Hi, I am working with analog to digital conversion of high batteries voltage ( 40V and 12 V), I am using a voltage divider for each one, and I am considering for over voltage protection, using Schottky diode, my concern is the leakage current , and data accuracy, because I am trying to store the data , within 24Hours. and the data is involved on advance calculation. I am asking the best solution for this problem.what is the best considered solution for protection of over-voltage , and with a best accuracy possibility. and I am using 125mW rated resistors for the voltage divider.It is good if you could mention the protection device rating.
With all of the diodes that are on the market, you want us to research each one and give you the best option? Go to Digikey and use there refinement selection to find a diode.
You don't need overvoltage protection if the current that your divider can put into the pin is below the max input protection diode current of the A/D converter. In this case (ADS1115) 10mA max.
That means if the "top" resistor of your divider is e.g. 33k, you're protected to 330volt.
The value of the "resistor to ground" of the divider is not important for this calculation, because you have to assume protection is also needed when the A/D converter is off (0volt on the input).
Leo..
thanks wawa for your effort , I know that i can use high values of resistors.it is just thinking for worst case.
What would be "worst case".
A 33k resistor theoretically protects this A/D to +330volt and -330volt.
You could connect the input pin with this value resistor directly to 230volt mains without damaging it.
I assume you don't understand how clamping diodes work.
And the difference between max A/D input voltage and max A/D input current.
Leo..