2N3904 NPN General Purpose Transistor (10-Pack)

2N3904 NPN General Purpose Transistor — TO-92, 40V / 200mA, 10 Pieces

The 2N3904 is one of the most widely used NPN bipolar junction transistors (BJT) in electronics, found in virtually every hobbyist parts bin and professional prototype lab. It is a general-purpose small-signal transistor optimized for low-power amplification and switching applications, with a collector-emitter voltage of 40V, 200mA collector current, and a transition frequency of 300MHz. Its TO-92 plastic package with standard EBC (Emitter-Base-Collector) pinout makes it compatible with breadboards, perfboards, and PCBs.

10 pieces per pack.

Key Specifications

• Type: NPN Bipolar Junction Transistor (BJT), silicon
• Package: TO-92 (through-hole, plastic)
• Pinout (flat face forward, left to right): Emitter (E) — Base (B) — Collector (C)
• Collector-Emitter Voltage (Vceo): 40V
• Collector-Base Voltage (Vcbo): 60V
• Emitter-Base Voltage (Vebo): 6V
• Collector Current (Ic): 200mA continuous
• DC Current Gain (hFE): 100–300 (@ Ic=10mA, Vce=1V)
• Power Dissipation (Pd): 625mW
• Transition Frequency (fT): 300MHz
• Saturation Voltage (Vce(sat)): 0.2V @ Ic=10mA
• Manufacturer: Fairchild / ON Semiconductor
• Quantity: 10 pieces

TO-92 Pinout (Flat Face Forward)

• Pin 1 (left): Emitter (E)
• Pin 2 (center): Base (B)
• Pin 3 (right): Collector (C)

Basic Switching Circuit (Arduino GPIO Buffering)

To switch a load that exceeds Arduino GPIO current limits (20–40mA), use the 2N3904 as a low-side switch:

• Base (B) → Arduino GPIO via 4.7kΩ resistor (limits base current to safe levels)
• Collector (C) → Load negative terminal
• Emitter (E) → GND
• Load positive → Supply voltage (up to 40V)
• Add flyback diode across inductive loads (motors, relays, solenoids)
• GPIO HIGH = transistor ON (load powered); GPIO LOW = transistor OFF

Example: driving 3 LEDs (60mA total) from a single Arduino pin — base resistor 4.7kΩ, current-limiting resistor 50Ω in series with LEDs.

Base Resistor Calculation

For switching (saturation): Rb = (Vb − 0.7V) / Ib, where Ib = Ic / hFE. For Ic=100mA, hFE=100: Ib = 1mA. Rb = (5V − 0.7V) / 1mA = 4.3kΩ. Use 4.7kΩ standard value. For amplification, bias the base for the desired operating point.

2N3904 vs. PN2222A vs. TIP120

• 2N3904: 40V, 200mA, hFE 100–300. Best for signal switching, LED driving, relay coil activation at low current.
• PN2222A: 40V, 600mA, hFE 100–300. Higher current for loads up to 600mA (small motors, multiple LEDs).
• TIP120: 60V, 5A, hFE ≥1000 (Darlington). For high-current loads (motors, fans) up to 5A.

Typical Applications

• Arduino/ESP32 GPIO current buffering (driving loads beyond GPIO current limit)
• LED driver (single or multiple LEDs up to 200mA total)
• Relay coil driver (5V/12V relay coils, typically 50–150mA)
• Signal amplification in audio and RF circuits
• Logic-level signal inversion (common emitter configuration)
• Oscillator and timer circuits
• Sensor signal conditioning
• Gate drive for small MOSFETs (NPN transistor as gate driver)

Package Contents

• 10 × 2N3904 NPN general purpose transistor, TO-92

Enjoy free standard shipping on all orders over $199 USD. Orders are processed within 1–2 business days.

Not satisfied? Return any item within 90 days of purchase for a full refund or exchange. Items must be in original condition.

We are committed to quality, reliability, and customer satisfaction. Every product is carefully selected and tested to meet the highest standards.