Lecture #3 ( 2 weeks) Transistors

Transcription

1 Spring 2015 Benha University Faculty of Engineering at Shoubra ECE-291 Electronic Engineering Lecture #3 ( 2 weeks) Transistors Instructor: Dr. Ahmad El-Banna 1

2 Agenda BJT Structure Basic Operation Transistor as an Amplifier Transistor as a Switch DC & AC Analysis 2

3 BIPOLAR JUNCTION TRANSISTOR (BJT) STRUCTURE 3 BJT symbol

4 Transistor Packages 4

5 Basic Operation Biasing & Operation Transistor Currents 5

6 BJT Configurations Configuration Input Output Common Emitter Base Collector Common Base Emitter Collector Common Collector Base Emitter Base terminal can t be output Collector terminal can t be input 6

7 BJT Parameters The dc current gain of a transistor is the ratio of the dc collector current (I C ) to the dc base current (I B ) and is designated dc beta (β DC ). Typical values of β DC range from less than 20 to 200 or higher. β DC is usually designated as an equivalent hybrid (h) parameter, h FE, on transistor datasheets. The ratio of the dc collector current (I C ) to the dc emitter current (I E ) is the dc alpha (ɑ DC ). 7

8 Transistor DC Model I c = βi B 8

9 Collector characteristic curves Operation Regions Active Cut-off Saturation Active Region 9

10 BJT as an Amplifier Phase shift = 180 Voltage gain magnitude: 10 r e = 26 mv/ I E I E = I C + I B

11 BJT as a Switch 11

12 The Phototransistor 12

13 Phototransistor Application Relay circuits driven by a phototransistor A relay is an electrically operated switch. relays use an electromagnet to mechanically operate a switch 13

14 Optocouplers Basic optocouplers Examples of optocoupler packages 14

15 Project Motion Detection Alarm LED Transmitter Phototransistor Circuit Alarm Circuit 15

16 555 Timer Siren Circuit 16

17 Siren Using Op-Amp 17

18 Transistor Bias Circuit What s Biasing? Bias establishes the dc operating point (Q-point) for proper linear operation of an amplifier. Why? If an amplifier is not biased with correct dc voltages on the input and output, it can go into saturation or cutoff when an input signal is applied. 18

19 Q-point Adjustment 19

20 DC Load Line Variations in collector current and collector-to-emitter voltage as a result of a variation in base current. 20

21 Waveform Distortion 21

22 VOLTAGE-DIVIDER BIAS 22

23 Loading Effects of Voltage-Divider Bias 23

24 Thevenin s Theorem Applied to Voltage-Divider Bias 24

25 Linear Amplifier 25

26 C.E. AC Analysis DC Analysis: Capacitors Open Circuit (See before) AC Analysis: Capacitors short Circuit DC supply ground 26

27 AC r-parameter Model Input resistance Output resistance Voltage gain Current gain Power gain 27

28 Multistage Amplifier A two-stage common-emitter amplifier. 28

29 Project II Audio Preamplifier for PA System 29 Pre AMP, chapter 4 Class AB Power AMP, chapter 7

30 For more details, refer to: Chapters 4-6, T. Floyd, Electronic Devices and Circuit Theory, 11 th edition, Prentice Hall. The lecture is available online at: For inquires, send to: 30