How to use a potential divider to control voltage in a circuit

Part ofDesign and TechnologyElectronic and microelectronic control systems

Key points about using potential dividers

  • a voltage divider reduces the voltage in a circuit
  • the resistance value of the resistors will set the output voltage
  • potential dividers can be two resistors connected in series across a circuit
  • it is important to identify potential dividers in a circuit diagram
  • variable resistors adjust sensitivity in a potential/voltage divider
  • the output voltage is calculated using resistors (R1) and (R2) and the input voltage \((\text{V}_{\text{in}}) \)
  • use the formula \( \text{V}_{\text{out}} = \frac{\text{R2}}{\text{R1+R2}} \times \text{V}_{\text{in}}\)
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What is a potential divider

A potential divider, also known as a voltage divider, is a simple yet essential circuit used to reduce voltage to a desired level. It consists of two resistors connected , with the output voltage taken from the junction between them. This setup splits the input voltage into smaller parts, with the division of voltage being proportional to the resistance values of the two resistors.

The resistors in a potential divider can have fixed values, or one may be a variable component like an LDR (light dependent resistor) or a thermistor. These variable resistors allow the output voltage to change in response to environmental conditions, such as light or temperature. This makes potential dividers versatile for various applications.

Potential dividers are commonly found in everyday devices like radios, games, and toys. For instance, if you have a 9V battery but need 6V for a part of your circuit, you can use a potential divider to achieve this. By carefully selecting the resistor values, you can ensure the output voltage meets the specific requirements of your circuit.

Potential divider circuit diagram - Vs, Vout and resistors R1 & R2 labelled
A potential divider (or voltage divider), circuit diagram

  • \(\text{V}_{\text{s}}\) (Supply Voltage): This is the input voltage applied across the series combination of R1 and R2. This is the total voltage applied to the circuit.

  • R1 and R2: These are the two resistors connected in series. One end of R1 is connected to the positive terminal of the supply voltage (\(\text{V}_{\text{s}}\)), and the other end is connected to one end of R2. These resistors divide the supply voltage into two parts.

  • 0V (Ground): The other end of R2 is connected to the ground (0V).

  • The output voltage\((\text{V}_{\text{out}})\) is taken from the junction between R1 and R2. The voltage measured across R2, which is a fraction of the total supply voltage.

The output voltage \((\text{V}_{\text{out}})\) depends on the values of the two resistors (R1 and R2).

By picking the right resistor values, you can make \(\text{V}_{\text{out}}\) be any part of the input voltage (\(\text{V}_{\text{s}}\)) that you want.

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How to calculate the output voltage of a potential divider

The output voltage (\(\text{V}_{\text{out}} \)) of a potential divider can be calculated by using this formula:

\(\text{V}_{\text{out}}=\frac{\text{R2}}{\text{R1+R2}}\times\text{V}_{\text{in}}\)

  • R1 and R2 represent the resistors connected in series.
  • \(\text{V}_{\text{in}} \) is the input voltage to the circuit.
Worked example - calculating Vout of a potential divider
Worked example - calculating Vout of a potential divider

  • When R1 and R2 are equal, the voltage will split in half.

  • When R2 is larger than R1, the voltage split will be larger.

  • When R2 is smaller than R1, the voltage split will be smaller

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How to adjust the sensitivity in a potential divider

  • In a potential divider, you have two resistors connected in series. One of these resistors can be a variable resistor, like an LDR (light dependent resistor) or a thermistor
  • variable resistors/potentiometers can be used in potential dividers to adjust the output voltage \((\text{V}_{\text{out}}) \)
  • by using a variable resistor to manually change the resistance, you can control the sensitivity and the voltage output of the circuit, useful in applications like volume controls in radios
  • sensitivity refers to how much the output voltage changes in response to changes in the input voltage or the resistances in the circuit
Worked example - calculating Vout of a potential divider with a variable resistor
Worked example - calculating Vout of a potential divider with a variable resistor

In this case R1 is a variable resistor - which has been set at a resistance of 50kΩ

  • If the variable resistor's resistance increases, \((\text{V}_{\text{out}}) \) will decrease because more voltage is dropped across the variable resistor.
  • If the variable resistor's resistance decreases, \((\text{V}_{\text{out}}) \) will increase because less voltage is dropped across the variable resistor.

By adjusting the variable resistor, you can control \((\text{V}_{\text{out}}) \) to match the needs of your circuit.

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