What Is the 2N3904? NPN Transistor: Pinout (E-B-C) and Uses
The 2N3904 is a very common, cheap NPN bipolar transistor (BJT). It is used for small-signal amplification and low-current (≤200 mA, V_CEO 40 V) switching. Its TO-92 pinout, flat face front and left to right, is E-B-C — note that the European BC547 is the reverse (C-B-E).
The 2N3904 is one of the most common NPN bipolar transistors (BJTs) in the world. Cheap, it is a standard "jelly-bean" part for small-signal amplification and low-current switching. For the concept, see what is a transistor · what is a BJT.
What is the 2N3904 used for?
Small-signal preamplifiers, driving LEDs/buzzers, low-current relay/switching and oscillator circuits. With its PNP complement, the 2N3906, it is used in push-pull and level-shifting circuits.
2N3904 pinout (TO-92)
With the flat face toward you, leads down, left to right: E – B – C (Emitter, Base, Collector).
| Lead (from left) | Function |
|---|---|
| 1 | Emitter (E) |
| 2 | Base (B) |
| 3 | Collector (C) |
Note: the European BC547 has the reverse layout (C-B-E) — confusing the two is the most common mistake!
Key electrical specifications
| Parameter | Typical value |
|---|---|
| Type | NPN BJT |
| VCEO | 40 V |
| IC (max) | 200 mA |
| hFE | ~100 – 300 |
| fT | ~300 MHz |
As a switch/amplifier
The base is driven through a base resistor (typically 1–10 kΩ). As a switch, ensure IB ≈ IC/hFE; as an amplifier, set proper bias. To check it: test a transistor with a multimeter.
2N3904 equivalents and alternatives
- 2N3906: the PNP complement.
- 2N2222: higher current (800 mA).
- BC547: the European equivalent (different pinout).
- BC337: a higher-current NPN.
- MMBT3904: the SMD (SOT-23) version.
Find it in our catalog
To compare price and stock for the 2N3904 and its alternatives, use the 2N3904 search.