2N4031 Bipolar Transistor

• Type: NPN
• Collector-Emitter Voltage, max: 80 V
• Collector-Base Voltage, max: 80 V
• Emitter-Base Voltage, max: 5 V
• Collector Current − Continuous, max: 1 A
• Collector Dissipation: 0.8 W
• DC Current Gain (h_fe): 40 to 120
• Transition Frequency, min: 400 MHz
• Operating and Storage Junction Temperature Range: -55 to +175 °C
• Package: TO-39

Here is an image showing the pin diagram of this transistor.The BCP56 (SOT-223) and BSR42 (SOT-89) is the SMD version of the 2N4031 transistor. These transistors are of the same type, have similar parameters and are designed for surface mounting.You can replace the 2N4031 with the 2N3020, 2N4239, 2N5320, 2N5335, 2N5336, 2N5338, 2N5681, 2N5682 or 2SC510.