Transistors, Bipolar (BJT) Transistors, MMBT5550LT1G, onsemi

 MMBT Series 140 V 60 mA SMT NPN Silicon Transistor - SOT-23

https://www.futureelectronics.com/p/semiconductors--discretes--transistors--bipolar-transistors/mmbt5550lt1g-onsemi-7874126