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"The Scavenger" A Joule Thief inspired Boost regulator. (unfinished)

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()blivion

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Hello everyone. I've got a project I'm working on finishing for submission to the circuits page of this site, and was wondering if anyone wanted to see it first and provide input on it. A new pair of eyes might catch something I missed.

Synopsis.
The main circuit is a boost design I started working on yesterday and have almost finalized. It was designed based on parts from three different circuits. The first part is the infamous "Joule Thief" LED boost circuit. I started the design with this as the base circuit because of it's great efficiency and amazing ability to "steal" usable power from very low battery's. The second circuit inspiration came from Mr RBs great two transistor boost circuit (which you can read about *HERE*). I really liked his two transistor positive feedback system because it slams things on and off, making switching very efficient. The third pieces of circuitry are very simple but effective modifications I came up with myself when playing with Mr RBs circuit. These modification give these circuits more energy efficient regulation and a flatter more noise free voltage output, suitable for more sensitive electronics.

Not to toot on my own horn, but these three expert designs coming together create probably one of the best simple and efficient boost regulator circuits on the internet that doesn't involve an integrated circuit and can be purchased for less than 5$. For it's ability to suck the last bit of juice right out of a battery and put it to work for more than just lighting LED's, I am naming it "The-Scavenger". I still need to make 100% sure it works in hardware, and figure out a few caveats if I can. But as is the circuit should already be workable, and the future of modifications to the base design look very promising.

The circuit.
There are two versions to look at right now. I'm mostly going to focus on the first one, the second one will be explained in relation to it.

The first one I will present is 100% working in theory and needs little to no modifications. It pretty good in it's own right. It's only real problem is a minor efficiency quirk that I would like to do away with. Here is the schematic of this version...

View attachment 67221

Notes:
(1)R2 Should be 1K, not 10K. I'm too lazy to fix it right now. It actually is 10K in the second version of the circuit though. So don't confuse the two.
(2)R1 may need to be adjusted, lower values are for lower frequency's and lower Vin conditions and higher currents. Higher R1 does the inverse of this. R1 can also go on either the top or the bottom of the sense half of the transformer T1, it doesn't seem to matter much electronically. Putting it on the bottom allows one to use a center tapped transformer though. This is easy to make by hand wrapping a toroidal inductor. All of my builds will likely use this method for T1.
(3)R3 is optional, it is the main RC filter component. Having it installed creates a much flatter Vout, but causes a little bit of extra loss, especially at higher loads. You can replace it with a piece of wire if energy efficiency is more important to you than low noise.
(4) Under certain conditions, there may be a significant ripple current on C2. Such could also be the case if you remove R3 as per above. C2 needs to be able to handle this ripple current or it may heat to the point of destruction and/or you may loose efficiency. Using a polly cap or large Tantalum/silver mica is preferred. If you want efficiency, AND want ripple free Vout + C2, It should be possible to replace R3 with a suitable inductor. I have not tested this yet, but I do plan to.

And here are the main points....

Pros.
It has decent load and line regulation, At around 1500uV with the filter circuit.
It uses very common parts with a low low parts count, 11 parts with the filter, 10 Without.
It is very forgiving with parts tolerances. You can vary most of the parts by 50%.
It will run from a supply all the way down to 700mV!!! Allowing you to use the deadest of battery's.
It has a high energy efficiency when under normal load. And a decent efficiency when lightly loaded.
Using a transformer for current sense instead of a resistor allows for more efficiency.

Cons.
Has some ripple on the Vout if there is no filter circuit.
Has lower efficiency when lightly loaded, needing to shunt Q1's base current directly to ground.
Can't have very high a Vout filter capacitor, or it will start to effect the rest of the circuit.
The circuits frequency varies widely with operation, causing it to possibly emit annoying noises.
Requires an odd transformer, larger ones are more efficient, but will sacrifice other parameters.
It can only boost, and will only work well at no more than 1/2 to 3/4 of target Vout.

