Joule Thief 101

[MileHigh]

Here's something else to consider. In the standard JT, the toroidal windings actually form one continuous winding in the same direction, with a center tap. You can save yourselves a lot of trouble by simply taking one strand of wire, winding the toroid or ferrite rod etc. with one continuous single-layer, connecting the ends to Collector and Base resistor/capacitor (if used). Then use sandpaper to remove the insulation of the magnet wire in a "stripe" along the outside of the toroid or along the length of the rod, and locate the tap (which goes to positive rail) in the best place by experimenting with connecting to the uninsulated stripe. Once you have found the correct ratio location, solder the "center" tap to the bare stripe at that spot. This is similar to the way that a traditional inductively-tuned crystal set has taps located along the coil for tuning to particular stations.

That sounds really cool.  I can easily envision a "spikey Mohawk" toroid with the single winding and a dozen taps with soldered wires coming off of the single coil.  So then not only can you experiment with the best position for the center tap, but you can experiment to your heart's content with the number of turns in the L1 main coil and the L2 feedback coil.

[sm0ky2]

you generally don't want to saturate the ferrite
the ferrite may reach saturation at peak amplitudes, through regenerative feedback
but driven from the battery, to saturate the ferrite, uses much more energy than necessary to power the load.
it is better to operate under full saturation, or at a point approaching saturation.
since we have no way of limiting ourselves to the exact point of saturation,
we almost always go well beyond it, wasting energy into space.
for the small application of tracing scope images, or lighting an LED,
we don't need a lot of flux, just slightly more than the coil alone provides.
(and even that is not always necessary - see air-coil JT)

[Magluvin]

MH:


Quote:  "When you decrease the base resistance the operating frequency lowers and thus the energizing time for the main L1 coil increases - obviously that can lead to a brighter LED."


It has been my experience, as I have stated, that decreasing the resistance to the base increases the operating frequency as in the example of the low voltage battery causing the led flashes to be seen by the human eye...decrease the base resistance and now the led flashes on/off faster than you can see and appears "on".  I have seen this many times first hand on my own units.


Maybe I am not understanding you here?


Thanks,


Bill

"
It has been my experience, as I have stated, that decreasing the resistance to the base increases the operating frequency...."

That has not been my experience at all.  Decreasing the resistance gives me lower freq, longer(stronger) on and off times. It is when I 'increase' the resistor that I get shorter(weaker) on and off times thus higher freq of operation.



Mags

[Magluvin]

you generally don't want to saturate the ferrite
the ferrite may reach saturation at peak amplitudes, through regenerative feedback
but driven from the battery, to saturate the ferrite, uses much more energy than necessary to power the load.
it is better to operate under full saturation, or at a point approaching saturation.
since we have no way of limiting ourselves to the exact point of saturation,
we almost always go well beyond it, wasting energy into space.
for the small application of tracing scope images, or lighting an LED,
we don't need a lot of flux, just slightly more than the coil alone provides.
(and even that is not always necessary - see air-coil JT)

I may have to order a core with low srf, and will know what the srf is by doing so. I have many toroid cores but I dont know what I have spec wise.  Next purchase is a func/sig gen..  Havnt found resonance other than the battery with the caps at 1.4 or so mhz, depending on which of the disks I put in, of the same lot and value. Scanned the no signal zone beyond clean sine wave range.  Was only able to get the battery to show up at near 1.45mhz and the led lit some.  And Im pretty sure it is the battery ringing, as it changes with the added caps and across the battery is the only component oscillating according to the scope, individually checking components with probe and gnd lead of scope.

Mags

[Magluvin]

Hmm. This is the second time Ive heard of the led going into blink mode. Smoky said it once earlier.  Is that when the battery is super low? Because it seems to me that would indicate the battery is at a level that it needs some refresh time before being able to fire the transistor again. Im getting high enough freq levels at very low battery levels that you cannot see the blinking with the eye. No way. I havnt taken a battery ALL the way down yet to see if I can get it to blink. Will run one down hard to see, soon.
But as far as I can see so far, I dont think it is circuit operation that is giving visible blink, unless the windings were more than we have been playing with here, meaning way more inductance, low freq. Other than that, Id bet on battery weakness at the time of slow visible blink.

Mags