Bridge amp feedback

sangram · 4th April 2003, 04:18 PM

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 · 4th April 2003, 04:19 PM

Attachment

rljones · 4th April 2003, 04:40 PM

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

Andypairo · 4th April 2003, 04:44 PM

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

Cheers

Andrea

sangram · 5th April 2003, 07:03 AM

Thanks for clearing that up.

Elso Kwak · 5th April 2003, 08:16 AM

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 · 6th April 2003, 08:23 AM

Quote:

Originally posted by Andypairo
Inverting gain is Rfb/Ri, non-inverting gain is 1+Rfb/Ri.

Cheers

Andrea

Quote:

Originally posted by Elso Kwak
... 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 ) ??

4th April 2003, 04:18 PM	#1
sangram diyAudio Member Join Date: Sep 2002 Location: India	Bridge amp feedback 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?

5th April 2003, 08:16 AM	#6
Elso Kwak Banned Join Date: Dec 2001 Location: Zamboanga, City of Flowers, Mindanao	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)

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4th April 2003, 04:40 PM	#3
rljones diyAudio Member Join Date: Mar 2001 Location: california	Because one op-amp is inverting and the other is non-inverting.

4th April 2003, 04:44 PM	#4
Andypairo diyAudio Member Join Date: Sep 2002 Location: near Milano , Italy	Inverting gain is Rfb/Ri, non-inverting gain is 1+Rfb/Ri. Cheers Andrea

5th April 2003, 07:03 AM	#5
sangram diyAudio Member Join Date: Sep 2002 Location: India	Thanks for clearing that up.