Going Farther.
The main problem, and the entire reason for the second version is because the above version is less energy efficient. When regulating for a light load, it shunts some mA of current directly to ground. I will be building this first version soon and I expect no major divergences from simulations as the main sub circuits have been proven elsewhere.

The second version I came up with to combat and correct for the problems of the first. But it too has problems. Here is the schematic of it...

View attachment 67222

The difference and thing to notice with this second version, is that instead of shunting Q1 base current directly to ground to stop Q1 from turning on, I instead block it altogether with a high side PNP switch. This work just as well to keep Q1 off (in simulation), but I have removed the quiescent current associated with grounding R1. The problem this creates is that the point at which Q2 turns on is now determined by Zd1 + Vin. This means to make a target Vout of 5 volts, you need Zd1 to breakdown at 4 Volts AND you need Vin to be exactly 1 volt. This is very not optimal.

The whole point of this circuit is to use as much of the systems battery energy as possible. This means we want to BOTH convert the energy efficiently, AND drain as much as we can from the battery's. So as you can see, each version has a road block that needs to be solved before it is ready for service.

Ideas?
So I'm looking for ideas, I left the first circuit up as a fall back design because it almost certainly works. And because it may be found out that it's actually possible to take it farther than the second one. But I really want to focus on the second version.

With the second version, all current STOPS in the simulator when the regulation kicks in! The only current that is still flowing is the load and a very tiny Zd1+R2 current. When the regulation kicks on in the first version, most every thing stops, but there is still a decent amount of current drain from R1 being shorted to ground. Under light loads, the global power drain is actually dominated by this current. It's only a few mA with the right choice of R1. But if this current can be removed while the circuit is still functioning, it will be nothing but profit. So I'm at least giving it some deserved thought.

I have considered somehow stabilizing the voltage that is fed to the sense half of T1 so that it will not vary with supply. But I think this will add as much or more power loss as the first circuit and it will raise the floor for how low Vin can be. Both these things are very counterproductive. I have also considered and tested the idea of using different parts and configurations for blocking Q1 base current. The PNP seems to be the best choice so far, though the sim isn't very good with MOSFET's. I was also looking into possibly using the negative kickback produced on T1 sense as the voltage feedback instead of Vout. This voltage kickback voltage seems to be directly proportional to output voltage, so it seams just as viable to create a breakdown based control circuit here as it is for how I already have i. The only difference is this area creates a negative voltage that may allow for tricks that wouldn't be possible otherwise.

Conclusion.
Anyway, that's where I'm at now. I would love to hear some input from the elites and hopefully some good advice as how to proceed. If not, I will prolly just run with version number one as it's only major problem right now is efficiency and the fact that it has not been physically built and tested yet.

Thanks for reading.
-()blivion
 
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*Update* I built one...

The first version works 100%. Man does it work. I'm powering it off of two AA batteries right now. These batteries TOGETHER IN SERIES are 0.8 Volts. This combined voltage is so low that you would have thrown them in the garbage long ago if it was just one battery, AND THE CIRCUIT IS STILL BOOSTING TO 5 Volts at ~5mA!!! Highly impressive.

Here are some images with voltage readings for your viewing pleasure...

View attachment 67228View attachment 67229View attachment 67230

But it's sleep time thirty o-clock for me (5:30 AM here). I look forward to reading reviews tomorrow.

(P.S. It's really going to bum me out if I find out this exact circuit has been built before. (D:)
 
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what you going to do with the 5ma now :)....
over here in the uk we can sell power back into the grid... not sure you will be able to retire on your saving LOL
 
LOL, 0.025 Watts really ain't much... no, but boosting 5 Volts from totally and completely dead batteries, and having a circuit do it from voltage just over silicon forward voltage drop is tremendous.

If this were used with fresh batteries for a very low low low low power device (like a small LCD clock) it would run for years. Probably longer than the batteries shelf life when not being used. Also note that the circuit as is can run up to several hundred mA without breaking a sweat. And with the right transistors it could easily do Amps. The second circuit, if it ever gets improved upon, can do this and have even less quiescent power drain. As low as some micro amps in theory.

