I've played with adjustable voltage regulators already (such as nte956). My question is about "non-adjustable" voltage regulators (78xx). What is the easy way to adjust these? And by easy, I mean just using one or two resistors. I've seen some solutions using zener diodes, but I would like to use parts at hand. I would think that changing the "reference ground" for the 7805 up by 0.25 volts, I should get 5.25 (in theory, forgetting about margins of error). So why not just use two resistors: one between real ground and the ground pin, and another between input positive and the ground pin? Shouldn't this work? We could easily calculate a ratio for those resistors. Say input is 12V. 0.25 / 12 = ~0.02. I would think to use higher values (1MΩ on the positive and 220KΩ on the -ve side) to use less power. I'm wondering if I'd be hampering the ground pins ability to discharge current (i don't know if it's an issue, just a thought, if it's a pure reference voltage, it shouldn't matter). What about using the output voltage to create a reference voltage (resistor to the output instead of the input +ve)? Would that be better (since it's regulated)? Or would that be worse (feedback)?