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Op-Amp Voltage Follower

Tutorial Index

Recipe #10 — op-amp voltage follower

The voltage follower is another circuit that appears to do almost nothing — and is useful for exactly the same reason as the transistor emitter follower and digital buffer.

OP-AMP VOLTAGE FOLLOWER IN + − OUT negative feedback: output returned to − input Ideally: VOUT ≈ VIN

The simple rule

Connect the op-amp output directly to the inverting (−) input. Apply the signal to the non-inverting (+) input.

VOUT ≈ VIN

Negative feedback makes the op-amp adjust its output so the two input voltages stay nearly equal while operating in its linear region.

Real-world uses: buffering sensors, isolating a voltage divider, driving an ADC input, preventing one stage from loading another, and providing more output current than a weak source can supply directly.

Three buffers, one broad idea

Digital buffer: logical 1 stays 1 and logical 0 stays 0, with better drive.

Emitter follower: analog voltage follows the input, with better current drive.

Op-amp follower: analog output closely follows the input using negative feedback.

Real op-amps are not ideal

Input voltage range, output swing, supply voltage, output current, bandwidth, slew rate, offset, input bias current, and capacitive-load stability can all matter. The datasheet tells us where the simple “VOUT = VIN” approximation is valid.

Try these yourself

How is the op-amp wired as a voltage follower? OP-AMP VOLTAGE FOLLOWER IN + − OUT negative feedback: output returned to − input Ideally: VOUT ≈ VIN
Negative feedback from output to the inverting input makes the op-amp drive its output until V− closely follows V+.
What is the ideal closed-loop voltage gain of the voltage follower?
The follower is a unity-gain buffer: ideally VOUT ≈ VIN.
What must still be checked for a real op-amp?
Real op-amps have voltage, current, speed, and stability limits that must be respected.

What these ten recipes have in common

Each one is small enough to understand by following a signal or current path, but each also appears as a building block inside much larger equipment.

The next cookbook pages can naturally add comparators, zener regulators, bridge rectifiers, transformer supplies, oscillators, simple audio mixers, tone networks, and more speaker crossover examples without changing this basic teaching style.

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