The MMSZ4711 from Micro Commercial Components is a Zener Diode with Zener Voltage 27 to 28.35 V, Zener Current 50 mA(zener test current), Voltage Forward 0.95 V, Current Reverse Leakage Current:- 0.01 uA, Power 500 mW. More details for MMSZ4711 can be seen below.