

[sm0ky2]

@ TK - I love the clothespin battery holder


@ MH - in your comparative analysis of the two circuits, did you notice the functional difference between the two diagrams?

essentially, they operate the same, minus one important factor.

the R-C component of the tank circuit vs the L of the coil are set to resonate with each other.
This, not taken into consideration in the JT equivalent circuit, reduces performance.

The same could be said about the Armstrong circuit, if one chose to change the value of R or C.

[MileHigh]

Smoky2:

a JT can oscillate without the LED present in the circuit.
the LED is only there so you can "see" when the circuit is oscillating.
There are other ways to see this, without using an LED wasting away your energy....

Amplitudes of both voltage AND current increase when the LED is removed.

In a regular Joule Thief if you remove the LED it will presumably still operate like you state.  The inductor would have no choice but to discharge through the transistor.  The average power is low so presumably it would not fry the transistor junctions.

The voltage output from the coil will spike to a quite high voltage, it all depends on the speed that the transistor switches off.  However, I have "caught" you here with respect to the discharge current.  The current will NOT increase.  Are you sure that you fully understand the complete dynamics of an inductor?

the "on" - "off" state of the transistor is a function of the inductor/battery circuit, NOT the LED.
you can change the location of the LED, or remove it completely.

I strongly suggest that you go back and watch the clip about the operation of a Joule Thief that I linked to the other day to review the positive-feedback "snapping" mechanism that switches the transistor ON and OFF and governs the operating frequency of the device.  It is also related to the rate of change of current flow through the main coil which is indeed related to the characteristics of the inductor and battery combination.

The signal at the base from the inductor is what turns the transistor on.
It boosts the voltage from the "dead" battery to above the cut-on voltage of the transistor.
That's what makes the transistor turn on (and the LED light up).
Inductance.
It is a factor of the number of turns on the primary winding.
This is why it is usually such a low number (8-15 turns)

More turns = higher voltage. at some point, you exceed the operating voltage of the transistor.

I agree that you can experiment with the number of turns in the coil that connects to the base resistor.  If you do that then you may want to change the value of the base resistor.  In the context of what you are stating, a transistor does not have an "operating voltage" it has an operating current.

MileHigh