The MMBT5551 from Diotec Semiconductor is a Bipolar Junction Transistor with Emitter Base Voltage 6 V, Base Emitter Saturation Voltage 1 V, Emitter Cut off Current 50 nA, Collector Base Voltage 180 V, Collector Cut off Current 0.05 to 50 µA. Tags: Surface Mount, NPN Transistor. More details for MMBT5551 can be seen below.