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Diode circuits

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Prof. Dr. K. Adisesha
Prof. Dr. K. Adisesha

This document discusses semiconductor diodes and rectifiers. It begins by explaining the physical principles of semiconductors, including intrinsic semiconductors and how doping with materials like phosphorus or boron creates n-type and p-type semiconductors. When a p-type and n-type material meet, it forms a pn junction with interesting electrical properties. Diodes are made from pn junctions and exhibit asymmetric conduction, allowing current in one direction but blocking it in the other. Diode circuits and models are also covered, along with important applications like rectification where diodes are used to convert AC to DC power.

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Semiconductor Diodes and Rectifiers 5.1 The Physical Principles of Semiconductor 5.2 Diodes 5.3 Diode Circuits By K. Adisesha Bangalore City College Prof. K. Adisesha
Diodes and Rectifiers The Physical Principles of Semiconductor Key Words: Intrinsic(pure) Semiconductors Electrons, Holes, Carriers, Phosphorus Doping (N-type) Boron Doping (P-type) PN Junction Prof. K. Adisesha
Diodes and Rectifiers The Physical Principles of Semiconductor Intrinsic (pure) Semiconductors  Different types of solids: Conductor  < 10-4 ·cm Insulator   1010 · cm Semiconductor  Si  Cu*1011 · cm , Ge  Cu*107 · cm  The atomic structure of a neutral silicon atom Valence electrons Valence electrons Prof. K. Adisesha
The Physical Principles of Semiconductor  Intrinsic(pure) silicon Intrinsic (pure) Semiconductors A free electron A hole • An electron-hole pair is created when an electron get excited by thermal or light energy; • Recombination occurs when an electron loses energy and falls back into a hole. Diodes and Rectifiers Prof. K. Adisesha
The Physical Principles of Semiconductor Intrinsic (pure) Semiconductors Diodes and Rectifiers • Holes also conduct current. In reality, it’s the movement of all the other electrons. The hole allows this motion. • Holes have positive charge. • Current flows in the same direction as the holes move.  Both electrons and holes carry current-- carriers.  In intrinsic semiconductors the electron and hole concentrations are equal because carriers are created in pairs  The intrinsic concentration depends exponentially on temperature.  At room temp (300K), the intrinsic carrier concentration of silicon is: 310 /105.1 cmni  Prof. K. Adisesha
The Physical Principles of Semiconductor Phosphorus Doping (N-type) Diodes and Rectifiers • Phosphorus has 5 valence electrons. • P atoms will sit in the location of a Si atom in the lattice, to avoid breaking symmetry, but each will have an extra electron that does not bond in the same way. And these extra electrons are easier to excite (and can move around more easily) • These electrons depends on the amounts of the two materials. Prof. K. Adisesha
The Physical Principles of Semiconductor Phosphorus Doping (N-type) Diodes and Rectifiers • In equilibrium, • At room temp (300K), if 1/1010 donors are added to the intrinsic silicon, then the electron carrier concentration is about 1013cm－3; the hole carrier concentration is about 106cm－3. Phosphorus Intrinsic silicon Electrons---Majority carrier. Holes---Minority carrier Phosphorus---Donor materials. 22 iiii npnppn  ;3.89 cm cm 5 1014.2 Prof. K. Adisesha
The Physical Principles of Semiconductor Boron Doping (P-type) Diodes and Rectifiers • Boron has 3 valence electrons. • B will sit at a lattice site, but the adjacent Si atoms lack an electron to fill its shell. This creates a hole. Holes---Majority carrier; Electrons---Minority carrier Boron---acceptor materials. Prof. K. Adisesha
The Physical Principles of Semiconductor PN Junction Diodes and Rectifiers  N-type materials: Doping Si with a Group V element, providing extra electrons (n for negative) .  P-type materials: Doping Si with a Group III element, providing extra holes (p for positive). What happens when P-type meets N-type? Prof. K. Adisesha
