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2: Bipolar Transistors

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    • 2.1: Intro to Bipolar Resistors
      This page details the structure and operation of NPN bipolar transistors, consisting of an emitter (n-type), base (p-type), and collector (lightly doped n-type). It covers biasing configurations crucial for functionality, particularly forward active biasing, which involves forward biasing the emitter-base junction and reverse biasing the base-collector junction.
    • 2.2: Transistor Equations
      This page covers key performance metrics for transistors, focusing on emitter injection efficiency (\(\gamma\)) and base transport factor (\(\alpha_T\)). It explains how \(\gamma\) reflects junction doping effects on electron currents, while \(\alpha_T\) pertains to electron movement through the base influenced by geometry. Additionally, it establishes the connection between base and collector currents, leading to the definition of current gain (\(\beta\)).
    • 2.3: Transistor I-V Characteristics
      This page explains the current-voltage relationships in bipolar transistors, focusing on the collector-base (CB) and emitter-base (EB) junctions. It details the operational characteristics under various bias states, noting that in reverse bias, the transistor acts like a diode.
    • 2.4: Common Emitter Models
      This page explains the common emitter configuration of a transistor, contrasting it with the common base model. It details the diode between the base and emitter, and a current-controlled current source between the collector and emitter. While \(V_{BE}\) follows the exponential principle, the saturation current varies due to the configuration. The aim is to enhance circuit analysis, although the nonlinearity indicates a requirement for a simplified linear model for practical use.
    • 2.5: Small Signal Models
      This page explores the development of a linear model for diode behavior through the application of bias and signal voltages. It details the total current as a combination of bias and signal currents, aiming to establish a linear relationship between the small signal voltage and current.
    • 2.6: Small Signal Model for Bipolar Transistor
      This page explores the small signal model of a common emitter transistor, focusing on its behavior with small AC signals compared to large DC currents. It derives the equivalent small signal resistance, \(r_{\pi}\), and discusses how base width modulation affects collector current \(I_C\) and introduces Early Voltage \(V_A\). Additionally, it addresses the transconductance model and the implications of breakdown in bipolar transistors.

    This page titled 2: Bipolar Transistors was last modified on Tue, 25 Aug 2026 20:54:05 GMT and is shared under a CC BY 1.0 license and was authored, remixed, and/or curated by Bill Wilson via source content that was edited to the style and standards of the LibreTexts platform.