2. 3-1 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Electronics Principles & Applications Eighth Edition Chapter 3 Diodes (student version) Charles A. Schuler ©2013

3. 3-2 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill The PN Junction Characteristic Curves of Diodes Diode Lead Identification Diode Types and Applications Photovoltaic Energy Sources INTRODUCTION Diodes are two-terminal workhorses.

4. 3-3 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Dear Student: This presentation is arranged in segments. Each segment is preceded by a Concept Preview slide and is followed by a Concept Review slide. When you reach a Concept Review slide, you can return to the beginning of that segment by clicking on the Repeat Segment button. This will allow you to view that segment again, if you want to.

5. 3-4 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Concept Preview Diodes have both P-regions and N-regions. The boundaries are called junctions. The P-region is the anode side. The N-region is the cathode side. There are three possible bias conditions: zero, forward, and reverse. Zero bias is accompanied by a depletion region. Forward bias can collapse the depletion region. Reverse bias enhances the depletion region. Bias determines if diodes will be off or on.

6. 3-5 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill P The P-side of a junction diode is doped with acceptor atoms. N The N-side of a junction diode is doped with donor atoms. Schematic Symbol Cathode Anode junction A silicon crystal

7. 3-6 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Zero Bias Depletion region The electrons near the junction cross over and fill the holes near the junction. Having no carriers, the depletion region is an insulator.

8. 3-7 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Forward Bias The carriers move toward the junction and collapse the depletion region. The diode is on (conducting).

9. 3-8 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Reverse Bias The carriers move away from the junction. The depletion region is reestablished and the diode is off.

10. 3-9 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Diode quiz At zero bias, diodes show a depletion region which acts as an________. insulator The depletion region is collapsed by applying _________ bias. forward The depletion region is made wider by applying ________ bias. reverse A forward-biased diode has its anode________ with respect to its cathode. positive Diode forward voltage drop decreases as temperature ________. increases

11. 3-10 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Concept Review Diodes have both P-regions and N-regions. The boundaries are called junctions. The P-region is the anode side. The N-region is the cathode side. There are three possible bias conditions: zero, forward, and reverse. Zero bias is accompanied by a depletion region. Forward bias can collapse the depletion region. Reverse bias enhances the depletion region. Bias determines if diodes will be off or on. Repeat Segment

12. 3-11 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Concept Preview The volt-ampere graph for a resistor is a straight line (a resistor is a linear device). The volt-ampere graph for a diode is non-linear. The knee voltage for a silicon diode is approximately 0.7 volts. This is the voltage required to collapse the depletion region. Excess reverse bias will result in diode breakdown. The cathode end might be marked with a band. Diodes can be tested with an ohmmeter.

13. 3-12 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill mA 0 0.51.0 1.5 0 25 50 75 100 125 150 175 200 Volts 10 ohms 5 ohms 20 ohms Resistor volt-ampere characteristic curves

14. 3-13 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Forward current in mA 0 0.51.0 1.5 0 25 50 75 100 125 150 175 200 Forward bias in volts Silicon diode volt-ampere characteristic curve knee

15. 3-14 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Linearity The volt-ampere characteristic curve for a resistor is a straight line (linear). A diode has a non-linear characteristic curve. The barrier potential produces a knee in the diode curve. The knee voltage is approximately 0.6 to 0.7 volts for silicon diodes.

16. 3-15 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Forward current in mA 0 0.51.0 1.5 0 25 50 75 100 125 150 175 200 Forward bias in volts The effect of temperature -50 o C 25 o C 100 o C

17. 3-16 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 0 200 400 600 20 40 60 80 100 120 140 Reverse bias in Volts Reverse current in mA Silicon diode reverse bias characteristic curve breakdown

18. 3-17 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Cathode lead Anode lead

19. 3-18 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Anode lead 0 V mA Cathode lead The diode is forward biased by the ohmmeter. 

20. 3-19 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Cathode lead Anode lead 0 The diode is reverse biased by the ohmmeter. V mA 

21. 3-20 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Silicon diode ohmmeter testing Low resistance in both directions: the diode is shorted. High resistance in both directions: the diode is open. Relatively low resistance in the reverse direction: the diode is leaky. The ratio of reverse resistance to forward resistance is > 1000: the diode is good.

22. 3-21 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Concept Review The volt-ampere graph for a resistor is a straight line (a resistor is a linear device). The volt-ampere graph for a diode is non-linear. The knee voltage for a silicon diode is approximately 0.7 volts. This is the voltage required to collapse the depletion region. Excess reverse bias will result in diode breakdown. The cathode end might be marked with a band. Diodes can be tested with an ohmmeter. Repeat Segment

23. 3-22 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Concept Preview Zener diodes have a relatively low breakdown voltage and are often used as voltage regulators. Diode clippers limit signal amplitude. Diode clamps produce a dc signal component. Diodes can be used to suppress inductive kick. Optocouplers combine light emitting diodes and photodiodes. Fiber optic cables carry light signals. Varicap diodes are used to tune electronic circuits.

