I have a question regarding opamp,

i have a non-inverting amlifier problem with Rf and Ri is given but the input voltage is not given however input DC voltage is -1.7 volt.

according to the formula,

Vo = (1+ Rf/Ri)x Vi(ac)

how can i solve if the DC input voltage is given but not AC

 

But if circuit don't have any capacitor in signal path.
The DC gain is equal to AC gain
Av = 1+ Rf/Ri

 

why would there be a capacitor in a non-inverting amplifier :S

will it be Av = (1+ Rf/R)x Dc input ???

i have checked a non-inverting amp in multisim with a DC input voltage , the output is 'ZERO'

 

I have a question regarding opamp,

i have a non-inverting amlifier problem with Rf and Ri is given but the input voltage is not given however input DC voltage is -1.7 volt.

according to the formula,

Vo = (1+ Rf/Ri)x Vi(ac)

how can i solve if the DC input voltage is given but not AC

It's not clear what you want to solve. Do you want to know the gain? Well you have the formula... The AC-gain will also depend on the frequency of the AC-signal.
Or do you want to know the AC output voltage? That would be impossible, since you don't have the input voltage.

And what's the DC- voltage doing there?

 

Maybe it is time for you to show us the diagram.
Are we talking about the same circuit ??

 

It's not clear what you want to solve. Do you want to know the gain? Well you have the formula... The AC-gain will also depend on the frequency of the AC-signal.
Or do you want to know the AC output voltage? That would be impossible, since you don't have the input voltage.

And what's the DC- voltage doing there?

this is what i am thinking :S why there is no AC i/p voltage mentioned ?? :S

and what does DC voltage is doing there :S

this is what question says,

Determine the output voltage of Non-inverting amplifier if Rf=120k and Ri =39k and the DC input voltage is -1.7 volts ?


Book: Fundamentals of Operational Amplifiers and Linear Integrated Circuits by Howard M.Berlin and Frank C Getz, Jr.

Problem 10 , Chapter 2

 

Maybe it is time for you to show us the diagram.
Are we talking about the same circuit ??

yeah, the same circuit

 

yeah, the same circuit

If so the DC gain = AC gain = 1+ R2/R1
So for Vin =1.7V
Vout = -1.7V * (1 + 120K/39K) = -6.93V

 

If so the DC gain = AC gain = 1+ R2/R1
So for Vin =1.7V
Vout = -1.7V * (1 + 120K/39K) = -6.93V

how DC gain could be equal to AC gain :S

 

Because opamp is also DC voltage amplifier.


http://focus.ti.com/lit/an/slod006b/slod006b.pdf

 

i didn't know that , thank you

 

Determine the output voltage of Non-inverting amplifier if Rf=120k and Ri =39k and the DC input voltage is -1.7 volts ?


Book: Fundamentals of Operational Amplifiers and Linear Integrated Circuits by Howard M.Berlin and Frank C Getz, Jr.

Problem 10 , Chapter 2

It doesn't say anything about AC. <they want to know the DC-output voltage.

edit: oops I guess I'm several posts too late