One use of a comparator is to compare the input to a standard voltage and switch the output if the input is above that threshold. If goes more positive than the voltage set by the voltage divider for , then the output switches to . When drops below that value it switches back to .

Though useful for slow, stable variations like a temperature probe, this circuit has a serious problem with signals which might have noise superimposed. Noise variations can cause rapid switching back and forth at the threshold point. This problem is adressed with negative feedback in the Schmitt trigger variation of this idea.

The use of a comparator for level switching by a set reference comparison is complicated by the presence of noise variations which may cause troublesome rapid cycling at the switch threshold. This problem is overcome in the Schmitt trigger circuit by setting a lower threshold for the switching when the voltage is going down. .