In the end, it's less about total power, and more about efficiency. Which is obviously the point of doing switch mode energy conversion to begin with.

Edit: It was actually drawing 5 Volts - 2.01 LED drop / 470 Ohms = 6.36170212765957446808510638298 mA to be exact.
 
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Sorry, your answer can only be to zero decimal places, so 6 mA it is. Now if you had 5.00 V, 470.00 Ohms, then you can have 6.36 mA
 
...
The first version works 100%. Man does it work. I'm powering it off of two AA batteries right now. These batteries TOGETHER IN SERIES are 0.8 Volts. This combined voltage is so low that you would have thrown them in the garbage long ago if it was just one battery, AND THE CIRCUIT IS STILL BOOSTING TO 5 Volts at ~5mA!!! Highly impressive.
...

Congrats! A 5v regulator running from a dead 0.8v battery is very cool.

I think you are wise doing testing on the first design, it looks quite usable. The main benefit of using the regulator "killer" transistor is that the 0.6v Vbe to ground is a reliable voltage controlled switching point reference, activated by Vout. So it pretty much forces the thing to regulate output voltage as Q1 cannot turn on if Vout > setpoint.

The feedback winding gives you tons of positive feedback so it shoul dswitch fast and clean, however it would still be nice to see some waveforms!

My suggestion would be to take advantage of the fact that the feedback winding generates good base current drive, relatively independent of ground or Vin. So if you put a resistor between Q1 base and Q2 collector you still get full turnon and turnoff current from the winding, but you greatly reduce the waste current through Q2 in the entire OFF period, your critical period when operating at low currents (as you said). That resistor must be small enough so when Vin is max the voltage on Q1 base is still <0.6v, as it will form a voltage divider with R1.

Also, by using a high gain Q1 (like a BC337-40) it will saturate nicely even with a base current of 0.5mA so you can probably increase R1 quite a bit, especially since you have the extra current kick from the feedback winding into Q1 base.

Also you still have a hard dump of flyback energy through the zener into Q2 base (which also acts like a zener), so I would put a resistor in series with Q2 base, right at the base. That will also allow C1 voltage to rise a bit more which may reduce the frequency. Also R2 can probably be a higher value, saving a bit of power there.

I think this a cool (and useful!) circuit and has a beautiful simplicity. Maybe the next step is to pick a good transistor, fine tune some parts values and do some charting of efficiency and Vin regulation and Iout regulation. Being able to run a 5v PIC from a single AA battery is a good achievement. :)
 
Congrats! A 5v regulator running from a dead 0.8v battery is very cool.

Thanks for the moral support, Yeah the idea of it's actual applications is very thriling.

The feedback winding gives you tons of positive feedback so it should switch fast and clean, however it would still be nice to see some waveforms!

Yeah. I'm pretty positive it works good as the base circuit, The Joule Thief, has been proven to have excelent switching and efficiency already. Still this is a slightly different circuit and some parts may have changed the situation a great deal. So I agree it would be nice to see whats really happening on the inside.

I need a working spice model for T1 before I can share reasonably accurate waveforms though. I tried some transformers from a model library I downloaded **broken link removed**. But the simulator choked on the circuit for some reason. I don't really know why. I may give it another shot, as I would be interested in seeing the results too. For what it's worth, in the falstad simulator it appears to be either completely in saturation or cutoff at any given time. Except for a very brief moment under odd situations. I will look into it more soon.

My suggestion would be to take advantage of the fact that the feedback winding generates good base current drive, relatively independent of ground or Vin. So if you put a resistor between Q1 base and Q2 collector you still get full turnon and turnoff current from the winding, but you greatly reduce the waste current through Q2 in the entire OFF period, your critical period when operating at low currents (as you said). That resistor must be small enough so when Vin is max the voltage on Q1 base is still <0.6v, as it will form a voltage divider with R1.

