The BZT55C3V9 from Micro Commercial Components is a Zener Diode with Zener Voltage 3.7 to 4.1 V, Zener Current 1 mA, Voltage Forward 1.5 V, Current 5 mA, Current Reverse Reverse Leakage Current:- <2.0 - <40 uA. More details for BZT55C3V9 can be seen below.