The BFY51 is a classic, medium-power silicon planar NPN bipolar junction transistor (BJT) encapsulated in a rugged metal TO-39 can package. Engineered for linear amplification, VHF oscillator, and medium-speed switching applications, the BFY51 features high current-handling capability up to 1A, a collector-emitter breakdown voltage of 30V (with V_CBO up to 60V), and high bandwidth with a transition frequency of 50MHz. It is widely used in audio driver stages, RF oscillators, relay drivers, laboratory equipment, and retro audio electronics.

Specifications

• Brand / Manufacturer: Central Semiconductor / STMicroelectronics / Industry Standard
• Part Number: BFY51
• Transistor Type: Medium-Power NPN Bipolar Junction Transistor (BJT)
• Collector-Emitter Voltage (V_CEO): 30V
• Collector-Base Voltage (V_CBO): 60V
• Emitter-Base Voltage (V_EBO): 6.0V
• Continuous Collector Current (I_C): 1.0A
• Peak Collector Current (I_CM): 1.5A
• DC Current Gain (h_FE): 40 to 120 (at I_C = 150mA, V_CE = 10V)
• Collector-Emitter Saturation Voltage (V_CE(sat)): < 0>C = 150mA, I_B = 15mA / < 1>C = 1.0A, I_B = 100mA
• Transition Frequency (f_T): 50 MHz (Minimum at I_C = 50mA, V_CE = 10V)
• Total Power Dissipation (P_tot): 0.8W (at T_amb = 25°C in free air) / Up to 5.0W (at T_case = 25°C with heatsink)
• Operating Junction & Storage Temperature Range: -65°C to +200°C
• Package / Case: TO-39 (3-Lead Metal Can: Pin 1: Emitter, Pin 2: Base, Pin 3: Collector connected to Case)

Features

• Heavy-Duty TO-39 Metal Can Package: Provides rugged mechanical protection, hermetic sealing, and effective heat dissipation when fitted with push-on or bolt-on heatsinks.
• High Collector Current Handling: Safely drives continuous loads up to 1.0A, making it ideal for bridging the gap between low-power signal transistors and large power devices.
• High Transition Frequency (50MHz): Well-suited for HF/VHF communication circuits, oscillators, and RF preamplifier stages.
• High Thermal Headroom: Supports extreme operating junction temperatures up to +200°C, ensuring reliability in demanding industrial and laboratory environments.
• Proven Industrial Reliability: Standardized pinout and broad electrical characteristics make it an excellent choice for legacy audio amplifiers, DIY repairs, and educational electronic labs.

Common Applications

• Audio Driver & Preamplifier Stages: Voltage amplification and intermediate driver stages in Class-AB and vintage transistorized audio amplifiers.
• Medium-Power Relay & Solenoid Switching: Driving inductive electromechanical relays, indicator lamps, and DC actuators from logic controllers.
• HF & VHF Oscillators / Transmitters: Frequency generation and small-signal RF amplification in amateur radio and communication gear.
• Linear Power Supply Regulators: Pass-transistor driver and error amplifier regulation in benchtop power supplies.
• Educational & Prototyping Projects: Classic discrete transistor experiments on breadboards and perfboards.

Usage Tips

• Pinout and Case Connection: The TO-39 metal can has an alignment tab located closest to the Emitter (Pin 1); the Base (Pin 2) is in the center, and the Collector (Pin 3) is electrically connected to the metal can. Ensure the metal casing does not accidentally short to adjacent grounded components or chassis metal.
• Base Current Limiting: Always include an appropriately calculated base resistor (R_B) to prevent excessive base current; provide an overdrive current (I_B ≈ I_C / 10) to ensure full saturation during switching.
• Heatsink Selection: When operating with continuous currents above 300mA or dissipating more than 0.8W, fit a star/fin clip-on TO-39 heatsink over the metal can to maintain junction temperatures well below maximum limits.
• Inductive Clamping: Always place a flyback diode (such as a 1N4007 or 1N5819) across inductive loads (relays, motor coils) to protect the collector against reverse inductive kickback spikes exceeding the 30V V_CEO rating.

Datasheet