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overvoltage protection technique

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yougarage

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I'm going to read (with an ADC) an analog signal.
I scale it down from 20v to 5v using a voltage divider, but I'd like to protect the adc pin from overvoltages.
right after the divider,is it better a small zener rated at 5.1 volt to ground, or a simple signal diode (like 1n4148) connected to regulated 5v ?
Which of them could affect less the linearity of the readings?
 

yes i suppose we shud use zener .because zener can effect better at this place
but men b'fore to ground zener must use resistor with zener to ground
 

but men b'fore to ground zener must use resistor with zener to ground

They do not need extra resistor, because of voltage divider 20/5V (there are 2 resistors).

yougarage Your question is what is better to use zener 5V1 or 1N4148 to supply.

I always use zenner diode 5V1, and I'll make divider in your case that on 20V inputs I have 4.7V or 4.8V max to be sure that zenner diode do not do much on that voltage.


Regards,

Mr.Cube


Mr.Cube
 

I have the similar question. I'd like to monitor supply voltage, so it is directly connected to ADC thru resistor divider.

Please suggest several ways to protect the ADC input from any abnormal voltage supply.
 

Hi leekc_83,

you could use a normal diode(or Schottky diode if needed) from the ADC input to the Vcc of the ADC or a universal IO-port for a microcontroller to connect to higher voltages (e.g. industrial 24V). Here your find some applications: https://www.ichaus.biz/mcu_interface .

Enjoy your design work!
 

In my experience, zeners are pretty poor for clamping, especially if the impedance of the signal is high. The reverse bias knee of most zeners is quite soft in comparison to the forward bias knee of most silicon diodes. So if you don't want distortion you should use a low leakage schottky diode.
 

In my experience, zeners are pretty poor for clamping, especially if the impedance of the signal is high. The reverse bias knee of most zeners is quite soft in comparison to the forward bias knee of most silicon diodes. So if you don't want distortion you should use a low leakage schottky diode.

"especially if the impedance of the signal is high"

hi mtwieg, May I know what is the "high impedance signal" means? I curious about it quite long ago.. I see somewhere before.. but I not really understand what its means.. Thanks
 

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