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Project Notes

#158 ML741/Inverter

Test an inverter circuit using the ML741 discrete component opamp

Notes

This is a demonstration of an inverter/inverting buffer circuit using the ML741 discrete component opamp. The general operation of the circuit is for the output to follow the inverse of the inverting input. This is a special case of the general inverting amplifier configuration with gain set to -1, i.e.

Vout = -Vin
Rf = Rin

Op-Amp_Inverting_Amplifier

How it works

Fundamentally, an op-amp strives to keep its inverting an non-inverting inputs equal by modulating the output.

In the inverter/inverting amplifier configuration, the inverting input is at the midpoint of the Rin:Rf voltage divider. Hence the op amp achieves inverting/non-inverting input equilibrium when Vout = -Vin.

Construction

In this circuit, I am using a single rail supply (V- = GND) instead of the “conventional” dual rail supply (V+/V-).

For this reason, the non-inverting input is pegged to V+/2 with a voltage divider. In a dual rail configuration, V+/2 is usually “ground”.

Breadboard

The Schematic

ML741 on the right, and a standard UA741CN on the left waiting to be put to the test..

The Build

ML741 v “real” 741 Test

Here are some results comparing the behaviour of a standard UA741CN chip with the ML741 (protoboard version).

Setup:

  • power is 5V single rail, i.e. V- = GND
  • non-inverting input is fed a sine wave 1Vpp with 2.5V DC offset
  • the function generator sine wave input replaces the manual 10kΩ input pot in the schematic above (at node FG)

Scope connections

  • CH1: non-inverting input
  • CH2: output

I’ve purposely driven the input signal such that it clips the lower output rail of both the ML741 and UA741CN, because things get interesting around the rails.

At 1kHz

  • ML741 is performing nicely
  • UA741CN hitting the lower rail at ~1.9v

ML741:

ML741_1kHz

UA741CN:

UA741CN_1kHz

At 40kHz

  • ML741 starting to distort at the lower end
  • UA741CN still performing similar to 1kHz

ML741:

ML741_40kHz

UA741CN:

UA741CN_40kHz

At 100kHz

Both ML741 and UA741CN exhibiting similar distortion patterns: waveforms have lost definition, are phase-shifted and attenuated

ML741:

ML741_100kHz

UA741CN:

UA741CN_100kHz

Measurements in action…

Inverter_benchtest

Credits and References

About LEAP#158 OpAmp
Project Source on GitHub Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is my personal collection of electronics projects, usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.