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Project Notes

#161 ML741/NonInvertingAmplifier

Test a non-inverting amplifier circuit using the ML741 discrete component opamp

Notes

This is a demonstration of a non-inverting amplifier circuit using the ML741 discrete component opamp.

The non-inverting amplifier has an arbitrary gain determined by the input and feedback resistor selection:

Vout = (1 + R2/R1) * Vin

Op-Amp_Non-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 non-inverting amplifier configuration, the non-inverting input is at the inflexion point of the R1:R2 voltage divider. Since the inflexion point must equal the non-inverting input voltage, as the non-inverting input voltage changes, the output voltage must change proportional to R1:R2 in order to maintain equilibrium.

Construction

The circuit diagrams are drawn with a standard 741 DIP8 package for both the UA741CN and “ML741”. See the ML741 project for details of the actual construction of the ML741.

Both op-amps are configured for a gain of approximtely 3.

Single-supply Configuration

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 “ground” end of R1 is pegged to V+/2 with a voltage divider. In a dual rail configuration, V+/2 is usually “ground”.

The voltage divider is high impedance, to minimise its interaction with the amplifier circuit. It is also stabilised with a 100nF capacitor.

To improve the isolation of the V+/2 supply, it uses 1/4 of the LM324 as a voltage follower/buffer. The buffer may be omitted at the expense of some gain and DC offset (depending upon frequency).

Without the buffer and capacitor, a simple voltage divider resonates with the circuit and cannot provide a stable supply. Gain will tends towards 1

Input Buffer

An LM324 is used as an input buffer/splitter so that the ML741 and a standard 741 can be compared at the same time.

Breadboard

The Schematic

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
  • input is a sine wave 200mVpp with 2.5V DC offset, connected at node “FG”
  • CH1,CH2 and CH2 signals are DC coupled and vertically shifted by -2.5V

Scope connections

  • CH1: input (yellow)
  • CH2: UA741CN output (blue)
  • CH3: ML741 output (red)

At 1kHz

  • both the ML741 and UA741CN (the real 741) are performing similarly, delivering a gain of just under 3

NonInvertingAmplifier_1kHz

At 100kHz

  • gain is being attenutated already, to a similar degree for both the ML741 and UA741CN (the real 741)
  • the UA741CN output is phase shifting more than the ML741

NonInvertingAmplifier_100kHz

Credits and References

About LEAP#161 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.