BC108 Transistor pinout Datasheet and applications

BC108 Transistor Datasheet, Pinout, Applications, Replacement, and Equivalent

Introduction

The BC108 is an NPN silicon transistor widely used in low-power amplification and switching circuits. Known for its durability and reliability, the BC108 has been a favorite in the electronics industry for decades. In this post, we'll dive into the datasheet specifications, pinout configuration, key applications, and explore equivalent transistors or potential replacements.

BC108 Transistor Overview

ParameterSpecification
Transistor TypeNPN
Max Collector Current (I<sub>C</sub>)100mA
Max Collector-Emitter Voltage (V<sub>CE</sub>)20V
Max Collector-Base Voltage (V<sub>CB</sub>)30V
Max Emitter-Base Voltage (V<sub>EB</sub>)5V
Max Power Dissipation (P<sub>D</sub>)300mW
Transition Frequency (f<sub>T</sub>)150MHz
DC Current Gain (h<sub>FE</sub>)110 - 800
PackageTO-18 metal can

BC108 Pinout Configuration

The BC108 comes in a TO-18 metal can package, a round metallic body, which protects the transistor from environmental damage. The three pins of the BC108, as seen from the bottom of the package, are:

  1. Emitter (E) 
  2. Base (B) 
  3. Collector (C)

Pinout Summary:

Transistor BC108 pinout

Features of the BC108 Transistor:

  • Low noise and distortion characteristics, making it suitable for audio preamplifiers.
  • High transition frequency (fT), which supports high-frequency applications.
  • Relatively high gain, with an h<sub>FE</sub> ranging between 110 to 800, depending on operating conditions.
  • Compact TO-18 metal can package, offering protection and reliable performance in extreme environments.
  • Low collector-emitter saturation voltage, ensuring efficient switching operation.

Applications of BC108 Transistor

  1. Audio Amplifiers: The BC108 is well-suited for low-power audio amplification circuits due to its low noise characteristics. It is often used in pre-amplifier stages of audio systems.

  2. Switching Circuits: In digital logic circuits and control systems, the BC108 functions effectively as a switch. It can be used to control small loads like LEDs and relays.

  3. Oscillators and Signal Generators: With its high transition frequency, the BC108 is suitable for use in high-frequency oscillators, where stability and low noise are critical.

  4. General-Purpose Circuits: It is a go-to choice for a wide range of hobbyist and professional circuit designs, including radio receivers, signal processing, and general signal amplification tasks.

Replacement and Equivalent Transistors

If you need to replace the BC108 in your design, there are several equivalent transistors available that share similar characteristics:

  1. BC107 – An NPN transistor with very similar electrical specifications, also commonly used in amplifier circuits.
  2. BC548 – A more modern equivalent in a plastic TO-92 package, it is often used as a replacement in newer designs.
  3. 2N2222 – A popular NPN transistor with higher current-handling capabilities (up to 800mA), though it might require adjustments in the circuit design due to higher power dissipation.
  4. 2N3904 – Another general-purpose NPN transistor, often chosen for small-signal switching and amplification applications.

Always check the exact specifications of the replacement to ensure they match your circuit's requirements. Power handling, gain, and voltage ratings may vary slightly among these alternatives.

How to Use the BC108 in a Circuit

Let’s consider the most basic use of the BC108 in a common-emitter configuration:

Common-Emitter Amplifier Circuit:

  • Collector Load: A resistor (R<sub>C</sub>) is connected between the collector and the supply voltage (V<sub>CC</sub>).
  • Biasing: A voltage divider network, usually made from two resistors (R<sub>B1</sub> and R<sub>B2</sub>), is connected to the base to set the operating point.
  • Input Signal: The input signal is applied to the base, modulating the current flow from the collector to the emitter.
  • Output Signal: The output is taken from the collector and is typically larger (amplified) compared to the input signal.

This configuration is widely used in amplifier stages to boost weak signals.

Conclusion

The BC108 is a versatile and reliable NPN transistor ideal for various low-power amplification and switching applications. Its durability, high gain, and low noise make it an excellent choice for audio circuits and other general-purpose electronic projects. With several equivalents and modern replacements available, the BC108 continues to be a popular choice among both professional engineers and hobbyists.

When choosing a replacement, ensure that the electrical characteristics match your design's requirements to avoid circuit instability or performance issues

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