The Physical Principles of Semiconductor PN Junction Diodes and Rectifiers What happens when P-type meets N-type? • Holes diffuse from the P-type into the N-type, electrons diffuse from the N-type into the P-type, creating a diffusion current. • Once the holes [electrons] cross into the N-type [P-type] region, they recombine with the electrons [holes]. • This recombination “strips” the n-type [P-type] of its electrons near the boundary, creating an electric field due to the positive and negative bound charges. • The region “stripped” of carriers is called the space-charge region, or depletion region. • V0 is the contact potential that exists due to the electric field. Typically, at room temp, V0 is 0.5~0.8V. • Some carriers are generated (thermally) and make their way into the depletion region where they are whisked away by the electric field, creating a drift current.Prof. K. Adisesha
The Physical Principles of Semiconductor PN Junction Diodes and Rectifiers  There are two mechanisms by which mobile carriers move in semiconductors – resulting in current flow – Diffusion • Majority carriers move (diffuse) from a place of higher concentration to a place of lower concentration – Drift • Minority carrier movement is induced by the electric field.  In equilibrium, diffusion current (ID) is balanced by drift current (IS). So, there is no net current flow. What happens when P-type meets N-type? Prof. K. Adisesha
The Physical Principles of Semiconductor PN Junction Diodes and Rectifiers Forward bias: apply a positive voltage to the P-type, negative to N-type. Add more majority carriers to both sides shrink the depletion region lower V0 diffusion current increases. • Decrease the built-in potential, lower the barrier height. • Increase the number of carriers able to diffuse across the barrier • Diffusion current increases • Drift current remains the same. The drift current is essentially constant, as it is dependent on temperature. • Current flows from p to n Prof. K. Adisesha
The Physical Principles of Semiconductor PN Junction Diodes and Rectifiers Reverse bias: apply a negative voltage to the P-type, positive to N-type. • Increase the built-in potential, increase the barrier height. • Decrease the number of carriers able to diffuse across the barrier. • Diffusion current decreases. • Drift current remains the same • Almost no current flows. Reverse leakage current, IS, is the drift current, flowing from N to P. Prof. K. Adisesha
Diodes and Rectifiers Diodes Key Words: Diode I-V Characteristic Diode Parameters, Diode Models Prof. K. Adisesha
Diodes and Diode Circuits PN Junction Diode V-A Characteristic Diodes and Rectifiers Typical PN junction diode volt-ampere characteristic is shown on the left. – In forward bias, the PN junction has a “turn on” voltage based on the “built-in” potential of the PN junction. turn on voltage is typically in the range of 0.5V to 0.8V – In reverse bias, the PN junction conducts essentially no current until a critical breakdown voltage is reached. The breakdown voltage can range from 1V to 100V. Breakdown mechanisms include avalanche and zener tunneling. Prof. K. Adisesha
• The forward bias current is closely approximated by where VT =kT/q is the thermal voltage (~25.8mV at room temp T= 300K or 27C ) k = Boltzman’s constant = 1.38 x 10-23 joules/kelvin T = absolute temperature q = electron charge = 1.602 x 10-19 coulombs n = constant dependent on structure, between 1 and 2 (we will assume n = 1) IS = scaled current for saturation current that is set by diode size – Notice there is a strong dependence on temperature – We can approximate the diode equation for vD >> VT , Diodes and Diode Circuits PN Junction Diode V-I Characteristic Diodes and Rectifiers )1()1(  T DD nV v s nkT qv sD eIeIi Current Equations T D V v SD eIi  Prof. K. Adisesha
Diodes and Diode Circuits PN Junction Diode V-A Characteristic Diodes and Rectifiers Current Equations • In reverse bias (when vD << 0 by at least VT ), then • In breakdown, reverse current increases rapidly… a vertical line 0 SD Ii P5.1, PN Junction when T = 300K, Find iD whenAIS 14 10  VvD 70.0 mAeeIi T D V v sD 93.4)1(10)1( 026.0 7.0 14   AeeIi T D V v sD 14026.0 7.0 14 10)1(10)1(     Prof. K. Adisesha
