Adjustable linear regulators: A tutorial

Adjustable linear regulators use feedback networks to set output voltage, with the 78 family using a Darlington NPN pass transistor and high bias current (up to 8mA) that causes significant error across divider resistors, while the LM317 uses a floating topology with much lower bias current (50μA) but requires minimum output current to sustain operation; loop gain analysis shows that output resistance in closed loop equals the open-loop resistance divided by (1+loop gain), where loop gain equals the amplifier gain multiplied by (1-T) with T being the divider ratio.