One-wire parasitic power question

Discussion in 'General Electronics Chat' started by sohcahtoa, Sep 12, 2008.

  1. sohcahtoa

    Thread Starter Member

    Nov 7, 2006
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    Can anyone explain to me how, in using a one-wire in parasitic mode, you can be providing power and sending a signal out the same terminal?

    For instance, I've been involved in a project using a thermocouple IC in a TO-92 package that uses parasitic power. If you have a serial data bus that provides power through the data bus, you only need the output terminal and ground terminal of the TO-92 for it to function. You can also get a version with a dedicated VDD terminal, which makes a lot more sense to me currently.

    Thanks!
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    Here is a link to the wikipedia article covering the 1-wire topic.

    hgmjr
     
  3. sohcahtoa

    Thread Starter Member

    Nov 7, 2006
    15
    0
    Ah, ok. Pull-up resistors allow you to pull the data line to ground for a 0, while an internal capacitor holds the charge from when the line was a 1. Very cool. Thanks. I didn't think to look on Wikipedia for some reason.
     
  4. hgmjr

    Moderator

    Jan 28, 2005
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    You got it. Parasitic is a clever way to power a low power consuming device.

    hgmjr
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    Isn't that the way RFID tags work?
     
  6. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    Basically that is true beenthere. RFID does use a portion of the RF signal on which the data is being modulated to power the passive RFID tags.

    hgmjr
     
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