Also, by using a high gain Q1 (like a BC337-40) it will saturate nicely even with a base current of 0.5mA so you can probably increase R1 quite a bit, especially since you have the extra current kick from the feedback winding into Q1 base.

Also you still have a hard dump of flyback energy through the zener into Q2 base (which also acts like a zener), so I would put a resistor in series with Q2 base, right at the base. That will also allow C1 voltage to rise a bit more which may reduce the frequency. Also R2 can probably be a higher value, saving a bit of power there.

These are all excellent suggestions, I'll try them out and see what happens shortly.
 
Well not to be a killjoy, but do boost converter ICs do the same job as these circuits? I've tried this once, but the transformer part was a bit difficult since I don't have the same core dimensions.
 
Well not to be a killjoy, but do boost converter ICs do the same job as these circuits?

No joy being killed here, but thanks for softening the blow and being polite about it.

Some boost IC's can do this, some can't. There are some by Maxim and Liner Technology that are SOT25, SOT26, SOIC8 package that can do more or less the same thing as whats being done here. There are some charge pump units that don't even need an inductor, so can be made stupid small.

The point with this here is that this is easy to get parts for, you can salvage every thing you need from just about any electronic device, with almost no chance of parts being discontinued. (unless the transistor goes the way of the thermionic valve) Also, it's some what about building it yourself and hopefully learning some electronics in the process.

I've tried this once, but the transformer part was a bit difficult since I don't have the same core dimensions.

You don't need any particular inductor/transformer for this really. Turns out it's very non critical. It just needs to be 1:1 turns ratio, at least 20 turns, some decent magnetic material for a core, and you need to make certain you have the wiring phase correct for the two halves of the transformer. That last part is probably the most difficult thing as it can trick you easily depending on how you wind it, and there is no simple multimeter test for it, you just have to know or try it both ways.

Anyway, all of these inductors have worked wonderfully for me so far...

View attachment 67273

Bigger ones are easier to wind, and give more efficiency and can handle more power. But the larger ones have lower operating frequency so tend to whine and cause more ripple. The smaller red colored one in the center there was just a ferrite bead that I wrapped with fine magnet wire. Works great. Some good sources for toroids are. CFL circuits (the new light bulbs), computer motherboards, the power section of most small wall adapter powered devices, Computer power supplies, and a bunch of other places. And you can get normal non coated inductors from a large number of electronics too.

Honestly, a nail/bolt/screw would probably work in a pinch. Though... eddy losses would murder your efficiency.
 
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thanks for softening the blow and being polite about it.
Dude, I'm the nice guy in this site. No blows intended at all. Haha. :)

Thanks for the input man. *Rummaging my inventory* Here's mine (Z. Kaparnik's design though):
View attachment 67274

But it ain't working. I think I'll rebuild sometime later. :D
 
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I've been thinking one of the things that will really make or break the usability of your circuit ()blivion will be reliable starting.

The main reason I would use a single AA cell to 5v converter is for something like a torch, or a microcontroller circuit that may be used infrequently. From the little I know of "joule thief" type circuits they will only start over X volts, then after that they can keep running until the battery is quite low.

It would be good if your circuit was proven to start even from a low voltage (say <1v), so then it would have greater value when the user has a switch between the battery and the circuit.

One suggestion might be to put a small cap between the Vin terminal and Q1 base. So on switch closed it will provide a higher current pulse to the base of Q1 to try to kick it into oscillation.

One thing I tried with some success was an electro cap in parallel with the battery, but before the switch. Even with a poor condition battery when the switch is open and 0mA load the battery voltage will rise a little and charge the cap, so when the switch is closed the cap will deliver a current and voltage pulse much higher than what the battery can deliver in constant oscillation.
 
