The 2N2222 and 2N3904 are two of the most widely used NPN bipolar junction transistors (BJTs) in electronics. While they share similarities, their distinct specifications make them suitable for different applications. This article explores their differences in detail, covering electrical characteristics, packaging, and use cases.

Key Specifications at a Glance

Detailed Differences

1. Current and Voltage Ratings

• 2N2222: Designed for higher current applications, it handles up to 800 mA continuously (e.g., driving relays, motors, or LEDs). The plastic variant (PN2222) is often rated for 600 mA.

• 2N3904: Limited to 200 mA, making it ideal for low-power circuits like signal amplification or digital logic.

Both share a 40 V Vceo rating, suitable for low-to-medium voltage circuits.

2. Power Dissipation and Thermal Performance

• 2N2222: The TO-18 metal can version dissipates 500 mW, while the TO-92 plastic variant handles 625 mW due to better thermal design. The metal package offers superior heat dissipation for high-power scenarios.

• 2N3904: Rated for 625 mW in a TO-92 package, but its smaller size limits sustained high-power use compared to the 2N2222.

3. Frequency Response

• 2N2222: A 250 MHz transition frequency (ft) suits it for moderate-speed switching and amplification.

• 2N3904: Higher 300 MHz ft enables better performance in RF and high-frequency analog circuits (e.g., oscillators, preamps).

4. Gain Characteristics

• 2N2222: Maintains higher current gain (hFE) at elevated currents (e.g., ~100 at 150 mA), optimizing it for switching.

• 2N3904: Offers more linear gain across low currents, preferred for amplification in analog stages.

5. Switching Speed

• 2N2222: Slower switching due to higher capacitance (turn-on delay: 35 ns, storage time: 225 ns). Optimized for robust switching rather than speed.

• 2N3904: Faster small-signal switching (turn-on delay: 12 ns, storage time: 200 ns) but struggles at higher currents.

6. Packaging

• 2N2222: Available in TO-18 (metal) for durability and heat resistance or TO-92 (plastic) for cost efficiency.

• 2N3904: Exclusively in TO-92, making it compact and economical.

Applications

• 2N2222:

• High-current switching (relays, solenoids).

• Motor and LED drivers.

• Power regulation in medium-current circuits.

• 2N3904:

• Low-noise amplification (audio/RF stages).

• Signal processing and digital logic (e.g., Arduino projects).

• Oscillators and high-frequency circuits.

Cost and Availability

• 2N3904: More economical (≈ $0.10 per unit) and ubiquitous in consumer electronics.

• 2N2222: Slightly costlier (≈ $0.20\text{–}$0.50) but widely available for high-current needs.

Substitutability

While both are NPN transistors, substitution requires careful consideration:

• Use the 2N2222 in high-current/power scenarios.

• Opt for the 2N3904 in low-power, high-frequency, or cost-sensitive designs.

Conclusion
The 2N2222 and 2N3904 cater to different niches: the former excels in power handling, while the latter shines in signal amplification. Understanding their specifications ensures optimal performance in your circuit designs. Always consult datasheets for critical parameters like pin configurations and derating guidelines.