ECE 4991 Electrical and Electronic Circuits Chapter 10

1. ECE 4991 Electrical and Electronic CircuitsChapter 10

2. Where We Are • Chapter 2 - The basic concepts and practice at analyzing simple electric circuits with sources and resistors • Chapter 3 – More harder networks to analyze and the notion of equivalent circuits • Chapter 4 – Capacitors and inductors added to the mix • Chapter 5 – Analyzing transient situations in complex passive networks • Chapter 8 – New subject – the wonders of operational amplifiers as system elements • Chapter 9 – Introduction to semiconductors – the basics and diodes – more network analysis • Chapter 10 – Bipolar junction transistors and how they work – now you can build your own op amp

3. What’s Important in Chapter 10 • Definitions • How bipolar transistors work • Building a transistor • Transistor basics • Collector characteristics • Load lines and operating points

4. 1. Definitions • Bipolar transistor • Emitter • Base • Collector • NPN, PNP • Gain () • Cutoff region • Active linear region • Saturation region • Breakdown region • Load lines • Operating points

5. 2. How Bipolar Transistors Work • Transistors are made by creating a PNP (or NPN) “sandwich” • Carriers are “emitted” by the emitter and “collected” by the collector • The base controls how much gets through

6. Transistor Operation • A small amount of base current can control a large amount of collector current • Gain = IC / IB = 

7. Transistor Operation in Silicon

8. 3. Building a Transistor

9. Transistor Fabrication

10. 4. Transistor Basics RC + VCC RB + VBB Typical NPN transistor schematic

11. There are four operating regions for a transistor RC + VCC RB + VBB • Cutoff Region – Both junctions reverse-biased – Very little base or collector current • Active Linear Region – BE junction forward biased, CB junction reverse-biased – amplifying mode • Saturation Region – Both junctions forward biased – low VCE – switch mode • Breakdown Region – Determines the operating limits of the device

12. RC + VCC RB + VBB 5. Collector Characteristics “Collector characteristic” is a plot of collector current versus collector-emitter voltage for different base currents

13. Collector Characteristics “Collector characteristic” is a plot of collector current versus collector-emitter voltage for different base currents

14. Real Transistor Collector Characteristics IB = 10 µA, 20 µA, 30 µA, ... , 80 µA

15. 6. Load Lines and Operating Points IB = 10 µA, 20 µA, 30 µA, ... , 80 µA

16. RC + VCC RB + VBB Consider this schematic… • VCC = 15V, RC = 1000, VBB = 3V • Design a circuit that operates around the center of the active region collector characteristics

17. RC + VCC RB + VBB First, generate a load line, then set the operating point • VCC = 15V, RC = 1000 , VBB = 3V • What is IC @ VCE = 0? • What is VCE @ IC = 0? • Generate load line • Pick desired IB • Set RB to get it IB = 10 µA, 20 µA, 30 µA, ... , 80 µA

18. Practice with Bipolars

19. Practice with Bipolars

20. Practice with Bipolars

21. Practice with Bipolars

22. Practice with Bipolars

23. Practice with Bipolars