## Re: [Electronics_101] max 197 + zener curiousity

Expand Messages
• 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, 2013
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

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]
• ... To clarify: the zener is connected from the + sign to ground. Source - 47KOhm - + - MAX197 . | . zener . | .
Message 2 of 7 , Feb 19, 2013
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
• OK, will do. Thanks! --Yan ... --
Message 3 of 7 , Feb 19, 2013
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!
>

--
• 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, 2013
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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