OPAMP undervoltage detection - Trouble in real life

Thread Starter


Joined Jan 20, 2018
I've been trying to realize an OPAMP undervoltage protection circuit (see attachment, OPAMP voltage comparator topology).

I'm using the AD8032 2.7 V Rail-To-Rail Amplifier for this task.

In LTSPICE simulation the Voltage on the output drops to 0V (-VCC) when the input at the inverting input is over the reference voltage at the noninverting input and goes to +VCC when the input at the inverting input is below the reference. That's what is supposed to happen.

However in the real-life breadboard test circuit the voltage at the output only drops to 1.3V and not near -VCC when the voltage on the inverting input is over the reference voltage on the noninverting pin.

I'm really not an OPAMP expert. What am I doing or thinking wrong?

Thank you very much!



Joined Mar 30, 2015
Welcome to AAC!

What is the opamp driving and do you have the power supply decoupled? What are the measured voltages at the inputs?

General question, why are you using an opamp instead of a voltage comparator? Why are you using a rail to rail opamp? A comparator output will switch between the rails (depending on the load being driven), and you can use voltage dividers to stay within the common-mode input range of a common LM393 that costs less than $0.25.