What is a Voltage Divider or Potential Divider, Formula and Practical Uses?

(Last Updated On: November 9, 2019)

Voltage Divider

Description:

Voltage Divider or Potential Divider- A voltage divider or Potential divider is basically a passive linear circuit consisting of resistors connected in series that produces an output voltage (Vout) that is a fraction of its input voltage (Vin). The applied voltage Vin is distributed among the components of the divider circuit.

I have been using voltage divider circuits in different projects. In this article, you will learn the practical use of a voltage divider or a Potential divider circuit. You will also learn why we need a potential divider and how to use a potential divider circuit. But before you can use a voltage divider circuit in any project, first you will need to understand the basics like

What is a voltage divider?

How to make a voltage divider circuit?

How and when to use a voltage divider circuit?

When not to use a voltage divider?

What is the formula and how to use it in practical circuit designing?

Can we use a voltage divider circuit as a permanent supply to power up any load?

You will get answers to all of these questions.

First, let’s talk about the basics and then I will show you how to practically use a potential divider. Let’s get started.


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What is a Voltage divider or Potential Divider?

Voltage Divider

Voltage Divider or Potential Divider- A voltage divider or Potential divider is basically a passive linear circuit consisting of resistors connected in series that produces an output voltage (Vout) that is a fraction of its input voltage (Vin). The applied voltage Vin is distributed among the components of the divider circuit. Voltage dividers are one of the most fundamental circuits in electronics. For the same input voltage, we can get different output voltages by changing the values of the resistors connected in series.



Note: For the same value resistors, the voltage is equally divided.

Voltage Divider

To best explain the voltage divider circuit or Potential divider circuit, I made three potential divider circuits in Proteus simulation software. Each Potential divider circuit has two resistors connected in series. The applied voltage remains the same. The resistors R1, R3, and R5 are 10K resistors, while the resistor R2 = 1K, R4 = 2K, and R6 = 10K.

In the potential divider circuit number 1, the resistors R1 and R2 are connected in series.

Vin = 12 volts

R1 = 10K

R2 = 1K

Using the following voltage divider or Potential divider formula, we can find the output voltage Vout.

Potential divider formula or Voltage divider formula:

Vout = (1000/11000) x 12

Vout= (1/11) x 12

Vout = 1.09 volts

Similarly, for the circuit number 2, you can find the output voltage Vout.

In the voltage divider circuit number 3, you can see the same value resistors are used, due to which the voltage is equally divided. When the same value resistors are used the voltage is equally divided, and there is no need to use the formula.

In all the above circuits, fixed value resistors are used, due to which a fixed output voltage is produced. In order to produce the variable voltage, you can replace any of the resistors with a potentiometer. A voltage divider circuit in which a variable resistor or potentiometer is used is best suited for setting up the reference voltage, which I will explain in detail.

One of the most frequently asked questions about the voltage divider circuit is,

How to make a voltage divider circuit?

When two or more resistors are connected in series it makes a voltage divider circuit. This way you can get different voltages as you can see in the picture below.

Voltage Divider

Voltage Divider Application with Practical uses:

From the above discussion, you know the purpose of the Voltage divider or Potential divider is to reduce the voltage. The voltage divider or Potential dividers are also used for the voltage conversion. Let’s say you have a circuit that needs 3.3 volts and it needs to be interfaced with the Arduino’s digital pins which give 5 volts when turned ON. In a situation like this, you need some kind of converter that can convert 5 volts into 3.3 volts. This converter can be a simple potential divider circuit I will explain this practically in a minute.

The nonlinear resistors like, Thermistor, LDR, Varistor, Flexible resistor, etc are connected in series with other resistors to make a Voltage divider circuit. Let’s start with the most commonly used electronic components LDR “light dependent resistor” which is a nonlinear resistor.

  1. Voltage divider application/use in a Solar Tracker Project:

In a Solar Tracking system, the first circuit that we start with is the light-sensing circuit which consists of an LDR. As you know LDR stands for the Light Dependent Resistor which means that the resistance changes as the light intensity changes.

Voltage Divider

When an LDR is connected in series with a fixed value resistor it makes a voltage divider circuit. This way we can get different voltages as the light intensity changes. To make it Arduino compatible you can replace the 12 volts with +5 volts. Then you can connect the Vout with the analog input of the Arduino and read the voltages.

Let’s make it a bit complicated, let’s control a 12v relay with this LDR. The circuit which I am going to explain can be used in solar trackers, Night and Day detection system, and laser security systems.


Voltage Divider

The voltage Vout that is coming from the potential divider formed by the LDR1 and a 10k resistor is compared with the reference voltage coming from the RVI Potentiometer using lm741 which is used as a voltage comparator in this circuit. The reference voltage is set using a potentiometer which also works as a voltage divider, by rotating a potentiometer we can set different voltages.

So after comparing the voltage that is coming from a voltage divider circuit with the reference voltage, the lm741 IC gives an output that is approximately equal to the input supply which is 12v. The output voltage may be around 10 to 11v. Until now everything is fine.

