A comparator compares the voltage on the input signals with a reference voltage at the other input. In picture 1 the output voltage Vo is divided between R1 and R2. Most of Vo turn fed to the input (+). When Vo = + Vsat, the feedback voltage is called the voltage-threshold (vut), where:

For Gain of Ei below VUT, the voltage at the input (+) is greater than the voltage at the input (-). That it is Vo locked in + Vsat. If Ei is made slightly more positive than VUT, then the polarity of Ed reverse as shown and started gain of Vo is down. Now most of Vo which in turn feed into the positive input becomes smaller, so that Ed becomes larger. Vo then dropped even more quickly and moved quickly to-Vsat. Further the circuit becomes stable at the state shown in Figure 2.

When Vo is on -Vsat, the voltage fed to the feedback input (+) is called under-voltage threshold (VLT), where:
VLT is Negative to ground, then Vo will remain on -Vsat for Ei still above, or positive on the VLT. Vo will turn move to + Vsat if Ei be more negative than or below the VLT.

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