1. Basic Electronics Ninth Edition Basic Electronics Ninth Edition ©2002 The McGraw-Hill Companies Grob Schultz

2. Basic Electronics Ninth Edition Basic Electronics Ninth Edition ©2003 The McGraw-Hill Companies 28 CHAPTER Electronic Devices

3. Topics Covered in Chapter 28  Semiconductors  The PN Junction  Semiconductor Diodes  PNP and NPN Transistors  Field-Effect Transistors

4. Topics Covered in Chapter 28 (continued)  Thyristors  Semiconductor Type Numbers and Case Styles  Special-Purpose Diodes  Visual Character Displays  Testing Diodes, Transistors, and Thyristors

5. Semiconductor Materials Elements used in semiconductors:  Silicon (Si)  Germanium (Ge) Two types of doped semiconductors:  P type  N type

6. One Atom of Silicon Diodes and transistors are usually silicon devices.

7. Silicon Crystal This structure is doped with impurities to manufacture diodes and transistors.

8. Doped Crystals (N-type and P-type) Phospherous has 5 valence electrons (free electron) Aluminum has 3 valence electrons (hole) N-type P-type Ph Al

9. The PN Junction Diode A PN junction diode is formed when a silicon crystal is doped with both P- and N-type impurities. The P-side is called the anode. The N-side is called the cathode. A PN junction allows forward current when forward voltage V F is applied. A PN junction blocks current flow when a reverse voltage is applied.

10. P-type (anode) N-type (cathode) The junction is the boundary between the anode and cathode. Depletion Zone Diodes are doped to have holes at one end and free electrons at the other. When a diode is manufactured, some of the electrons cross the junction and fill the holes. This creates the depletion zone which has no current carriers. Missing electrons (holes) Free Electrons

11. + + + + + + + ++ + + + + + + + + + + + + + + + + + ++ + + + + + + + + + + + + + + + + + ++ ++ + ++ + ++ + + + ++ ++ + + + + + + + + + + + + + + + + ++ + + + Forward Bias + + + + + + + ++ + + + + + + + + + + + + + + + + + ++ + + + + + + + + + + + + + + + + + ++ ++ + ++ + ++ + + + ++ ++ + Zero Bias Cathode Lead Anode Lead

12. Forward Bias Reverse Bias Zero Bias Cathode LeadAnode Lead Electron Current

13. } Diodes Cathode Lead Diodes have polarity (they must be installed correctly). Anode Lead

14. Diode Testing A good diode:  Low resistance in the forward direction  High resistance in the reverse direction A shorted diode:  Low resistance in both directions A leaky diode:  Low resistance in the forward direction  Medium resistance in the reverse direction A diode can be tested with an ohmmeter.

15. Bipolar Transistors PNP and NPN transistors have two junctions. Transistors have three electrodes:  Emitter  Base  Collector The emitter supplies free charges through the base to be received at the collector.

16. E B C Bipolar Transistors Base Collector Emitter Base Collector N P N P N P Emitter

17. Transistor Biasing The collector-base junction requires reverse voltage. The emitter-base junction requires forward voltage. Typical forward voltages are:  0.6 V for silicon  0.2 V for germanium

18. Reverse bias Forward bias Transistor Biasing IEIE ICIC IBIB I E = I B + I C Base Emitter Collector N P N

19. Field-Effect Transistors FETs have a high input impedance. FETs have three (or four) terminals:  Source  Gate (some have two)  Drain

20. Drain Source Drain Source Gate Structure of an N-channel JFET P-type substrate P N-channel No current flows in the gate circuit