BC337 — NPN General Purpose Bipolar Junction Transistor

Overview

The BC337 (BC337-40) is a high-current NPN bipolar junction transistor (BJT) manufactured by ON Semiconductor, Nexperia, and STMicroelectronics. Enclosed in a standard TO-92 package, it is widely used across European and global electronics designs as a step-up current driver compared to the standard BC547.

Capable of handling collector-emitter voltages up to $45\text{ Volts}$ and continuous collector currents up to $800\text{ mA}$ (with peak currents up to $1.0\text{ A}$ ), the BC337 is ideal for driving small DC motors, relay coils, buzzers, high-brightness LEDs, and medium-power audio output stages. Its complementary PNP transistor is the BC327.

Quick reference


Transistor Type	NPN Bipolar Junction Transistor (BJT)
Package	TO-92 (Flat face front, leads pointing down)
Collector-Emitter Voltage ( $V_{CEO}$ )	$45\text{ V}$ max
Collector-Base Voltage ( $V_{CBO}$ )	$50\text{ V}$ max
Continuous Collector Current ( $I_C$ )	$800\text{ mA}$ continuous ( $1000\text{ mA}$ peak)
DC Current Gain ( $h_{FE}$ )	100 to 630 (BC337-16: 100–250, BC337-25: 160–400, BC337-40: 250–630)
Transition Frequency ( $f_T$ )	$100\text{ MHz}$ min ( $210\text{ MHz}$ typical)
Power Dissipation ( $P_D$ )	$625\text{ mW}$ ( $T_A = 25^\circ\text{C}$ )

Pinout (TO-92 Package)

Looking at the flat face of the TO-92 package with leads pointing down:

text

        ┌─────────────┐
        │    BC337    │  (Flat Package Face)
        └─┬───┬───┬───┘
          1   2   3
          C   B   E

Pin	Name	Description
1	`COLLECTOR` (`C`)	Collector terminal (Load connection)
2	`BASE` (`B`)	Base terminal (Control input via base resistor)
3	`EMITTER` (`E`)	Emitter terminal (Ground reference 0 V)

Warning

Pinout Warning: European C-B-E Pinout!

BC337 (TO-92): Pin 1 = Collector, Pin 2 = Base, Pin 3 = Emitter (C-B-E).
2N3904 (TO-92): Pin 1 = Emitter, Pin 2 = Base, Pin 3 = Collector (E-B-C).
Always double-check European BC-series pinouts when replacing American 2N-series transistors.

Specifications

Parameter	Symbol	Min	Typ	Max	Unit	Conditions
Collector-Emitter Voltage	$V_{CEO}$	45	—	—	V	$I_C = 10\text{mA}, I_B = 0$
Collector Cutoff Current	$I_{CBO}$	—	—	100	nA	$V_{CB} = 20\text{V}, I_E = 0$
DC Current Gain (BC337-40)	$h_{FE}$	250	—	630	—	$V_{CE} = 1\text{V}, I_C = 100\text{mA}$
Collector Saturation Volts	$V_{CE(sat)}$	—	350	700	mV	$I_C = 500\text{mA}, I_B = 50\text{mA}$
Base-Emitter On Voltage	$V_{BE(on)}$	—	—	1.2	V	$V_{CE} = 1\text{V}, I_C = 300\text{mA}$

Common mistakes

Exceeding $625\text{ mW}$ thermal dissipation: When operating near the maximum $800\text{ mA}$ collector current, ensure $V_{CE(sat)}$ is minimized by supplying adequate base drive current ( $I_B \ge I_C / 10$ ). High $V_{CE}$ under heavy load causes thermal breakdown.
Connecting Base directly to MCU GPIO: Connecting a 5V or 3.3V GPIO pin directly to the Base destroys the transistor. Always insert a series Base resistor (e.g. $220\ \Omega$ to $1\text{ k}\Omega$ ).

Notes

BC337 vs BC547: BC337 handles $800\text{ mA}$ continuous current; BC547 is rated for $100\text{ mA}$ . Use BC337 when driving relays, motors, or power indicators.