Close BOTH switches to start.
A Two-Quadrant Voltage Regulator is a voltage regulator that can both source and sink current, i.e., it can maintain it's output voltage (positive in this case) for both positive and negative load current. You can see from the simulation that the output voltage is maintained at 5V and the current swings between +1A and -1A. It uses 2 MOSFETs (IRF540N & IRF4905) for voltage regulation, along with BJTs for over-current protection (short circuit current of 1.4A).
This circuit uses a single op amp to control both MOSFETs by tying their gates together. I plan to make a circuit with the MOSFETs controlled seperately. I also plan to switch the positions of the N and P Channel MOSFETs for rail-to-rail output voltage swing.
