A single bipolar transistor, also known as a bipolar junction transistor (BJT), is a solid-state device that regulates current flow between two terminals through a third terminal. BJTs are utilized in various applications, including switching and amplification, and remain popular in modern electronics.

What is a bipolar junction transistor?

Discrete Bipolar Junction Transistors (BJTs) are widely utilized for analog signal amplification in audio, radio, and various other applications. As one of the earliest semiconductor devices to be mass-produced, their characteristics are not as advantageous for high-frequency switching or for high-current and high-voltage applications. However, they remain the preferred technology for applications needing analog signal reproduction with minimal noise and distortion. BJTs come in two forms: NPN and PNP, which describe the arrangement of semiconductor layers within the transistor. NPN transistors feature a thin P-type layer sandwiched between two N-type materials, while PNP transistors have an N-type layer between two P-types. This arrangement leads to opposite polarity operation; NPN transistors sink current, whereas PNP transistors source current.