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 ($\Omega$)
• R2 = resistance of resistor 2 ($\Omega$)
• 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$\Omega$ to $\Omega$

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

3.9 k$\Omega$ = 3,900 $\Omega$

Step 3: Substitution and correct evaluation

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