Joule Thief

[MrMag]

Pardon,

I am not sure where you found this information but I am not sure if they are talking about a joule thief. The explanation doesn't make sense.

In the jt circuit, when power is first applied the transistor is fully turned on.
There is a small magnetic field setup on the inductor.
Flow through the Collector/Emitter junction flows.
This sets up a larger magnetic field in the inductor in the opposite direction.
This opposite field chokes out the flow to the base turning the transistor off.
When transistor is turned off, flow stops at the Collector/Emitter junction removing the magnetic field.
With the field removed, power is now able to flow again to the base of the transistor and it starts all over again.

This is why you are getting the high frequency on the jt.
As soon as power is applied, the circuit quickly quenches it or turns it off.

Also the reason the inductor to the base is weaker than the C/E inductor is that the base of the transistor only requires a small current to turn on the transistor. But, when the transistor is turned on, it is pretty much a direct short ( large current) across the C/E junction.

Tim

[Koen1]

Yeah, I'm not so sure either...

Certainly most of the story is correct in that it accords with standard
transformer theory, and the positive feedback part is explained quite
nicely.
But I do get the impression this is more of a general explanation,
much like the Mag-Amp explanation(s).
Sure, a JT is a form of mag-amp setup, just like it is a form of
boost-converter setup, which is a specific transformer circuit,
which a flyback transformer is another variation of...
... so yeah they are all related and share certain characteristics,
some are largely similar, others have specific differences.

But is there really a problem with how the JT works?
I thought it was fairly clear?
The two JT coils act like a boost converter, switch the transistor,
this causes regular pulses in the JT coils and regular flux
pulsing in the core. The pickup coils now do exactly that, they
pick up that flux in the form of a moving charge. Ratio of pickup
coil turns to JT coil turns should determine the voltage produced
by the pickup coil. It's as simple as that.
The only thing I still find a bit unclear is whether or not there is
any actual power gain. Some posts from a while back seemed to
indicate an actual gain in power, as in the actual energy output
in watts being larger than the energy input (in watts). However,
the suggestive posts along that line seem to have disappeared
now and seem to have been followed up by posts mentioning
voltage gain only... and that is entirely possible and understandable
as transformer effect.
Sure, output in the order of 100s of volts with an input of only 1.5 volts
is quite remarkable, but possible and understandable. So I assume
nobody is actually claiming power gain, and the voltage gain well,
that's cool but not magic nor OU.

Still, JTs are quite cool little things!
just the other day I bought a couple of those cheap stick-on LED lights
that you see so many of in shops nowadays... This type needs 3 AAAs
to run 3 ultrabrights... Or at least, that's what they want you to think.
After cracking one open it turns out there's zero circuitry in there, only
the LEDs, a little switch, and a little resistor. I can simply stick one
AAA in there, and hook a tiny bead-wound JT to the battery and the
connector, and the thing works like a charm. Now I can light all of those
lamps on one pack of AAAs, instead of having to buy 4 packs of batteries.
Oh, and it's fun to watch your friends be amazed when you show them
you're not using 3 batteries but rather 1 batt and 1 tiny gizmo.

Kind regards,
Koen

[xee2]

@ hazens1

I was able to get 365 volts from a 1.3 volt 125ma input.

Excellent. The voltage coming out of the rectifiers is DC. But, the DC voltage is going up and down in voltage with the input voltage to the pickup coil. Because the coils are on the same toroid, the voltages out of the two rectifiers will probably go up and down together. But by adding capacitors between the positive and negative outputs of each rectifier you can keep the outputs of each at the maximum voltage and then if you put the caps in series you will get the sum of the maximum voltages. It is always a good idea to use caps across the output of rectifiers to smooth the DC ripple. If you add the two caps you may be able to get a slightly higher output voltage.

[gyulasun]

I am not sure where you found this information but I am not sure if they are talking about a joule thief. The explanation doesn't make sense.

Hi Tim,

He probably found that info here: http://www.talkingelectronics.com/projects/LEDTorchCircuits/LEDTorchCircuits-P1.html

My take on this jt circuit is it is a blocking oscillator and works like that.

rgds, Gyula

[Mk1]

@all




Hi , Again.

Current and Voltage Ratios. In a well-designed induction coil the energy in the secondary, i.e., the induced current, is for all practical purposes equal to that of the primary current, yet the values of the voltage and the amperage of the induced current may vary widely from the values of the voltage and the amperage of the primary current. With simple periodic currents, such as the commercial alternating lighting currents, the ratio between the voltage in the primary and that in the secondary will be equal to the ratio of the number of turns in the primary to the number of turns in the secondary. _{Since the energy in the two circuits will be practically the same, it follows that the ratio between the current in the primary and that in the secondary will be equal to the ratio of the number of turns in the secondary to the number of turns in the primary}. In telephony, where the currents are not simple periodic currents, and where the variations in current strength take place at different rates, such a law as that just stated does not hold for all cases; but it may be stated in general that the induced currents will be of higher voltage and smaller current strength than those of the primary in all coils where the secondary winding has a greater number of turns than the primary, and vice versâ.

@koen1

You are the only one that had some comment last time, i posted this.
Yes in a single pickup coil design there is no ou. The law say same current in all the coils.
But that law also say the current is the same in all the coil, The law is the law , but a good lawyer would tell you to go technical, so i will be the lawyer today.

Since the current is the same in all the coil primary and secondary that are equal but at different voltage, and all the coil are the same , you put more pickup coil on there by law the current will be the same in all coil (btw you can't decreace the jt side, so therefore all coil will have the current that the jt coil has by law)they will still have the same current , now those pickup coil are all containing the same current as the jt coil , now tell me is that more or less ? So lets do maths
so the same current in all pickup coil , that are equal to jt coils , we know only one pickup coil has the same so you need at lest 2 pickup coil to get more current and interesting result.

Last time i just posted the law , and ask if you are a positive guy, because i think if it works for Bedini(on some design you clearly see many coil windings but only 2 are used ?, the guys is telling us about it , but not giving it up he doesn't uses those for triger believe me , those with Bedini's maybe time is for some new coils.)
As a Lawyer I think we have a case .

We need to stop looking at the box !

The last time i posted i should have made it more to the point, really sorry about that.

Mark

source http://www.gutenberg.org/files/15617/15617-h/15617-h.htm  page 166