Voltage Follower Circuit Calculation

A voltage follower is a basic amplifier circuit that provides a high-input impedance and low-output impedance, making it ideal for buffering signals. This guide explains how to calculate key parameters of a voltage follower circuit and provides an interactive calculator for quick results.

What is a Voltage Follower?

A voltage follower is an amplifier circuit that maintains the same voltage at its output as at its input. It's called a "follower" because the output voltage follows the input voltage. The most common implementation uses an operational amplifier (op-amp) configured in a unity-gain configuration.

Key characteristics of a voltage follower include:

High input impedance (minimal current drawn from the source)
Low output impedance (strong drive capability)
Unity voltage gain (output voltage equals input voltage)
Inverted phase (output is 180 degrees out of phase with input)

Voltage followers are widely used in signal conditioning, buffering, and impedance matching applications.

Voltage Follower Formula

The basic voltage follower circuit consists of an operational amplifier with the non-inverting input connected to the input signal and the inverting input connected to the output through a feedback resistor.

Voltage Follower Gain (A_v)

A_v = V_out / V_in = 1

Where:

V_out = Output voltage
V_in = Input voltage

The voltage follower provides unity gain, meaning the output voltage is equal to the input voltage. The phase is inverted (180 degrees), but this is typically not a concern in most applications.

How to Calculate Voltage Follower

Calculating a voltage follower involves determining the output voltage based on the input voltage and understanding the circuit's behavior. Here's a step-by-step approach:

Identify the input voltage (V_in)
Determine the power supply voltages (V_CC and V_EE)
Calculate the output voltage (V_out) using the voltage follower formula
Verify the circuit's performance considering the op-amp's specifications

Note: The voltage follower's output voltage is limited by the power supply voltages. The output cannot exceed the positive supply voltage or go below the negative supply voltage.

Example Calculation

Let's consider a voltage follower circuit with the following parameters:

Input voltage (V_in) = 2.5 V
Positive supply voltage (V_CC) = +15 V
Negative supply voltage (V_EE) = -15 V

Using the voltage follower formula:

V_out = V_in = 2.5 V

The output voltage will be 2.5 V, following the input voltage. The phase will be inverted, but this is typically not a concern in most applications.

This example demonstrates how a voltage follower maintains the input voltage at its output while providing buffering and impedance matching.

FAQ

What is the purpose of a voltage follower?: A voltage follower is used to buffer signals, provide impedance matching, and maintain the same voltage at the output as at the input. It's commonly used in signal conditioning and interfacing applications.
What is the gain of a voltage follower?: The gain of a voltage follower is unity (1), meaning the output voltage is equal to the input voltage. The phase is inverted (180 degrees).
What are the key characteristics of a voltage follower?: Key characteristics include high input impedance, low output impedance, unity voltage gain, and inverted phase. Voltage followers are widely used in buffering and impedance matching applications.
What are the limitations of a voltage follower?: Limitations include the output voltage being limited by the power supply voltages, potential noise issues, and the requirement for a stable power supply.
How do I calculate the output voltage of a voltage follower?: The output voltage of a voltage follower is equal to the input voltage. You can use the formula V_out = V_in to calculate the output voltage.