Joule Thief 101

[TinselKoala]

Why not just use a J/FET,and have a high winding ration between the primary and secondary,where the(high turn) secondary would turn the J/FET off.


Brad

In my box of JTs I have one which was designed, IIRC, by conradelectro, that uses a 2sk170 JFET and a 5:80 (or maybe even 5:100) winding ratio on a small ferrite bead. Its _maximum_ input voltage is 0.7 V, above that it stops working, and it works down to under 0.3 V.

Ah... here's his schematic. In my build I used a random ferrite bead instead of the specified Ferroxcube part, and only a single JFET instead of 4 in parallel, so mine doesn't work to quite as low voltage as his.

[TinselKoala]

A couple of demos of the above circuit:
http://www.youtube.com/watch?v=35IMWNp2akg
http://www.youtube.com/watch?v=OgndINJHnd0

[SeaMonkey]

Common sense say's that if there is not enough voltage to switch on a transistor or mosfet,then you use one that is already in an on state,and boost the voltage via a step up transformer to switch the fet off.

Yeah well I would have to say that that doesn't make any sense at all.  But don't let that stop you since this whole thread is filled with nonsensical statements by you and just about nobody says anything about it.

Miles, you may wish to examine the attached document.

Edit:

Ah, good to see that TK responded with his usual most
excellent recollection of a prior project which stimulated
lively discussion and experimenter participation.

"Normally On" devices do come in handy from time to time.
   

[MileHigh]

Miles, you may wish to examine the attached document.

Edit:

Ah, good to see that TK responded with his usual most
excellent recollection of a prior project which stimulated
lively discussion and experimenter participation.

"Normally On" devices do come in handy from time to time.

How about you enlighten all of us and say exactly what it is in the patent that's germane to the discussion?

Incidentally, I don't think I have ever seen any "experimenter participation" from you.  So I suppose that we are both in the "same boat" for that.   

[SeaMonkey]

How about you enlighten all of us and say exactly what it is in the patent that's germane to the discussion?

As you wish:

A circuit which is able to boost ultra low voltage to a
level sufficient to switch a MOSFET which permits
efficient boosting of millivolt level source voltage
to several volts as desired.

The initiating oscillator for priming boost is a
JFET switch.

Another paper with interesting analysis attached.

Incidentally, I don't think I have ever seen any "experimenter participation" from you.  So I suppose that we are both in the "same boat" for that. 

Quite true for the time being.  My "laboratory" and all of
my equipment is in storage until a family emergency is
resolved.  The present project with limited effort capability
(until my workbench is once again functional) is a lead-acid
battery desulfation rejuvenation system.  I'm modifying two
Harbor Freight battery chargers to include additional circuitry
to desulfate/rejuvenate batteries.  I have a bunch of lead-acids
which need TLC to bring them back to life.