1. DIODES AND APPLICATIONS
CHAPTER 17
DIODES AND APPLICATIONS

2. HALF-WAVE RECTIFIERS The basic DC power supply
The dc power supply converts the standard 220 V,50 Hz into a constant dc voltage
They consist of three parts : Rectifier, Filter, and Regulator
The dc voltage produced by a power supply is used to power all types of electronic circuits, such as television receivers, stereo systems, VCRs, CD player

3. Power supply
Figure 17-1

4. The Half-Wave Rectifier
Average Value of the Half-wave output voltage
VAVG=Vp (out) / 
Figure 17-2

5. Effect of Diode Barrier Potential on Half-Wave Rectifier Output Voltage
During the positive half-cycle, the input voltage must overcome the barrier potential before the diode becomes forward-biased
Vp (out) =Vp (in) V
Figure 17-5

6. Peak Inverse Voltage (PIV)
The maximum value of reverse voltage, sometimes designated as PIV, occurs at the peak of each negative alternation of the input cycle when the diode is reverse-biased
Figure 17-7

7. Average Value of the Full-wave rectified output voltage
FULL-WAVE RECTIFIERS
The full-wave rectifier is the most commonly used type in dc power supplies
allowing unidirectional current to the load during the entire input cycle differ from the half-wave rectifier that allows only during one-half of the cycle
Figure 17-9
Average Value of the Full-wave rectified output voltage
VAVG= 2Vp (out) / 

8. Center-Tapped Full-Wave Rectifier
Using two diode connected to the secondary of a center-tapped transformer
At the positive half-cycle
Forward-biases the upper diode D1
Reverse-biases the upper diode D2
At the negative half-cycle
Reverse-biases the upper diode D1
Forward-biases the upper diode D2

9. Center-Tapped Full-Wave Rectifier

10. Effect of the Turn Ratio on Full-Wave Output Rectifier
If the turn ratio of the transformer is 1:1, the output of the rectifier is equal to ½ of the input voltage Vp
Owing to the voltage input is approximately equal to the output voltage, we must use the step-up transformer

11. Peak Inverse Voltage (full-wave rectifier)

12. Full-Wave Bridge Rectifier

13. Bridge Output Voltage

14. POWER SUPPLY FILTER AND REGULATORS
After passed the rectifier, the output of the power supply is filtered for reduce the ripple, on the other hand, for make an output smoothly
Capacitor-Input filter
Ripple Voltage
The voltage which change due to charging and discharge of the capacitor is called “ripple voltage”

15. Ripple Factor (r)
Ripple factor is the ratio of the Vr to VDC, expressed as :
NOTE: the frequency in the full-wave rectifier is
twice of the half-wave rectifier

16. Ripple Voltages for half-wave and full-wave

17. Surge Current in the Capacitor-Input Filter

18. IC Regulators
An integrated circuit regulator is a device that is connected to the output of a filtered rectifier and maintains a constant output voltage
The capacitor-input filter reduces the input ripple to the regulator to an acceptable level and it is combined in IC regulator.
The most IC regulators have three terminal
Input terminal
Output terminal
Reference terminal

19. IC Regulators

20. Basic regulated power supply

21. Percent Regulation Line regulation Load regulation ∆VOUT
Specifies how much change occurs in the output voltage for a given change in the input voltage
Load regulation
Specifies how much change occurs in the output voltage over a certain range of load current value
∆VOUT
Line regulation =
∆VIN
VNL- VFL
Load regulation =
VFL

22. Diode Limiting and Clamping Circuits
Diode Limiters
Diode limiters (clipper) cut off above or below specified levels

23. Diode Limiting and Clamping Circuits
Diode Limiters
Adjustment of the limiting level

24. Diode Clampers Diode clamper known as a dc restorer
Add a dc level to an ac signal

25. Diode Clampers

26. ZENER DIODES
The zener diode is a silicon pn junction device and operate in the reverse breakdown region
symbol

27. Zener Breakdown (Vz) Two types of reverse breakdown in a zener diode
Avalanche
also occures in the rectifier diode
Zener
Occurs in a zener diode at low reverse voltages
NOTE : Zeners with breakdown voltage of 1.8 to
200 V are commercially available

28. Breakdown Characteristic

29. Zener Equivalent Circuit

30. Zener diode impedance
The ration of ∆Vz to ∆Iz is the zener diode impedance
Normally, ZZ is specified at IZT
ZZ is approximately constant over the full range of reverse-current values
∆VOUT
Zz =
∆VIN

31. Zener Voltage Regulation
Zener diodes can be used for voltage regulation in noncritical low-current applications

32. Zener Voltage Regulation
As the input voltage varies, the zener diode hole the constant voltage across the output terminals

33. Zener Regulation with a Varying Load
The zener diode maintains a constant voltage across RL as long as the zener current is greater than IZK and less than IZM, this process is called load regulation

34. Percent Regulation Line regulation Load regulation
Specifies how much change occurs in the output voltage for a given change in the input voltage
Load regulation
Specifies how much change occurs in the output voltage over a certain range of load current value

35. VARACTOR DIODES
A varactor is basically a reverse-biased pn junction that utilizes the inherent capacitance of the depletion region
The depletion region acts as a capacitor dielectric

36. VARACTOR DIODES

37. VARACTOR DIODES

38. VARACTOR DIODE APPLICATIONS

39. LEDs and PHOTODIODES There are two types of optoelectronic devices
The Light Emitting Diode (LED)
The photodiode (light detector)

40. The Light Emitting Diode (LED)
When the device is forward-biased, electrons across the pn junction from the n-type material and recombine with the holes in the p-type material
When recombination takes place, the recombining electrons release energy in the form of heat and light

41. The Light Emitting Diode (LED)
The semiconductive materials used in LEDs are gallium arsenide(GaAs), galium arsenide phosphide (GaAsP), and Gallium phosphide (GaP)
Silicon and Germanium are not used because they are very poor at producing light
GaAs LEDs emit infrared (IR) radiation
GaAsP produces either red or yellow visible light
GaP emits red or green visible light

42. The Light Emitting Diode (LED)
symbol
electroluminescence

43. The Light Emitting Diode (LED)

44. The Light Emitting Diode (LED) Applications

45. The Photodiode
The photodiode is a pn junction device that operates in reverse bias

46. The Photodiode

47. The Photodiode operation

48. The Photodiode Applications

49. The diode data sheet

50. TROUBLESHOOTING

51. Homework
Basic problems
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