Voltage Follower (Unity Gain Buffer) Calculator
This Voltage Follower Calculator estimates the ideal output voltage of a unity-gain op-amp buffer and checks whether the ideal output exceeds the selected supply rails.
Use it for first-pass signal buffering, ADC input driving, source isolation, cable driving, and analog signal-chain checks where the ideal voltage follower model is appropriate.
Engineering tool
Voltage Follower Calculator
Calculate ideal unity-gain buffer output voltage and check whether the ideal output exceeds the selected op-amp supply rails.
Signal voltage applied to the voltage follower input.
Positive op-amp supply rail used for the ideal output swing check.
Negative op-amp supply rail used for the ideal output swing check.
Output voltage (Vout)
5 V
Result console
- Output voltage (Vout)
- 5V
- Unity gain
- 1V/V
- Output swing status
- Normal
- Supply margin
- 10V
- Input voltage (Vin)
- 5V
- Positive supply
- 15V
- Negative supply
- -15V
Output is within the selected ideal supply rails.
Formula reference
Voltage Follower Formula
The ideal voltage follower assumes negative feedback, unity gain, high input impedance, low output impedance, and valid linear operation within the selected supply rails.
Av = 1Vout = VinPositive margin = V+ − VoutNegative margin = Vout − V−Supply margin = min(Positive margin, Negative margin)Variable definitions
- Vin
- Input voltage applied to the buffer
- Av
- Ideal closed-loop voltage gain
- Vout
- Ideal output voltage
- V+
- Positive op-amp supply rail
- V−
- Negative op-amp supply rail
- Supply margin
- Nearest ideal distance from Vout to a supply rail
Variable Description
- Input voltage Vin
- The signal voltage applied to the op-amp non-inverting input.
- Unity gain
- The ideal voltage follower gain. In the ideal model, Av is exactly 1 V/V.
- Output voltage Vout
- The ideal output voltage. For a voltage follower, Vout equals Vin before real output swing limits are applied.
- Positive supply V+
- The upper supply rail used to check whether the ideal output is above the available op-amp supply.
- Negative supply V−
- The lower supply rail used to check whether the ideal output is below the available op-amp supply.
- Supply margin
- The nearest ideal voltage margin from the output to either supply rail. Negative margin indicates ideal rail overrun.
Worked Examples
Example 1: Normal Buffer Output
- Vin
- 5 V
- Positive supply
- +15 V
- Negative supply
- −15 V
Av = 1; Vout = Vin
Vout = 5 V; positive margin = 15 V − 5 V = 10 V; negative margin = 5 V − (−15 V) = 20 V
Output = 5 V, Output Status = Normal
The ideal output is comfortably inside the selected supply rails.
Example 2: Ideal Output Above Positive Supply
- Vin
- 16 V
- Positive supply
- +15 V
- Negative supply
- −15 V
Av = 1; Vout = Vin
Ideal Vout = 16 V, but the positive supply rail is only +15 V.
Ideal output = 16 V, Status = Output exceeds positive supply.
The ideal op-amp calculation is shown, but a real device may saturate before reaching 16 V.
Unity gain buffer
A voltage follower provides a closed-loop gain of one, so it copies the input voltage without intentional voltage amplification.
Voltage buffer
The buffer is useful when one circuit stage should not significantly load or disturb another stage.
High input impedance
A real voltage follower can present high input impedance to a sensor, divider, filter, or signal source.
Low output impedance
The op-amp output can drive a load more effectively than many high-impedance signal sources.
Load isolation
Buffers reduce interaction between source impedance, load impedance, filters, ADC inputs, and long traces or cables.
Driving ADC inputs
A voltage follower can help charge ADC sample capacitors and reduce conversion errors when the op-amp is fast and stable enough.
Driving long cables
Long cables add capacitance and noise pickup, so real buffer designs should verify stability and output drive capability.
Rail-to-rail vs standard op-amps
Rail-to-rail output devices can swing closer to the supplies than standard op-amps, but they still have datasheet output limits.
Common Mistakes
Thinking a voltage follower has no purpose
Even without voltage gain, a buffer can isolate stages, reduce loading, and improve signal-chain behavior.
Ignoring supply limits
The output cannot exceed the real op-amp supply rails, even though the ideal equation says Vout equals Vin.
Ignoring output swing
Many op-amps cannot swing all the way to either rail, especially under load.
Ignoring output drive capability
A buffer is not unlimited. Check output current, load impedance, short-circuit limits, and thermal behavior.
Treating a buffer as a voltage regulator
A voltage follower follows an input signal. It does not replace a regulator for supply generation or power delivery.
Support reference
FAQ
What is a voltage follower?
A voltage follower is an op-amp buffer circuit where the output is directly fed back to the inverting input. Ideally, the output voltage follows the input voltage with a gain of one.
Why is the gain equal to one?
The direct negative feedback connection forces the op-amp output to match the input voltage in the ideal linear model, so Av = Vout/Vin = 1.
Why use a buffer instead of connecting directly?
A buffer provides high input impedance and low output impedance, which helps isolate a weak signal source from a load, ADC input, cable, or following circuit stage.
Can the output exceed the supply rails?
No real op-amp can drive beyond its supply rails. This calculator still shows the ideal Vout = Vin result, but it warns when the ideal output exceeds the selected rails.
What is the difference between a voltage follower and a voltage regulator?
A voltage follower buffers a signal and follows its input. A voltage regulator creates or maintains a supply voltage and is designed for power delivery and regulation.
When should I use a unity gain buffer?
Use a unity gain buffer when a signal source needs isolation, when driving ADC sample capacitors, when feeding a lower impedance load, or when reducing interaction between circuit stages.
Can a voltage follower drive capacitive loads?
Some op-amps become unstable with capacitive loads. Real designs should check unity-gain stability, output drive, phase margin, and whether a small series output resistor is needed.
Related Engineering Guides
Dedicated op-amp guides are planned for this topic cluster. These guide topics are reserved for future publication and are shown without links until the pages exist.
Planned Engineering Guide
Voltage Follower Basics
Planned guide covering unity gain buffers, direct feedback, input impedance, and output impedance.
Planned Engineering Guide
Unity Gain Stability
Planned guide explaining why some op-amps are not stable at unity gain and how to read stability specifications.
Planned Engineering Guide
Buffer Amplifier Applications
Planned guide covering source isolation, signal chain buffering, cable driving, and load interface examples.
Planned Engineering Guide
Driving ADC Inputs
Planned guide covering ADC sample capacitors, source impedance, settling time, and op-amp buffer selection.
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Engineering Disclaimer
This calculator uses an ideal voltage follower model for estimation and education. Real designs must verify supply rails, output swing, input common-mode range, unity-gain stability, slew rate, bandwidth, output current, capacitive load behavior, load impedance, noise, and device-specific datasheet limits before hardware release.