Is Vo Independent of Rs in Non-Inverting Op-Amps?

[Inept]

Homework Statement

Homework Equations

v_o = G*v_s

where G = ((R₁+R₂)/(R₂)

therefore,
v_o = v_s * ((R₁+R₂)/(R₂)

would v_o be independent of R_s ?

The Attempt at a Solution

I assumed it was a Non Inverting Op Amp...but I haven't come across one with (two?) input resistances? I'm not sure where to go with it. I began to use the equation I have above, but I don't think it's right. I think (or I keep telling myself) that I have to use R_s or R_x in part a somehow.

For part b) I believe I have to figure out the linear range of R_x, which should be doable. So I'm not worried about that, assuming what I'm thinking is correct...

If anyone can help thanks! If not, thanks anyways!

 

[phyzguy]

One question that may help - What is the voltage at the + input of the Op Amp. Is it 750 mV, or something else?

 

[Redbelly98]

Homework Statement

Homework Equations

v_o = G*v_s

where G = ((R₁+R₂)/(R₂)

therefore,
v_o = v_s * ((R₁+R₂)/(R₂)

would v_o be independent of R_s ?

The Attempt at a Solution

I assumed it was a Non Inverting Op Amp...but I haven't come across one with (two?) input resistances? I'm not sure where to go with it. I began to use the equation I have above, but I don't think it's right. I think (or I keep telling myself) that I have to use R_s or R_x in part a somehow.

For part b) I believe I have to figure out the linear range of R_x, which should be doable. So I'm not worried about that, assuming what I'm thinking is correct...

If anyone can help thanks! If not, thanks anyways!

For starters, what is the voltage at the + input (in terms of Vs)?

EDIT: phyzguy had the same thought.

 

[Inept]

I solved it, I had to solve for a non-inverting (positive) input voltage (v_p) first and then created a "new" circuit. Using that circuit I found the output voltage using that equation I listed above while replacing v_s with v_p . I got v_p = [(80k/(80k+20k)]*750 mV = 600 mV

then v_o = [(3.3k+46.2k)/3.3k]*600 mV = 9000 mVIt feels good to figure my own answer out...lolEDIT: I didnt refresh, so I didn't see your guys replies. Thanks all! :)

 

[DeeNos]

Sure, I would be happy to help you solve this Op-Amp problem. It seems like you have already made some progress by identifying the circuit as a non-inverting Op Amp and writing out the relevant equation for the output voltage. To answer your question, yes, the output voltage (vo) will be independent of Rs as long as the ideal assumptions of the Op Amp are satisfied (infinite input impedance and zero output impedance). This means that the input resistor Rs will not affect the output voltage.

To solve part a), you can simply plug in the given values for R1, R2, and vs into the equation you have written and solve for vo. To solve part b), you can use the linear range equation, which is vo(max) = Vcc - Vee, where Vcc is the positive supply voltage and Vee is the negative supply voltage. This will give you the maximum output voltage that the Op Amp can provide.

I hope this helps you solve the problem. If you need further assistance, please let me know. Remember to always check your circuit assumptions and make sure they are satisfied before solving any Op Amp problem. Good luck!