This document contains lecture notes on diode applications and types. It discusses topics like full wave and bridge rectifiers, power supply filters, diode clippers and clampers, zener diodes, varactor diodes, LEDs, photodiodes, and schottky diodes. It provides circuit diagrams and explanations of how each component works, along with example calculations for determining voltage, current, and resistance values.

1. Full Sessional pack II
Muhammad Faseeh

2. Diode Applications
Full wave Rectifiers
Week 07
Lecture 12

3. Peak Inverse voltage in
Centre-tapped Full-wave Rectifier

4. The Bridge Full-Wave Rectifier

5. The Bridge Full-Wave Rectifier

6. Ideal diode

7. Practical diode

8. Power Supply Filters and regulators

9. Filters in Half wave rectification

10. Capacitor discharging - filter

11. Charging of capacitor- filter

12. Diode Applications and
Types
Week 07
Lecture 13

13. Bridge Rectifiers

14. Bridge rectifier

15. Ripples and ripple factor
Ripple factor (r) is an indication of the effectiveness of the filter,
r = Vr (pp) / VDC
The lower the ripple factor, the better the filter.
It can be lowered by increasing the value of filter capacitor or increasing the load
resistance.

16. Surge Current in the Capacitor-Input Filter

17. Diode Clippers
• These circuits are also called limiters
• Used to clip off portions of signal voltages
above or below certain levels.
• Half wave rectifier can also be called as a
clipper circuit

18. Example of diode limiters

19. Example of diode limiters

20. Finding Vp(out)

21. Biased Limiters - Positive

22. Biased Limiters - Negative

23. Positive limiter with modification

24. Negative limiter with modification

25. Diode Applications – Diode Clampers
Lecture 15
April 04, 2013

26. Diode Clampers
• A clamper adds a dc level on an ac voltage.
• Prevents the signal from exceeding certain
defined magnitude by shifting its dc value.
• They are also called dc restorers.

27. Positive Clamper operation
• Consider the first negative half cycle of
the input voltage.
• When the input voltage initially goes
negative, the diode is forward-biased, the
capacitor get charged
• ??

28. Positive Clamper operation

29. Working and operation
• The capacitor is now charged to Vp (in) – 0.7 V.
• Just after the negative peak, the diode is reverse biased because the cathode is held near Vp
(in) – 0.7 V by the charge on capacitor.
• The capacitor can only discharge through the high resistance of RL.

30. Operation and working
• So, from the peak of one negative half cycle to the next, the capacitor
discharges very little.
• This discharged amount depends on the value of RL.
• For good clamping action, the RC time constant should be at least ten times the period of
the input frequency.

31. Negative Clamper operation

32. Diode Types
• Key Terms
• Zener Diode
• Zener Breakdown
• Varactor
• Light Emitting Diode (LED)
• Photodiode
• Laser

33. Zener Diode
• A zener diode is a silicon pn junction device that is designed for operation in reverse-
breakdown region.
• A major application
• A type of voltage regulator for providing stable reference voltages for use in power
supplies, voltmeters etc.

34. General diode VI Characteristics

35. Zener Breakdown
• Zener diodes are designed to operate in reverse breakdown.
• The two types of reverse breakdown in a zener diodes are avalanche and zener.

36. Zener Breakdown
Avalanche Breakdown
Occurs in both rectifier and zener
diodes at a significantly high reverse
voltage.
Zener Breakdown
Zener breakdown occurs in a zener
diode at a low reverse voltages.
• A zener diode is heavily doped to reduce the breakdown voltage.
This causes a very thin depletion region. As a result a very intense
electric field exists within the depletion region.
•Near the zener breakdown voltage (Vz), the field is intense enough
to pull electrons from their valence bands and create current.

37. Zener Breakdown
• Zener diodes with breakdown voltages of less than approx 5V operate
predominately in zener breakdown.
• Those with breakdown voltages greater than approx 5 V operate in avalanche
breakdown.

38. Zener Summary
• Both types are called Zener diodes.
• They are commercially available with breakdown voltage of 1.8 V to 200 V
with specified tolerances from 1% to 20 %.

39. Reverse Characteristics of Zener

40. Equivalent Circuit

41. Zener Impedance (Zz)

42. Answer

43. Diode Types
Lecture 17

44. Temperature Coefficient
• This is the percent change in zener voltage for each 0C change in
temperature.
• e.g., a 12 V zener diode with a positive temperature coefficient of 0.01% / 0C will
exhibit a 1.2 mV increase in Vz when the junction temperature increases one degree
centigrade.
• ∆Vz = Vz * TC * ∆T
• Vz is the nominal zener voltage at 25 0C, TC is the temperature coefficient, and ∆T is the change in
temperature.

