Joule Thief 101

[sm0ky2]

Tried 3 different transformers, all with equal 1 to 1 turns on the primary and trigger coils. In all cases once I get them to be in the clean sine zone, there is very limited range in which I can get it to show before it cuts out completely. So maybe a different ratio of turns would be next.

I can see that when the circuit is running normal with say a 1k resistor, that there is more on time of the transistor than off/discharge. So I would like to change things to possibly get a near to equal on/off time when running normal mode, which would hopefully help in producing the sine, instead of the long on and short off time Im getting which would kill off any ringing of resonance if the on time is too long.

I suppose that more trigger turns would shorten the on time as it would increase the base voltage in a shorter time period than with a 1 to 1 ratio. So Ill go that route for now.

Mags

there I likely only one or two nodes you can approach with your VR
it tends to be fairly exact.
you are either on it or you are not.
You can notice the "sineish" wave forming as you approach the freq, and dismantling as you leave it.
there is also and abrupt change before and after this range,
where the transistor switches sharply leaving a similar scope to what MH shows above
(of a non-MH JT, he obviously is using someone elses scope image here)

[if your VR can go low enough, you can get the transistor to not-switch, but at that point you could probably just power the led with the battery and coil.]

the more exact to the resonant freq you can get the better the results, but once you are there, further adjustment will only take you away from that point.

leaving it at this resistance value, we can then examine the other parameters.
for instance, if an impedance on one side of the coil were to be examined as "the same as"
a longer wire, to represent the same impedance.

we could then lengthen the wire on the other side to balance the two impedances.
however, changing the number of turns will significantly alter the inductance,
this will change the frequency, and require an additional adjustment of the VR. (<-- avoid this step backwards!)

[edit: avoid, when you are looking at a "standard JT", in your 1 to 1 coil test circuit, please continue experimenting as you feel fit]

[Magluvin]

Ok. Just played with the larger transformer I had made for a project way back. With it, I did a sloppy 3rd winding shorted. With a fairly low ohms on the resistor value, I can get from an almost normal waveform, stronger n longer downward curve from the top, to the ones below. Both are set to the same parameters but one with a weak battery and one with a fresher battery..  So I must be close as the freq shown on the scope is the exact same with different voltage levels. Where before when the voltage changed, if it went lower, the freq would be higher. But here it sticks.  Man. Im glad I conjured up using those shorted windings.  I havnt gotten what seem like Im getting here without it.   

Will try to tune it with the 3rd winding by adding or deleting turns. Gotta tighten it up and solidify how and where it sits.

Farted around with the disk caps and there were points where the freq just jumped to another octave when adjusting the pot. And would jump back down when I turned it back. When it jumped down, the led was bright, and got brighter as the resistance was lowered. But on the way up, right at the jump area you can see an area of transition where the led is very dim, then as bright or more than below that point when in the higher freq jump. Also the batt voltage had shown down around 1.12v just below the transition and 1.33 above, led lit very well on both sides. Will do those things again with scope shots.  I had just found this more interesting to show for now.


Mags

[Magluvin]

Also strange is the pk-pk, min and max are very similar in each shot yet the input is a pretty big difference.  All why I thought this was more important to show.  Like the circuit is regulating somewhat.

Mags

[Magluvin]

Here are 2 shots of different led placement. 1st is across transistor as in typical circuits and the 2nd across the coil.

Resistor is 22ohm. Will try my 1ohm resistor block for a power in measurement for each later. Gota work today.


Mags

[Magluvin]

The reason I did the led position test again was to see the difference in on/off time for each. Across the transistor shot shows closer to s 50% duty cycle than the across the coil shot. Possibly that is where my issue is with getting that sine to work out here. Like I was talking about earlier a few posts, wanting to try different winding ratios to fix that, and I think it might work in both cases to bring out a nice 50% duty. At the low frequencies, what in the 300hz min so far, the duty cycle could probably be very short off times. So I think the winding ratio changes are key there, if it helps, not sure yet.

Looking at the 2 shots, you can see the led across the transistor when conducting holds the battery down as the led dissipates, as I described it would days ago before building my first JT, and it looks like enough that the battery is lower at turn off than the led across the coil shot.  So I am pretty interested in testing out the power in differences. I figure using a fresh 1,5v battery during the test will give a much better resolution of the differences than a very depleted battery. If it is possible to get an extra couple of hours by putting the led across the coil instead of the transistor(typical placement) then it is a winner to me.    The wrong vs the right.

lol Also tried the led in reverse, both placements, and the led still lit. Not like it does when proper in polarity, but did light. I had at first did it by accident figuring it probably wouldnt light if reversed not bothering to check the led for polarity, and when it did light, I figured it was correct. But I wasnt getting the blinding brightness.  Then I noticed the pk-pk was 84v.  lol  Hey. These are all experiences here. really getting to know this thing , backwards and forwards, literally.  Anyway, having a good time with it.

Mags

Mags