2N3904 NPN BJT Transistor TO-92

The 2N3904 is a widely used NPN Bipolar Junction Transistor (BJT) in a TO-92 through-hole package, ideal for general-purpose switching and signal amplification. Trusted by electronics engineers and hobbyists, it integrates seamlessly with microcontroller-based projects and modules.

Key Features ✅

• General-purpose NPN transistor for switching and amplification
• TO-92 package for easy breadboard and PCB prototyping
• Suitable for 3.3 V and 5 V logic control with microcontrollers
• Reliable choice for electronics components libraries and educational builds
• Great for driving small loads and interfacing with sensor/relay modules (with appropriate base resistor)

Technical Specifications 📐

• Polarity: NPN BJT
• Package: TO-92 (through-hole)
• Collector–Emitter Voltage (Vceo): up to 40 V
• Collector–Base Voltage (Vcbo): up to 60 V
• Emitter–Base Voltage (Vebo): up to 6 V
• Continuous Collector Current (Ic): up to 200 mA

Typical Applications 🔌

• General-purpose switching for low-to-moderate current loads
• Amplification circuits (small-signal, audio pre-stages)
• Signal processing and level interfacing with microcontrollers
• Power management for driving indicators, small motors, or relays (with flyback diode)

Design Notes for Microcontroller Projects 💡

• Use a base resistor to limit base current. Choose the value based on desired collector current and expected gain (hFE). A simple approach is to size the base current to 1/10 of the collector current for saturation.
• Stay within the voltage and current ratings listed above to ensure reliability.
• When switching inductive loads (coils, relays, motors), add a flyback diode across the load to protect the transistor.
• Refer to the manufacturer datasheet for pinout and detailed characteristics; TO-92 pin assignments can vary by vendor.

This versatile 2N3904 NPN transistor is a staple in electronics components kits and a dependable choice for rapid prototyping, education, and production-ready designs requiring compact, efficient switching and amplification.