1. Chapter 3: Bipolar Junction Transistors
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

2. Transistor Construction
Slide 1
Transistor Construction
There are two types of transistors: pnp and npn-type.
Note: the labeling of the transistor:
E - Emitter
B - Base
C - Collector
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

3. Transistor Operation Slide 2
With the external sources (VEE and VCC) in the polarities as shown:
The E-B junction is forward-biased and the B-C junction is reverse biased.
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

4. Currents in a Transistor
Slide 3
Currents in a Transistor
[Formula 3.1]
Note that IC is comprised of two currents:
[Formula 3.2]
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

5. Common Base Configuration
Slide 4
Common Base Configuration
The base is common to both input (emitter – base) and output (collector – base) of the transistor.
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

6. Input Characteristics for a Common-Base Amplifier
Slide 5
Input Characteristics for a Common-Base Amplifier
This demonstrates the input current IE to input voltage VBE for various levels of output voltage VCB.
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

7. Output Characteristics for a Common-Base Amplifier
Slide 6
This demonstrates the output current IC to an output voltage VCB for various levels of input current IE.
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

8. Operating range of the amplifier. • Cutoff
Slide 7
3 Regions of Operation
• 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 little voltage but lots of current.
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

9. Approximations Slide 8 [Formula 3.3] [Formula 3.4]
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

10. Ideally  = 1, but in reality it is between 0.9 and 0.998.
Slide 9
Alpha ()
Alpha () relates the DC currents IC to IE : 
[Formula 3.5]
Ideally  = 1, but in reality it is between 0.9 and
Alpha () in AC mode: 
[Formula 3.6]
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

11. Transistor Amplification
Slide 10
Transistor Amplification
The AC input is amplified.
[Fig. 3.12]
IC  IE so IL  Ii = 10mA
VL = IL * R = (10mA)(5k) = 50V
Voltage Gain (AV):
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

12. Common – Emitter Configuration
Slide 11
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.
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

13. Characteristics of Common-Emitter
Slide 12
Characteristics of Common-Emitter
Collector characteristics = output characteristics.
Base characteristics = input characteristics.
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

14. Amplifier Currents Slide 13 IE = IC + IB IC =  IE
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

15. Actual Amplifier Currents
Slide 14
Actual Amplifier Currents
IC =  IE + ICBO
ICBO = minority collector current. This is usually so small that it can be ignored, except in high power transistors and in high temperature environments.
[Formula 3.9]
When IB = 0A the transistor is in cutoff, but there is some minority current flowing called ICEO.
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

16. Beta () Slide 15 In DC mode: [Formula 3.10] In AC mode:
 indicates the amplification factor of a transistor. ( is sometimes referred to as hfe, a term used in transistor modeling calculations)
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

17. Determining beta () from a Graph
Slide 16
Determining beta () from a Graph
Note:  AC =  DC
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

18. Relationship between  and 
Slide 17
Relationship between  and 
Both indicate an amplification factor.
[Formula 3.12a]
[Formula 3.12b]
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

19.  provides a Relationship between Currents
Slide 18
 provides a Relationship between Currents
[Formula 3.14]
[Formula 3.15]
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

20. Common – Collector Configuration
Slide 19
Common – Collector Configuration
The input on the Base and the output is on the Emitter.
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

21. Characteristics of Common Collector
Slide 20
Characteristics of Common Collector
The Characteristics are similar to those of the Common-Emitter.
Except the vertical axis is IE. IE
IB1
IB2
IB3
VCE
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

22. Limitations of Operation for Each Configuration
Slide 21
Limitations of Operation for Each Configuration
Note: 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.
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

23. Power of Dissipation Slide 22 Common – Base: [Formula 3.18]
Common – Emitter: [Formula 3.16]
Common – Collector: a
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

24. Transistor Specification Sheet
Slide 23
Transistor Specification Sheet
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

25. Transistor Testing Slide 24 1. Curve Tracer
Provides a graph of the characteristic curves.
2. DMM
Some DMM’s will measure DC or HFE.
3. Ohmmeter
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.

26. Transistor Terminal Identification
Slide 25
Transistor Terminal Identification
Robert Boylestad Digital Electronics
Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.