Introduction to the potential divider

A potential divider is a simple circuit containing resistors in series, across which the source voltage is divided. It allows only a fraction of the total voltage to be used a the output voltage.

Calculating the output voltage

The output voltage (Vout) depends on the resistor values and input voltage (Vs) according to this equation:

${\text{V}}_{\text{out}}=\frac{{\text{R}}_2}{{\text{R}}_1+{\text{R}}_2}{\text{ V}}_{\text{s}}$

Where:

• V_out = output voltage (V)
• R${}_1$ = resistance of resistor 1 ($\mathrm{\Omega }$)
• R2 = resistance of resistor 2 ($\mathrm{\Omega }$)
• V_s = source voltage (V)

So the output voltage is always a fraction of the input voltage, determined by the resistor ratio.

Worked example - Calculating output potential

Calculate V_out for a potential divider with R1 = 560 Ω, R2 = 3.9 kΩ, and V_s = 12 V.

Step 1: Formula

${\text{V}}_{\text{out}}=\frac{{\text{R}}_2}{{\text{R}}_1+{\text{R}}_2}{\text{V}}_{\text{s}}$

Step 2: convert k$\mathrm{\Omega }$ to $\mathrm{\Omega }$

to convert from k$\mathrm{\Omega }$ to Ω, multiply by 1,000

3.9 k$\mathrm{\Omega }$ = 3,900 $\mathrm{\Omega }$

Step 3: Substitution and correct evaluation

${\text{V}}_{\text{out}}\text{ = }\frac{\text{3,900}}{\text{560 + 3,900}}\times \text{ 12 = 10.49 V}$