An operational amplifier can be used as a convenient device for analog comparator applications that require two different trip points. The addition of a positiverfeedback network introduces a precise variable hysteresis into the usual comparator switching action. Such feedback develops two comparator trip points centered about the initial trip point or reference point
The voltage difference, AV, between the trip points can be adjusted by varying resistor R2. When the output voltage is taken from the zener diode, as shown, it switches between zero and Vz, the zener voltage.