I drew this schematic up a few years ago (2009, IIRC) when I first made the Supercharged Joule Thief. It was supposed to help me keep track of the several SJTs that I built, and continued to build to validate the design. I suppose I should delete all of the text in the schematic, and put that text in a full sized sheet of paper with the schematic in the upper right corner. But that takes a lot of time and I’ve already spent the better part of an hour just getting it to where it is now (no thanks to Irfanview, which keeps on crashing when I use it in Win 8). Maybe later…
Hello; I wonder if it would be a good idea to “mirror” 2 joule “thieves”: first one as usual with NPN and second one with PNP with emitter to + alim; the middle of secondary connected in between 2 condensers connected to +/-, just like in most CFL lamps? Usually driving a transformer with “push pull” is giving more energy. I have driven a schematic but I don’t find the way to send it. Second question did you test if the supercharged JT gives better efficiency also with Mosfets? Thank you. Jean-Louis
First, the MOSFETs. I’ve built a few versions with the 2N7000, TN0702, 2SK170, and J105 JFET. Because the gate requires more than 1.5 volts to turn on, certain methods have to be used to boost the gate V. One is to put a regular BJT such as the 2N3904 in parallel. However, because of the circuit requirements, they aren’t really SJTs. Do a search of my blog for MOSFET or search for the part numbers.
For higher voltage or power I use a very high current transistor such as the 2SC2500, KSD5041 or NTE11 (which is too expensive). The problem with putting anything in series is that the supply voltage is only 1.5V and that restricts the circuit to keeping V drops to much less than 1 V to prevent excessive loss. Check Quantsuff’s website for other ideas for higher power JTs. http://www.quantsuff.com.