BJTs - Electronics I - Lecture Slides, Slides of Electronics

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Chapter 4 – Bipolar Junction Transistors (BJTs)

Introduction

http://engr.calvin.edu/PRibeiro_WEBPAGE/courses/engr311/311_frames.html

A simplified structure of the npn transistor.

Physical Structure and Modes of Operation

Current flow in an npn transistor biased to operate in the active mode, (Reverse current components due to drift of thermally generated minority carriers are not shown.)

Operation of The npn Transistor Active Mode

Profiles of minority-carrier concentrations in the base and in the emitter of an npn transistor operating in the active mode; vBE  0 and vCB  0.

Operation of The npn Transistor Active Mode

Large-signal equivalent-circuit models of the npn BJT operating in the active mode.

Equivalent Circuit Models

The Constant n

The Collector-Base Reverse Current

The Structure of Actual Transistors

Two large-signal models for the pnp transistor operating in the active mode.

The pnp Transistor

Circuit Symbols and Conventions

• Example 4.
• Exercise 4.8 and 4.

The iC-vCB characteristics for an npn transistor in the active mode.

Dependence of ic on the Collector Voltage – Early Effect

Fig. 4.15 (a) Conceptual circuit for measuring the iC-vCE characteristics of the BJT. (b) The iC-vCE characteristics of a practical BJT.

Fig. 4.24 Linear operation of the transistor under the small-signal condition: A small signal vbe with a triangular waveform is superimpose din the dc voltage VBE. It gives rise to a collector signal current ic, also of triangular waveform, superimposed on the dc current IC. Ic = gm vbe, where gm is the slope of the ic - vBE curve at the bias point Q.

Fig. 4.26 Two slightly different versions of the simplified hybrid- model for the small-signal operation of the BJT. The equivalent circuit in (a) represents the BJT as a voltage-controlled current source ( a transconductance amplifier) and that in (b) represents the BJT as a current-controlled current source (a current amplifier).