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

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

4. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-3 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

5. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-4 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.

6. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-5 Forward Bias The carriers move toward the junction and collapse the depletion region. The diode is on (conducting).

7. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-6 Reverse Bias The carriers move away from the junction. The depletion region is reestablished and the diode is off.

8. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-7 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

9. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-8 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

10. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-9 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

11. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-10 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.

12. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-11 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

13. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-12 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

14. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-13 Cathode lead Anode lead

15. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-14 Anode lead 0 V mA Cathode lead The diode is forward biased by the ohmmeter. 

16. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-15 Cathode lead Anode lead 0 The diode is reverse biased by the ohmmeter. V mA 

17. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-16 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.

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

19. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-18 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.

20. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-19 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

21. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-20 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

22. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-21 V IN V OUT When V IN > 1.2 V PP + 0.6 V - 0.6 V V OUT is clipped The diodes conduct.

23. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-22 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

24. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-23 The inductive kick can cause damage. CEMF

25. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-24 The coil discharges through the diode and there is no arc. Transient suppression diodes can be used with inductive loads. CEMF

26. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-25 LED As the electrons cross the junction, they lose energy in the form of photons.

27. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-26 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

28. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-27 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!

29. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-28 Power supply VSVS RSRS Photodiodes are reverse biased and conduct in the presence of light. Photodiode

30. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-29 Input Output Input Output Optocoupler

31. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-30 Step-index multimode fiber Input pulse Output pulse The combined shorter and longer path lengths act to stretch the output pulse.

32. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-31 Step-index multimode fiber Input Output Due to pulse stretching, high speed data transmission is not possible.

33. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-32 Input Output Single mode fiber A single path means no pulse stretching and high speed data transmission is possible.

34. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-33 L C ZERO BIAS C is maximum and f R is minimum. Tuning diode

35. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-34 L C REVERSE BIAS C is less and f R increases. Tuning diode

36. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-35 L C MAX. REVERSE BIAS C is minimum and f R is maximum. Tuning diode

37. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-36 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

38. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-37 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.

39. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-38 For a given level of illumination, there is one and only one load that will result in maximum power transfer to the load.

40. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-39 The MPPT controller maintains system efficiency for varying levels of illumination.

41. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-40 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.

42. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-41 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

43. © 2013 The McGraw-Hill Companies, Inc. All rights reserved. McGraw-Hill 3-42 REVIEW The PN Junction Characteristic Curves of Diodes Diode Lead Identification Diode Types and Applications Photovoltaic Energy Sources