Calculation for Voltage Divider

In previous post we had gone through the formula and the circuit used as voltage divider using two resistors.

Example Circuit :

A resistive divider is the case where both the resistors R₁ and R₂, are purely resistive (Image 1).

Substituting R₁ and R₂ into the previous expression gives:

Given : Vin = 9V , Vout = 3V

If R₁ = R₂ then

If V_out = 6V and V_in = 9V (these are widely used voltages), so:

and from above value of R₂ must be twice value of R₁.

Here, both the resistors are unknown. So we have to assume one resistor R₁/R₂, keeping above ration in mind.

Let R₂ = 10 KΩ 

To solve for R₁ (if R₂ is assumed ):

By using : V_out = 3V , V_in = 9V and R₂ = 10 KΩ  in above equation

We get R₁ = 5 KΩ 

Similarly,

To solve for R2 (if R₁ is assumed):

NOTE: This V_out/V_in ratio being >1 is not possible. By using these resistors alone it is not possible to either increase V_out above V_in or invert the voltage.