Potential divider

This lesson covers: 

  1. What a potential divider circuit is and its purpose
  2. Calculating the output voltage of a potential divider
  3. Choosing resistance values to obtain a desired output voltage
  4. Using a potential divider for voltage calibration
  5. Issues with connecting a low resistance load

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.

Diagram of a potential divider circuit with resistors R1 and R2, source voltage Vs, and output voltage Vout.

Calculating the output voltage

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


Vout​=R1​+R2​R2​​ Vs​


Where:

  • Vout = output voltage (V)
  • R1​ = resistance of resistor 1 (Ω)
  • R2 = resistance of resistor 2 (Ω)
  • Vs = 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 Vout for a potential divider with R1 = 560 Ω, R2 = 3.9 kΩ, and Vs = 12 V.

Circuit diagram showing a potential divider with R1 equals 560 ohms, R2 equals 3.9 kilo ohms, and Vout.

Step 1: Formula

Vout​=R1​+R2​R2​​Vs​


Step 2: convert kΩ to Ω

to convert from kΩ to Ω, multiply by 1,000 

3.9 kΩ = 3,900 Ω


Step 3: Substitution and correct evaluation

Vout​ = 560 + 3,9003,900​× 12 = 10.49 V