1. Chapter 2: Diode Applications

2. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Load-Line The applied load to the circuit will normally have an important impact on the point or region of operation of a device.

3. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Load-Line Analysis 3 The load line (the applied load) plots all possible combinations of diode current (I D ) and voltage (V D ) for a given circuit. The maximum I D equals E/R, and the maximum V D equals E. The point where the load line and the characteristic curve intersect is the Q-point, which identifies I D and V D for a particular diode in a given circuit. Quiescent point (abbreviated “Q- pt.”) to reflect its “still, unmoving”

4. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Series Diode Configurations Constants Silicon Diode: V D = 0.7 V Germanium Diode: V D = 0.3 V Analysis (for silicon) V D = 0.7 V V R = E – V D I D = I R = I T = V R / R 4 Forward Bias

5. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Series Diode Configurations Diodes ideally behave as open circuits Analysis V D = E V R = 0 V I D = 0 A 5 Reverse Bias

6. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky EXAMPLE For the series diode determine (a) V DQ and I DQ. (b) V R.

7. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky

8. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky EXAMPLE For the series diode configuration, determine V D, V R, and I D.

9. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Since the applied voltage establishes a current in the clockwise direction to match the arrow of the symbol and the diode is in the “on” state, V D = 0.7 V

10. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky EXAMPLE Determine Vo and I D for the series circuit

11. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky

12. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Parallel Configurations 12

13. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Example Determine the current I for the network:

14. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky

15. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Example: Determine the voltage Vo for the network

16. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Half-Wave Rectification 16 The diode only conducts when it is forward biased, therefore only half of the AC cycle passes through the diode to the output. The DC output voltage is 0.318V m, where V m = the peak AC voltage.

17. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky PIV (PRV) 17 Because the diode is only forward biased for one-half of the AC cycle, it is also reverse biased for one-half cycle. It is important that the reverse breakdown voltage rating of the diode be high enough to withstand the peak, reverse-biasing AC voltage without entering the zener region. PIV (or PRV) > V m PIV = Peak inverse voltage PRV = Peak reverse voltage V m = Peak AC voltage

18. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Full-Wave Rectification 18 V dc = 0.318V m Half-wave: V dc = 0.318V m V dc = 0.636V m Full-wave: V dc = 0.636V m The rectification process can be improved by using a full-wave rectifier circuit. Full-wave rectification produces a greater DC output:

19. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Full-Wave Rectification 19 Bridge Rectifier Four diodes are connected in a bridge configuration V DC = 0.636V m

20. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Full-Wave Rectification 20 Center-Tapped Transformer Rectifier Requires Two diodes Center-tapped transformer V DC = 0.636V m

21. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Summary of Rectifier Circuits 21 V m = peak of the AC voltage. I In the center tapped transformer rectifier circuit, the peak AC voltage is the transformer secondary voltage to the tap. Rectifier Ideal V DC Realistic V DC Half Wave Rectifier DC V DC = 0.318V m Bridge Rectifier DC V DC = 0.636V m Center-Tapped Transformer Rectifier DC V DC = 0.636V m

22. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky EXAMPLE Determine the output waveform for the following network and calculate the output dc level and the required PIV of each diode.

23. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky For the positive region of the input voltage

24. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky For the negative part of the input the roles of the diodes will be interchanged and vo will appear as

25. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky AND/OR GATES Positive logic OR gate.

26. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky

27. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky positive logic AND gate AND/OR GATES

28. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky PIV For The Bridge Configuration The required PIV of each diode at the peak of the positive region of the input signal. For the indicated loop the maximum voltage across R is Vm and the PIV rating is defined by PIV Vm full-wave bridge rectifier

29. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky PIV For Center-tapped Transformer

30. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Diode Clippers Diode Clippers 30 Clipper is a variety of diode networks that have the ability to “clip” off a portion of the input signal without distorting the remaining part of the alternating waveform.

31. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Series Clippers series clipperThe diode in a series clipper “clips” any voltage that does not forward bias it, such as half-wave rectifier series clippers

32. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Biased Clippers 32 Adding a DC source in series with the clipping diode changes the effective forward bias of the diode.

33. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Example Determine the output waveform for the network

34. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky The network will appear as below, and vo=vi +5V.

35. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Example Determine the output waveform for the network

36. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky

37. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Parallel Clippers 37 parallel clipper The diode (ideal) in a parallel clipper circuit “clips” any voltage that forward bias it. DC biasing can be added in series with the diode to change the clipping level.

38. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Example Determine vo for the following network

39. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky

40. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Summary of Clipper Circuits 40 more…

41. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Summary of Clipper Circuits 41

42. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Clampers 42 A diode and capacitor can be combined to “clamp” an AC signal to a specific DC level.

43. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Biased Clamper Circuits 43 The input signal can be any type of waveform such as sine, square, and triangle waves. The DC source lets you adjust the DC camping level.

44. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky In general, the following steps may be helpful when analyzing clamping networks: 1. Start the analysis of clamping networks by considering that part of the input signal that will forward bias the diode. 2. During the period that the diode is in the “on” state, assume that the capacitor will charge up instantaneously to a voltage level determined by the network. 3. Assume that during the period when the diode is in the “off” state the capacitor will hold on to its established voltage level. 4. Throughout the analysis maintain a continual awareness of the location and reference polarity for Vo to ensure that the proper levels for Vo are obtained. 5. Keep in mind the general rule that the total swing of the total output must match the swing of the input signal.

45. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Example Determine vo for the following network for the input indicated.

46. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky The analysis will begin with the period t1 → t2 of the input signal since the diode is in its short-circuit state as recommended by comment 1. For this interval the output is across R, but it is also directly across the 5-V battery the result is Vo 5 V for this interval. Applying Kirchhoff’s voltage law around the input loop will result in The capacitor will therefore charge up to 25 V, as stated in comment 2.

47. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky The open-circuit equivalent for the diode will remove the 5-V battery from having any effect on Vo, and applying Kirchhoff’s voltage law around the outside loop of the network will result in

48. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky

49. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Summary of Clamper Circuits 49

50. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Zener Diodes 50 The Zener is a diode operated in reverse bias at the Zener Voltage (V z ). When V i  V Z –The Zener is on –Voltage across the Zener is V Z –Zener current: I Z = I R – I RL –The Zener Power: P Z = V Z I Z When V i < V Z –The Zener is off –The Zener acts as an open circuit

51. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky V i and R 1.Determine the state of the Zener diode by removing it from the network and calculating the voltage across the resulting open circuit. 2.Substitute the appropriate equivalent circuit and solve for the desired unknowns.

52. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Example For the following Zener diode network, determine V L, V R, I Z, and P Z.

53. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Following the suggested procedure: Since V L is less than V Z, the diode is in the “off” state. Substituting the open-circuit equivalent will result in;

54. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Fixed Vi, Variable R L To determine the minimum load resistance that will turn the Zener diode on, simply calculate the value of R L that will result in a load voltage V L =V Z. That is, Solving for R L, we have Once the diode is in the “on” state, the voltage across R remains fixed at

55. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky and I R remains fixed at The Zener current

56. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky EXAMPLE (a) For the following network, determine the range of R L and I L that will result in V RL being maintained at 10 V. (b) Determine the maximum wattage rating of the diode.

57. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky (a) To determine the value of RL that will turn the Zener diode on The voltage across the resistor R

58. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky For fixed values of R L, the voltage Vi must be sufficiently large to turn the Zener diode on. The minimum turn-on voltage Vi Vimin is determined by

59. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Voltage-Multiplier Circuits Voltage Doubler Voltage Tripler Voltage Quadrupler 59 Voltage multiplier circuits use a combination of diodes and capacitors to step up the output voltage of rectifier circuits.

60. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Voltage Doubler 60 This half-wave voltage doubler’s output can be calculated by: V out = V C2 = 2V m where V m = peak secondary voltage of the transformer

61. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Voltage Doubler 61 Positive Half-Cycle oD 1 conducts oD 2 is switched off oCapacitor C 1 charges to V m Negative Half-Cycle oD 1 is switched off oD 2 conducts oCapacitor C 2 charges to 2V m V out = V C2 = 2V m

62. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Voltage Tripler and Quadrupler 62

63. Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Practical Applications Rectifier Circuits –Conversions of AC to DC for DC operated circuits –Battery Charging Circuits Simple Diode Circuits –Protective Circuits against overcurrent –Polarity Reversal Zener Circuits –Overvoltage Protection –Setting Reference Voltages 63