Transcript Slide 1
Chapter 3: Bipolar Junction Transistors Transistor Construction There are two types of transistors: • pnp • npn pnp The terminals are labeled: • E - Emitter • B - Base • C - Collector npn Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 2 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 3 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: IE IC IB The collector current is comprised of two currents: IC IC I CO majority minority Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 4 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. 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. 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 6 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 7 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 8 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Approximations Emitter and collector currents: I C I E Base-emitter voltage: VBE 0.7 V (f orSilicon) 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. Alpha (a) Alpha (a) is the ratio of IC to IE : IC αdc IE Ideally: a = 1 In reality: a is between 0.9 and 0.998 Alpha (a) in the AC mode: αac Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky ΔI C ΔI E 10 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Transistor Amplification Currents and Voltages: Voltage Gain: Vi 200mV I E Ii 10mA Ri 20Ω I C I V I Av VL Vi 50V 250 200mV E L I 10 mA i L I R (10 ma)(5 kΩ) 50 V L 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. 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 12 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Common-Emitter Characteristics Collector Characteristics Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Base Characteristics 13 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Common-Emitter Amplifier Currents Ideal Currents IC = a IE IE = IC + IB Actual Currents IC = a 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. I CEO Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky I CBO 1 α 14 I B 0 μA 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: βdc IC IB In AC mode: ac Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky IC IB 15 VCE constant Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Beta () Determining from a Graph (3.2m A 2.2 mA) (30 μA 20 μA) 1mA V 7.5 10 μA CE 100 β AC 2.7 m A VCE 7.5 25 A 108 β DC 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. Beta () Relationship between amplification factors and a α β β1 β α α 1 Relationship Between Currents I C βIB Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky I E (β 1)IB 17 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 18 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 19 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 20 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Power Dissipation Common-base: PCmax VCBI C Common-emitter: PCmax VCEI C Common-collector: PCmax VCEI E 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. Transistor Specification Sheet 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. Transistor Specification Sheet 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. Transistor Testing • Curve Tracer Provides a graph of the characteristic curves. • DMM Some DMMs measure DC or hFE. • Ohmmeter 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. Transistor Terminal Identification 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.