Dude, I'm the nice guy in this site. No blows intended at all. Haha. :)

Thanks for the input man. *Rummaging my inventory* Here's mine (Z. Kaparnik's design though):
View attachment 67274

But it ain't working. I think I'll rebuild sometime later. :D

At least it's tinny and cute looking. LOL

So is that just the basic "make the light go" design? It is a good circuit, don't get me wrong. But it has a serious problem. It uses peek pulses of current sent to the LED and persistence of vision to trick you into thinking the LED is lit full time. The fatal flaw with this is the current spikes almost certainly go beyond manufacturers specs, which leads to easily blowing up LED's if they are week (Chinese) and you're not careful. Also, I see you are using a red LED. You will be sending about twice the current through a red LED with that circuit than you will through a white one. This is because red LED's forward drop is only about 1.7-2 and white/blue LED's are about 3-4 Volts. Finally make sure not to forget that LED's are polarized, cuz the circuit will happily create a voltage spike high enough to blow a pretty little hole right through an innocent LED.

My garbage can full of LED corpses can attest to this single fact, the basic circuit breaks LED's. :D



I've been thinking one of the things that will really make or break the usability of your circuit ()blivion will be reliable starting.

The main reason I would use a single AA cell to 5v converter is for something like a torch, or a microcontroller circuit that may be used infrequently. From the little I know of "joule thief" type circuits they will only start over X volts, then after that they can keep running until the battery is quite low.

It would be good if your circuit was proven to start even from a low voltage (say <1v), so then it would have greater value when the user has a switch between the battery and the circuit.

One suggestion might be to put a small cap between the Vin terminal and Q1 base. So on switch closed it will provide a higher current pulse to the base of Q1 to try to kick it into oscillation.

One thing I tried with some success was an electro cap in parallel with the battery, but before the switch. Even with a poor condition battery when the switch is open and 0mA load the battery voltage will rise a little and charge the cap, so when the switch is closed the cap will deliver a current and voltage pulse much higher than what the battery can deliver in constant oscillation.

Good points. Starting is certainly important. I didn't know the Joule Thief would run lower than the starting voltage though? If it's true, it's news to me. I always thought they would only run down until the forward voltage drop of the base-emitter junction of Q1. Then Q1 can't turn on and charge the inductor anymore.

Anyway, I am able to get the hardware version I have to start without problems down to 0.7 volts as is. It is a little rough, but it does work. The other shoe is you have to have no load on the thing, any load sucks current through the transformer, sticking it in one phase and not letting it oscillate. There are a number of automagic fixes for this as a whole though, such as the things you mentioned. I am going to test the cap to Q1 base thing, sounds like a great simple fix.

Simulations and Waveforms.
LOL... So, it was stupid simple to make the transformer I needed to model this circuit properly. Turns out that you can just lay down two inductors, do a little spice directive magic, and *POOF* 100% transformer. Another problem I was having, and one that really shows my n00bishness to LTspice is that I forgot to add the damn ground like you ALWAYS have to. And I even knew all about this before hand. I just forgot. There needs to be a warning that pops up when you try to run the simulation with out a ground, since it's mandatory. Or better yet, when you start a new schematic... it should just have one already down that you can't delete... or something.

Anyway...

I figured every thing out and have waveforms now. They have color coded notes on them to give you the most important information and break it down into easy to understand EE gibberish :)

You will need the schematic first obviously...
View attachment 67278

And here is the waveform for full running, (not near regulator cutoff voltages).
View attachment 67277

And here is the "discontinuous" waveforms.
View attachment 67279

My notes could be way off the mark, I really don't understand exactly where on the waveform Q1 turns on after the inductor has discharged, but I'm pretty sure it's just before the little negative going blip.

Anyway, I will keep playing with it and try and get a more ideal waveform shape to be sure.
-()blivion
 
So is that just the basic "make the light go" design? It is a good circuit, don't get me wrong. But it has a serious problem. It uses peek pulses of current sent to the LED and persistence of vision to trick you into thinking the LED is lit full time. The fatal flaw with this is the current spikes almost certainly go beyond manufacturers specs, which leads to easily blowing up LED's if they are week (Chinese) and you're not careful. Also, I see you are using a red LED. You will be sending about twice the current through a red LED with that circuit than you will through a white one. This is because red LED's forward drop is only about 1.7-2 and white/blue LED's are about 3-4 Volts. Finally make sure not to forget that LED's are polarized, cuz the circuit will happily create a voltage spike high enough to blow a pretty little hole right through an innocent LED.

