What's the purpose of a joule thief?

BR-549

Joined Sep 22, 2013
4,928
I would agree, maybe a few more turns.

But I don't like that nail. I don't like the way it looks.

Is that a modern nail?

Just how flux worthy is that nail?
 

ian field

Joined Oct 27, 2012
6,536
You don't have to break the tube, just separate and base from the bulb. I've done it numerous times. But I doubt you'll find a toroid. You'd have a better chance with an old computer power supply.

.
Much easier from a PC PSU is the mains common mode choke which is already wound, some are toroid and some are E - E ferrite core. They usually have the 4 pins on a more or less square footprint, just continuity test to identify the 2 windings - linking the 2 windings in series with a link wire mounted diagonally across 2 pins will give you the correct phasing - either end can be the B or C winding.

It should work straight off with out any difficulty once you've found the best resistance for the B current limiting resistor - but you have no control over the inductance values, so the JT will be more or less suited to your application depending on what inductor you happen to find.

There's usually a big fat toroidal choke on the secondary side with a variety of windings on it. A great resource for the enthusiastic experimenter - with any 2 windings, you have a 50:50 chance of getting the phasing right first time, if it doesn't oscillate - just reverse one of the windings and try again.
 

ian field

Joined Oct 27, 2012
6,536
No, just ferro.

Irony.
Actually - a ferrite core is basically powdered rust mixed with powdered whatever ceramic they use and sintered.

An intact iron/steel nail will be high on eddy currents (basically a mass shorted turn) - but I have seen people get away with a nail cored blocking oscillator JT inductor. A bundle of nails would at least be a closer approximation to a laminated core. A trick I saw in an early wireless magazine was use a bundle of soft iron wire that's sold for flower arranging.

A ferrite core of almost any description will be better than a nail, and easier to get working.

Any appliance with an EMC sticker on it should contain a ferrite of some description somewhere.
 

BR-549

Joined Sep 22, 2013
4,928
I was just trying to troubleshoot the established circuit. Not design.

The nail looks suspicious to me.

Most "nail use" circuits have many more turns for the reasons you state.

I suspect not enough flux. Either add more turns or add a flux concentrator(core).

A nail is not a good concentrator as you say, so we need to add turns also like I said.

I just didn't want him to go out and look for a rusty nail.
 

Thread Starter

tjohnson

Joined Dec 23, 2014
611
You don't have to break the tube, just separate and base from the bulb. I've done it numerous times. But I doubt you'll find a toroid. You'd have a better chance with an old computer power supply.

The explanation of my post can be found in post #50.
I've tried several different resistor values (10, 330, 1k, 10k) and none of them made the circuit work. I think the problem is likely the poor quality of my inductor.
 

ian field

Joined Oct 27, 2012
6,536
I've tried several different resistor values (10, 330, 1k, 10k) and none of them made the circuit work. I think the problem is likely the poor quality of my inductor.
Try a bundle of nails - it approximates a bit nearer to a laminated core.

A bundle of the soft iron wire used for flower arranging is said to work.

Better yet, get hold of some form of ferrite - you'd have to be trying to fail real hard......................
 

Brownout

Joined Jan 10, 2012
2,390
I've tried several different resistor values (10, 330, 1k, 10k) and none of them made the circuit work. I think the problem is likely the poor quality of my inductor.
Well, do what you think is right. But I don't see any way your circuit can start, regardless of the inductor. The transistor needs to be biased at the edge of conduction for the circuit to work. I have a feeling you didn't follow my suggestion of using a variable resistor, as you listed different fixed resistance values. I'm not saying if you do that it will work, just saying I don't think it will work the way you have it configured.
 

Thread Starter

tjohnson

Joined Dec 23, 2014
611
Well, do what you think is right. But I don't see any way your circuit can start, regardless of the inductor. The transistor needs to be biased at the edge of conduction for the circuit to work. I have a feeling you didn't follow my suggestion of using a variable resistor, as you listed different fixed resistance values. I'm not saying if you do that it will work, just saying I don't think it will work the way you have it configured.
@Brownout: I'm confused. If that's the case, why didn't @DickCappels need a variable resistor in his flooring nail inductor circuit?

@DickCappels: I'm also confused because in one place, your article says to use a 1k resistor, but in another place it mentions a 330R.
 
Last edited:

Brownout

Joined Jan 10, 2012
2,390
@Brownout: I'm confused. If that's the case, why didn't @DickCappels need a variable resistor in his flooring nail inductor circuit?
However, in Dick Cappels JT, transistor bias is supplied directly through the coil and base resistor. As far as a I tell from your picture, you don't do that. Your coil is grounded on one end and connected to the base at the other end. thus, you have no base bias. Also, your coil is constructed much differently than Dick's, therefore you might need more bias to get it started.
 

ian field

Joined Oct 27, 2012
6,536
Well, do what you think is right. But I don't see any way your circuit can start, regardless of the inductor. The transistor needs to be biased at the edge of conduction for the circuit to work. I have a feeling you didn't follow my suggestion of using a variable resistor, as you listed different fixed resistance values. I'm not saying if you do that it will work, just saying I don't think it will work the way you have it configured.
The blocking oscillator is a bit more crude than that, basically any voltage that causes significant base current to flow will bias the transistor on and cause collector current to flow. The inductor is an auto-transformer, and by transformer action causes a large increase in base current, that in turn ensures collector saturation. When the collector current causes core saturation, the inductor loses its property of inductance - at that point, the regenerative action driving the base collapses and the transistor comes out of saturation.

