Op Amp Regulator Scheme DiagramThree basic components are needed to achieve good voltage regulation.
1. A precision reference (zener diode) to set the output voltage.
2. A muscle component (transistor) to deliver the required current.
3. An automatic controller (opamp) to adjust the transistor drive. The “prime directive” of the op amp is to adjust the base drive of Q1 delivering the required load current while keeping the output voltage at a fixed value.