Diodes and Diode Circuits PN Junction Diode V-A Characteristic Diodes and Rectifiers Prof. K. Adisesha
Diodes and Diode Circuits PN Junction Diode V-A Characteristic Diodes and Rectifiers P5.2, Look at the simple diode circuit below. E=1.5V D 100Ώ I 20 15 i D (mA) 1.0 10 0.5 1.5 vD(V) Q operating point Load line ID=7(mA), VD=0.8(V) Prof. K. Adisesha
Diodes and Diode Circuits Diode Parameters Diodes and Rectifiers VR The maximum reverse DC voltage that can be applied across the diode. IR The maximum current when the diode is reverse-biased with a DC voltage. IF The maximum average value of a rectified forward current. fM The maximum operation frequency of the diode. Prof. K. Adisesha
Diodes and Diode Circuits Diodes Diodes and Rectifiers Prof. K. Adisesha
Diodes and Diode Circuits Light Emitting Diodes Diodes and Rectifiers • When electrons and holes combine, they release energy. • This energy is often released as heat into the lattice, but in some materials, they release light. • This illustration describes the importance of the plastic bubble in directing the light so that it is more effectively seen. Prof. K. Adisesha
Diodes and Diode Circuits Diodes and Rectifiers Diode Models-- The Ideal Switch Model v (v) O iD (mA) When forward-biased, the diode ideally acts as a closed (on) witch. When reverse-biased, the diode acts as an open (off) switch. Prof. K. Adisesha
Diodes and Diode Circuits Diodes and Rectifiers Diode Models-- The Offset Model Si diode：Von ≈ 0.7(V)（0.6～0.8） Ge diode：Von ≈ 0.2（V） vD (v) Von iD (mA) Von V  Von， closed switch V < Von， open switch Von iD Prof. K. Adisesha
Diodes and Diode Circuits Diodes and Rectifiers Diode Models--The Small-Signal Model D T d I V r  Cj rd=rS+rj rj 频率不高时 rS id ＋ － vd Frequency is not high. Prof. K. Adisesha
Diodes and Rectifiers Diode Circuits Application of Diode Radio Demodulation Power Conversion/ Rectifiers Over-voltage protection Logic gates Temperature measuring Current steering Musical Keyboards Prof. K. Adisesha
Diode Circuits Diodes and Rectifiers Diode Limiter + + - vi vo vo - + R D t t Von vi vo When vi > Von , D on vo  vi； vi < Von， D off  vo = 0。 Prof. K. Adisesha
Diode Circuits Diodes and Rectifiers Rectifier Circuits One of the most important applications of diodes is in the design of rectifier circuits. Used to convert an AC signal into a DC voltage used by most electronics. Prof. K. Adisesha
Diode Circuits Diodes and Rectifiers Rectifier Circuits Simple Half-Wave Rectifier What would the waveform look like if not an ideal diode? Prof. K. Adisesha
Diode Circuits Diodes and Rectifiers Rectifier Circuits Bridge Rectifier Looks like a Wheatstone bridge. Does not require a enter tapped transformer. Requires 2 additional diodes and voltage drop is double. Prof. K. Adisesha
Diode Circuits Diodes and Rectifiers Rectifier Circuits Peak Rectifier To smooth out the peaks and obtain a DC voltage, add a capacitor across the output. Prof. K. Adisesha
Diodes and Rectifiers Zener Diode Key Words: Reverse Bias Piecewise Linear Model Zener diode Application Prof. K. Adisesha
Zener Diode Diodes and Rectifiers Reverse Bias Piecewise Linear Model z z z I V r    + - D2 VZ rZ D1 perfect Zener symbol (VBR) Prof. K. Adisesha
Zener Diode Diodes and Rectifiers Zener diode Application 1.0k + 10V - Assume Imin=4mA, Imax=40mA, rz=0, What are the minimum and maximum input voltages for these currents? Solution: For the minimum zener current, the voltage across the 1.0k resistor is VR = IminR = 4(V) Since VR = Vin - Vz, Vin = VR + Vz=14(V) For the maximum zener current, the voltage across the 1.0k resistor is VR = ImaxR = 40(V) Therefore, Vin = VR + Vz = 50(V) Prof. K. Adisesha
Zener Diode Diodes and Rectifiers Zener diode Application        k m R mIand m k I kmA VRIV R R BRzDD L 6646.3 )A(61.1 1.612 )A(61.1 )A(61.0 10 1.6 )V(1.661.01 Design forID=-1mA Prof. K. Adisesha
