Circuit knowledge

This is a simple Op Amp Regulator Circuit Diagram. This op amp offers a straightforward method of developing a single-polarity stable voltage source (see the figure). Transistor Ql gets a base drive through resistor Rl, and conducts to develop a voltage (Vi) across the IC`s supply pins. Amp Al, R2, and Ql form a positive-feedback closed loop, along with R3 and the zener diode. Al, R2, and Ql also form a negative-feedback closed loop with R4 and R5. 

The effect of positive feedback is predominant as the non-inverting input receives Vx while the inverting input receives only: This happens until the zener comes into play. When the voltage at the inverting input exceeds the voltage at the non-inverting input, Al`s output takes away Ql`s base current through R2, which reduces Vi. Hence, an equilibrium condition is reached. Now: This schema can source more than 30 mA.