JBNTronics: Voltage Divider, The First Concept in Electronics

A voltage divider (also known as a potential divider) is a simple circuit which turns a large voltage into a smaller one. Using just two series resistors and an input voltage, we can create an output voltage that is a fraction of the input.

The supply voltage (V_in) is divided between the two resistances (R₁and R₂ ) to give an output voltage V_out which is the voltage across R₂.

Voltage dividers are one of the most fundamental circuits in electronics.

Examples of voltage divider schematics. Shorthand, longhand, resistors at same/different angles, etc.

We’ll call the resistor closest to the input voltage (V_in) R₁, and the resistor closest to ground R₂. The voltage drop across R₂ is called V_out, that’s the divided voltage our circuit exists to make.

That’s all there is to the circuit! V_out is our divided voltage. That’s what’ll end up being a fraction of the input voltage.

The Equation

The voltage divider equation assumes that you know three values of the above circuit: the input voltage (V_in), and both resistor values (R₁ and R₂). Given those values, we can use this equation to find the output voltage (V_out):

This equation states that the output voltage is directly proportional to the input voltage and the ratio of R₁ and R₂.

Simplifications

There are a few generalizations that are good to keep in mind when using voltage dividers. These are simplifications that make evaluating a voltage dividing circuit just a little easier.

First, if R2 and R1 are equal then the output voltage is half that of the input. This is true regardless of the resistors' values.

If R₂ is much larger (at least an order of magnitude) than R₁, then the output voltage will be very close to the input. There will be very little voltage across R₁.