Overview
The 2N3904 is a silicon NPN bipolar junction transistor (BJT) designed for general-purpose low-power amplifying and switching applications. It is famous for its fast switching speeds and high frequency response (up to 300MHz). Housed in a standard TO-92 through-hole package, it is a favorite for students and engineers across Pakistan for prototyping on breadboards and teaching the fundamentals of semiconductor physics.
Key Features
Universal Compatibility: The go-to NPN transistor for almost all low-current switching tasks.
High-Speed Switching: Excellent for Pulse Width Modulation (PWM) and fast digital logic.
Wide Gain Range: Provides a stable DC current gain (hFE) between 100 and 300.
Compact & Reliable: The TO-92 package is durable and fits perfectly into standard 0.1″ pitch breadboards.
Complementary Pair: Works seamlessly with the 2N3906 (PNP version) for complex push-pull circuits.
Technical Specifications
| Feature | Specification |
| Transistor Type | NPN |
| Package | TO-92 |
| Collector-Emitter Voltage (VCEO) | 40V |
| Collector Current (IC) | 200mA (Continuous) |
| Power Dissipation (PD) | 625mW |
| DC Current Gain (hFE) | 100 to 300 |
| Transition Frequency (fT) | 300MHz |
Ideal Applications
Microcontroller Interfacing: Driving 5V/12V components from a 3.3V GPIO pin (Arduino/ESP32).
LED Drivers: Switching indicator lights or small LED segments.
Audio Pre-amps: Boosting low-level audio signals for further processing.
Signal Inverters: Creating NOT gates and other basic logic circuits.
Sensor Buffering: Interfacing high-impedance sensors with low-impedance loads.
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