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Re: [Electronics_101] max 197 + zener curiousity

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  • Derek
    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,
    Message 1 of 7 , Feb 19 11:08 AM
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      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]
      > >
      > >
      > >
      > > !DSPAM:5123cb97114941804284693!
      > >
      >
      > --
      >
      >



      [Non-text portions of this message have been removed]
    • Yan Seiner
      ... To clarify: the zener is connected from the + sign to ground. Source - 47KOhm - + - MAX197 . | . zener . | .
      Message 2 of 7 , Feb 19 11:13 AM
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        On Tue, February 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).

        To clarify: the zener is connected from the + sign to ground.

        Source - 47KOhm - + - MAX197
        . |
        . zener
        . |
        . ground
      • Yan Seiner
        OK, will do. Thanks! --Yan ... --
        Message 3 of 7 , Feb 19 11:19 AM
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          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 4 of 7 , Feb 19 1:44 PM
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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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