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Voltage Divider

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Voltage Divider

The voltage divider (also known as the potential divider) is a basic but very important electric circuit used to convert a high voltage to a small value in electronics. Voltage dividers are often used to decrease the size of a voltage or provide a reference voltage. They may also be used as a signal attenuator at low frequencies. Let’s study this in more detail.

What is the voltage divider rule?

In electric circuits, the voltage divider rule is used to decrease or increase the voltage levels of a source. This is an important concept, especially when creating increasingly complicated circuits. Engineers use this rule to analyse resistance and optimise electronic equipment.

Voltage divider Voltage divider circuit example StudySmarterAn example diagram of a voltage divider circuit, Oğulcan Tezcan – StudySmarter Originals

Voltage divider formula

So, how is the voltage divider rule applied to electric circuits? Look at the diagram above: there is n number of resistors, and we want to take the voltage output from R1, so we want to calculate the voltage value of R1. The formula for finding the voltage value of R1 (VR1) is

Lets break this down:

  • Recall that the current of the resistors connected in series is the same.
  • Because of Ohms law, we have V = I⋅R
  • So if I stays at the same value, then the voltage level V is directly proportional to the resistance value R.
  • In the above formula, the voltage value of a resistor is equal to the resistance value of the component divided by the total resistance and multiplied by the voltage value of the source (V).

In the circuit below, the given values for the resistors are R1 = 3Ω, R2 = 7Ω, and R3 = 5Ω. Find the output voltage (Vo).

Voltage divider Voltage divider circuit example StudySmarterAn example diagram of a voltage divider circuit, Oğulcan Tezcan – StudySmarter Originals

Solution

We take the output voltage (Vo) from the R3 resistors poles, which means it will be the same value as R3 resistances value voltage. To calculate the voltage value of R3, we can put the given values into the voltage divider equation:

From this calculation, we can find the output voltage:

In some sources, you may see that the voltage divider circuit is a little more simplistic. To help you feel comfortable with both voltage divider diagram types, lets look at another example below.

In the circuit below, the given value for the input voltage (Vin) is 20 volts and the given values for the resistors are R1 = 5Ω and R2 = 5Ω. Find the value of the output voltage (Vo).

Voltage divider Voltage divider circuit example StudySmarterAn example diagram of a voltage divider circuit, Oğulcan Tezcan – StudySmarter Originals

Solution

To solve a question in this diagram style, you must first understand what it represents. This is a complete loop circuit, and it is shown below.

Voltage divider Voltage divider circuit example StudySmarterAn example diagram of a voltage divider circuit, Oğulcan Tezcan – StudySmarter Originals

The point shown as Vin in the first diagram shows the positive pole of the voltage source, and the ground resembles that the circuit is a loop connecting to the negative pole of the source Vin. Now let’s apply the voltage divider equation to find the output voltage (Vo), which is equal to the voltage value of R2.

Lets put the values in their correct places in the equation:

Where are voltage dividers used?

Voltage dividers are used to control the level of a signal and to test voltages. They are also used for the bias of active components in amplifiers. Voltage dividers are found in multimeters as well.

High voltage measurement

Although there are many types of voltmeters for different levels of voltage measurement, if the voltage value to be measured is too big, it cant be done with a voltmeter alone. This is where voltage dividers come into play: the voltage is applied across the voltage divider, and then the voltage output, which is the lowered amount of voltage, will be measured by a voltmeter. For the final step, the measured voltage is multiplied by the factor that the input voltage was lowered by.

Sensor measurement

A microcontroller can read the resistance value of a sensor using voltage dividers. A voltage divider is formed by wiring the sensor in series with a known resistance and applying a fixed voltage across the divider. The analogue-to-digital converter on the microcontroller is linked to the dividers centre tap. This is so that it can read the tap voltage and calculate the sensor resistance using the observed voltage and determined resistance and voltage.

Logic level shifting

Voltage dividers are also used as logic level shifters. Logic level shifters connect two logic circuits in series to each other.

Some logic circuits operate at 5V, and others operate at 3.3V. Lets say we are going to connect two circuits in series to each other:

  • The first one operates at 5V. This means its input and output voltage will be 5V.
  • The second one operates at 3.3V, which means its input and output voltage will be 3.3V.

If we connect these two circuits directly, the first circuits output of 5V can damage the second circuit over time because its input value is 3.3V. However, the problem will be solved if we connect a voltage divider circuit with an output ratio of 3.3/5 serial between these two circuits.

Voltage Divider - Key takeaways

  • In electronics, a voltage divider is a fundamental and important electric circuit that is used to transform a large voltage into a smaller value.
  • Voltage dividers are used to control the level of a signal and to test voltages. They are also used for the bias of active components in amplifiers.
  • Voltage dividers are used in sensor measurement, high voltage measurement, and logic level shifting.
  • The output voltage of a voltage divider can be found from the resistance value of the output component divided by the total series resistance and multiplied by the voltage value of the source.

Frequently Asked Questions about Voltage Divider

A voltage divider is used to scale up or scale down the voltage of a source for different purposes.

You can build a voltage divider using two resistors connected in series and an input voltage.  

A voltage divider is a circuit that consists of a series of resistors. The divide-down ratio is set by two resistors, and the output voltage is a fixed proportion of the input voltage.

After you note down the variables, input voltage, the resistance of the resistor (which the output voltage is measured on), and the total series resistance, then the output voltage of a voltage divider can be found from the resistance value of the output component divided by the total series resistance and multiplied by the voltage value of the source.

After you note down the variables, input voltage, the resistance of the resistor (which the output voltage is measured on), and the total series resistance, then the output voltage of a voltage divider can be found from the resistance value of the output component divided by the total series resistance and multiplied by the voltage value of the source.

Final Voltage Divider Quiz

Question

Which of the following is not one of the areas that voltage dividers are used in?


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Answer

Current measurement.

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Question

Are voltage dividers used on multimeters?


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Answer

Yes, voltage dividers are used on multimeters.

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Question

Which output ratio should be used to transform 10 volts into 2.5 volts?


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Answer

2.5/10

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Question

Can voltage dividers be used to optimise electronic equipment?


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Answer

Yes, voltage dividers can be used to optimise electronic equipment. 

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Question

Considering Ohm’s law, if the current value is constant, what is the relation between the voltage and the resistance?


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Answer

They are directly proportional.

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Question

Can voltage dividers be used as signal attenuators?


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Answer

Yes, voltage dividers can be used as signal attenuators.

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Question

When do voltmeters need voltage dividers to measure the value of the voltage?

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Answer

When the voltage value is too big.

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Question

After you have measured an amount of voltage that is applied through a voltage divider, which factor should it be multiplied/divided by to get the right result?


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Answer

The factor that the input voltage was lowered by in the first place.

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Question

Can a microcontroller read the resistance value of a sensor using voltage dividers?


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Answer

Yes, a microcontroller can read the resistance value of a sensor using voltage dividers.

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Question

What are logic level shifters used for?


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Answer

To connect two logic circuits.

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Question

What happens when you don’t use a voltage divider when connecting two logic circuits that operate at different voltages?


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Answer

The circuits will be damaged.

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Question

The output voltage of a voltage divider can be found from the resistance value of the output component divided by the total series resistance and multiplied by the voltage value of the source. True or false?


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Answer

True.

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Question

Can you take multiple output voltages out of a voltage divider circuit with more than two resistors?


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Answer

Yes, you can take multiple output voltages out of a voltage divider circuit with more than two resistors.

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