My garbage can full of LED corpses can attest to this single fact, the basic circuit breaks LED's.

Yes it is (Z Kaparnik's design WAS the first). Well if that's the case I'll use your design and see where it'll go (may I?).
But right now I don't have white LEDs at hand. :D
 
Yes it is (Z Kaparnik's design WAS the first).

Good to know. I'm not going to challenge this as I know I got the base design from someone. LOL.

Well if that's the case I'll use your design and see where it'll go (may I?).

Sure you can use it. It's public domain, so you don't need my permission. I plan on tweaking it and running it through a battery(no pun intended) of tests, then submitting it as an article to the circuits section of this website. So you may want to wait, but the circuit does work so you don't have to. If all your doing is powering an LED though, then you can use the original circuit. I only recommend you add a resistor in between the LED and the rest of the circuit, to limit peek current and maybe save your LEDs. :)

But right now I don't have white LEDs at hand.

It's a little known fact that the LED color *DOES* in fact matter. It changes the voltage drop.

My circuit produces a more or less pure DC voltage on it's output at whatever voltage the Zener diode breaks down at. To power an LED from this, you need to know what the forward voltage drop of the LED your using is, and you need to know how to calculate a safe resistor value for it. Most 5mm LEDs usually run at around 20mA. And the normal voltage for each LED color increases in the order of the rainbow, or is as follows...

Infra red = 1 volt
Red = 1.7 volts
yellow/green = 2.1 volts
White/blue = 3.5 volts
UV = 4.3

The formula for calculating the resistor is...

(Vin - V-LED) / Iout = resistor

Where "Vin" is the Zener voltage (the voltage that my circuit will produce). "V-LED" is one of the numbers above, also in volts. "Iout" is the LED max current in Amps. which is usually ~20mA or 0.02 Amps.

So... for a yellow LED and a zener of about 5 volts in my circuit, you would do...

(5 - 2.1) / 0.02 = 145 ohms.

Edit: The following is the drunken ramblings of a homeless man, and should be ignored as such... Just use a 150 Ohms E6 resistor.

Unfortunately, As is often the case when you do these kinds of calculations, there is no "standard" value that is at or close to 145 Ohms, so you would have to parallel some higher value resistors to get the oddball value. 470 Ohms is a very common resistor and is the closest one to 145. 3 in parallel would be 156.6r Ohms. This is likely as close as your going to get unless you buy precision resistors, which cost more.

Anyway, You should be able to take the above example and extend it to and LED and supply voltage within reason.

I hope this was helpful, and I hope building my circuit works out for you as well as it did for me. If you have any problems, don't hesitate to ask for help here on the forms.
-()blivon
 
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()blivion said:
... Starting is certainly important. I didn't know the Joule Thief would run lower than the starting voltage though? If it's true, it's news to me. I always thought they would only run down until the forward voltage drop of the base-emitter junction of Q1. Then Q1 can't turn on and charge the inductor anymore.
...

From my understanding they will keep running because of the feedback current pulse which is generated by the transformer winding. So once started they will run even with a very low input voltage, which is common enough in transformer based oscillators. :)

Your waveforms look pretty good! I would not worry about the green resonant ringing in the last diagram as Q1 is OFF, there is no significant current drawn from the battery at that time, and that bell like ringing is very low energy LC ringing and probably not affecting efficiency or circuit oepration much at all.

