zener reverse vltg

I was wrong.
The BAT85 is a Schottky diode, not a zener diode.
It conducts when the input goes negative by only 0.2V to avoid destruction of the input of the opamp that has a max allowed negative voltage of -0.3V.
 
The Schottky diode has the required 0.2V to 0.3V forward voltage to stop the negative input to the opamp from exceeding its max allowed negative voltage of -0.3V.

An ordinary diode has a forward voltage of 0.6V to 0.7V so the input of the opamp will be damaged.
 
1N400X series are general purpose diodes for AC-to-DC applictions. 1N4148 is a fast switching diode. schottky diodes are little bit different from these, because of their low forward voltage drop leading to lower levels of power loss compared to ordinary P-N junction diodes. schottky diodes are also known as surface barrier,hot carrier, or even hot electron diode. they are widely used in radio frequencies as mixer or detector,and in power applications as rectifiers where low forward voltage drop is required.

You can try google for different types of diodes or even wikipedia can help.
 
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