Tri-State Gate from Transistors

Discussion in 'General Electronics Chat' started by jcarsw04, Sep 21, 2012.

  1. jcarsw04

    Thread Starter New Member

    Sep 21, 2012
    Is it possible to build a tri-state gate from npn transistors? I'm trying to make an electronically controlled switch that allows current to flow in either direction but has a high impedance when open. I was hoping to use the transistors I have on hand but it looks like I might have to order an additional IC.
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    I'm not sure if you want a tri-state output which either sources current, sinks current or floats. Or possibly you want a series pass element like a switch which conducts current in either direction when on, and passes no current when off???
  3. Dyslexicbloke

    Well-Known Member

    Sep 4, 2010
    Have a look at half bridge drivers and full bridge drivers.
    these are often transistors but can be FET's

    Also look at CMOS output design and you will see how this is achieved within many chips.

    Googling any of these will get you loads of good info in the first few hits.

    Which method you decide to employ will depend on the supply you are using and your application.
    Last edited: Sep 22, 2012
  4. jcarsw04

    Thread Starter New Member

    Sep 21, 2012
    Yes, I want something that would behave exactly like a mechanical switch. Something similar to a 2:1 demultiplexer except the signal needs to be able to flow in either direction whereas I believe demultiplexers only allow signals to flow in one direction.
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
    Google "spdt analog switch" and "bus switch".