The thing to improve for good efficiency would be the lowish turnon and turnoff times. Their combined time is maybe 10 to 15% of the Q1 in period, which is costing you maybe 10% in circuit efficiency. If you could chart Q1 collector voltage vs current (Iin) that will give more info on whether you should reduce turnon or turnoff time as a priority. It's only going to draw battery current when Q1 collector is under 2v so that is the critical area, so probably the turnoff time is more critical.

It looks pretty good for such a simple circuit. Some charts of Vin regulation amd Iload regulation would be nice, and some efficiency figures.

()blivion said:
...Anyway, I am able to get the hardware version I have to start without problems down to 0.7 volts as is.

That's good!

()blivion said:
... The other shoe is you have to have no load on the thing, any load sucks current through the transformer, sticking it in one phase and not letting it oscillate.

And that's not so good. If using it for a microcontroller power it's probably ok to insist on very low load while it starts up, but it would be nice to be able to use it for something thak takes 20mA or 50mA etc like a project with a display and LED backlight. But like you said that can probably be fixed and should come out in testing when you have stats on startup voltages vs load currents. :)

Vizier87 said:
... Yes it is (Z Kaparnik's design WAS the first). ...

Actually single transistor oscillators based on a two winding transformer have been around since the dawn of time. ;) The "joule thief" name and publicity just made it a fun beginner project, and popularised it for lighting a LED from every last scrap of energy in a 1.5v cell.

What ()blivion is working on is a much more useful circuit, a 5v or 3.3v regulated supply from every last scrap of energy in a 1.5v cell. It's been discussed a ton of times, I've even discussed adding a second transistor regulator in a joule thief thread somewhere here on the forum but never bothered to do all the work to fine tune a circuit and make it good. Here's something from this old June 2011 thread; https://www.electro-tech-online.com/threads/attempt-at-a-simple-boost-converter-3v-5v.119773/

Mr RB said:
crutschow said:
Aye, there's the rub. There's no easy way to regulate the output voltage of a joule-thief other than using a lossy linear regulator.
I'm not sure that's true.

You could a regulator transistor that turns the joule thief off when the output is over X volts, so assuming the JT (joule thief) has good reliable startup it will regulate fine.

Or the base of the JT could be decoupled somewhat from the transformer by a resistor, so the transformer becomes part of the base drive (not all of the base drive) then a regulator transistor can be used to bias the base "more off" when output voltage is >X volts. That should keep the JT oscillating but reduce duty cycle.

()blivion's design is clean and sensible, he's putting in the work and already seems to be working quite well. Now it's just for the proving, the reliability of startup under different conditions and tweaking efficiency and regulation quality. All in all it is a good idea and probably deserves a neat little PCB design once it has been tweaked and proven so it can be even more useful for people.

As I said before being able to run projects from a 1.5v AA cell is VERY nice! I have a house full of little projects and tools, mostly running from expensive 9v batteries.
 
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Actually single transistor oscillators based on a two winding transformer have been around since the dawn of time. ;) The "joule thief" name and publicity just made it a fun beginner project, and popularised it for lighting a LED from every last scrap of energy in a 1.5v cell.

Whoops. Thanks for the input. I guess citing it as a "design" at the first place sounds pretty funny. :D
 
there is no "standard" value that is at or close to 145 Ohms
How about 150?
 
How about 150?

I'm an idiot... there are actually lots of standard resistors closer that would work. LOL. I shouldn't make posts when I'm tired...

For some reason I though the gap for E6 was 470 to 100... :rolleyes:

... I need to quit drinking.
 
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Hi,

Beer i hope? :)

I did a similar thing for the two transistor circuit quite a long time ago which only requires an inductor. It's somewhere on the web :)
The circuit uses two transistor, but doesnt require a specially hand wound transformer, only an inductor.
If you are interested i'll try to find it.
 
I did a similar thing for the two transistor circuit quite a long time ago which only requires an inductor. It's somewhere on the web :)
The circuit uses two transistor, but doesnt require a specially hand wound transformer, only an inductor.
If you are interested i'll try to find it.

Sure, it's always nice to have new input. Is it anything like Mr RB's circuit?
 
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