Power Supplies

Opamp Voltage Regulator

The circuit is indicated schematically in the diagram. A constant current is supplied to the Zener diode D₂ by means of transistor Q₁ and associated components. The voltage drop across D₂ is compared by means of the high-gain operational amplifier IC₁ with a similar voltage obtained by means of a voltage divider across the +V output and the ground terminal. The extremely high gain of the amplifier causes the difference between these voltages to be very small, however, any variation between the compared voltages is supplied as an error signal by IC₁ to the series transistor Q₂. The sense of the error signal is such as to cause the voltage drop across Q₂ to decrease if the output voltage becomes lower, or to increase if the output voltage rises.