Linear Series Pass Voltage Regulator Saved

This circuit is comprised of a NPN Darlington transistor as the current regulating device. It is controlled by a PNP transistor that is controlled by another NPN transistor and a op-amp in a closed loop. The drop-out voltage is about 1.5 Volts below the input voltage, this is the maximum output voltage possible. A inductor is included in the circuit because the supply is a voltage source and the load is capacitive and the inductor is a buffer of sorts between the input and output voltages. The control system is comprised of a proportional integral control system. It functions by regulating the output voltage at two times the voltage reference. The reference compare value is created by a one-half voltage divider. The simulation illustrates a reference step at .05 seconds, a load step at .1 and .2 seconds, and a supply step at .18 seconds. The circuit shows good reference tracking and also good load and line regulation.