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Re: [Electronics_101] max 197 + zener curiousity

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  • Derek
    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
    Message 1 of 7 , Feb 19, 2013
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      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'.

      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]
    • Yan Seiner
      ... 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
      Message 2 of 7 , Feb 19, 2013
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        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!
        >


        --
      • 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 3 of 7 , Feb 19, 2013
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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 4 of 7 , Feb 19, 2013
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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 5 of 7 , Feb 19, 2013
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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 6 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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