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Whats the point of the Op-Amp in this D/A converter

Discussion in 'General Electronics Discussion' started by Braeden Hamson, Feb 25, 2018.

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  1. Braeden Hamson

    Braeden Hamson

    Feb 18, 2016
    I've been tasked with building a digital to analogue converter for my class. Like so:

    It needs to have 5 volts in on the inputs and 1 2 3 4 on the output corresponding to pressing 1 2 3 4. I understand how to do this, but I don't see why I can't just accomplish this with a voltage divider. If I eliminated the amp all together I think the circuit would achieve the same thing.

    Thanks guys!
  2. Kabelsalat


    Jul 5, 2011
    That is becasuse:
    - 1. This is not a voltage divider. It doesn't work as a voltage divider at all.
    - 2. Why: The negative input terminal at the opamp will always be at zeero, at least very close - probably less than your multimeter can measure.
    - 3. And why is that: The negative terminal is keept close to zero because the opamp output will compensate so that the negative voltage will try to stabilize in a point where the current through Rf is excact the same as the current you provide via V1, V2, or V3.

    Also: Try to do some calculations of voltage drop when different input voltage is applied - and remember to follow the rules of resistor value doubles for each.
    Remember: the sum of currents into a node is always zeero.

    Some important things to be aware of:
    - The output function will generate a voltage representation of a binary input given that the resistor network is correctly set up.
    - Opamps have limitations. It may not be able to deliver a voltage close to Vee/Vcc.
    - Won't work unless you have a negative voltage supply also.
  3. Braeden Hamson

    Braeden Hamson

    Feb 18, 2016
    Thank you for the clarification
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