I'm kind of new to the world of electronics, so bear with me. I need to regulate +24 volts down to about +21 volts (for supplying a really pretentious heating resistor). I already have the circuit for the v-reg using +24v. The problem I'm having is that I don't have +24 volts, but I do have +12 and -12 volts. Could I connect the input of the v-reg to +12v and use the -12v as the circuit's GND? The voltages come from a PC PSU.
This is basically what I need:
EDIT: I calculated the output as +9V. Combined with -12V the load should get 21V, right? But now I'm not sure about what I use for the ULN2003's ground? Should I use the actual GND or should I leave it to -12V. Thanks.