Zener Diode Diodes and Rectifiers Zener diode Application Design Verification: Apply Thevinen’s Equivalent to simplifyCase study 1:       8.7818 2.6818K 0.1K 6V 1.000mA 1m 0.1K 6 6.1V th out V I I I V          =8.7818VthV  3.6646K 10K 3.6646K / /10K 2.6818K 3.6646K 10K thR      Prof. K. Adisesha
Zener Diode Diodes and Rectifiers If VDD = 15 V instead of 12 what is Vout? Case study 2: Note that Vout only went from 6.1V to 6.1789V as VDD went from 12 to 15V.The circuit is a voltage regulator.  15 10K = 10.977V 3.6646K 10K thV    3.6646K 10K 2.6818K 3.6646K 10K thR        10.977 2.6818K 0.1K 6VthV I I       10.977 6 2.7818K 1.7891mAI     1.7891m 0.1K 6 6.17VoutV    Prof. K. Adisesha
Zener Diode Diodes and Rectifiers Zener diode Application If RL = 8 KΩ instead of 10 KΩ; what is Vout?Case study 3: The circuit again shows voltage regulation .Vout only went from 6.1V to 6.0853V RTh=2.513KΩ Ri=0.1KΩ 6VVTh=8.23V               12 8K = 8.230V 3.6646K 8K 3.6646K 8K 2.513K 3.6646K 8K 8.230 2.513K 0.1K 6V 8.230 6 2.613K 0.8534mA 0.8534m 0.1K 6 6.0853V th th th out V R V I I I V                 Prof. K. Adisesha
Zener Diode Diodes and Rectifiers Zener diode Application VI↑ → IR↑ → VL↑ → Iz↑↑→ IL↑→ ILRL↑→ VO↑ Case study 1、 2: RL have no changed: RL↓→IR↓→IL↓→ VO↓ Case study 1、 3: VI have no changed: Prof. K. Adisesha
Zener Diode Diodes and Rectifiers Zener diode Application RR RV Vo L LI   LRZ III  R VV R V I LIR R   PZ＝IZVZ Prof. K. Adisesha
iV oV Si VL=20V Zener Diode Diodes and Rectifiers Given a source voltage being with applying in this circuit: t 60V -60V Vi(t) iV oV 0.7V 20V Determine Vo When Vi>0, the equivalent circuit is: Vo=20V iV oV 0.7V 20V When Vi<0, the equivalent circuit is: Vo=0V Zener diode can be seen as a voltage regulator. Therefore: t 60V -60V Vi(t) 20V Vo Prof. K. Adisesha

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Diode circuits

  • 1. Semiconductor Diodes and Rectifiers 5.1 The Physical Principles of Semiconductor 5.2 Diodes 5.3 Diode Circuits By K. Adisesha Bangalore City College Prof. K. Adisesha
  • 2. Diodes and Rectifiers The Physical Principles of Semiconductor Key Words: Intrinsic(pure) Semiconductors Electrons, Holes, Carriers, Phosphorus Doping (N-type) Boron Doping (P-type) PN Junction Prof. K. Adisesha
  • 3. Diodes and Rectifiers The Physical Principles of Semiconductor Intrinsic (pure) Semiconductors  Different types of solids: Conductor  < 10-4 ·cm Insulator   1010 · cm Semiconductor  Si  Cu*1011 · cm , Ge  Cu*107 · cm  The atomic structure of a neutral silicon atom Valence electrons Valence electrons Prof. K. Adisesha
  • 4. The Physical Principles of Semiconductor  Intrinsic(pure) silicon Intrinsic (pure) Semiconductors A free electron A hole • An electron-hole pair is created when an electron get excited by thermal or light energy; • Recombination occurs when an electron loses energy and falls back into a hole. Diodes and Rectifiers Prof. K. Adisesha
  • 5. The Physical Principles of Semiconductor Intrinsic (pure) Semiconductors Diodes and Rectifiers • Holes also conduct current. In reality, it’s the movement of all the other electrons. The hole allows this motion. • Holes have positive charge. • Current flows in the same direction as the holes move.  Both electrons and holes carry current-- carriers.  In intrinsic semiconductors the electron and hole concentrations are equal because carriers are created in pairs  The intrinsic concentration depends exponentially on temperature.  At room temp (300K), the intrinsic carrier concentration of silicon is: 310 /105.1 cmni  Prof. K. Adisesha
  • 6. The Physical Principles of Semiconductor Phosphorus Doping (N-type) Diodes and Rectifiers • Phosphorus has 5 valence electrons. • P atoms will sit in the location of a Si atom in the lattice, to avoid breaking symmetry, but each will have an extra electron that does not bond in the same way. And these extra electrons are easier to excite (and can move around more easily) • These electrons depends on the amounts of the two materials. Prof. K. Adisesha
