AZ431A is Voltage Tolerance 0.4%.

AZ431B is Voltage Tolerance 0.8%.

The AZ431-A, AZ431-B is a three-terminal adjustable shunt regulator with guaranteed thermal stability over a full operation range. It features sharp turn-on characteristics, low temperature coefficient and low output impedance, which make it ideal substitute for Zener diode in applications such as switching power supply, charger and other adjustable regulators.