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  1. 2

    Op amp configuration with 1 resistor ?

    okay (*Steve*), I guess I am lost here... so I will have to build the circuit and see whats happening..... thanks for your help
  2. 2

    Op amp configuration with 1 resistor ?

    Are we looking at the same diagram? Confused!
  3. 2

    Op amp configuration with 1 resistor ?

    Hello, I understand how to evaluate several op amp circuits now namely, non-inv, Inv, diff etc... , but today I have come across an untypical op amp configuration with only the rf resistor? Please view attachment. At first I thought it looked simple but I was wrong. My question is, how is one...
  4. 2

    Quick question about equal input voltages for op amp?

    :D:D lol 24v
  5. 2

    Quick question about equal input voltages for op amp?

    Hi Duke37, So these op amps, internally are not perfect... so, even though I provide the same voltage at the two inputs, there is still some difference internally and therefore the amplifier will amplify this difference. okay, thanks duke37
  6. 2

    Quick question about equal input voltages for op amp?

    Hello, If we have an op amp (LM324) with rail voltages of +/- 15Vdc, and we short both inputs to +5Vdc, is it normal that we get 13.7Vdc as the output??? I read everywhere that if both inputs are equal, the output should be 0 Vdc !!!! But here on my test bench I get +13.7Vdc ...
  7. 2

    Op amp calculations for ramps!

    Thanks Laplace, Yes I figured it out as for my requirements to work out, I need a differential op amp configuration with gain plus offset. I am working on this ... Thanks for your help, If I have other question I will come back! Thanks 24v
  8. 2

    Quick current direction for op amp question?

    I wasn't sure... but yes that's what I thought! Thanks John Monks for confirming this.... 24v
  9. 2

    Quick current direction for op amp question?

    Hello, In reference to the attachment below, which way is the current going. Please choose from A or B. Thank you 24v
  10. 2

    Op amp calculations for ramps!

    thanks Bobk All help is much appreciated ! thanks
  11. 2

    Op amp calculations for ramps!

    Hello BobK.... Okay now its getting clearer... you did a differential amplifier. You took the difference of (4-2)*2.5 =5 and (6-4)* 2.5 =10 So first we take the desired slope as Harald Kapp suggested and then we apply it to: vout = (vin-2)*2.5 Thanks that helped me a lot... I will try to...
  12. 2

    Op amp calculations for ramps!

    You meant: at v2 at 4v and v1 at 0 volts makes a difference of 4 v multiplied by 2.5 is 10 vdc out ... yes! So to subtract an offset, we need to raise v1 right? What do we mean when we say the transfer function?? Slowly getting a little clearer! Thanks
  13. 2

    Op amp calculations for ramps!

    Please view attachment. I don't think if I make v1 = 1vdc and rf equal to 50K will produce me the ramp mentioned in previous post? I am lost ... Am I on the right track ? I see the slope is 2.5. Sorry to let you down Laplace... but I don't know how to do this.... Can you please show me...
  14. 2

    Op amp calculations for ramps!

    Hello Harald Kapp, aaarh!!! your right Harald Kapp... I am sorry! Its my typo.... yes in this case it's: vo = [1 + rf/ri] vb Yes, If I ramp up the input from 4vdc to 6 vdc, when the input reaches 6 vdc, I measure 7.5vdc! In other words, the output makes a ramp from 5 to 7.5vdc when I ramp...
  15. 2

    Op amp calculations for ramps!

    Hello, In attachment below, I have an op amp which takes in 4 vdc and outputs 5vdc. The circuit has been calculated by using the non-inv op amp formula: vo = [1 + rf/ri] v2 5 = [1 + 15k/10k] x 2 However, if I ramp up the input from 4vdc to 6 vdc, I measure 7.5vdc at the output when the input...
  16. 2

    Quick op amp question?

    Thanks (*steve)! The reason I am asking is because I am a little confused on how to calculate my own ramps when it comes to op amps. To keep subjects separated, I strat a new post on this. thanks 24v
  17. 2

    Quick op amp question?

    Hello, I have very little experience with op amps. I know how to calculate the voltage outputs of a differential, non inverter and inverter op amp circuits. But can someone explain to me in a simple sentence as to why it is important to be able to calculate the common mode gain and the...
  18. 2

    How does gain apply in diff op amp?

    thanks Laplace... I appreciate your help
  19. 2

    How does gain apply in diff op amp?

    Hi Laplace, I know how to calculate the output ! and yes: -50ua + 50ua = 0 and -1ma + 1ma = 0 So, what does this mean? I think what I was looking for is the intuitive solution of why we have a positive voltage... and I guess I figured out my own question... its because we know va has 1.5VDC...
  20. 2

    How does gain apply in diff op amp?

    thanks duke, .... this is exactly what I was looking for ... a simple explanation for the gain. One more thing, if I may ask. How did you determine that this was an inverting op amp? They say that if the + input is > than the - input, then its an non inverting op amp!!! Isn't this our case...
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