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Sinking Output?

Discussion in 'Electronic Basics' started by [email protected], Jan 13, 2005.

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  1. Guest

    I have an application for a sensor that calls for a Sinking Output. I
    am not familiar with electronics. Can someone help me understand what
    this means.

  2. JeffM

    JeffM Guest

    I have an application for a sensor that calls for a Sinking Output.
    To "source" something means the juice comes out of your device.
    To "sink" something means the the juice comes out of a source,
    through the load (if there is a separate load),
    and through your device to ground.

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  3. Chris

    Chris Guest

    Hi. A current-sourcing output will source current, a sinking output
    will sink current. Sourcing outputs are also called "PNP" and sinking
    outputs are also called "NPN". Here's the details.

    "Sinking"| |
    NPN | |
    Sensor | .-.
    ..------o---. | | R
    | | | |
    | .--o-----. '-'
    | | | | |
    | | | | | OUT
    | |/ | '---------o---o
    | -| | <------
    | |> | I (sink)
    | | |
    | | |
    created by Andy´s ASCII-Circuit v1.24.140803 Beta

    Here's a "sinking" NPN sensor, say, a proximity switch. Internally, at
    the output of the sensor is an NPN transistor. When an object comes in
    proximity to the sensor, it is made so that the NPN transistor at the
    output turns on, "sinking" current to GND. When the transistor is off,
    no current flows and you can read a voltage close to or equal to V+ at
    the output because of the + referenced load (R). Sensors of the
    "sinking" or NPN type are more common than sourcing.

    These sensors work well with programmable controllers, which have
    optoisolators built in which have their commons tied to V+, like the
    resistor above. They can sometimes be used with logic level power
    supplies, and can sometimes be connected to logic inputs, but you have
    to be careful and read the sensor literature. One big problem with
    this type of output is that it is somewhat susceptible to electrical
    noise when the transistor is off (false ON). Also, note that usually
    these sensors have small signal transistors at their outputs, and can't
    switch more than 50 to 100 mA. Also, do not use these to switch relays
    or non-resistive loads -- inductive kick can crash the output
    transistor. Since it's built-in and non-repairable, that means you've
    got to throw the sensor out.

    Possibly if you ask for an "NPN-type" sensor you might have more luck.
    Or, if you can be more specific as to your sensor requirements, someone
    can recommend something for you on this newsgroup.

    Good luck
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