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Re: [Electronics_101] max 197 + zener curiousity

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  • Yan Seiner
    OK, will do. Thanks! --Yan ... --
    Message 1 of 7 , Feb 19, 2013
    • 0 Attachment
      OK, will do.

      Thanks!

      --Yan

      On Tue, February 19, 2013 11:08 am, Derek wrote:
      > Ahh, that makes sense. What you are seeing is a floating input voltage.
      > The zener has a high impedance to ground if not above the breakdown
      > voltage. Properly, you can add a 1MEG to ground, parallel to the zener
      > and that should set the input voltage to 0 and not affect the connected
      > reading to any major concern.
      >
      > Derek Koonce
      > DDK Interactive Consulting Services
      >
      >
      > On 2/19/2013 11:04 AM, Yan Seiner wrote:
      >>
      >>
      >> On Tue, February 19, 2013 10:50 am, Derek wrote:
      >> > What is the purpose of the zener on the ground leg? Is it to raise the
      >> > level of conversion? Sounds to me to be an application issue somehow
      >> > with the IC trying to read a negative input voltage - 0V instead of
      >> the
      >> > zener-level as the '0'.
      >>
      >> The ascii art didn't quite turn out; the zener is on the input leg
      >> between
      >> the 47KOhm resistor and the chip (where the + sign in my diagram). Its
      >> purpose is to limit load dumps (this is in an automotive application so
      >> voltages can spike to 70V).
      >>
      >> Any spike over 5V gets dumped to ground.
      >>
      >> >
      >> > Derek Koonce
      >> > DDK Interactive Consulting Services
      >> >
      >> >
      >> > On 2/19/2013 9:04 AM, Yan Seiner wrote:
      >> >>
      >> >> I have a Max 197 AD connected as follows:
      >> >>
      >> >> Source - 47KOhm - + - MAX197
      >> >> |
      >> >> zener
      >> >> |
      >> >> ground
      >> >>
      >> >> With the source disconnected, the Max 197 reads about .22V.
      >> >>
      >> >> With it connected to a voltage source, it reads about what I expect
      >> >> (3.38V
      >> >> @ 12V source).
      >> >>
      >> >> Why would the MAX197 read a voltage with no voltage input? The other
      >> >> pins
      >> >> read 0.0 when disconnected; only the two connected to the zener show
      >> >> this
      >> >> weird voltage.
      >> >>
      >> >>
      >> >
      >> >
      >> >
      >> > [Non-text portions of this message have been removed]
      >> >
      >> >
      >> >
      >> >
      >> >
      >>
      >> --
      >>
      >>
      >
      >
      >
      > [Non-text portions of this message have been removed]
      >
      >
      >
      > !DSPAM:5123cf94126799633161998!
      >


      --
    • Kerim F
      I usually got such weird (induced and rectified) voltages when a non linear device is almost open circuited and if the testing wires are somehow long hence
      Message 2 of 7 , Feb 19, 2013
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        I usually got such weird (induced and rectified) voltages when a non linear device is almost open circuited and if the testing wires are somehow long hence acting as receiving antenna ;)

        --- In Electronics_101@yahoogroups.com, "Yan Seiner" <yan@...> wrote:
        >
        > OK, will do.
        >
        > Thanks!
        >
        > --Yan
        >
        > On Tue, February 19, 2013 11:08 am, Derek wrote:
        > > Ahh, that makes sense. What you are seeing is a floating input voltage.
        > > The zener has a high impedance to ground if not above the breakdown
        > > voltage. Properly, you can add a 1MEG to ground, parallel to the zener
        > > and that should set the input voltage to 0 and not affect the connected
        > > reading to any major concern.
        > >
        > > Derek Koonce
        > > DDK Interactive Consulting Services
        > >
        > >
        > > On 2/19/2013 11:04 AM, Yan Seiner wrote:
        > >>
        > >>
        > >> On Tue, February 19, 2013 10:50 am, Derek wrote:
        > >> > What is the purpose of the zener on the ground leg? Is it to raise the
        > >> > level of conversion? Sounds to me to be an application issue somehow
        > >> > with the IC trying to read a negative input voltage - 0V instead of
        > >> the
        > >> > zener-level as the '0'.
        > >>
        > >> The ascii art didn't quite turn out; the zener is on the input leg
        > >> between
        > >> the 47KOhm resistor and the chip (where the + sign in my diagram). Its
        > >> purpose is to limit load dumps (this is in an automotive application so
        > >> voltages can spike to 70V).
        > >>
        > >> Any spike over 5V gets dumped to ground.
        > >>
        > >> >
        > >> > Derek Koonce
        > >> > DDK Interactive Consulting Services
        > >> >
        > >> >
        > >> > On 2/19/2013 9:04 AM, Yan Seiner wrote:
        > >> >>
        > >> >> I have a Max 197 AD connected as follows:
        > >> >>
        > >> >> Source - 47KOhm - + - MAX197
        > >> >> |
        > >> >> zener
        > >> >> |
        > >> >> ground
        > >> >>
        > >> >> With the source disconnected, the Max 197 reads about .22V.
        > >> >>
        > >> >> With it connected to a voltage source, it reads about what I expect
        > >> >> (3.38V
        > >> >> @ 12V source).
        > >> >>
        > >> >> Why would the MAX197 read a voltage with no voltage input? The other
        > >> >> pins
        > >> >> read 0.0 when disconnected; only the two connected to the zener show
        > >> >> this
        > >> >> weird voltage.
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