LM324 voltage follower with a single supply to rectify an AC signal?
have a question that is mostly related to voltage input common mode ranges. The LM324 should be able to go pretty close to it's negative rails, as a voltage follower would the common mode voltage pretty much always be close to 0V?
My goal is to clip out the negative portions of a slow ac signal (10Hz, magnitude 2.5V centered at 0V) and then manipulate the now positive signal with a few stages of op-amp circuits. The following circuit is my first stage. The original circuit included a diode going from the ac signal to the non-inverting terminal of the op-amp which, accompanied by a large pull down resistor (1M+) functions, but attenuates the signal somewhat. If I remove the diode/resistor and plug the source directly into the op-amp, my output is exactly what I want: only the positive half of the signal comes through at the output (and the input actually reflects this as well).
All of the research I have done suggests not using inputs outside the rails of an op-amp but everything I've read says the problem is with unpredictable outputs, not necessarily the possibility of damaging the op-amp. My gut told me that the op-amp would simply clip the negative portion of the signal to the negative rail, and that is exactly what happened, but as reliability is very important for this circuit, I can't implement the following design without knowing exactly why it works and whether it will be reliable over time.
1. What is the common mode voltage of a voltage follower?
2. Can op-amp inputs safely exceed the rails if the common mode voltage is still within spec?
3. Is it safe to use a single-supply op-amp to half-wave rectify a slow ac signal?
Is this a good question?