Developing Equations for Single-Rail Op Amps

Discussion in 'General Electronics Chat' started by nDever, Jun 27, 2014.

  1. nDever

    Thread Starter Active Member

    Jan 13, 2011
    154
    4
    Hey Guys,

    I built an inverting amp with a LM324N (sorry, I forgot to make a scheme). I applied a +5v signal to V- and got back +5v at Vout. I'm guessing that you can't get a negative voltage with a positive supply? If this is the case, shouldn't I have gotten 0v? Do you have develop equations differently for single supply op amps as opposed to dual rail amps?

    If you were wondering about the circuit, I have Vcc connected to 5v; GND is 0v. Feedback resistor (Rf) is across V- and Vout. I have +5v connected through R to V- and V+ is connected to GND.

    Closed loop gain is 0.1.
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    Yes, an op amp can't generate a voltage different from its power supply.

    The equations are the same.

    And yes, the output should be at zero. What is the value of the resistors? Post your circuit diagram.
     
  3. nDever

    Thread Starter Active Member

    Jan 13, 2011
    154
    4
    Don't know the next time I'll be able to get back. I've got limited internet access right now, but my input resistor was 10k and the feedback resistor was 1k.
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    So the output should be near zero. Double-check all the pin connections on the op amp. Sounds like one or more are wrong.
     
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