The BZT55C20 from Micro Commercial Components is a Zener Diode with Zener Voltage 18.8 to 21.2 V, Zener Current 1 mA, Voltage Forward 1.5 V, Current 5 mA, Current Reverse Reverse Leakage Current:- <0.1 - <2.0 uA. More details for BZT55C20 can be seen below.