Electronics > Projects, Designs, and Technical Stuff

Low-Noise Front End Protection

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Marco:

--- Quote from: Evan.Cornell on February 14, 2020, 07:49:45 pm ---The sensor I'm amplifying is piezoelectric, and can easily generate several volts or more if dropped, knocked, or something like that. Supply rails are +-2.5V, so I need to make sure input pin doesn't exceed voltage rails during an event like that.

--- End quote ---

It's not about voltage, for a short amount of time it can already take 3kV ... unless the piezo generates enough power to heat up the AD8655 ESD protection to destruction the voltage generated is irrelevant.

Evan.Cornell:

--- Quote from: Marco on February 14, 2020, 07:57:17 pm ---It's not about voltage, for a short amount of time it can already take 3kV ... unless the piezo generates enough power to heat up the AD8655 ESD protection to destruction the voltage generated is irrelevant.

--- End quote ---

I understand that, and the energy profile of piezo pulse is undefined, so I want to operate on the safer side. I am thinking series R = 10ohm or thereabouts with BAV199 to each rail, and another series R ~10ohm before AD8655 input.

Kleinstein:
The BAV199 diodes have a rather high forward voltage ( e.g. ~ 1 V), especially with a high current peak. So it would take considerably more than 10 Ohms for protecting the OP.

It would likely need more something like 2 of the diodes in series directly parallel to the piezo. This would limit the voltage to some +-1 V without much loading and some +-2.5 V with higher current. For lower leakage current one could use bootstrapping from the amplifier for the 1st. pair of diodes.

Chances are the diodes can take enough of a current pulse so one may not need an extra current limiting resistor.

Evan.Cornell:

--- Quote from: Kleinstein on February 14, 2020, 08:53:11 pm ---It would likely need more something like 2 of the diodes in series directly parallel to the piezo.
--- End quote ---

Do you mean like this?

Kleinstein:
That would be the minimal version.  Another pair of diodes in series to the diodes would be the next step up.

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