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# diode.ppt

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### diode.ppt

1. 1. CHAPTER 17 DIODES AND APPLICATIONS
2. 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. 3. Power supply Figure 17-1
4. 4. The Half-Wave Rectifier Figure 17-2 Average Value of the Half-wave output voltage VAVG=Vp (out) / 
5. 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) - 0.7 V Figure 17-5
6. 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. 7. • 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 FULL-WAVE RECTIFIERS Figure 17-9 Average Value of the Full-wave rectified output voltage VAVG= 2Vp (out) / 
8. 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. 9. Center-Tapped Full-Wave Rectifier
10. 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. 11. Peak Inverse Voltage (full-wave rectifier) (sec) p (sec) p (sec) p ) out ( p (sec) p (sec) p (sec) p 2 D V 2 2 V 2 V V V 2 V 2 V V               ) out ( p (sec) p V 2 V PIV  
12. 12. Full-Wave Bridge Rectifier
13. 13. Bridge Output Voltage ) out ( p (sec) p V V PIV  
14. 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. 15. Ripple Factor (r) • Ripple factor is the ratio of the Vr to VDC, expressed as : % 100 V V r DC r   NOTE: the frequency in the full-wave rectifier is twice of the half-wave rectifier
16. 16. Ripple Voltages for half-wave and full-wave
17. 17. Surge Current in the Capacitor- Input Filter
18. 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. 19. IC Regulators
20. 20. Basic regulated power supply
21. 21. Percent Regulation • Line 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 ∆VOUT ∆VIN % 100  Line regulation = VNL- VFL VFL % 100  Load regulation =
22. 22. Diode Limiting and Clamping Circuits • Diode Limiters – Diode limiters (clipper) cut off above or below specified levels in L S L out V R R R V          
23. 23. Diode Limiting and Clamping Circuits • Diode Limiters – Adjustment of the limiting level
24. 24. Diode Clampers • Diode clamper known as a dc restorer – Add a dc level to an ac signal
25. 25. Diode Clampers
26. 26. ZENER DIODES • The zener diode is a silicon pn junction device and operate in the reverse breakdown region symbol
27. 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. 28. Breakdown Characteristic
29. 29. Zener Equivalent Circuit
30. 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 ∆VIN Zz =
31. 31. Zener Voltage Regulation • Zener diodes can be used for voltage regulation in noncritical low-current applications
32. 32. • As the input voltage varies, the zener diode hole the constant voltage across the output terminals Zener Voltage Regulation
33. 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. 34. Percent Regulation • Line 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. 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 dielectric constant A C d    
36. 36. VARACTOR DIODES
37. 37. VARACTOR DIODES
38. 38. VARACTOR DIODE APPLICATIONS LC fr  2 1 
39. 39. LEDs and PHOTODIODES • There are two types of optoelectronic devices – The Light Emitting Diode (LED) – The photodiode (light detector)
40. 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. 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. 42. The Light Emitting Diode (LED) symbol electroluminescence
43. 43. The Light Emitting Diode (LED)
44. 44. The Light Emitting Diode (LED) Applications
45. 45. The Photodiode • The photodiode is a pn junction device that operates in reverse bias
46. 46. The Photodiode
47. 47. The Photodiode operation
48. 48. The Photodiode Applications
49. 49. The diode data sheet
50. 50. TROUBLESHOOTING
51. 51. Homework • Basic problems – 1, 6, 12,16 12 16