BC547 NPN transistor — 45V, 100mA, hFE 110–800, TO-92, amplifier and switching

The BC547 is one of the most widely used general-purpose NPN bipolar junction transistors (BJT), available in the compact TO-92 through-hole package. With a collector-emitter voltage of 45V, a continuous collector current of 100mA, and a DC current gain (h_FE) ranging from 110 to 800, it is an extremely versatile component for both signal amplification and low-power switching applications.

Its high gain range makes it suitable for audio pre-amplification, signal conditioning, and sensor interface circuits, while its fast switching characteristics make it a reliable choice for driving LEDs, relays, and logic-level loads in microcontroller-based designs.

Key Specifications:

• Part number: BC547
• Type: NPN bipolar junction transistor (BJT)
• Collector-emitter voltage (V_CEO): 45V
• Collector-base voltage (V_CBO): 50V
• Emitter-base voltage (V_EBO): 6V
• Continuous collector current (I_C): 100mA
• DC current gain (h_FE): 110 to 800
• Maximum base current (I_B): 5mA
• Power dissipation (P_D): 500mW
• Package: TO-92 (through-hole, 3-pin)
• Pin order: CBE (Collector, Base, Emitter) — flat face left to right

Key Features:

• High h_FE up to 800 — excellent amplification for low-level audio and sensor signals
• 45V V_CEO — suitable for a wide range of low-voltage circuit designs
• 100mA I_C — drives LEDs, small relays, and logic loads directly
• TO-92 package — compact, easy to insert on breadboards and PCBs
• Low noise — suitable for audio pre-amplifier stages
• Widely available and well-documented — extensive reference designs and application notes

Applications:

• Audio signal pre-amplification
• Sensor signal conditioning and buffering
• LED and small relay switching from microcontroller GPIO
• Logic-level signal inversion and buffering
• Darlington pair base transistor
• General-purpose low-power switching circuits
• Arduino, ESP32, and Raspberry Pi GPIO load switching

Note: Limit base current to 5mA max. For loads exceeding 100mA, use a higher-rated transistor such as BC337, 2N2222, or TIP31. Verify pin orientation (CBE) before soldering.