24. 3-23 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 0 2 4 6 20 40 60 80 100 120 140 Reverse bias in Volts Reverse current in mA A zener diode is designed to break down and conduct backwards at lower voltages.

25. 3-24 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 0 2 4 6 20 40 60 80 100 120 140 Reverse bias in Volts Reverse current in mA I V V The voltage across a conducting zener is relatively constant.

26. 3-25 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Unregulated Supply Load The load is in parallel with the zener and will see a relatively constant voltage as long as the zener is conducting. Using a zener diode as a voltage regulator

27. 3-26 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill V IN V OUT When V IN < 1.2 V PP The diodes do not conduct. This circuit is called a clipper or limiter. V OUT is not clipped

28. 3-27 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill V IN V OUT When V IN > 1.2 V PP + 0.6 V - 0.6 V V OUT is clipped The diodes conduct.

29. 3-28 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill V IN V OUT When V IN > 1.2 V PP This circuit is called a clamp or dc restorer. 0.6 V V OUT is clamped. dc C is charged. C 2 V OUT(dc) = V PP - 0.6 V

30. 3-29 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill The inductive kick can cause damage. CEMF

31. 3-30 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill The coil discharges through the diode and there is no arc. Transient suppression diodes can be used with inductive loads. CEMF

32. 3-31 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill LED As the electrons cross the junction, they lose energy in the form of photons.

33. 3-32 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Power supply VSVS RSRS The typical voltage drop for most LEDs is from 1.5 to 2.5 V. LED I S = V S - V D RSRS LED circuit VDVD

34. 3-33 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill VISIBLE AND/OR INVISIBLE LASER RADIATION-AVOID DIRECT EXPOSURE TO BEAM AVOID EXPOSURE visible and/or invisible Laser Radiation is emitted from this aperture VISIBLE AND/OR INVISIBLE LASER DIODE Ultraviolet LEDs are also dangerous and invisible!

35. 3-34 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Power supply VSVS RSRS Photodiodes are reverse biased and conduct in the presence of light. Photodiode

36. 3-35 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Input Output Input Output Optocoupler

37. 3-36 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Step-index multimode fiber Input pulse Output pulse The combined shorter and longer path lengths act to stretch the output pulse.

38. 3-37 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Step-index multimode fiber Input Output Due to pulse stretching, high speed data transmission is not possible.

39. 3-38 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Input Output Single mode fiber A single path means no pulse stretching and high speed data transmission is possible.

40. 3-39 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill L C ZERO BIAS C is maximum and f R is minimum. Tuning diode

41. 3-40 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill L C REVERSE BIAS C is less and f R increases. Tuning diode

42. 3-41 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill L C MAX. REVERSE BIAS C is minimum and f R is maximum. Tuning diode

43. 3-42 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Diode applications quiz A circuit used to control the amplitude of a signal is the ________. clipper A circuit used to add a dc component to a signal is the ________. clamp A device containing an LED and a photo- diode is the ________. optocoupler A tuning diode shows less capacitance as reverse bias ________. increases The device that is often used to regulate voltage is the ________ diode. zener

44. 3-43 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Concept Review Zener diodes have a relatively low breakdown voltage and are often used as voltage regulators. Diode clippers limit signal amplitude. Diode clamps produce a dc signal component. Diodes can be used to suppress inductive kick. Optocouplers combine light emitting diodes and photodiodes. Fiber optic cables carry light signals. Varicap diodes are used to tune electronic circuits. Repeat Segment

45. 3-44 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Here we see a photon enter a PV cell and liberate an electron. Then we see the electron move to the front contact and through the load.

46. 3-45 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill For a given level of illumination, there is one and only one load that will result in maximum power transfer to the load.

47. 3-46 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill The MPPT controller maintains system efficiency for varying levels of illumination.

48. 3-47 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Measuring the current output from a PV source is a common troubleshooting task. A camp type current probe is a safer and more convenient method of measuring output current.

49. 3-48 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill Photovoltaic quiz Photovoltaic devices directly convert light energy to ________ energy. electrical A photon entering a PV cell might liberate a free ________. electron The ideal (best power transfer) load on a PV source varies with the level of_______. illumination MPPT improves PV system efficiency by adjusting the ________ resistance. load PV troubleshooting might involve measuring the voltage and/or the ____ output. current

50. 3-49 © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill REVIEW The PN Junction Characteristic Curves of Diodes Diode Lead Identification Diode Types and Applications Photovoltaic Energy Sources