Structure and Types of Bipolar Junction Transistors

Bipolar Junction Transistors (BJTs) are essential semiconductor devices widely used in amplification, switching, and signal processing. As a professional manufacturer, YFW Microelectronics excels in producing high-performance BJTs, catering to automotive, industrial, and consumer electronics sectors. Understanding their structure and types is key to leveraging their functionality effectively.

Basic Structure

A BJT consists of three doped semiconductor layers: emitter, base, and collector, forming two PN junctions. The base is a thin, lightly doped layer sandwiched between the heavily doped emitter and moderately doped collector. This structure enables current modulation: a small base current controls a larger current between emitter and collector.

The two PN junctions are the emitter-base (EB) junction and collector-base (CB) junction. Proper biasing (forward for EB, reverse for CB) allows charge carriers to flow, enabling the transistor’s operational modes—active, saturation, and cutoff.

Main Types

BJTs are categorized by charge carrier polarity into two types:

1. NPN Transistors
   Composed of two N-type layers (emitter, collector) and one P-type base. Electrons (majority carriers) flow from emitter to collector, with a small base current (holes) controlling the process. They offer higher switching speeds and are widely used in high-frequency amplifiers, switching circuits, and digital logic—core products in YFW’s industrial-grade lineup.
2. PNP TransistorsConsist of two P-type layers (emitter, collector) and one N-type base. Holes are the primary carriers, flowing from emitter to collector, controlled by electron flow in the base. They are ideal for low-power applications, complementary symmetry circuits, and voltage-follower designs, often paired with NPNs in push-pull configurations.

YFW’s BJT portfolio includes both types in various packages (SOT-23, TO-92, DPAK) to meet diverse requirements, ensuring reliability in harsh environments per AEC-Q101 and IEC standards. For technical specifications, visit www.yfwdiode.com.