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Home > Other > Exploring Op-Amp Voltage Follower: Circuit, Working, and Applications

Exploring Op-Amp Voltage Follower: Circuit, Working, and Applications

Update Time: 2023-11-09 12:03:05


The operational amplifier is a versatile and user-friendly device that has found its way into various circuits and applications. One of the key reasons behind the op-amp's widespread adoption is its unique blend of simplicity and performance. Op-amp circuits can enhance various systems without being overly complex to design, often needing just a minimal number of external components.

In this article, we will delve into the voltage follower, which serves as an excellent illustration of a straightforward yet efficient op-amp circuit.

What is the Op-Amp Voltage Follower?

A voltage follower, known by various names such as a unity-gain amplifier, buffer amplifier, or isolation amplifier, is an op-amp circuit with a voltage gain of 1.

In practical terms, this signifies that the op-amp does not amplify the signal. It garners its name "voltage follower" because the output voltage precisely tracks the input voltage, resulting in the output voltage mirroring the input voltage. Consequently, when, for instance, a 10V signal is introduced as input to the op-amp, the output also registers 10V. Essentially, a voltage follower serves as a buffer, introducing neither amplification nor attenuation to the signal.

Voltage Follower Circuit.png

Voltage Follower Characteristics

High Output Voltage Stability

The primary purpose of a voltage follower is to duplicate the input voltage signal at the output while ensuring a consistent and stable output voltage. Consequently, voltage followers maintain high output voltage stability, effectively minimizing noise and interference in the output signal.

Versatile Application

Due to their straightforward design and minimal component requirements, voltage followers find utility in various electronic devices. They can preserve a steady voltage in multiple applications, ranging from small-scale sensors to extensive audio systems.

Clean Output Waveform

Voltage followers generate exceptionally pristine output waveforms devoid of distortion or impurities. This purity stems from their singular function of amplifying and mirroring the input signal at the output without introducing any signal processing or filtering.

High Precision

Voltage followers deliver a remarkable output voltage precision, often attaining precision levels extending to multiple decimal places or higher. This precision renders them invaluable in applications that demand exacting voltage output.

Purposes of Voltage Followers

Voltage followers deliver a remarkable output voltage precision, often attaining precision levels extending to multiple decimal places or higher. This precision renders them invaluable in applications that demand exacting voltage output.

Signal Replication

The primary function of a voltage follower is to replicate the input voltage signal at the output. It can achieve precise and stable signal replication, making it highly valuable in various electronic applications.

Maintaining Voltage Stability

Voltage followers are capable of maintaining a stable output voltage. This makes them particularly useful in applications that require a consistent voltage output, such as in analog circuits, where a sound voltage signal is crucial for circuit performance and accuracy.

Signal Amplification

Voltage followers are commonly used as signal amplifiers, capable of amplifying the input signal to a larger magnitude while maintaining a stable output voltage. This is highly beneficial in applications that require signal amplification, such as in audio amplifiers and measurement instruments.

Signal Isolation

Voltage followers can also be employed for signal isolation, completely separating one circuit from another. This significantly reduces the impact of interference and noise, preserving the integrity of the signal.

Reasons for Using a Voltage Follower


The Advantages of Voltage Follower

  • An operational amplifier in a voltage follower configuration results in minimal current draw from the input power source.

  • A voltage follower displays a combination of high and low output impedance.

  • This configuration offers both current and power gain.

  • Voltage followers effectively eliminate the loading effect.

  • It's important to note that a voltage follower neither amplifies nor diminishes the input signal's voltage.

  • A voltage follower provides a unity voltage gain, which maintains the input signal's amplitude.

  • It yields unity transmission gain, ensuring the signal's amplitude remains unchanged.

  • This design enhances both current and power gain.

  • The output capitalizes on the circuit's lower output impedance.

  • In this operational amplifier setup, no current is drawn from the input source.

Key Advantages of Using a Voltage Follower Circuit

Operational amplifier circuits are known for their very high input impedance. It's this high input impedance that makes voltage followers a valuable choice.

Purpose of Voltage Followers.jpg

Low Current Consumption of Voltage Followers

When a circuit has extremely high input impedance, the current drawn by the load from the circuit is minimal. Therefore, the larger the resistance, the less current is drawn from the power source. The advantage is that when current is fed into a high-impedance load, it doesn't affect the circuit's power. In the following circuit, the load requires and consumes a significant amount of current because the load has a low impedance. According to Ohm's law, I=V/R. If the load's resistance is very low, it will absorb much current. This draws a significant amount of electrical energy from the power source, leading to high interference.

Voltage Followers in Voltage Divider Circuit.png

The circuit below now draws minimal current from the power source. Because operational amplifiers have such high input impedance, they consume minimal current.

Voltage Followers in Voltage Divider Circuit-2.png

This is one of the reasons for using voltage followers. Due to their high input impedance, they consume minimal current, don't interfere with the original circuit, and provide the same voltage signal as the input. They act as isolation buffers, separating the circuit and keeping interference from the power source minimal.

Voltage Followers in Voltage Divider Circuit-3.png

Importance of Voltage Followers in Voltage Divider Circuits

For instance, in the circuit below, if we require to have a 5V power supply voltage across the load's terminals, it's evident that this circuit won't work as expected. Since the load resistance is relatively low and in parallel with the 10K resistor below, the impedance changes. So, how can we address this issue?

