The MMBZ5251C from Micro Commercial Components is a Zener Diode with Zener Voltage 21.56 to 22.44 V, Zener Current 5.6 to 0.25 mA, Voltage Forward 1.2 V, Current Reverse Leakage Current:- 0.1 uA, Power 300 mW. More details for MMBZ5251C can be seen below.