Now we want to control a relay with output voltage, but the problem is we cannot connect a relay directly with lm741, as it does not provide enough current to energize the relay coil. If you look at the datasheet of the lm741 operational amplifier IC, you will come to know that lm741 can provide 25mA which is not enough to energize the relay coil.

If we measure the relay coil resistance which is .426k ohms equals 426ohms, as it a 12v relay so the voltage is 12v.

Then using ohm’s law

v = I R

We can find the current

I  = v / R.

I = 12 / 426

I = .028 amps

Which is equals to

I = 28mA

So 28mA milliamps needed to energize the relay coil. As you can see the current needed for the relay coil is greater than the current that lm741 can supply.

but thank God we have a transistor which can be used as a switch, as we calculated the relay coil current which was 32mA, now let’s select a transistor that can handle this much current, I selected 2n2222 NPN transistors as it can handle larger current than 28mA so best for controlling this relay, but wait…. we also cannot use 2n2222 NPN transistor directly with the lm741, because it will damage the 2n2222 NPN transistor, if we look at the datasheet of the 2n2222 NPN transistor we can see that the emitter-base voltage should not be greater than  6v, while the output of the lm741 is greater than even 10volts. Connecting 10v to the base of 2n2222 will damage the transistor.


Now, this is the time to use a potential divider circuit, to reduce the output voltage of the lm741 enough that can turn on a transistor but never exceeds 6v. Now we need to find out the value of R2 that gives voltage greater than or equal to 1v and less than 6v.

Use this formula to find the voltage.

Vout  =  R2 ( Vin  /  R1 + R2 )

Vout  = (11v  * 1k) / 11 k

Vout  = 11/11 = 1v

Now the circuit is ready and we can control a relay, now we can connect a load with this relay or we can use this relay to signal a microcontroller. This circuit can be used with or without the Arduino.


  1. Voltage divider use in a Power Supply based on LM317T.

Voltage Divider

The output voltage of the LM317t variable adjustable voltage regulator is determined by the ratio of two resistors R1 and R2 which basically forms a potential divider circuit across the output terminal of the lm317t voltage regulator.

The voltage across the feedback resistor R1 is constant 1.25 volts reference voltage, Vref, produced between the output and adjustment terminal of the voltage regulator. The current is constant at the adjustment terminal which is 100uA. Since the reference voltage Vref across the resistor R1 is constant, so a constant current I will flow through the other resistor R2, which results in an output voltage which can be calculated using the following formula.

Vout = 1.25( 1 + (R2/R1) )

The input voltage Vin to the LM317t must be at least 2.5 volts greater than the required output voltage.

Lm317 voltage regulator calculator:

If we know the value of the required output voltage, let’s say 9 volts, and the feedback resistor R1 is 214 ohms, then we can calculate the value of resistor R2.

R1.((Vout/1.25)-1) = 214.((9/1.25)-1) = 1326 ohm

Of course, in practice, the resistor R2 is normally replaced by a potentiometer so as to produce the variable voltage.

Voltage Divider

Note: voltage dividers should not be used to supply power to a load. Any current that the load requires is also going to have to run through R1. The current and voltage across R1 produce power, which is dissipated in the form of heat. If that power exceeds the rating of the resistor (usually between ⅛W and 1W), the heat begins to become a major problem, potentially melting the poor resistor. If you need to drop down a voltage to use it as a power supply, look into voltage regulators or switching supplies.



  1. Voltage divider as the Voltage convertor for Arduino

Voltage Divider

As you know Arduino is based on the 5v controller while the LoRa transceiver module by the Reyax technology can handle voltages from 2.8 to a maximum of 3.6 volts. The typical voltage is 3.3 volts as explained earlier. From this information we know that this module cannot be directly interfaced with the Arduino for this we need some kind of converter that can convert 5 volts into 3.3 volts. But instead of using the converter we can use a simple potential divider circuit. As you can see 4.7k and 10k resistors are connected in series which gives me 3.4 volts which is perfect for the Reyax LoRa Transceiver module.

A wire from the middle of these resistors is connected with the RXD pin of the module, the other leg of the 10k resistor is connected with the ground, while the other leg of the 4.7k resistor is connected with the TX of the Arduino. The Rx pin of the Arduino is connected with the TXD pin of the LoRa Module. The ground of the LoRa module is connected with the ground of the Arduino.

 

Voltage Divider

LED1 is 2.5 volts, to power up this LED using 5 volts we need to use a resistor connected in series with the LED. This makes a divider circuit. I have been using this circuit for quite a long time.


Watch Video Tutorial:

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About the Author: Engr Fahad

My name is Shahzada Fahad and I am an Electrical Engineer. I have been doing Job in UAE as a site engineer in an Electrical Construction Company. Currently, I am running my own YouTube channel "Electronic Clinic", and managing this Website. My Hobbies are * Watching Movies * Music * Martial Arts * Photography * Travelling * Make Sketches and so on...

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