Importance of Voltage Followers in Voltage Divider Circuits.png

Voltage Divider Circuit

We can use an operational amplifier to create a voltage follower. Because operational amplifier input resistance is very high, even in parallel with the 10K resistor below, the impedance remains close to 10K. Let's do the math; assuming the operational amplifier input resistance is 100MΩ, the parallel resistance of 10K and 100K is 9999Ω. Therefore, the voltage follower can serve as an isolation circuit to reduce interference between the load and the power source.

Voltage Divider Circuit.png

Isolation Circuit with Resistor Divider

By effectively using the operational amplifier as a voltage follower in the context of a voltage divider circuit, the resulting setup serves as an isolation circuit with the added capability of minimizing potential disturbances between the load and the power source.

Voltage Follower Gain

A voltage follower possesses a voltage gain of 1 (unity) since the output voltage closely tracks the input voltage. While a voltage buffer amplifier exhibits an almost unity voltage gain, it imparts significant current and power amplification. Nevertheless, it's customary to refer to it as having a gain of 1, specifically denoting its voltage gain (equivalent to 0 dB).

Voltage Follower in Voltage Divider Circuits

In every electronic circuit, voltage distribution occurs based on the impedance or resistance of the connected components. When an operational amplifier (op-amp) is introduced into the circuit, it presents a high impedance, resulting in a substantial voltage drop across it.

Therefore, when we employ a voltage follower in voltage divider circuits, it ensures that ample voltage is supplied across the load. Let's explore a voltage divider circuit with a voltage follower, as depicted in the figure below.

voltage divider circuit with a voltage follower.png

In this configuration, the voltage divider is positioned between two 10 KΩ resistors and the op-amp. This op-amp exhibits an input resistance of several hundred megaohms, which we can approximate as 100 MΩ. Consequently, the equivalent parallel resistance becomes 10 KΩ || 100 KΩ.

Equivalent Parallel Resistance = (10KΩ x 100MΩ) / (10KΩ + 100MΩ) =9999Ω ≈10KΩ

As a result, we have 10KΩ || 10KΩ. According to the voltage divider principle, a setup with two equal resistances will provide precisely half of the input voltage.

This can be demonstrated using the voltage divider formula as follows:

Hence, the 5V supply voltage is divided with 5V dropping across the top 10KΩ resistor and 5V across the bottom 10KΩ resistor, while the load resistance remains at 100Ω (since 10 KΩ||100 Ω results in equal voltage distribution across parallel resistors).

Vout=Vin x ( R2/(R1+R2) ) =10V  x ( 10KΩ / (10KΩ + 10KΩ) ) =5V

We have illustrated how the op-amp operates as a buffer to deliver the required voltage to the connected load. With a voltage follower in the same circuit, this would be feasible due to insufficient voltage across the load.

The primary applications of a voltage follower are twofold. It serves isolation purposes and also acts as a buffer to provide the desired voltage to the connected load in electrical or electronic circuits.

Voltage Followers Applications

Voltage followers find application in various scenarios, including:

  • Isolating input and output circuits.

  • Acting as buffers in electronic logic circuits.

  • Incorporation into bridge circuits alongside transducers.

  • Utilization in the sample and hold circuits.

  • Integration into active filter circuits.

  • Deployment within sample and hold (S & H) circuits.

Voltage Follower Stability

Generally, you can count on a voltage follower to perform precisely as the name suggests, maintaining an output signal that mirrors the input signal. However, there's a critical concern that every circuit designer must be mindful of, and that's stability. The voltage follower, like other op-amp circuits, is prone to oscillation.

Oscillation in negative feedback amplifiers is linked to phase shifts that can turn negative feedback into positive feedback. You might assume that a voltage follower, with no overall amplification, should be immune to stability issues. Surprisingly, voltage followers are more susceptible to oscillation than circuits with higher gain. For a deeper dive into this intricate subject, refer to AAC's article on gain margin and phase margin.

In most instances, ensuring your voltage follower doesn't oscillate is as simple as choosing an op-amp labeled "unity-gain stable." These op-amps are internally compensated to establish a frequency response that guarantees stable performance, even when used in a voltage follower configuration.

A High Current Voltage Follower

The remarkably low output impedance of voltage followers renders them highly advantageous. They excel in providing current to low load impedances. Nevertheless, it's important to note that most operational amplifiers do not offer high-current output capabilities.

High-Current Voltage Follower.png


To sum it up, a voltage follower is a straightforward yet valuable circuit recognized for its capacity to uphold high output voltage stability, broad utility, pristine output waveforms, and precision. Its core purpose revolves around duplicating the input voltage at the output while maintaining an unwavering output voltage. Voltage followers are integral components in various domains, including analog circuits, sensors, and audio equipment.

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  • What is the purpose of a voltage follower?
  • A voltage follower operates effectively as a buffer, primarily due to its minimal current draw resulting from the amplifier's elevated input impedance. This feature helps eliminate loading effects while preserving the output voltage at the same level.

  • Does voltage follower increase current?
  • When dealing with a circuit that can deliver ample voltage but has limited current capacity, incorporating a voltage follower can enhance the available current output.

  • What are other names for voltage follower?
  • Other names, including Isolation Amplifier, Buffer Amplifier, and Unity-Gain Amplifier, also know the voltage follower.

  • How do you calculate voltage follower?
  • Gain (Av) = Vout / Vin.

  • What is the purpose of a voltage buffer?
  • A voltage buffer amplifier serves the purpose of transferring a voltage from a source circuit characterized by a high output impedance to a destination circuit with a lower input impedance.

  • How much voltage gain is provided by the voltage follower?
  • In a voltage follower circuit, the output voltage precisely matches the input voltage, resulting in a gain of one (unity). It is important to note that the incoming signal is not amplified.

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