I'm currently doing some practices based on the Positive Feedback page from the Operational Amplifiers chapter of this website's ebook, and I'm getting the opposite result in some circuits when using Op-Amps and Comparators. This particular circuit, in which a comparator is used, works perfectly well when I try it in a simulator. But when I try it in real life, it doesn't work with comparators; it only works with Op-Amps. I tried it with a sine wave in ranges between 0 to 10 volts, and 50 Hz to 1 KHz; and with 2 different comparatos: the LM393 and the AZ339. In both cases I got the graph bellow. But with the Op-Amp (an AD822) I get the exact result previewed in the ebook for the comparator. What's going on?