The 2N3904 is one of the most common NPN bipolar junction transistors in the world, found in almost every electronics starter kit. It is designed for general-purpose switching and amplification. Unlike the BC-series transistors popular in Europe, the 2N3904 is the standard in North America and features a different pinout. It is capable of handling relatively high frequencies, making it useful in RF (radio frequency) applications up to 300 MHz. Its low cost and wide availability make it the first choice for students and professionals building small-signal prototypes.
2N3904 Pinout (TO-92)
For the 2N3904 in a TO-92 package, with the flat face towards you and pins down, the order from left to right is Emitter, Base, and Collector. Note: This is different from the BC547.
| Pin | Terminal | Function |
| 1 | Emitter (E) | Current flows out to the ground |
| 2 | Base (B) | Control pin for triggering the transistor |
| 3 | Collector (C) | Current flows in from the positive supply/load |
Technical Specifications
- Transistor Polarity: NPN
- Collector-Emitter Voltage (VCEO): 40V
- Collector-Base Voltage (VCBO): 60V
- Emitter-Base Voltage (VEBO): 6V
- Collector Current (IC): 200mA
- DC Current Gain (hFE): 100 to 300
- Transition Frequency (fT): 300 MHz
- Max Power Dissipation (PD): 625mW
Key Features & Benefits
- High Frequency Capability: Excellent for low-power radio and signal processing.
- Low Cost: Extremely affordable for mass-produced consumer electronics.
- Standard Small Signal: Perfect for switching small loads like LEDs and low-power sensors.
- Wide Gain Range: Provides consistent performance across various temperatures.
Common Applications
- Signal Amplification: Boosting weak signals in sensor circuits.
- Logic Gates: Building DIY digital logic circuits (AND, OR, NOT).
- Pulse Generators: Used in oscillators and timing circuits.
- Switching: Driving small loads under 200mA.
2N3904 Equivalent & Substitutes
- BC547 (Functional equivalent, but check the pinout)
- 2N2222 (Higher current NPN substitute)
- S8050 (High current NPN alternative)
- PN2222 (Plastic version of the 2N2222)
Related Tutorials on ElxHub
- Basics: Learn more in Transistors – Basics, Types, and Working
- Signal Shifting: Learn how to bridge logic levels in our Logic Level Shifter Tutorial
- Selection Guide: Compare power options in our Ultimate Transistor Selection Guide
Conclusion
The 2N3904 is a fundamental building block of modern hobbyist electronics. Its ability to perform both as a fast switch and a reliable amplifier at high frequencies makes it incredibly versatile. Whether you are building a simple LED flasher or a complex radio receiver, the 2N3904 provides the consistency required for successful electronic design.
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