Hi I need someone could explain me this situation, I have a voltage source that feeds an operational amplifier configured as a voltage follower. The follower is used to obtain an output with high precision and low impedance. After this, there is a voltage divider, which reduces the voltage level before reaching the next component. In this case, there is a 3.3V Zener diode that aims to regulate the voltage to 3.3V. In addition, the circuit includes a noise filter, which ensures that the signal is free of unwanted interference.

However, despite having the 3.3V Zener diode, the voltage does not consistently stay at 3.3V as it should. What could be the cause of this? I'm using this to protect a pin of a microcrontoller.. so Its crucial to that the output voltage stays in 3.3v

 

What happens to the signal when it should be 3.3V?

Don‘t forget that low voltage Zeners are not very good. If the datasheet says 3.3V@5mA you will only get 3.3V when there is 5mA through the zener. If the current is more or less then the voltage will change.
If you look at the datasheet, there will be a parameter called “slope resistance”. The zener behaves as though this resistance was in series with it.

 

The 1kΩ resistor in series with the Zener is preventing it from clamping the voltage (why is it there?).
Remove that and it will work properly.

 

Your circuit might be overkill. A simple RC low pass filter should be enough.

 

Nice it works. Thank you so much, but now I have another situation, if the voltage goes up, then of course the current rise as well.. What can I do to prevent this?... If anyone have another solution for protecting a pin please let me now.... basically what I need is that from 12v goes down to 3.3 for the pin pf the microcontroller.. but I have to protect the pin, for anything in the world, it can't turn up that voltage

 

You already have other threads on this topic. This thread is closed.
https://forum.allaboutcircuits.com/...m-accidental-overvoltage.203226/#post-1939776