# Voltage Dividers – Circuits, Equation and Applications

The voltage divider also known as the Potential Divider, is a very common simple circuit which is used to change a large voltage into a small voltage. Through this article, you will learn about:

• What is a Voltage Divider?
• Voltage Divider Circuits
• Voltage Divider Equation / Formula
• Applications of Voltage Dividers

## What is a Voltage Divider?

• Passive Linear Circuit that produces output voltage that is a fraction of its input voltage.
• It scales down input voltage to a smaller voltage based on the ratio of the 2 resistors through distributing input voltage among components of the divider.
• Often used to supply a voltage different from an available battery or power supply.
• Output voltage of voltage divider is dependent on the resistance of the incoming load.

## Voltage Divider Circuit

A voltage divider circuit will normally look like this in a circuit with a series of 2 resistors.

• R1 = Resistor closest to input voltage (Vin)
• R2 = Resistor closest to ground
• Vin= Input Voltage
• Vout = Output voltage across R2 which is the divided voltage (1/4 of input voltage)

## Voltage Divider Formula / Equation

Equation to find the output voltage of a Divider Circuit:

R2 / R1 + R2 = Ratio determines scale factor of scaled down voltage.

For example,
Vin = 100, R1= 20, R2= 10

With the help of a calculator you should get:

### Voltage Divider Rule

• The voltage division rule states that: The voltage divided between two series resistors, are in direct proportion to their resistance
• Which means your circuit can have more than 2 resistors!
• Voltage Divider Rule Formula:

Example of Voltage Divider Rule Equation:

### Ohm’s Law

Now, we can use Ohm’s Law to calculate the voltage flowing through each resistor:

• Equation for Ohm’s Law = E = IR
• E = Current across each resistor
• I = Circuit Current
• R = Resistance
 R1 R2 R3 Total E (Volts) 5 10 15 30 I (Amps) 2.5m 2.5 2.5m 2.5m R (Ohms) 2K 4K 6K 12K

Thus, the current across each resistor is 5V, 10V and 15V respectively!

### Simplified Equations

• If R1 = R2,

• If you are solving for R1,

• If you are solving for R2,

## Applications of Voltage Dividers

Voltage dividers circuits are very common and are found in many applications. Here are a few examples of where a Voltage Divider circuit is found:

### Potentiometer

• A potentiometer is passive electronic component with a sliding or rotating function that acts as an adjustable voltage divider.
• The voltage input is applied across the entire length of the Potentiometer and output voltage (voltage drop) is controlled with the fixed and sliding contact of the potentiometer.
• There are two types of Potentiometer
• Rotary Potentiometers (Rotary Knob)
• Linear Potentiometer (Slider)
• Here at Seeed, we offer both types!

#### Grove – Slide Potentiometer

• How does it work?
• The manual wiper which is movable, touches a resistive strip of material. When it is moved up closer to terminal 1 and away from terminal 2, resistance is lowered to terminal 1 while resistance is raised at terminal 2 and vice versa.
• The potentiometer is useful to help achieve a variable voltage from a fixed-voltage source. It can connect the outer terminals of a potentiometer across the voltage source and control the voltage you need between your potentiometer and one of the outer terminals for your circuit.
• The Grove – Slide Potentiometer incorporates a linear variable resistor with a maximum resistance of 10KΩ. As the slider moves, the output voltage will range from 0 V to the Vcc you apply.
• It connects to other Grove modules through a standard 4-pin Grove Cable.
• Below is an image of the Potentiometer schematic diagram:
• It has many purposes like being an Adjustable Resistor, standalone, voltage divider with Arduino or even as a human interface device (HID) which means it can be used to control a car!
• Some projects you can do with the Grove – Slide Potentiometer  are like making your very own Beatbox or Boombox with Arduino!

#### Grove – Rotary Angle Sensor(P)

• The Grove-Rotary Angle Sensor (P) is capable of producing analog output between 0 and Vcc (5V DC with Seeeduino) on its D1 connector.
• With a resistance value at 10k Ohms, it is perfect for Arduino use.
• It is supported on all MCU platforms like Arduino, Raspberry Pi, BeagleBone, Wio and also LinkIt ONE.
• One of the projects that you can do with this potentiometer is using it to control your LEDs brightness

### Grove – Voltage Divider

• The Grove – Voltage Divider provides an interface for measuring external voltage which eliminates the need to connect a resistance to input interface
• With a dial switch, you can easily select the voltage gain which makes it simple to use.

• Most sensors are simple resistive devices like our Grove – Infrared Reflective Sensor. However, most of them are only able to read voltage but not resistance.
• By adding another resistor to the circuit, we are able to create a voltage divider together with the sensor.
• As we are able to check the output of the voltage divider, we can now calculate the amount of resistance of the sensor.
• An example of the circuit is as shown below where R2 is a resistive sensor:
• For example, the resistive sensor is a Grove – Temperature Sensor which is a thermistor with a room temperature resistance of 350 Ω where the resistance of R1 is fixed at 350 Ω
• Using the Voltage Divider Equation:

TemperatureVin (Fixed) R2R1 R2 /
(R1+R2)
Vout
Cold5V300 Ω
350 Ω0.462.3V
Room Temperature5V350 Ω350 Ω0.52.5V
Hot5V400 Ω350 Ω0.532.65V

### Level Shifters

• What happens when a sensor and a microcontroller with two different voltage meets? Without the voltage leveled down, for example, directly interfacing a 5V logic output microcontroller to a 3.3V input sensor can cause damage to your 3.3V circuit.
• This is where the hero: A voltage divider comes in and saves the day acting as a level shifter which interfaces two circuits that use different operating voltages.
• The voltage divider can help level the voltage down from a microcontroller (eg. 5V to 3.3V) to avoid damage to the sensor which makes it safe for the sensor to handle.
• Do take note that the voltage divider can only work in one direction: level down voltages but not leveling up.
• Here is a table of resistor combinations for leveling down commonly encountered voltages:
Resistor CombinationVoltages to be leveled down
4.7 kΩ and 3.9 kΩ9V to 5V
3.6 kΩ and 9.1 kΩ12V to 3.3V
3.3 kΩ and 5.7 kΩ9V to 3.3V
• Do note that it is not recommended using a voltage divider to level down a large load like 12V to 5V as they are not meant to supply such power to a load as with such a load, it may melt the resistor. (You can use voltage regulators instead like our Adjustable DC&DC Power Converter (1.25V – 35V&3A)

## Summary

With all the knowledge of Voltage Divider in your hands, you are able to turn any voltage into a smaller one like a magician! Want to test your skills by making your very own Voltage Divider project? Here are some project ideas to get you started using a potentiometer and an Arduino to create a beatbox or a boombox on our wiki page: Grove – Slide Potentiometer Wiki

## 2 thoughts on “Voltage Dividers – Circuits, Equation and Applications”

1. Frank Medros says:

The formula is WRONG
The formula should be Vout = Vin x (R2/(R1 + R2))