Chapter 3 Bipolar Junction Transistors Introduction 1 In

Chapter 3: Bipolar Junction Transistors

Introduction 1. In 1904, the vacuum-tube diode was introduced by J. A. Fleming. 2. In 1906, Lee De Forest added a third element, called the control grid, to the vacuum diode, resulting in the first amplifier, the triode. 3. In the early 1930 s the four-element tetrode and five-element pentode gained prominence in the electron-tube industry. 4. On December 23, 1947, Walter H. Brattain and John Bardeen demonstrated the amplifying action of the first transistor at the Bell Telephone Laboratories. The advantages of this three-terminal solid-state device over the tube were immediately obvious: It was smaller and lightweight; had no heater requirement or heater loss; had rugged construction; and was more efficient since less power was absorbed by the device itself; it was instantly available for use, requiring no warm-up period; and lower operating voltages were possible. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

The first transistor. (Courtesy Bell Telephone Laboratories. ) Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Transistor Construction The transistor is a three-layer semiconductor device. pnp There are two types of transistors: • pnp • npn The terminals are labeled: • E - Emitter • B - Base • C - Collector Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky npn 4 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Transistor Operation With the external sources, VEE and VCC, connected as shown: • The emitter-base junction is forward biased • The base-collector junction is reverse biased Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 5 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Currents in a Transistor Emitter current is the sum of the collector and base currents: The collector current is comprised of two currents: ICO is the minority-current component and called the leakage current (IC current with emitter terminal Open). Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 6 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Common-Base Configuration The base is common to both input (emitter–base) and output (collector–base) of the transistor. In addition, the base is usually the terminal closest to, or at, ground potential. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 7 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Common-Base Amplifier Input Characteristics This curve shows the relationship between of input current (IE) to input voltage (VBE) for three output voltage (VCB) levels. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 8 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Common-Base Amplifier Output Characteristics This graph demonstrates the output current (IC) to an output voltage (VCB) for various levels of input current (IE). Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 9 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Operating Regions • Active – Operating range of the amplifier. • Cutoff – The amplifier is basically off. There is voltage, but little current. • Saturation – The amplifier is full on. There is current, but little voltage. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 10 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Approximations Emitter and collector currents: Base-emitter voltage: Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 11 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Alpha ( ) is the ratio of IC to IE : Ideally: = 1 In reality: is between 0. 9 and 0. 998 Alpha ( ) in the AC mode: mode Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 12 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Transistor Amplification Currents and Voltages: Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Voltage Gain: 13 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

• The Typical values of voltage amplification for the commonbase configuration vary from 50 to 300. • The basic amplifying action was produced by transferring a current I from a low to a high-resistance circuit. • The combination of the two terms results in the label transistor; that is, transfer resistor → transistor Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Common–Emitter Configuration The emitter is common to both input (base-emitter) and output (collectoremitter). The input is on the base and the output is on the collector. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 15 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Common-Emitter Characteristics For the output characteristics: The curves of IB are not as horizontal as those obtained for IE in the common-base configuration, which indicating that the collector-to -emitter voltage will influence the magnitude of the collector current. Collector Characteristics Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 16 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

For the input characteristics Base Characteristics Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Common-Emitter Amplifier Currents Ideal Currents IC = IE IE = IC + IB Actual Currents IC = IE + ICBO where ICBO = minority collector current ICBO is usually so small that it can be ignored, except in high power transistors and in high temperature environments. When IB = 0 A the transistor is in cutoff, but there is some minority current flowing called ICEO. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 18 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Beta ( ) represents the amplification factor of a transistor. ( is sometimes referred to as hfe, a term used in transistor modeling calculations) In DC mode: In AC mode: Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 19 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Beta ( ) Determining from a Graph Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 20 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Beta ( ) Relationship between amplification factors and Relationship Between Currents Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 21 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Common–Collector Configuration The input is on the base and the output is on the emitter. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 22 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Common–Collector Configuration The characteristics are similar to those of the common-emitter configuration, except the vertical axis is IE. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 23 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Operating Limits for Each Configuration VCE is at maximum and IC is at minimum (ICmax= ICEO) in the cutoff region. IC is at maximum and VCE is at minimum (VCE max = VCEsat = VCEO) in the saturation region. The transistor operates in the active region between saturation and cutoff. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 24 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.

Power Dissipation Common-base: Common-emitter: Common-collector: Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 25 Copyright © 2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.