For more current output, try this:
Feed the LM regulator via 1 ohm. Feed emitter of 2N2955 (PNP!) also. Take PNP Base to other side of the 1E resistor (regulator input) and PNP Emitter to regulator output.
Now, as load increases the reg. develops voltage across the 1E resistor, and at around 0.6V (0.6A through the regulator), PNP turns on. By the time the regulator is taking 0.7A it is developing 0.7V across the 1E resistor (which is dissipating I^2R = 0.49W), and PNP is turned fully on and well and truly taking the rest of the load!
2 components: 2N2955 (and heatsink of course - water-cooled, anyone?) and 1E 1W resistor.
Drop-out voltage = that of the regulator + Vbe(PNP).
The 2N2955 is rated to 10A, and you can add many of them by adding a (1A rated) diode in series with the regulator and 1E0 (compensates for the Vbe of the 2955/s), and 0E1 resistors in the emitters. The 2955s are then sharing the load to 10 * Ireg each, well within rating, and all protected by the regulator.
Boost the Vout? add 1k regulator out to 'ground' (lifted) and resistors / pot to suit then to ground.
This works for *any* LM regulator, just adjust the 'grounding' resistance.
From the datasheet, LM317 is 1.2V out so, given 1k across that, the grounding resistor will be about (desired Vout - 1.2) / (1.2 / 1k).
So, e.g., given regulator LM7812 and 1k across its output, wanting 13.8V out, grounding resistance will be about (13.8-12) / (12 / 1k) = 150E.
Have fun, folks!
73 de Dex ZL2DEX
