The BZX84C51 from Micro Commercial Components is a Zener Diode with Zener Voltage 48.45 to 53.55 V, Zener Current 5 mA, Voltage Forward 0.9 V, Current 1 mA, Current Reverse Reverse Leakage Current:- 0.1 µA. More details for BZX84C51 can be seen below.