# Function of a operational amplifier curcuit and a transistor ciurcuit.

#### WarOfCurrents

Joined Jan 22, 2021
2
Hello.

I would like to know if the main component of the first ciurcuit is a inverting operational amplifier or a differential amplifier.
And is it possible, if anybody could explain me the function of both circuits?
Thank you.

#### dl324

Joined Mar 30, 2015
12,871
Welcome to AAC!

The opamp is an inverting amplifier. The transistor is able to drive a low impedance load better than the opamp.

Something like LM386 would be more appropriate.

#### WarOfCurrents

Joined Jan 22, 2021
2
Welcome to AAC!

The opamp is an inverting amplifier. The transistor is able to drive a low impedance load better than the opamp.

Something like LM386 would be more appropriate.
I have a question about the inverting amplifier.
A square-wave voltage of 0-5 volts is applied to the first circuit.
Why is the output voltage of the amplifier -0,1 - + 0,1 V.
Is this due to the voltage divider that reduced the input voltage from 5 volts?

#### dl324

Joined Mar 30, 2015
12,871
I should have asked before. Is this school work?

#### LvW

Joined Jun 13, 2013
1,247
A square-wave voltage of 0-5 volts is applied to the first circuit.
Why is the output voltage of the amplifier -0,1 - + 0,1 V.
Is this due to the voltage divider that reduced the input voltage from 5 volts?
It is an inverting amplifier with a gain smaller than unity. An input between 0 and +5V would produce an output in the negative range only. However, if you need an output between -0.1 and +0.1 it is necessary to shift the output signal somewhat into the positive range. That is the purpose of the voltage divider which feeds the non-inv. input of the opamp.