The industry standard 431 series was initially designed as a shunt regulator for precious voltage reference, which is an ideal substitute for Zener diode in applications such as switching power supply, charger and other adjustable regulators. Nowadays, some engineers use it as a comparator for its error amplifier and 2.5V precious band gap reference in the function block. However, different manufactures provide *431 with different inner topological circuits, which may cause some mismatching or application issues in the real application conditions. So it’s better to pay more attention when using *431 as a comparator.