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Connecting two open collector devices

Discussion in 'Electronic Basics' started by Zul, Aug 11, 2008.

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  1. Zul

    Zul Guest


    Currently I building a circuitry to have 8 I/O pins being demux into
    64 mutually exclusive outputs to control switching of 64 selenoid
    relays. I am planning to place a Darlington array in between the
    output of the demux and the ground for the relay because I believe a
    demux output can't sink high current enough to operate a relay.

    My problem arises as both the demux and the darlington array are open
    collector devices. In this case the output of the demux are either
    ground or floating. For darlington array the input must be LO (output
    to floating) or HI (output to 0.6V). As I see it, I could not get a HI
    input from an output of a demux with open collector configuration.

    I was thinking to place an inverter between the demux and the
    darlington array. I also looked for a demux with totem pole
    configuration with active HI to match it with the darlington array but
    could not find it. All I can find are demux with active LO.

    If anybody have the opinion this, appreciate the response.

  2. Use PNP-Darlingtons instead of NPNand switch Supply with it instead of GND.
    It's the easiest way.

    Falko Rudolph
  3. Zul

    Zul Guest

    Fields - Thanks for active HI demux options

    Rudolph & Walcott - Driving 6V relay with 0.35W power consumption.
    Thanks for the alternative approaches and well as the explanations.

  4. (snip)
    Why? As long as they are based on the same GND you only need to adjust the
    base resistor. That's what o.c. outputs are made for( and more, right).
    As John suggested normal transistors may be better than darlingtons when V+
    is only 6V.
    What do I not see?

    Falko Rudolph
  5. neon


    Oct 21, 2006
    Why Don't You Use Tristate Devices Like 74245 74244 They Made For I/o Buss.
  6. .... and Base to controlling signal and collector to the relay. That's what I
    thought of.

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