Electronics > Beginners
Over voltage protection not working
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mitrynicolae:
Hi everyone,
Let me explain the issue first. I try to design a protection on the inputs of a differential amplifier. At first I did not paid much attention to details and I only develop the circuit from the Figure1. Everything worked fine until the voltage drop to 5V or bellow. From this step on the measurement is useless. Please ignore the voltage offset, it was due an incorrect resistor, and it can be easily fixed.
My suspicion of the incorrect measurement goes on the zenner diode and its leakage current.
Anyway I was not happy with the protections so I have tried to design another circuit dedicated for this purpose. The issue is that regardless how hard I am struggling I cannot fulfill all the specifications. These are:
- voltages between 0 and 20V should pass unaltered (or with minimum distorsion of any sort)
- if input voltage is above 20V the output should be either shut down or clamped but in any situation the input voltage should not get to the opamp
- if the input voltage is somehow reversed then the output should be shut down.
- the protections should not use any external power supply (so using a relay and a monitoring circuit is out of option)
- optional, the circuit should contain the minimum parts possible.
Again as I previously said, no mater how hard I struggled I cannot find a valid solution for the above problem. For example using a P channel mosfet as reverse voltage protection will not work for low voltages.
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