Joule Thief

[Pirate88179]

Well, the modified flash circuits are indeed Joule Thief circuits.  (In my humble opinion anyway)  The Inverter transformer has 3 coils and uses feedback to the transistor and it also works in resonance.  If you retain the original transistor, it will run down the battery to about .5 volts.  I am working on using another transistor that will run down well below that.  Testing is still ongoing.

My point is that you can use this circuit with a single AA battery in a flashlight and run an 800 lumen led.  Maybe I will make one to demonstrate this.  I am not impressed with any flashlight that needs more than 1.5 volts to run.  I looked into using IC's but all of the ones I looked at require 5 volts to run.

Obviously these flash circuits were not designed to be used this way but, I believe that they accidently gave us something great to work with that will run a lot of light from "dead" batteries.

Bill

[Farmhand]

As I said an IC exists that self boosts a very low voltage in some way so that the micro processor boost converter can work from less than 1 volt but supply the micro processor with the correct voltage so as to allow the micro to control the Flashlight LED voltage by way of a boost circuit. I think I seen it in a email as well from mouser electronics, but I cannot remember the exact chip or exactly what it did.  RC4190N Chip is one. ZXLD383 works to 0.9v. PDF's attached.

The ZXLD383 is a simple PFM, DC-DC controller combined with a high performance internal switching transistor, enabling
the production of a high efficiency boost converter for use in single cell applications.

Call it what we will the feed back oscillator itself did not begin with the Joule Thief I don't think. I think the Joule Thief is based on principals long known and used.

[Pirate88179]

As I said an IC exists that self boosts a very low voltage in some way so that the micro processor boost converter can work from less than 1 volt but supply the micro processor with the correct voltage so as to allow the micro to control the Flashlight LED voltage by way of a boost circuit. I think I seen it in a email as well from mouser electronics, but I cannot remember the exact chip or exactly what it did.  RC4190N Chip is one. ZXLD383 works to 0.9v. PDF's attached.

Call it what we will the feed back oscillator itself did not begin with the Joule Thief I don't think. I think the Joule Thief is based on principals long known and used.

I don't disagree with that at all.  what we call the Joule Thief now has been around for some time.  The earliest I can recall is a Russian fellow making one in the 1960's.  So, I agree it is not new and it is NOT overunity at all.  However,  I can and do get free light from "dead" batteries in my home and I like that.

Bill

[Farmhand]

Yeah the thing I like about the "open source" flashlight is that it can be programmed to work in almost any way we could think of and code, which is very cool, the price is a bit much but it does have some neat features as well, still can be lost easy enough though.. One of the problems with the one I have is the modes and how they cycle. The remote pressure switch could just be a trigger for the open source one to do whatever we wanted it to do, through the coding, whereas with the one i have it just turns the light on, and each time it is in the next mode.. Writing hack code with no experience is kinda fun, but I much prefer to copy and reverse engineer it. 

I confess I haven't experimented much with JT's, I have some trouble with small self oscillating systems, not my strong point at all.

I have a great appreciation of the many very nice JT setups around.

Cheers

[MileHigh]

I clipped out the nice block diagram + external schematic for the RC4190 chip.

You can see how the comparator is sensing the voltage output through a resistor divider network.  If the voltage output is too high, the comparator output goes true and that blocks the oscillator signal from going to the transistor, which in turn prevents the inductor from being pulsed on.  If the voltage output is too low, the comparator output goes false and that allows the transistor to start switching, which energizes the inductor, which then pumps current through the diode into the capacitor.  I'm pretty sure that that's the basic negative feedback loop design for most switching power supplies.

So the basic design in the schematic is for a voltage source output, which is not a Joule Thief type output.  Again, you need a current source output to emulate a Joule Thief.

However, the building blocks are all there.  Another breadboarding adventure possibility.  You notice that the signal that is going to the comparator input that forms the heart of the negative feedback loop is a "version" of the output voltage (from the resistor divider network.)   So, in theory if you could feed a signal to the comparator input that is a "version" of the current going into the load, then you might be able to do it.

That suggests that with a current sensing resistor, and an external op-amp you could sense the voltage across the current sensing resistor with the op-amp's differential inputs and do something to condition the output signal from the op-amp to make it suitable to feed into the comparator input.  In addition, if you were to do some experimentation, you will likely also be able to have the same op-amp input another signal, perhaps from a potentiometer acting as a variable resistance or perhaps as a potentiometer acting as a control voltage.  That would be your adjustment for the current output level which could be used as a brightness control if you are driving one or more LEDs in series.  Sounds like fun!

MileHigh