Lecture 4 ver2 diode_app

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Lecture 4 ver2 diode_app

  1. 1. Chapter 2:Diode Applications (cont.) Prepared by: Ikhwan Hafiz Muhamad ikhwanh@ump.edu.my Block 1, E10-C13Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 1
  2. 2. Recap Last Lecture HALF-WAVE RECTIFIER CENTER-TAPPED FULL BRIDGE FULL-WAVE WAVE RECTIFIER RECTIFIER V p (sec)V p ( out ) V p (sec) 0 . 7V V p ( out ) 0 . 7V V p ( out ) V p (sec) 1 . 4V 2 V p ( out ) 2V p ( out ) 2V p ( out )V AVG V AVG V AVGPIV V p (sec) PIV 2V p ( out ) 0 . 7V PIV V p ( out ) 0 . 7V Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 2
  3. 3. Diode Applications1. Half-wave & full-wave rectification2. Power supply filter & regulators3. Clippers & Clampers Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 3
  4. 4. Power Supply Filters and Regulators Sub-Chapter Outcomes• Explain and analyze the operation and characteristics of power supply filters and regulators• Explain the purpose of a filter• Describe the capacitor-input filter• Define ripple voltage & calculate the ripple factor• Discuss surge current & voltage regulation Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 4
  5. 5. Power Supply Filters AL Difference AC & DC?• Filter is a capacitor in a power supply used to reduce the variation of the output voltage rectifier Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 5
  6. 6. Capacitor-Input Filter Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 6
  7. 7. Power Supply Filters Capacitor-Input FilterRipple Voltage: the small variation (undesirable) inthe capacitor voltage due to the charging &discharging of the filter capacitor Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 7
  8. 8. Power Supply Filters Capacitor-Input FilterFull rectifier easier to filter because of the shortertime between peaks (smaller ripple) Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 8
  9. 9. Power Supply Filters Capacitor-Input FilterRipple Factor, r, is an indication of filter effectiveness (thelower the ripple factor the better filter) 1 V r ( pp ) V p ( rect ) V r ( pp ) f RLC r V DC 1 V DC 1 V p ( rect ) 2 f RLC Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 9
  10. 10. Power Supply Filters Capacitor-Input Filter Eg. Determine the ripple factor for the filtered bridge rectifier with a load as indicated in figure belowAnswer: 0.079 @ 7.9% Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 10
  11. 11. Power Supply FiltersSurge Current At the instant the switch is closed, voltage is connected to the bridge and the uncharged capacitor appears as a short.  Produce ISurge through D1 & D2  ISurge could destroy the diodes  RSurge used to prevent the diodes from destroy.  RSurge < RL; V p (sec) 1 . 4V R surge I FSM Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 11
  12. 12. Voltage Regulators Voltage Regulators Combination of capacitor- input filter with integrated circuit voltage regulator Operation: Input 78XX Output from i. the input to the regulator rectifier is first filtered with a capacitor to reduce the ripple to<10% ii. The regulator reduce the ripple to a negligible amount (acceptable level) 3 terminals: input, output & reference Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 12
  13. 13. Voltage Regulators Percent Regulation – present the performance of a voltage regulator• Line regulation specify how much change occurs in the output voltage for a given change in input voltage Line regulation V OUT 100 % V IN• Load regulation specify how much change occurs in the output voltage over a certain range of load current values. Load regulation V NL V FL 100 % V FL Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 13
  14. 14. Exercise 1) A certain 7805 regulator has a measured no-load output voltage of 5.18V and a full load output of 5.15V. What is the load regulation expressed as a percentage? 2) If the no-load output voltage of a regulator is 24.8V and the full-load output is 23.9V, what is the load regulation expressed as a percentage? 14
  15. 15. Review section1) When a 60Hz sinusoidal voltage is applied to the input of a half-wave rectifier, what is the output frequency?2) When a 60Hz sinusoidal voltage is applied to the input of a full-wave rectifier, what is the output frequency?3) What cause the ripple voltage on the output of a capacitor-input filter?4) If the load resistance connected to a filtered power supply is decreased, what happens to the ripple voltage? 15
  16. 16. 5. A certain rectifier filter produce a dc o/p voltage of 75V with peak-to-peak ripple voltage of 0.5V. Calculate the ripple factor?6. A certain full-wave rectifier has a peak o/p voltage of 30V. A 50uF capacitor-input filter is connected to the rectifier. Calculate the peak-to-peak ripple and the dc o/p voltage developed across a 600ohm resistance.7. What is the percentage of ripple for the rectifier in question 6? 16
  17. 17. Diode Applications1. Half-wave & full-wave rectification2. Power supply filter & regulators3. Clippers & Clampers Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 17
  18. 18. Clippers and Clampers Sub-Chapter Outcomes• Explain and analyze the operation of diode limiting & clamping circuits• Explain the operation of diode limiters• Determine the output voltage of a biased limiter• Explain the operation of diodes clampers Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 18
