Joule Thief: LSGadget Mystery Circuit with Variable Cap, Scoposcopy
This is the basic circuit that started out as the LaserSaber Crossover circuit, morphed into the Earth-ground-effect-coupled Ghost Light, and now with gadgetmall’s mods is the selfcharger, or in my case, the runner-on-zero voltage drop with occasional battery voltage recovery. I’ve added the variable capacitor in place of the fixed 100 pF, and I’ve experimented with a bunch of different transistors. The pair I use here seem to be the best performers, in terms of low current drain, sharp fast risetime spikes and high frequency. Of course I have no idea if those are actually desirable but there it is. I use the germanium 2n1304 for the first stage driver and the 2n2222 for the driven transistor (instead of the original GhostLight or crossover which used 2n2222 (or MPSA18) for the first stage and 2n3055 for the second stage). First I show the schematic and explain the changes and the measurement points, then I show the board itself, then do the scoposcopy part showing the qualitative changes caused by varying the added capacitance from none to the full range of the trimmer, about 100 pF or so. In passing I compared the screen display of the venerable HP180a to the Tek 2213 scope that finally arrived in the DeepBunker along with some other stuff from my previous undisclosed location. Even on the video I think you can see that the HP has the better looking display, it’s sharper and easier on the eye and has a better graticule. But the trigger is better on the Tek.