The mathematics to design a blocking oscillator are convoluted to say the least, but if you follow the guidelines that are abundant on the web, its one of the easiest circuits to get going.
 

Brownout

Joined Jan 10, 2012
2,390
Even a blocking oscillator needs transistor bias. It won't work without it. No matter what is done to the circuit in question, it won't work unless the transistor is biased above cutoff, no matter how crude the oscillator is. And the oscillator doesn't care how the transistor is biased, as long is it is biased. By using the method I described, you don't have an minimum design, but you have a working design, and you don't need to guess what bias is correct. One can then further refine the design.
 
Last edited:

Brownout

Joined Jan 10, 2012
2,390
It also might help to connect the coil to the "+" side of the battery, instead of ground, to bias the transistor, which is more commonly done, for example, in Dick's design.

EDIT: Now that I think about it, this is the only way to go. The coil voltage adds to the bias this way, producing a correct positive feedback voltage at the base.
 
Last edited:

ian field

Joined Oct 27, 2012
6,536
Even a blocking oscillator needs transistor bias. It won't work without it. No matter what is done to the circuit in question, it won't work unless the transistor is biased above cutoff, no matter how crude the oscillator is. And the oscillator doesn't care how the transistor is biased, as long is it is biased. By using the method I described, you don't have an minimum design, but you have a working design, and you don't need to guess what bias is correct. One can then further refine the design.
The base winding extends from the Vcc tap to the base via a current limiting resistor. With a JT the Vcc is going to be 1.5V and with a Si transistor the Vbe is going to be 0.7V - its as simple as making the resistor big enough to limit the current to what the B-E junction can handle.

If you are going to complicate the circuit by adding a potential divider, that by its very definition involves a shunt resistor across the B/E - the TS seems to be having enough trouble already - why add another hurdle?!!!
 

Brownout

Joined Jan 10, 2012
2,390
The base winding extends from the Vcc tap to the base via a current limiting resistor.
Not in the TS's picture. I've already suggested he change it.

If you are going to complicate the circuit by adding a potential divider, that by its very definition involves a shunt resistor across the B/E - the TS seems to be having enough trouble already - why add another hurdle?!!!
Hurdle???? the TS's circuit will NEVER work as it is constructed. Instead of trolling each and ever one of my posts, why not look at his picture and make suggestions, AS I ALREADY HAVE. And I've given him options that include changing his connections so that the coil can bias the transistor. And a voltage divider is one of the simplest solutions ever devised in electronics and sure as hell isn't complicated. And as I've pointed out, it can help him to establish a proper bias point. I've gotten many a oscillator working using the SIMPLE and UNCOMPLICATED method. It's sure as hell is not a hurdle. Moreover, there isn't a single way to build a JT. Some have divider bias networks, some do not.
 
Last edited:

ian field

Joined Oct 27, 2012
6,536
Not in the TS's picture. I've already suggested he change it.



Hurdle???? the TS's circuit will NEVER work as it is constructed. Instead of trolling each and ever one of my posts, .

Trolling you?!!! - I didn't even take any notice of who's silly remarks I was correcting, if your silly remarks were more prolific than anyone else's you got more corrections.

The TS seems to have responded to critique of the original attempt a couple of pages of posts ago - we're talking about the circuit now that is taking the shape of a blocking oscillator JT - why you're still harping on about the TS's ill informed original attempt, is anyone's guess!
 

Brownout

Joined Jan 10, 2012
2,390
Trolling you?!!! - I didn't even take any notice of who's silly remarks I was correcting, if your silly remarks were more prolific than anyone else's you got more corrections.
Well, when you actually make an actual correction, then maybe you'll have a point to make. But for now, you don't.

The TS seems to have responded to critique of the original attempt a couple of pages of posts ago - we're talking about the circuit now that is taking the shape of a blocking oscillator JT - why you're still harping on about the TS's ill informed original attempt, is anyone's guess!
I made my comments just after the TS posted a picture showing a breadboard circuit that won't work. Subsequent comments I made were at the behest of the OP, who by the way, is the person if interest here. Use the LRU method, Look, Read and Understand.
 

Brownout

Joined Jan 10, 2012
2,390
To reiterate my suggestion for the circuit about which I made my original comment (last one pictured) it would be insufficient to bias the transistor using a variable resistor and not change the coil connection to connect to the "+" side of the battery. You can try the bias idea or not, but you must change the way your coil is connected.

I reiterate this comment so that it doesn't get lost in the background noise. Please ask if you have any further questions ( I mean the TS )
 
Top