Answer to Question #85275 in Electric Circuits for Anand

Question

You are given one IC 7812 and you require +8V regulated voltage. Design and draw
a circuit to obtain the required voltage by using this IC and appropriate resistors.

Answer 1

IC 7812 is a voltage regulator with the input voltage 14.6 - 35 VDC and the output voltage of 12 V. We need 8 volts, so design the circuit:

We'll use a voltage divider to obtain 8 V from 12 V by the following expressions:

$$R_2=R_1\frac{1}{\frac{V_{out}}{V_{required}}-1}$$

Where $V_{out}$ is 12V and V required is 8V. Substitute:

$$R_2=2R_1.$$

Let's choose $R_1=10 \text{ }\Omega$ and $R_2=20 \text{ }\Omega$ because the load resistance must be high relatively to the divider's resistances to work effectively.