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Homework Help: Maximum Output Voltage of a LF411 inverting Op-Amp

  1. Nov 2, 2013 #1
    1. The problem statement, all variables and given/known data
    Prelab material, I know how to solve for the gain and vout on a circuit. But reading the actual manual of a op-amp is confusing and I just want to make sure i'm correct. The initial input voltage will be a 1V triangle wave. Then later we increase the voltage to 3V. R1 is 1K and R2 is 10k.Here is the manual:

    2. Relevant equations
    Vout/Vin = -R2/R1

    3. The attempt at a solution
    I know the output voltage will be ±10V for the 1V triangle wave. But for the 3v, if I am reading correctly, Vs = ±15 at the Vo tab under DC characteristics, which means the output voltage will be ±18 even though our gain is supposed to be a factor of 10. Is this correct? Thanks
  2. jcsd
  3. Nov 2, 2013 #2


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    Op amp output voltage is limited by the supply rails ... that's your voltage source.

    So if the max rating on the rails is +/-18 V, you can never exceed that, regardless of the amplification. Looking at the spec sheet I am not sure what the actual limits are ... about 15 V from a quick look, which is less than the max at the rails.

    So you want to limit your Vin to values which generate a Vout which is possible with the maximum voltages supported.
  4. Nov 3, 2013 #3


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    Many OP amps can't get within 3V of their rails so a general rule would be 18V-3V = 15V. That appears to be the case for this op amp. Interesting to consider what they use in 3V and 5V portable devices.

    Is the triangle wave 3V peak to peak? If so then with a gain of 10 the output will be 30V peak to peak. Half of that is 15V so you might just get away with it on +/- 18V supplies.

    Take a look at the circuit on page 9 of the data sheet. the reason the output cannot swing higher is the voltage drop across this path 300R -> Q1 -> 33R -> Q3 -> Q6 -10R
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