Amplifier Input prodection ?

[carpenter]

I have FET Amplifier witch input current <10pA and power supply +- 16V. On non inverting input is protective resistor 100k ohm . Working voltage on + input is 1uV - 8V.
Can you advise how to make the protection that would protect them from the amplifier input + - 200V and EDS?
This must not increase current in the work area amplifiers.

 

[FvM]

The FET amplifier protection diodes might be capable of handling the input current in overload case, check the datasheet. Otherwise you have to look for low leakage diodes.

 

[carpenter]

I admit that I completely understand the principle of calculating the OVP FET amplifiers
For examle page 16 datasheet AD8610 say
If the input source can deliver larger currents than the maximum forward current of the diode (>5 mA), a series resistor can be added to protect the inputs.
This 10 kΩ allows input voltages more than 5 V beyond either power supply
How to calculate?
https://www.analog.com/static/imported-files/data_sheets/AD8610_8620.pdf

 

[FvM]

How to calculate?

I suggest ohms law. You'd need a 40 k series resistor to widthstand +/- 200V. Depending on the power supply cicruit, it might be necessary to add zener diodes that prevent raisng the supply voltage beyond save limits.

Unfortunately AD8610 datasheet avoids to specify input ESD capability.

 

[carpenter]

Yeah, but Georg Simon Ohm says 10k through 5 mA at 50V and not at 5 V A DS in talks about adding 5V using 10k resistor :smile:

 

[FvM]

Apparently the datasheet calculation is wrong.