BC337 NPN General-Purpose Transistor – 45V, 500mA, TO-92

The BC337 is a general-purpose NPN bipolar junction transistor (BJT) designed for low-voltage switching, signal amplification, driver circuits, and general electronics applications.

With a collector-emitter voltage rating of 45V, continuous collector current up to 500mA, and a compact through-hole TO-92 package, the BC337 is a popular choice for electronics projects, microcontroller interfaces, LED drivers, small relay drivers, amplifier circuits, and educational applications.

The BC337 is the complementary NPN transistor to the BC327 PNP transistor, making the pair useful for complementary switching and amplifier circuits.

Technical Specifications

• Part Number: BC337
• Transistor Type: NPN Bipolar Junction Transistor (BJT)
• Polarity: NPN
• Collector-Emitter Voltage (VCEO): 45V Max
• Collector-Base Voltage (VCBO): 50V Max
• Emitter-Base Voltage (VEBO): 5V Max
• Continuous Collector Current (IC): 500mA Max
• Peak Collector Current (ICM): 1A Max
• DC Current Gain (hFE): 100–600, Depending on Gain Group
• Transition Frequency (fT): Approx. 100MHz Typical
• Total Power Dissipation: Up to Approx. 625mW under specified thermal conditions
• Maximum Junction Temperature: +150°C
• Package: TO-92 / SOT54
• Mounting Type: Through-Hole
• Complementary PNP Transistor: BC327

General-Purpose NPN Transistor

The BC337 is suitable for both switching and amplification.

As an NPN transistor, it can be controlled by applying an appropriate base current, allowing a smaller control signal to switch or control a larger collector current.

This makes it useful for interfacing microcontrollers and low-current logic circuits with external loads.

BC337 Gain Groups

The BC337 family is available in several current-gain selections:

• BC337-16: hFE 100–250
• BC337-25: hFE 160–400
• BC337-40: hFE 250–600

If your transistor is marked only BC337 without a -16, -25, or -40 suffix, it is better not to advertise a specific gain group.

Switching Applications

The BC337 can be used as an electronic switch for controlling loads such as:

• LEDs
• Buzzers
• Small Relays
• Small Lamps
• Signal Circuits
• Low-Power Loads
• Driver Stages

When controlled by an Arduino, ESP32, Raspberry Pi GPIO, or another microcontroller, an appropriate base resistor should be used.

For inductive loads such as relays, motors, and solenoids, a suitable flyback diode should normally be installed across the load to protect the transistor from inductive voltage spikes.

Signal Amplification

The BC337 can also operate as a small-signal amplifier.

Typical applications include:

• Audio Preamplifier Stages
• Signal Amplification
• Sensor Signal Conditioning
• Driver Circuits
• Oscillator Circuits
• Complementary Amplifier Stages

Its complementary BC327 PNP transistor allows the two devices to be combined in push-pull and complementary circuit configurations.

Microcontroller Interface

The BC337 is useful when a microcontroller output cannot directly supply enough current for the required load.

A typical circuit uses:

Microcontroller GPIO → Base Resistor → BC337 Base

BC337 Emitter → Ground

Load → Collector

Load Supply → Positive Supply

The microcontroller and load power supply should normally share a common ground unless the circuit uses electrical isolation.

Important Note

The 500mA collector-current specification is an absolute maximum rating, not a recommended continuous operating current for every circuit.

Safe operating current depends on the collector-emitter voltage, base drive, ambient temperature, power dissipation, PCB design, and thermal conditions.

The 1A peak rating must also not be interpreted as a continuous 1A capability.

Pin arrangement can vary between transistor manufacturers and package variants. Always verify the Collector, Base, and Emitter pinout for the exact BC337 supplied before connecting it to a circuit.

Applications

Ideal for general-purpose switching, signal amplification, LED drivers, relay drivers, buzzer control, microcontroller interfaces, Arduino projects, sensor circuits, audio circuits, complementary amplifiers, educational electronics, electronics repair, prototyping, and DIY electronics.

Package Includes

1 × BC337 NPN General-Purpose Transistor – TO-92