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Op Amp Inverting/Non-inverting terminal nomenclature

  1. Mar 3, 2014 #1

    Maylis

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    Hello,

    I am wondering why the inverting terminal is the negative terminal and the non-inverting terminal is the positive terminal by name?
     
  2. jcsd
  3. Mar 3, 2014 #2

    f95toli

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    The terms inverting/non-inverting refers to the AMPLIFIER as a whole, not the op-amp by itself. Inverting amplfiers (regardless of how they are are made) will invert the sign of the applied voltage (or, equivalently, invert the phase) , i.e. the gain will e.g be -10 meaning 1V in will results in MINUS ten volts out.

    Now, if you want to an inverting amplfier using an op-amp you will find that you will have to connect the input voltage to the negative terminal. Hence the name.
     
  4. Mar 3, 2014 #3

    jim hardy

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    All pins must be kept at voltages that lie between the power supply "rails".
    They're called "supply rails" because they are reminiscent of railroad tracks , ie rigid limits .
    The amplifier can't go outside them. (well, there's newfangled specialty ones that can but let's stick to basics)

    Driving the + terminal more positive than the - terminal causes the output terminal's voltage to move toward the positive supply rail.
    Conversely,
    Driving the - terminal more positive than the + terminal causes the output terminal's voltage to move toward the negative supply rail.

    Do you notice the reversal of sign?

    An AC signal that's had its sign reversed looks on an osciloscope (or graph paper ) to be upside down, ie inverted.

    It's really that old-fashioned and simple.
     
  5. Mar 4, 2014 #4

    meBigGuy

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    Increasing the + input makes the output go up
    Increasing the - input makes the output go down
     
  6. Mar 4, 2014 #5

    jim hardy

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    What meBigGuy said.
     
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