  19. 19. Diode Limiters (Clippers) Diode Limiters• A diode network that have the ability to “clip” (cut short/crop) off portions of signal voltages above or below certain limits, i.e. the circuits limit the range of the output signal.• Such a circuit may be used to; – protect the input of a CMOS logic gate against static – eliminate amplitude noise – fabricate new waveforms from an existing signal Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 19
  20. 20. Diode Limiters (Clippers) Diode Limiters• 2 general of clippers: a) Series clippers b) Parallel clippers• Parallel Clippers Diode in a branch parallel to the load.• Series Clippers Diode is in series with the load. Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 20
  21. 21. Diode Limiters (Clippers) Parallel ClipperCopyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 21
  22. 22. Diode Limiters (Clippers) Parallel Clipper• Whenever the input is below 0.7V, the diode is reversed biased and appears as an open.• The output voltage, VOUT looks like the negative part of the input, but with a magnitude determined by the voltage divider formed by R1 and RL, as follows:• If R1 is small compared to RL, then VOUT=VIN Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 22
  23. 23. Diode Limiters (Clippers) Analysis Steps for Parallel Clipper1. Define the input and output port2. Determine the current flow of the circuit3. Determine the applied voltage (transition voltage) that will result in a change of state for the diode from the “off” to “on” state4. Draw the output waveform directly below the applied voltage using the same scales Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 23
  24. 24. ExampleWhat should you expect to see displayed on anoscilloscope connected across RL in the limiter shownabove? Sketch the waveform for 2 cycles.Noted: +Vp= +10V; R1 = 100 ohm, RL=1kohm, diode model = 1N4001
  25. 25. Diode Limiters (Clippers) Parallel Clipper with Biased LimitersBy adding a DC source to the circuit, the voltage required to forward bias the diode can be changed. Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 25
  26. 26. Diode Limiters (Clippers) AL MatlabParallel Clipper with Biased Limiters Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 26
  27. 27. Diode Limiting Circuits - ExampleWhat is the output voltage of positive limiter shown? Sketch thewaveform R1 10 V 1.0 k RL 3.0 V Vin 0 VBIAS = 0 100 k 2.3 V + – The diode is forward-biased when the output tries to go above +3.0 V. This causes the output to be limited to voltages less than +3.0 V.
  28. 28. SolutionVinVout
  29. 29. Diode Limiters (Clippers) Parallel Clipper with Biased Limiters Eg: Determine the output voltage waveform for the circuit below.Answer: Clipped at ±5.7V Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 29
  30. 30. Eg: Solution
  31. 31. Diode Limiters (Clippers) Voltage-Divider BiasCopyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 31
  32. 32. Diode Limiters (Clippers) Voltage-Divider Bias Eg: Describe the output voltage waveform for the diode limiter in Figure below.Answer: Clipped at +8.95V Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 32
  33. 33. Eg: Solution 33
  34. 34. Diode Limiters (Clippers) Series ClipperCopyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 34
  35. 35. Example :•Determine the Vo and sketch the o/p waveformfor the below network. Assume diode is ideal. Vi RL 16 + + t Vi Vo 0 T/2 T -16 V=4 V - -
  36. 36. Solution:• + ve region Vi Diode state Vo 1 ON V 2 ON V + 3 ON V + 4 ON V Vi Vo 5 OFF Vi - 6 OFF Vi V=4 V - 7 OFF Vi 16 OFF Vi + Vo + 16 Vi Vo 4 - 0 T/2 t V=4 V -
  37. 37. Vi Diode state Vo -1 ON V Solution (continued): -2 ON V • - ve region (always ON state) -3 ON V -4 ON V -5 ON V+ + Vo 16 -6 ON V VoVi -7 ON V- 4 t T/2 T V=4 V - 0 -16 ON V Vo 16 The resulting o/p waveform 4 t 0 T/2 T
  38. 38. Example :Repeat the previous example using a silicon diode with VD=0.7 V Solution: RL VD=0.7 V + + Vo Vi - V=4 V - Vi VD V 0 Vi V VD 4 0 .7 3 . 3V
  39. 39. Solution (continued):For i/p voltages greater than 3.3 V the diode open cct and Vo=Vi.For i/p voltages less than 3.3 V the diode short cct and thenetwork result as; RL VD=0.7 V + + Vo Vo 4 0 .7Vi - V=4 V - 3 . 3V Vo 16 The resulting o/p waveform 3 .3 t 0 T /2 T
  40. 40. Diode Limiters (Clippers) Summary of Series Clippers : Refer Electronic Devices and Circuit Theory: International Edition, 8thEdition (Robert L. Boylestad) page 87. 40
  41. 41. Diode Clampers• Known as DC-Restorer• Widely use in analogue television receivers• A clamper is a network constructed of a diode, resistor, and a capacitor that shifts a waveform to a different dc level without changing the appearance of the applied signal Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 41
  42. 42. Diode Clampers Positive ClamperCopyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 42
  43. 43. Diode Clampers Negative Clamper• Note: • RC time constant should be at least ten times the period of the input frequency. Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 43
  44. 44. Diode Clampers Negative ClamperEg: Determine the output voltage waveform. Assume that RC is large enough to prevent significant capacitor dischargeAnswer: Vdc = -23.3V Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 44
  45. 45. Eg: Solution
  46. 46. Diode Clampers Summary of clamping circuits : ReferElectronic Devices and Circuit Theory: International Edition, 8th Edition (Robert L. Boylestad) page 91. 46
  47. 47. Review section1) What component in a clamping circuit effectively acts as a battery?2) What is the difference between a +ve limiter and a –ve limiter?

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