BF258 Silicon Planar Transistor Technical Summary

Overview

The BF258 is a silicon planar epitaxial NPN transistor designed for general-purpose amplifier applications. Part of the BF25x series that includes BF257 and BF259 variants, this component offers reliable performance in low to medium power circuits. The transistor features good thermal stability and is suitable for both switching and amplification purposes in electronic designs.

Manufactured using planar epitaxial technology, the BF258 provides consistent electrical characteristics and robust performance across its operating temperature range. The device is particularly noted for its low noise characteristics, making it suitable for audio frequency applications.

Key Features

• NPN silicon planar epitaxial construction
• Low noise characteristics for audio applications
• Medium power dissipation capability
• Good thermal stability
• Complementary PNP types available in series
• Pb-free and RoHS compliant versions available
• Designed for general purpose amplification
• Suitable for switching applications

Applications

The BF258 transistor finds use in a wide variety of electronic circuits including:

• Audio frequency amplifiers
• Low noise preamplifier stages
• Signal processing circuits
• Driver stages in electronic equipment
• General purpose switching circuits
• Impedance matching circuits
• Oscillator circuits
• Educational and hobbyist projects

Its balanced characteristics make it particularly useful in designs where a compromise between gain, frequency response, and power handling is required.

Electrical Characteristics

(All values specified at T_amb = 25°C unless otherwise noted)

Absolute Maximum Ratings

• Collector-Base Voltage (V_CB): 30V
• Collector-Emitter Voltage (V_CE): 20V
• Emitter-Base Voltage (V_EB): 5V
• Collector Current (I_C): 100mA
• Total Power Dissipation (P_tot): 300mW
• Operating Junction Temperature Range (T_j): -55°C to +150°C
• Storage Temperature Range (T_stg): -55°C to +150°C

DC Characteristics

• DC Current Gain (h_FE):
  • Minimum: 40
  • Typical: 120
  • Maximum: 400
• Collector-Emitter Saturation Voltage (V_CE(sat)):
  • Maximum: 0.3V @ I_C = 10mA, I_B = 1mA
• Base-Emitter Voltage (V_BE):
  • Typical: 0.66V @ I_C = 2mA
• Collector Cut-off Current (I_CEO):
  • Maximum: 0.1μA @ V_CE = 10V

AC Characteristics

• Transition Frequency (f_T):
  • Typical: 150MHz @ V_CE = 10V, I_C = 10mA, f = 100MHz
• Capacitance (C_ob):
  • Typical: 3.5pF @ V_CB = 10V, f = 1MHz
• Noise Figure (NF):
  • Typical: 4dB @ I_C = 100μA, V_CE = 5V, R_G = 1kΩ, f = 1kHz

Package Information

The BF258 is available in several standard transistor packages:

TO-92 Package

• Package Type: Plastic, through-hole
• Dimensions: 4.95mm x 4.95mm x 3.68mm (typical)
• Lead Spacing: 2.54mm (0.1 inch) standard
• Weight: Approximately 0.13 grams
• Terminal Identification:
  • Pin 1: Emitter
  • Pin 2: Base
  • Pin 3: Collector
• Moisture Sensitivity Level (MSL): MSL 1 - Unlimited

SOT-23 Package (Alternative)

• Package Type: Surface mount
• Dimensions: 2.9mm x 1.3mm x 0.95mm (typical)
• Lead Pitch: 0.95mm
• Terminal Identification:
  • Pin 1: Base
  • Pin 2: Emitter
  • Pin 3: Collector

Thermal Characteristics

• Thermal Resistance, Junction to Ambient (R_thJA):
  • TO-92 Package: 357°C/W
  • SOT-23 Package: 312°C/W
• Thermal Resistance, Junction to Case (R_thJC):
  • TO-92 Package: 83.3°C/W

Reliability Data

• Mean Time Between Failures (MTBF): >10⁷ hours at 25°C
• ESD Sensitivity: Class 1B (Human Body Model, 500V)
• Flammability Rating: UL 94V-0

Handling and Storage Recommendations

• Store in anti-static packaging when not in use
• Maintain storage environment between -55°C and +150°C with <60% relative humidity
• Use proper ESD precautions during handling and assembly
• Avoid mechanical stress on leads during PCB insertion
• For SMD versions, follow recommended reflow profiles

Design Considerations

When designing with the BF258 transistor, consider the following:

• For optimal noise performance, operate at collector currents between 100μA and 1mA
• Ensure proper heat dissipation in applications approaching maximum power ratings
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