Circuits / 555 and op-amps
Op-amp voltage follower (buffer)
With the output on V−, the output copies V+: the potentiometer gives a voltage, the op-amp gives the current
Tap a part to see its voltages and currents. It is a model, not a measurement.
What do you need?
- Potentiometer 100 kΩSearch on Amazon
- Integrated circuit LM358Search on Amazon
- Resistor 330 ΩSearch on Amazon
- Red LEDSearch on Amazon
- Jumper wires × 8Search on Amazon
- BreadboardSearch on Amazon
What is an op-amp voltage follower for?
In a voltage follower the output is wired straight back to V−, so the op-amp drives its output until it matches V+: the output copies the input, gain 1. That sounds useless until you look at the currents. Here a 100 kΩ potentiometer on 9 V sets V+, at its middle 4.5 V. The LM358's input takes almost no current, so the potentiometer is not loaded. The output also sits at 4.5 V, and it drives the LED through R1 (330 Ω) at about 8.4 mA, current that comes from the op-amp's supply, not from the potentiometer. Connected directly, the LED would drag the wiper down, as in the potentiometer-and-LED circuit, where the middle of the knob gives only 0.36 mA. The follower, also called a buffer, separates a voltage that is easy to disturb from the load that uses it.
Values from the Protoboard ISO simulation: a model, not a bench measurement.
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