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Re: max 197 + zener curiousity

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  • 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 1 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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