The Original BC548 NPN Transistor is a standard general-purpose silicon Epitaxial Planar Bipolar Junction Transistor (BJT) housed in a compact TO-92 (TO-226AA) through-hole plastic package. Engineered for low-noise audio pre-amplification, small-signal processing, and general-purpose switching applications, the BC548 serves as the ubiquitous NPN counterpart to the complementary BC558 PNP transistor. It delivers a maximum collector-emitter breakdown voltage of 30V, continuous collector current capability of 100mA (with 200mA peak handling), low noise figure (typically 2 dB to 10 dB max), and high DC current gain across its sorted gain bins (A, B, and C). It is widely utilized in educational electronics, audio preamplifier driver stages, signal processing logic, relay driver circuits, and sensor interfaces.

Specifications

• Part Number / Model: BC548 (Available in gain bins BC548A, BC548B, BC548C)
• Transistor Polarity / Type: NPN Silicon Bipolar Junction Transistor (BJT)
• Package Type: TO-92 (TO-226AA) 3-Pin Through-Hole
• Collector-Emitter Voltage (Vceo): 30V (Max)
• Collector-Base Voltage (Vcbo): 30V (Max)
• Emitter-Base Voltage (Vebo): 5.0V (Max)
• Continuous Collector Current (Ic): 100mA (Max)
• Peak Collector Current (Icm): 200mA (Max)
• Peak Base Current (Ibm): 200mA (Max)
• Total Device Dissipation (Ptot): 500mW (at Ta = 25°C) / 625mW (standard TO-92 derating)
• DC Current Gain (hFE): 110 to 800 (BC548A: 110–220, BC548B: 200–450, BC548C: 420–800 at Vce = 5V, Ic = 2mA)
• Collector-Emitter Saturation Voltage (Vce(sat)): Typ. 90mV / Max. 250mV (at Ic = 10mA, Ib = 0.5mA); Max. 600mV (at Ic = 100mA, Ib = 5.0mA)
• Base-Emitter Saturation Voltage (Vbe(sat)): Typ. 700mV (at Ic = 10mA, Ib = 0.5mA); Typ. 900mV (at Ic = 100mA, Ib = 5.0mA)
• Base-Emitter On Voltage (Vbe(on)): 580mV to 700mV (at Vce = 5V, Ic = 2mA)
• Transition Frequency / Gain-Bandwidth Product (fT): Typ. 300 MHz (at Vce = 5V, Ic = 10mA, f = 100MHz)
• Collector Capacitance (Cc): Typ. 1.7pF / Max. 4.5pF (at Vcb = 10V, f = 1MHz)
• Noise Figure (NF): Typ. 2.0 dB / Max. 10 dB (at Vce = 5V, Ic = 0.2mA, Rs = 2kΩ, f = 1kHz, B = 200Hz)
• Operating Junction Temperature (Tj): -65°C to +150°C
• Storage Temperature Range (Tstg): -65°C to +150°C
• Thermal Resistance, Junction to Ambient (Rth(j-a)): 200°C/W to 250°C/W
• Pinout Configuration: Pin 1: Collector (C), Pin 2: Base (B), Pin 3: Emitter (E) [Standard European TO-92 layout with flat face toward viewer]

Features

• Industry Standard NPN Architecture: Seamless complementary pairing with the BC558 PNP transistor for push-pull output topologies and balanced H-bridge drivers.
• Low Noise Figure: Minimal internal noise characteristics make it ideal for high-fidelity audio preamplifiers, tone controls, and microphone input conditioning.
• Ultra-Low Saturation Voltage: Low Vce(sat) ensures high operational efficiency, low power drop, and minimal heat generation in digital switching applications.
• High Transition Frequency: 300 MHz typical fT rating provides clean switching transitions and wide bandwidth signal amplification in RF and high-speed analog stages.
• Durable TO-92 Packaging: Industry-standard 3-lead plastic mold ensures easy mounting on breadboards, perfboards, and high-density through-hole PCBs.

Common Applications

• Low-Noise Audio Preamplifiers: Audio input stages, microphone preamps, active filter circuits, and headphone driver buffers.
• Class-AB & Push-Pull Output Stages: Complementary driver stages paired with BC558 PNP transistors.
• Low-Side Signal Switching: Logic-level switching for indicator LEDs, buzzers, and miniature relays (up to 100mA continuous).
• Sensor Conditioning Circuits: Analog front-end amplification for LDR light sensors, thermistors, and capacitive touch triggers.
• Oscillators & Signal Generators: Multivibrator circuits, RC phase-shift oscillators, and pulse-shaping networks.

Usage Tips

• Low-Side Switching Configuration: As an NPN transistor, connect the Emitter directly to Ground (0V/GND) and the Collector to the low side of the load; apply a HIGH logic level (typically +3.3V or +5V) to the Base via a current-limiting resistor to energize the load.
• Base Resistor Calculation: Size the base resistor (Rb) for full saturation using the formula: Rb = (Vcontrol - Vbe) / Ib. For reliable saturation switching, design with a forced gain ratio (hFE forced) of 10 to 20 (Ib = Ic / 10).
• European Pinout Caution: The BC548 follows the standard European TO-92 pinout (Pin 1: Collector, Pin 2: Base, Pin 3: Emitter from left to right with the flat face facing you). Do not confuse it with American 2N-series transistors (e.g., 2N3904 / 2N2222), which typically feature an E-B-C pinout.
• Flyback Protection on Inductive Loads: When driving inductive loads such as small 5V/12V relay coils or DC buzzers, always place a reverse-biased flyback diode (such as a 1N4148 or 1N4007) across the load terminals to suppress back-EMF voltage spikes.

Datasheet