2013-01-20 Very Low Voltage Joule Thief Ver. 2

I removed the two core coil from the circuit of my previous blog and put the 550 turn coil in its place.  In my haste to see how well it worked, I connected the power supply clip leads backwards, so positive was connected to negative, etc.  But I really didn’t notice, because it was working.  But then as I was working on it, I realized the mistake, and corrected it.  But now it wasn’t working.  Okay, so it worked with the power backwards but not with it correctly  connected.  Then I remembered that JFETs can be symmetrical: the source and drain can be interchanged.  This must be what’s happening when I connected it backwards.  So what I needed to do was reverse one winding to get it to work.

I unsoldered the fine wires of the feedback winding, and reconnected them the correct way.  I turned the power on and it started working.  But the LED started to glow at 87 millivolts, which was 6 or 7 higher than the original coil.  And the oscillations showed up on the scope at 48 millivolts, about ten mV higher than the original.  These are still quite low, but I was disappointed that they were not as good as the original.  After all, I spent an hour or two winding all that wire onto the core – and got no benefit for it.

See the original blog here.

More on Low V JTs here in Ch. 3.

Back to experimenting…

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