Op-Amp Series – Part 3: Non-Inverting Operational Amplifier

-

Non-Inverting Operational Amplifier

In this post we will explore how a non-inverting operational amplifier is used when you want to increase the size of a voltage signal without changing its polarity. If the input goes up, the output goes up. If the input goes down, the output goes down.

This makes it one of the most common and useful op-amp configurations.

In a non-inverting amplifier:
  • The input signal is connected to the non-inverting (+) input
  • The output is fed back to the inverting (–) input using two resistors
  • The feedback resistors control how much the signal is amplified

The key idea is simple:

The op-amp adjusts its output so that the voltage on the – input matches the voltage on the + input.

Gain Formula

Assumed knowledge: This section builds on the rules and formulas introduced in Part 1 (Op-Amp Basics) and Part 2 (Inverting Amplifier). We assume you are already familiar with negative feedback, ideal op-amp assumptions, and how resistor ratios set gain.

The voltage gain of a non-inverting amplifier is:

Gain (Av) = 1 + (R1 / R2)

Where:

  • R1 is the resistor from output to the – input
  • R2 is the resistor from the – input to ground

Example: Gain of 2

Choose:

  • R1 = 10kΩ
  • R2 = 10kΩ

Now calculate the gain:

Av = 1 + (10k / 10k)
Av = 1 + 1
Av = 2

What Happens to the Voltage

If the input = 1V
Then with a gain of 2, the output = 1V × 2 = 2V
This is well within the limits of the circuit, so the output is clean and correct.

If the input= 3V
Then the output = 3V × 2 = 6V
This means the output voltage will be twice the input voltage.

Mathematically, this is correct, though now we need to think about the power supply.

Power Supply Limitation and Clipping

If we assume the op-amp is powered from:

  • 0V (ground)
  • +5V supply

An op-amp cannot output a voltage higher than its supply.

So even though the maths says the output should be 6V:

  • The op-amp runs out of voltage
  • The output hits the top of the supply rail
  • The output stops increasing

The result is clipping:

  • The top of the waveform flattens
  • The signal is no longer a faithful amplified version of the input

This is a real-world effect you will see immediately on the bench.

The important point:

The gain has not changed — the power supply simply limits how large the output can be.

Building the Circuit

This circuit is very easy to build on a breadboard and is ideal for demonstrating gain and clipping in the real world.

Parts Required

  • LM358 operational amplifier
  • 2 × 10kΩ resistors
  • Breadboard
  • 5V DC power supply
  • Input voltage source (potentiometer, signal generator, or fixed voltage source)
  • Multimeter or oscilloscope

Circuit Diagram

Circuit Diagram

LM358 Pinout (Single Op-Amp Use)

We will use op-amp A inside the LM358:

  • Pin 1 → Output
  • Pin 2 → Inverting (–) input
  • Pin 3 → Non-inverting (+) input
  • Pin 4 → Ground (0V)
  • Pin 8 → +5V

Step-by-Step Wiring

  1. Power the op-amp

    • Connect pin 8 to +5V

    • Connect pin 4 to ground

  2. Connect the input signal

    • Connect your input voltage to pin 3 (+ input)

    • Connect the input signal ground to circuit ground

  3. Add the feedback resistors (set the gain)

    • Connect R1 (10kΩ) from pin 1 (output) to pin 2 (– input)

    • Connect R2 (10kΩ) from pin 2 (– input) to ground

    This sets the gain to:

    Gain = 1 + (10k / 10k) = 2

  4. Take the output

    • Measure the output voltage from pin 1 relative to ground

Testing the Circuit

  • Apply 1V to the input

    • You should measure approximately 2V at the output

  • Increase the input to 3V

    • The calculated output is 6V

    • With a 5V supply, the output will clip at around 5V

This makes the limitation of the power supply very obvious and easy to demonstrate.

What Is This Circuit Used For?

Non-inverting amplifiers are used when you need:

  • Voltage amplification without inversion
  • Very high input impedance (the source is not loaded)
  • A predictable gain set by resistors

Typical uses include:

  • Amplifying sensor outputs
  • Buffering signals so they can drive other circuits
  • Audio input stages and preamps

For these reasons, the non-inverting amplifier is one of the first op-amp circuits every electronics beginner should understand.

YouTube Video

Below is a short YouTube video showing the build and operation of this circuit.

Next: Part 4 - The Summing Amplifier

This is using an op-amp to add multiple input voltages together.

Hope you have enjoyed this post and visit again.
Thanks for reading,
Matty

Comments

Post a Comment

Popular posts from this blog

6502 - Part 2 Reset and Clock Circuit

-
Image
6502 Retro Console Part 2 Add a Reset and Clock Circuit In Part 1 we powered up the 6502 and watched it running a NOP test with just the CPU and LEDs on the address bus. Now we’ll give it a clock and a clean start every time you power on, rather than relying on a function generator. In this post we will cover a simple 555 Timer Clock circuit and reset circuit. 555 Timer The 6502 needs a steady pulse on its Φ0 (pin 37) to step through instructions. A NE555 timer is perfect for low-speed testing reliable, simple, and easy to wire. Parts List NE555 timer 1 kΩ resistor 10 kΩ resistor 100 nF capacitor (timing) 0.1 µF capacitor (decoupling) Breadboard + jumper wires Circuit Diagram How to Wire It Add a 0.1 µF decoupling cap across the +5V and GND rails stability. Typical speed: ≈ 7–10 kHz perfect for a visible NOP test. Use larger resistors or capacitors to slow it down. Tip: Swap the timing capacitor for 1 µF and the 10 kΩ for 100 kΩ to step slowly enough ...
Read more

BBC Model B + MMFS: Command Guide

-
Image
BBC Model B + MMFS: Complete Command Guide for SD Card Systems If you’ve upgraded your BBC Model B with the MMFS SD-card interface , you’ve opened up a whole new way to use your retro computer. No more fragile floppy disks MMFS lets you browse, load, and run hundreds of disk images (.SSD or .MMB) straight from an SD card. This guide collects every useful command you’ll need to explore, manage, and boot software quickly on your setup. Quick Start — Create & Use Your Own MMFS Disk Here’s a simple first project to prove everything’s working. Goal: Create a blank disk, format it, write a BASIC program that prints “Hello, World!”, save it, and run it again. You can watch my YouTube video below and see the guides below for more commands. Create or Select a Blank Disk Slot Insert your SD card and power on. To check what’s available: *DCAT Then choose an empty slot (for example, disk 100): *DIN 0 100 This mounts disk 100 into drive 0 (your working drive). Format the Disk ...
Read more

Math Behind Logic Gates

-
Image
Understanding the Real Electronics Behind Logic Gates (The Practical Math Behind Digital Circuits) When we build circuits with logic chips like the 74LS series, it’s easy to think only in 1s and 0s. But under the hood, every logic gate follows the same rules as any other circuit, Ohm’s Law, current limits, and voltage thresholds. So yes, there is real-world math behind those blinking LEDs and logic tables.  1. Logic Levels — The Digital View At the logic level, everything is simple: 0 V → LOW (logic 0) 5 V → HIGH (logic 1) We don’t care about exact voltages here just whether a signal crosses a defined threshold. For TTL (Transistor-Transistor Logic) chips like the 74LS86 XOR gate , these thresholds are: This means a logic gate “decides” based on whether the voltage is above or below that boundary, which is how binary logic becomes real voltage levels. 2. Inside the Circuit — Real Electrical Math Even though logic circuits process bits, they still obey Ohm’s Law ...
Read more