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Thread: ac coupled???

  1. #1

    Default ac coupled???

    what do we mean by saying that output of the detector or sensor(photodiode or phototransistor ) is ac coupled,

    does it mean that output is passed through a capacitor??

    what is the benifit of this ??
    and what should be type and value of the capacitor???

  2. #2
    Senior Member T-1000
    Join Date
    Oct 2006
    Agra, India


    In the broadest sense, AC coupling means that AC signal is passed on while the DC component of the signal is blocked. A capacitor will do this, yes.

    Advantage would be in applications where we have to pass on the common mode signal to between systems at different DC levels.

    For example, your sensor circuit works at 12V and the sensor signal is actually an AC component (voltage swings) plus a DC component. The sensor circuit is now to be connected to a signal conditioning and display circuit which works on 5V. You obviously cannot directly connect the two. And you are interested in the AC component only and don't care about the DC part. So you AC couple the two circuits, which just passes on the voltage swings from the sensor circuit to the signal conditioning circuit.

    Values depend on what frequency of the signal you would like to pass on. Its not DC but slowly swinging AC signals that would be blocked too, well, not blocked but attenuated with a capacitor. So it depends.
    Mohit Mahajan,

  3. #3

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