op amp- differential amp learning - question

[thannara123]

https://www.electronics-tutorials.ws/opamp/opamp_5.html

How do get the value Vout = -V(R3/R1)

how the resistance calculated so .. R3/R1 ?

 

[Borber]

In the same way as inverting amplifier is calculated from wanted gain Vout/V.

 

[crutschow]

How do get the value Vout = -V(R3/R1)

how the resistance calculated so .. R3/R1 ?

If you connect V2 to ground, then the circuit becomes a simple inverter with Vout = -V1(R3/R1).

 

[Borber]

And only thing left to you is to first select R1 or R3 and then calculate other resistor.

 

[D.A.(Tony)Stewart]

A balanced differential amp. Uses R4=R2 and R4/R2=R3/R1

For single supply , the R2 is not grounded but tied to a lower impedance Vcc/2.

There are many other uses for introducing level shift and gain, but the key to remember is (+) = (-) input always in the linear range, not withstanding input offsets.