2N4400 Bipolar Transistor

• Type: NPN
• Collector-Emitter Voltage, max: 40 V
• Collector-Base Voltage, max: 60 V
• Emitter-Base Voltage, max: 6 V
• Collector Current − Continuous, max: 0.6 A
• Collector Dissipation: 0.625 W
• DC Current Gain (h_fe): 50 to 150
• Transition Frequency, min: 200 MHz
• Operating and Storage Junction Temperature Range: -55 to +150 °C
• Package: TO-92

The 2N4400 is manufactured in a plastic TO-92 case. When looking at the flat side with the leads pointed downward, the three leads emerging from the transistor are, from left to right, the emitter, base, and collector leads.
Here is an image showing the pin diagram of this transistor.The complementary PNP transistor to the 2N4400 is the 2N4402.The MMBT4400 (SOT-23) is the SMD version of the 2N4400 transistor. These transistors are of the same type, have similar parameters and are designed for surface mounting.You can replace the 2N4400 with the 2SC1008, BC537, BC538, KSC1008, ZTX451 or ZTX452.