Joule Thief

[jadaro2600]

That would be nice - ...I'll obviously be looking for a way to reduce that interference, if I have to put it in a brass case, I will.

The diagram is rather tricky to get a good picture of, please post one.

- - - - -

I have also been looking for a decent cheat-sheet on transistor terminology.  ..what the significance of a particular stat means is becoming tedious.  I've found some, sparse, but nothing solid.

[mscoffman]

So, my considerations are for operating a mosfet in linear mode, I need a voltage controlled resistor or some rigging of a mosfet which scales predictably in ohmic mode.  Has anyone had any experience with rigging mosfets in this manner?

@jadaro

There are numerous ways of doing this, but they require lots of components,
potentially dual polarity stable power supplies, and some are not efficient
uses of electric power - all of these characteristics are inconsistent with
the design of the basic JT JouleThief. The best bet probably is some sort
of bipolar transistor series regulator.

Here's the thing - these things should not stop you from setting up a
system that will behave as you want...and if what the system does,
looks good to you, you can reduce that operation of the system to simpler
components in a separate experimental step.

Too many experimenters don't do this, they want to combine learning
how a circuit operates with greatly reduce component setup, and then
they can't do both sides of this simultaneously. I hate complexity too,
but I hate end unit complexity and not intermediate development complexity.
So what I am saying is learn how control the circuit and battery charger
to do what you want separately from reducing component complexity. I'm
telling you, I think you are correct about this, and I think you can do it, and
maybe make an actual contribution on here.

---

The methods for linearizing a MOSFET are:
Putting a negative feedback-loop operational amplifier in front
of the MOSFET that has sufficient accuracy to deal with the mosfet
voltage gain of about one million. Operating a transistor in linear
gain mode is not efficient at all when the device is in intermediate
part of the transfer curve. Bipolar transistor are easier to control
because they have less numerical gain...but their gain is in the current
domain (I) and you often need to convert that to the voltage or
power domain to be useful.

If you need output signals with bandwidth of 30Khz or less, look up
"MOSFET switching amplifiers". These synthesize the required voltage
by switching on and off at very high frequencies. Because the mosfet
is either on or off all the time, power efficiency is increased.

A "digital potentiometer" is an easy way to get what you want but
you will need to design a digital front-end for it.

There are a couple of IC amps designed for ACG operation - Automatic
Gain Control, where a voltage input can act as a "volume control"
on the output. But most of the time VFC Voltage Frequency Control of
an astable oscillator is all that is required and even the lowly NE555 has
that. (on pin5 - Control Voltage)

:S:MarkSCoffman

[jeanna]

very interesting my batter were set to only allow 10ma of power well the led was very dimm i adderd a capaciter across the + and - input lead of the joule thief and the led got brighter

Yeay!

Thank you for trying this and reporting it!

The nexy step is to get another tiny one that keeps the joules tossing back and forth across the secondary leads.
Keep going.
good work.

jeanna

this is cool cos no matter what i do nothing can draw more then 10ma the strange thing is i thoght the joule thief would pull the full 10 but it dosent seem to also i have a pot instead of a resister and the really funny thing is as you ajust the pot the light gets brighter then dim then brighter again and so on amlost like im changing gear
also putting a cap inline with the battery after the pot made thing brighter

When you see the light get brighter or dimmer you are watching the circuit go in and out of resonance.
good job.
It is easier with a scope, but as you can tell, you can see the resonance this way.

j

[jadaro2600]

@jadaro

...

Here's the thing - these things should not stop you from setting up a
system that will behave as you want...and if what the system does,
looks good to you, you can reduce that operation of the system to simpler
components in a separate experimental step.

Too many experimenters don't do this, they want to combine learning
how a circuit operates with greatly reduce component setup, and then
they can't do both sides of this simultaneously. I hate complexity too,
but I hate end unit complexity and not intermediate development complexity.
So what I am saying is learn how control the circuit and battery charger
to do what you want separately from reducing component complexity. I'm
telling you, I think you are correct about this, and I think you can do it, and
maybe make an actual contribution on here.

...

:S:MarkSCoffman

Thank you for the information.  I've been dealing with the peculiarities of the devices as of late.

I was reading somewhere on the Berkley website that switching diodes act like resistors until they reach they reach their saturation voltage.

I may wind up using a mosfet for other purposes, since their usually on or off.

I'll continue looking for a scaling resistor, it just seems logical to use one which is voltage oriented.

Also, I too have notices extreme reductionism occuring on circuits.  Although this may be good for hobbyists, it usually doesn't bode well for production runs, the pass/fail system would just as readily have most of them thrown out.   The idea is to make a quality product with predictable operation.

More often than not, the JTC is sensitive and prone to wild fits of good and bad behavior.  It's the Bi-Polar circuit, in other words.

[dasimpson]

have abread board now with a jt setup on it i have a cap on the in terminales
i then have it going to a bridge rectifire then to a cap after that i connects leds with the cap in the secondory the leds also get brighter
haveing the cap and bridge makes it easyer to measure the voltage

edit ps also have some 2n3904 trannys now