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Old 4th April 2003, 04:18 PM   #1
sangram is offline sangram  India
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Default 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?
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Old 4th April 2003, 04:19 PM   #2
sangram is offline sangram  India
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Default Oops:

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Old 4th April 2003, 04:40 PM   #3
rljones is offline rljones  United States
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Because one op-amp is inverting and the other is non-inverting.
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Old 4th April 2003, 04:44 PM   #4
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Inverting gain is Rfb/Ri, non-inverting gain is 1+Rfb/Ri.

Cheers

Andrea
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Old 5th April 2003, 07:03 AM   #5
sangram is offline sangram  India
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Thanks for clearing that up.
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Old 5th April 2003, 08:16 AM   #6
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Lightbulb 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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Old 6th April 2003, 08:23 AM   #7
sangram is offline sangram  India
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Default Re: Gain

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 ) ??
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