BC548 NPN General-Purpose Transistor – 30V, 100mA, TO-92

The BC548 is a general-purpose NPN bipolar junction transistor (BJT) designed for low-current switching, signal amplification, sensor interfaces, audio circuits, and general electronics applications.

With a 30V collector-emitter voltage rating, collector current up to 100mA, and compact through-hole TO-92 package, the BC548 is widely used in educational electronics, microcontroller projects, LED drivers, amplifier stages, oscillators, signal-conditioning circuits, and low-power switching applications.

Technical Specifications

• Part Number: BC548
• Transistor Type: NPN Bipolar Junction Transistor (BJT)
• Polarity: NPN
• Collector-Emitter Voltage (VCEO): 30V Max
• Collector-Base Voltage (VCBO): 30V Max
• Emitter-Base Voltage (VEBO): 5–6V Max, Depending on Manufacturer
• Continuous Collector Current (IC): 100mA Max
• DC Current Gain (hFE): 110–800, Depending on Gain Group
• Transition Frequency (fT): 150MHz Minimum on Common Versions
• Collector-Emitter Saturation Voltage: Up to Approx. 0.6V at IC = 100mA, IB = 5mA
• Power Dissipation: Approx. 500–625mW Max, Depending on Manufacturer & Package
• Maximum Junction Temperature: +150°C
• Package: TO-92
• Number of Pins: 3
• Mounting Type: Through-Hole
• Complementary PNP Type: BC558

General-Purpose NPN Transistor

The BC548 can operate as both an electronic switch and a small-signal amplifier.

A small base current controls a larger collector-emitter current, allowing the transistor to interface low-current control circuits with compatible electronic loads.

It is particularly suitable for low-current applications where high power handling is not required.

BC548 Gain Groups

The BC548 family is commonly available in gain-selected versions:

• BC548A: hFE 110–220
• BC548B: hFE 200–450
• BC548C: hFE 420–800

The exact gain depends on the device version, operating current, temperature, and manufacturer.

If your component is marked simply BC548 without an A, B, or C suffix, avoid advertising a specific gain group.

Switching Applications

The BC548 can be used as a low-current electronic switch for controlling:

• LEDs
• Buzzers
• Small Signal Relays
• Logic Circuits
• Sensor Outputs
• Low-Current Loads
• Driver Stages

When driven from an Arduino, ATmega, ESP32, STM32, Raspberry Pi GPIO, or another controller, an appropriate base resistor should be used.

For inductive loads such as relay coils, a suitable flyback diode should normally be connected across the load.

Signal Amplification

The BC548 is well suited to small-signal amplifier circuits.

Typical applications include:

• Audio Preamplifiers
• Microphone Amplifiers
• Sensor Signal Conditioning
• Small-Signal Amplifiers
• Oscillators
• Pulse Circuits
• Logic Interfaces
• General Analog Circuits

Its relatively high current gain makes it useful for amplifying small electrical signals in low-power circuits.

Microcontroller Interface

A BC548 can be used as an interface between a microcontroller GPIO and a compatible low-current load.

A typical low-side switching circuit uses:

• GPIO → Base Resistor → BC548 Base
• BC548 Emitter → Ground
• BC548 Collector → Load
• Other Side of Load → Positive Supply

If separate power supplies are used, their grounds normally need to be connected unless electrical isolation is intentionally provided.

BC548 vs BC547

The BC547 and BC548 are closely related NPN small-signal transistors, but their voltage ratings differ.

• BC547: Up to 45V VCEO
• BC548: Up to 30V VCEO
• Both: Up to 100mA collector current

For circuits operating below the BC548 voltage limits, either device may be suitable depending on the required gain group, manufacturer specifications, and circuit design.

The BC547 should not automatically be replaced by a BC548 in circuits requiring more than the BC548's 30V rating.

BC548 vs BC337

The BC548 and BC337 are both NPN transistors but are intended for somewhat different applications.

BC548: Small-signal transistor, 30V, 100mA

BC337: Higher-current general-purpose transistor, typically rated for substantially more collector current

The BC548 is better suited to small-signal amplification and low-current switching, while the BC337 is generally preferable when a load requires more current.

Important Note

The 100mA collector-current rating is an absolute maximum, not a recommended continuous operating current for every circuit.

Safe operating conditions depend on collector-emitter voltage, base drive, ambient temperature, power dissipation, switching duty cycle, and thermal conditions.

The BC548 should not be used to directly control high-current motors, large relays, high-power LEDs, or other loads exceeding its electrical and thermal limits.

Specifications such as power dissipation, emitter-base voltage, and exact pin arrangement can differ slightly between manufacturers. Always verify the datasheet and Collector, Base, and Emitter pinout for the exact component supplied.

Applications

Ideal for small-signal amplification, low-current switching, LED drivers, sensor circuits, audio amplifiers, microphone preamplifiers, oscillators, microcontroller interfaces, Arduino projects, educational electronics, electronics repair, breadboard prototyping, laboratory experiments, and DIY electronics.

Package Includes

1 × BC548 NPN General-Purpose Transistor – TO-92