Joule Thief

[Pirate88179]

TK:

Thanks.

How did you "arrive" at adding the 30 turns to the outside?  I mean....why not 25....or 35?  Did you base this upon some formula or, was it a shot in the dark?  However you did it appears to work very well indeed.  All of my "shots in the dark" of late have not worked at all.  Oh well, that is how it goes I suppose.

Bill

[gyulasun]

Hi Bill,

You can find similar coils with ferrite core at Digikey for instance but surely at other places, look for fixed inductors/ferrite chokes.
Hope this long link works:
http://www.digikey.com/product-search/en?FV=fff40003%2Cfff80013%2C400002%2C4c0056%2C4c0057%2C4c0059%2C4c005a&k=ferrite+choke&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&pbfree=0&rohs=0&quantity=&ptm=0&fid=0&pageSize=50

Gyula

ADDITION:  the above coils do not include the ferrite (ceramic) magnet which is diametrically magnetized and its flux can vary the coil core permeability hence change inductance. Such coils are not manufactured any more because color television sets with picture tube are not manufactured any more (at least in Europe) so these coils are not needed. They used to serve as horizontal linearity correction coils if I am not mistaken, see such at ebay with the magnet:
http://www.ebay.com/itm/Toshiba-Linearity-Coil-C-Original-Service-Part-Part-Nummer-V30032994-/380703229235?pt=DE_TV_Video_Audio_TV_Hauptplatinen_Teile&hash=item58a3ae4533

[Pirate88179]

Gyula:

Wow!  Thank you very much for posting this.  This is great.

Thanks,

Bill

[xee2]

Hi Bill,

You can find similar coils with ferrite core at Digikey for instance but surely at other places, look for fixed inductors/ferrite chokes.
Hope this long link works:
http://www.digikey.com/product-search/en?FV=fff40003%2Cfff80013%2C400002%2C4c0056%2C4c0057%2C4c0059%2C4c005a&k=ferrite+choke&mnonly=0&newproducts=0&ColumnSort=0&page=1&stock=1&pbfree=0&rohs=0&quantity=&ptm=0&fid=0&pageSize=50

Gyula

ADDITION:  the above coils do not include the ferrite (ceramic) magnet which is diametrically magnetized and its flux can vary the coil core permeability hence change inductance. Such coils are not manufactured any more because color television sets with picture tube are not manufactured any more (at least in Europe) so these coils are not needed. They used to serve as horizontal linearity correction coils if I am not mistaken, see such at ebay with the magnet:
http://www.ebay.com/itm/Toshiba-Linearity-Coil-C-Original-Service-Part-Part-Nummer-V30032994-/380703229235?pt=DE_TV_Video_Audio_TV_Hauptplatinen_Teile&hash=item58a3ae4533

Good idea. However, note the self resonant frequency. Above that it will act as a capacitor instead of an inductor.

[gyulasun]

Good idea. However, note the seld resonant frequency. Above that it will act as a capacitor instead of an inductor.

Hi xee2,

Well, I understand what you said but I need some pondering on how a blocking oscillator's operating frequency can be set when you build it. I did build such circuits (joule thiefs etc) in the past but have never done tests how to make them oscillate above the coil's self resonant frequency.
I think basically the frequency is defined mainly by: at which frequency the coil has the highest Q (quality factor) that gives the highest active load hence highest gain for the active device, and from this gain the feedback to the base should remain a positive feedback to maintain the in-phase relationship for the continuous oscillation. 
Normally the Q of a coil increases in the function of frequency till nearing its self resonant frequency (beyond which it falls) so normally the operating frequency is lower than that.  Stray and active device inter-capacitances do reduce the operating frequency.  All what I mean is that operation frequency is "inherently" set below the coil's self resonant frequency. You or others here may see this differently of cource, I would gladly read opinions.
Of course a capacitive phase-shift can also give a positive feedback (as one requirement for continuous oscillation)  but how can you achieve it i.e. force the coil to operate beyond its self resonant frequency? Perhaps using extra capacitors at the coupling coil in the base of the transistor to help shift the phase so that oscillation may be forced higher in frequency. It needs testing of course. MAybe you have found out this already, I wonder.

Greetings, Gyula