Bridge amp feedback

[Sangram]

Hi

Pulled this out of a datasheet.

Why are the values of the NFB resistor different in the two halves of the amp? I assume there is a quality buffer before the power amp (which this is), and the circuit below is used. Why is one having a gain of 20, and the other 21?

Or is it for impedance compensation?

 

[Sangram]

Oops:

Attachment

 

[rljones]

Because one op-amp is inverting and the other is non-inverting.

 

[Andypairo]

Inverting gain is Rfb/Ri, non-inverting gain is 1+Rfb/Ri.

Cheers

Andrea

 

[Sangram]

Thanks for clearing that up.

 

[Elso Kwak]

Gain

Hi,
Isn't Vo= (1+ Rfb/Ri) Vi (noninverting)
Vo= outputvoltage
Vi = inputvoltage
So the noninverting gain is Vo/Vi= 1+ Rfb/Ri
and the inverting gain is - Rfb/Ri (assuming zero source impedance)
😕

 

[Sangram]

Re: Gain

Inverting gain is Rfb/Ri, non-inverting gain is 1+Rfb/Ri.

Cheers

Andrea

... So the noninverting gain is Vo/Vi= 1+ Rfb/Ri
and the inverting gain is - Rfb/Ri (assuming zero source impedance)
😕

Yes, I guess, whatever, but both above look the same to me (with the exception of the (-) sign in Elso's ) ??