MMBT5551 Bipolar Transistor

• Type: NPN
• Collector-Emitter Voltage, max: 160 V
• Collector-Base Voltage, max: 180 V
• Emitter-Base Voltage, max: 6 V
• Collector Current − Continuous, max: 0.6 A
• Collector Dissipation: 0.35 W
• DC Current Gain (h_fe): 80 to 250
• Transition Frequency, min: 100 MHz
• Noise Figure, max: 8 dB
• Operating and Storage Junction Temperature Range: -55 to +150 °C
• Package: SOT-23

Here is an image showing the pin diagram of this transistor.The MMBT5551 transistor is marked as "3S".The complementary PNP transistor to the MMBT5551 is the MMBT5401.You can replace the MMBT5551 with the 2N5551S or KST5551.