45. Temperature Coefficient
• A positive TC means the zener voltage increases with an increase in
temperature or decreases with a decrease in temperature.
• A negative TC means that the zener voltage decreases with an increase in
temperature or increases with a decrease in temperature.

46. Temperature Coefficient
• In some cases, the temperature coefficient is expressed in mV/ 0C rather
than as %/0C.
• For these cases,
• ∆Vz = TC * ∆T

47. Practice Problem

48. Problem:

49. Zener Power Dissipation
• Zener diodes are specified to operate at a maximum power called maximum
dc power dissipation, PD(max).
• For example IN746 zener is rated at a PD (max)of 500 mW and IN3305A at PD
(max) of 50W.
• The dc power dissipated is determined by
• PD = VZIZ

50. Power Derating
• The max power dissipated of a zener diode is typically specified
for temperature at or below a certain value (500C for example).
• Above the specified temperature, the maximum power dissipation
is reduced according to a derating factor.
• The derating factor is expressed in mW/0C.
• The maximum derated power can be determined with the following formula:
• PD (derated) = PD(max) – (mW/0C) ∆T

51. Problem

52. Solution

53. Zener-From No Load to Full Load
• When RL = ∞, load current is 0 and all the
current is through the zener; this is a no load
condition.
• When RL is connected, current gets divided
between zener and RL.

54. Optical Diodes
• Two types of optoelectronic devices – the light emitting diode (LED) and
the photodiode
• LED
• Light emitter
• Photodiode
• Light detector

55. LED
• When the device is forward
biased, electrons cross the pn junction
from the n-type material and recombine
with holes in the P-type material.
• When the recombination takes place, the
recombining electrons releases energy in
the form of heat and light.
• A large exposed surface area on one layer
of the semiconductor material permits the
photons to be emitted as visible light.
• (electroluminescence process)

56. LED
• Various impurities are added during the doping
process to establish the wavelength of the
emitted light.
• The wavelength determines the color of the
light and if it is visible or infrared (IR)

57. Operation of LED

58. Spectral output curve

59. Typical LEDs

60. The Photodiode
• A device that operates in reverse bias, where
Iλ is the reverse current.
• The photodiode has a small transparent window that allows the light to strike at the
pn junction.
• Recall, when reverse biased, a rectifier diode has a very small reverse leakage current. The same is
true for a photodiode.

61. The Photodiode
• A photodiode differs from a rectifier diode in that when its pn junction is exposed to
light, the reverse current increases with the light intensity.
• When there is no incident light, the reverse current, Iλ, is almost negligible and is
called dark current.
• An increase in the amount of light intensity, expressed as irradiance (mW/cm2
), produces an increase in the reverse current.

62. General graph of Photodiode

63. Photodiode biasing and symbol

64. Typical photodiode characteristics

65. Finding resistance…
• Reverse current = 1.4 micro Ampere
• Reverse-bias voltage = 10 V
• Irradiance = 0.5 mW/cm2
• R = VR / Iλ
• 10 V / 1.4 μ A = 7.14 MΩ
• Find resistance at 20 mW/cm2 , current 55 μ A at VR = 10 V

66. Operation of photodiode

67. VARACTOR DIODES
• They are also known as variable-capacitance diodes because the junction
capacitance varies with the amount of reverse-bias voltage.
• They are specifically designed to take advantage of this variable-capacitance
characteristic.
• These devices are commonly used in electronic tuning circuits in
communications systems.

68. Capacitance and Varactor
• A varactor is a diode that always operates in reverse-bias and is doped to
maximize the inherent capacitance of the depletion region.
• The depletion region, widened by the reverse bias, act as a capacitor
dielectric because of its nonconductive characteristics.
• The p and n regions are conductive and acts as the capacitor plates.

69. Reverse-biased varactor diode

70. Operation…

71. Electronics 1
Lecture 18

72. Current Regulator Diode
• Often called constant-current diode.
• Rather than maintaining a constant
voltage, as the zener diode does, this diode
maintains a constant current.
• Forward bias operation.
• Current = Ip

73. Characteristic curve

74. Schottky Diode
• Used primarily in HF and fast-switching applications.
• Also called hot-carrier diodes.
• A schottky diode is formed by joining a doped semiconductor region (usually
n type) with a metal such as gold, silver or platinium.
• Rather than a pn junction, there is a metal-to-semiconductor junction.
• The forward voltage drop is typically typically around 0.3 V.

75. Internal construction of schottky diode

76. Schottky…
• Majority carriers only , there are no minority carriers.
• Hence no reverse or leakage current.`

77. A Zener-Regulated DC Power Supply

78. Power Supply schematic

79. A Zener-Regulated DC Power Supply-Full load