The BZT52C3V9LP from Micro Commercial Components is a Zener Diode with Zener Voltage 3.7 to 4.1 V, Zener Current 1 mA, Voltage Forward 0.9 V, Current 5 mA, Current Reverse Reverse Leakage Current:- 3 uA. More details for BZT52C3V9LP can be seen below.