Voltage Follower / Buffer Calculator

A voltage follower (or buffer) is a circuit that transfers a signal from a high-impedance source to a low-impedance load without changing the voltage — used to isolate stages in audio, sensor, and power circuits. Select your circuit type (Op-Amp, BJT Emitter Follower, or JFET Source Follower), then enter your input voltage, supply voltage, load resistance, and any device-specific parameters to get the output voltage. Secondary outputs include voltage gain, input impedance, output impedance, and current gain.

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Current gain for BJT circuits

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Output Voltage

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Voltage Gain

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Input Impedance

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Output Impedance

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Current Gain

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Frequently Asked Questions

What is a voltage follower circuit?

A voltage follower is a unity gain buffer that produces an output voltage equal to its input voltage. It provides high input impedance and low output impedance, making it ideal for impedance matching between circuits.

Why use a voltage follower buffer?

Voltage followers prevent loading effects between circuit stages, provide current amplification while maintaining voltage levels, and offer isolation between sensitive input circuits and varying load conditions.

What's the difference between op-amp and transistor voltage followers?

Op-amp followers offer near-perfect unity gain and very high input impedance, while transistor followers (BJT/JFET) have slightly less than unity gain but can handle higher currents and offer simpler, lower-cost implementations.

How do I calculate input impedance for a BJT emitter follower?

Input impedance of a BJT emitter follower is approximately β × (RE + re), where β is current gain, RE is emitter resistance, and re is the dynamic emitter resistance (about 26mV/IE at room temperature).

What affects the voltage gain in a practical voltage follower?

While ideal voltage followers have unity gain (1.0), practical circuits have slightly less due to finite open-loop gain in op-amps or the emitter resistance in transistor configurations, typically ranging from 0.95 to 0.999.

How do I choose between BJT and JFET for voltage following?

BJT followers offer higher current gain and lower output impedance but require base current. JFET followers provide very high input impedance with no gate current but have temperature-dependent characteristics and lower transconductance.

What's the typical output impedance of a voltage follower?

Op-amp followers typically have output impedance of 0.1-1Ω, BJT emitter followers around 10-100Ω (depending on β and RE), and JFET source followers range from 100Ω to several kΩ depending on transconductance.

Can voltage followers amplify current?

Yes, voltage followers provide significant current amplification while maintaining voltage unity gain. Op-amp followers can source/sink substantial current, and transistor followers provide current gain equal to β (BJT) or effectively infinite gain (JFET).