Circuits / 555 and op-amps
Inverting amplifier
Gain = −R2/R1 around the reference on V+: the output is twice the input, upside down
Tap a part to see its voltages and currents. It is a model, not a measurement.
What do you need?
- Resistor 10 kΩ × 3Search on Amazon
- Integrated circuit LM358Search on Amazon
- Resistor 20 kΩSearch on Amazon
- Jumper wires × 5Search on Amazon
- BreadboardSearch on Amazon
How does an inverting op-amp amplifier work?
In an inverting amplifier the signal enters through R1 into V−, and R2 feeds the output back to the same point. The op-amp holds V− at the voltage of V+, so whatever current the input pushes through R1 has to come back through R2, and the gain is G = −R2 / R1. With 20 kΩ and 10 kΩ the gain is −2: twice as large and upside down. On a single 9 V supply there is no negative voltage, so R3 and R4, two 10 kΩ resistors, set a 4.5 V reference on V+, and everything swings around it. The input is a sine of 0.5 V amplitude around 4.5 V. The output goes from 3.5 V to 5.5 V, swinging 1 V each way, and it falls exactly when the input rises.
Values from the Protoboard ISO simulation: a model, not a bench measurement.
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