OVP without Voltage Drop ???

[IamSynthetiC]

Greetings

i am trying to measure some voltage by directly conecting the line to a voltage divider an into an analog input of an ADC.
How can i protect the ADC from overvoltage or spikes, without affecting the measurement? (or affecting it in a predictable manner)

Thanks a lot.
Have a good day.

[Vovk_Z]

Some datasheets have a typical circuit how to do.
It is usually good to put opamp buffer before an ADC input. And make typical protection for this opamp (it can be or not in an opamp datasheet too).
Look at something like "Op amp application" books, or "The Art of Electronix" too.

[Laszlo]

As Vovk suggested you should use an opamp (such as an ua741) configured as a voltage follower to make sure that the output of your divider will not change once you connected it to your ADC.
If you have enough margin, you could use a Zener diode to clamp the spikes down. Or you could use TVS, or a MOV at the input of your voltage divider to provide overvoltage protection.

Nevertheless, without knowing the threshold of your ADC, and your input voltage, its a bit difficult to help.

[Kleinstein]

The input protection is usually working in 2 steps: clamp the voltage by something like diodes, MOV or Zener diodes and limit the input current by something like a resistor (this can already be the divider), PTC or depletion mode FETs.

Which way to go depends on the impedance, voltage levels, acceptable errors and the required level of protection.

With a divider at the input, the protection may actually be in 2 steps, coarse before the divider (e.g. with a MOV / sparc gap) and the final protection after the divider, using the divider for current limiting.