#159 ML741/InvertingAmplifier

Test an inverting amplifier circuit using the ML741 discrete component opamp

Notes

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

The inverting amplifier is a generalised case of the basic Inverter circuit, but with an arbitrary gain determined by the input and feedback resistor selection:

Vout = - Rf/Rin * Vin

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 inflexion point of the Rin:Rf voltage divider. Hence the op amp achieves inverting/non-inverting input equilibrium when Vout = - Rf/Rin * 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”.

The breadboard build has a fixed gain of -2 but of course the feedback resistor can be replaced with a pot for manual variable gain.

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
non-inverting input is fed a sine wave 200mVpp with 2.5V DC offset
the function generator sine wave input replaces the manual 10kΩ input pot in the schematic above (at node FG)
CH1 and CH2 signals are DC coupled and vertical shifted by -2.5V in the screenshots that follow

Scope connections