Question

Given an op-amp who’s gain is unknown but the output is saturated, which of the following is not possible?

(a) No feedback is being applied

(b) Negative feedback is applied while input is more than –VSat/AOL

(c) Positive feedback is applied

(d) Negative feedback is applied while the input is more than VSat/AOL

This question was posed to me by my school teacher while I was bunking the class.

The doubt is from Op-Amp Characteristics in portion Op-amps and its Applications of Analog Circuits

Answer 1

The correct choice is (b) Negative feedback is applied while input is more than –VSat/AOL

Easiest explanation: If op-amp is used without feedback or with positive feedback, the difference voltage VD will be large enough and hence op-amp can be considered to be in the saturation region. If op-amp is used with negative feedback then the input is smaller. Saturation of output occurs if the input is not between –VSat/AOL and +VSat/AOL.