Chapter 3: Bipolar Junction Transistors

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Transistor Construction There are two types of transistors: pnp npn The terminals are labeled: E - Emitter B - Base C - Collector pnp npn 2

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Transistor Operation With the external sources, V EE and V CC, connected as shown: The emitter-base junction is forward biased The base-collector junction is reverse biased 3

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Currents in a Transistor The collector current is comprised of two currents: Emitter current is the sum of the collector and base currents: 4

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Common-Base Configuration The base is common to both input (emitter–base) and output (collector–base) of the transistor. 5

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Common-Base Amplifier Input Characteristics This curve shows the relationship between of input current (I E ) to input voltage (V BE ) for three output voltage (V CB ) levels. 6

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky This graph demonstrates the output current (I C ) to an output voltage (V CB ) for various levels of input current (I E ). Common-Base Amplifier Output Characteristics 7

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 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. 8

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Approximations Emitter and collector currents: Base-emitter voltage: 9

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Ideally:  = 1 In reality:  is between 0.9 and Alpha (  ) Alpha (  ) is the ratio of I C to I E : AC mode Alpha (  ) in the AC mode:10

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Transistor Amplification Voltage Gain:Currents and Voltages: 11

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Common–Emitter Configuration The emitter is common to both input (base-emitter) and output (collector- emitter). The input is on the base and the output is on the collector. 12

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Common-Emitter Characteristics Collector Characteristics Base Characteristics 13

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Common-Emitter Amplifier Currents Ideal Currents I E = I C + I B I C =  I E Actual Currents I C =  I E + I CBO When I B = 0  A the transistor is in cutoff, but there is some minority current flowing called I CEO. where I CBO = minority collector current 14 I CBO is usually so small that it can be ignored, except in high power transistors and in high temperature environments.

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Beta (  ) In DC mode: In AC mode:  represents the amplification factor of a transistor. (  is sometimes referred to as h fe, a term used in transistor modeling calculations) 15

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Determining  from a Graph Beta (  ) 16

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Relationship between amplification factors  and  Beta (  ) Relationship Between Currents 17

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Common–Collector Configuration The input is on the base and the output is on the emitter. 18

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Common–Collector Configuration The characteristics are similar to those of the common-emitter configuration, except the vertical axis is I E. 19

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky V CE is at maximum and I C is at minimum (I Cmax = I CEO ) in the cutoff region. I C is at maximum and V CE is at minimum (V CE max = V CEsat = V CEO ) in the saturation region. The transistor operates in the active region between saturation and cutoff. Operating Limits for Each Configuration 20

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Power Dissipation Common-collector: Common-base: Common-emitter: 21

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Transistor Specification Sheet 22

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Transistor Specification Sheet 23

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Transistor Testing Curve TracerCurve Tracer Provides a graph of the characteristic curves. DMMDMM Some DMMs measure  DC or h FE. OhmmeterOhmmeter 24

Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Transistor Terminal Identification 25