The Schmitt trigger is a comparator application which switches the output negative when the input passes upward through a positive

The Schmitt trigger action uses a comparator to produce stable level-crossing switches in contrast to the action of a straight

Schmitt trigger action is a double threshold comparator process. The current equation at A gives:

where

This dependence upon the output voltage gives the dual threshold. The two output states give the thresholds shown at right.