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Voltage follower (buffer)

Op-amps and analog ICs · Intermediate · about 15 minutes · part of Zen’s Electronics Design Mastery

A divider makes a voltage, but loading it pulls that voltage down. An op-amp wired as a follower (OUT tied to IN−) copies the voltage while taking almost no current from the divider, then drives the load from its own supply.

Voltage follower (buffer): the circuit on the simulator's bench

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How it works

Unloaded divider: V = 12 × R2 / (R1 + R2) = 6 V

Loaded directly: R4 ∥ R_L = 909 Ω, so V = 12 × 909 Ω / (10 kΩ + 909 Ω) = 1 V

Buffered: the op-amp input draws nanoamps, so the divider stays at its unloaded voltage and the op-amp supplies the 6 mA the load needs.

Try it on the bench

  1. Change R_L buffered to 100 Ω: the LM358 hits its 30 mA current limit and the output sags.
  2. Raise V_s to 20 V: the follower tracks 10 V. The LM358 output only reaches about V+ − 1.5 V, so watch what happens above that.

Parts on the bench

In the course

Zen’s Electronics Design Mastery, module “Op-Amps & Analog ICs”.

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