  • 7. The Physical Principles of Semiconductor Phosphorus Doping (N-type) Diodes and Rectifiers • In equilibrium, • At room temp (300K), if 1/1010 donors are added to the intrinsic silicon, then the electron carrier concentration is about 1013cm－3; the hole carrier concentration is about 106cm－3. Phosphorus Intrinsic silicon Electrons---Majority carrier. Holes---Minority carrier Phosphorus---Donor materials. 22 iiii npnppn  ;3.89 cm cm 5 1014.2 Prof. K. Adisesha
  • 8. The Physical Principles of Semiconductor Boron Doping (P-type) Diodes and Rectifiers • Boron has 3 valence electrons. • B will sit at a lattice site, but the adjacent Si atoms lack an electron to fill its shell. This creates a hole. Holes---Majority carrier; Electrons---Minority carrier Boron---acceptor materials. Prof. K. Adisesha
  • 9. The Physical Principles of Semiconductor PN Junction Diodes and Rectifiers  N-type materials: Doping Si with a Group V element, providing extra electrons (n for negative) .  P-type materials: Doping Si with a Group III element, providing extra holes (p for positive). What happens when P-type meets N-type? Prof. K. Adisesha
  • 10. The Physical Principles of Semiconductor PN Junction Diodes and Rectifiers What happens when P-type meets N-type? • Holes diffuse from the P-type into the N-type, electrons diffuse from the N-type into the P-type, creating a diffusion current. • Once the holes [electrons] cross into the N-type [P-type] region, they recombine with the electrons [holes]. • This recombination “strips” the n-type [P-type] of its electrons near the boundary, creating an electric field due to the positive and negative bound charges. • The region “stripped” of carriers is called the space-charge region, or depletion region. • V0 is the contact potential that exists due to the electric field. Typically, at room temp, V0 is 0.5~0.8V. • Some carriers are generated (thermally) and make their way into the depletion region where they are whisked away by the electric field, creating a drift current.Prof. K. Adisesha
  • 11. The Physical Principles of Semiconductor PN Junction Diodes and Rectifiers  There are two mechanisms by which mobile carriers move in semiconductors – resulting in current flow – Diffusion • Majority carriers move (diffuse) from a place of higher concentration to a place of lower concentration – Drift • Minority carrier movement is induced by the electric field.  In equilibrium, diffusion current (ID) is balanced by drift current (IS). So, there is no net current flow. What happens when P-type meets N-type? Prof. K. Adisesha
  • 12. The Physical Principles of Semiconductor PN Junction Diodes and Rectifiers Forward bias: apply a positive voltage to the P-type, negative to N-type. Add more majority carriers to both sides shrink the depletion region lower V0 diffusion current increases. • Decrease the built-in potential, lower the barrier height. • Increase the number of carriers able to diffuse across the barrier • Diffusion current increases • Drift current remains the same. The drift current is essentially constant, as it is dependent on temperature. • Current flows from p to n Prof. K. Adisesha
  • 13. The Physical Principles of Semiconductor PN Junction Diodes and Rectifiers Reverse bias: apply a negative voltage to the P-type, positive to N-type. • Increase the built-in potential, increase the barrier height. • Decrease the number of carriers able to diffuse across the barrier. • Diffusion current decreases. • Drift current remains the same • Almost no current flows. Reverse leakage current, IS, is the drift current, flowing from N to P. Prof. K. Adisesha
  • 14. Diodes and Rectifiers Diodes Key Words: Diode I-V Characteristic Diode Parameters, Diode Models Prof. K. Adisesha
  • 15. Diodes and Diode Circuits PN Junction Diode V-A Characteristic Diodes and Rectifiers Typical PN junction diode volt-ampere characteristic is shown on the left. – In forward bias, the PN junction has a “turn on” voltage based on the “built-in” potential of the PN junction. turn on voltage is typically in the range of 0.5V to 0.8V – In reverse bias, the PN junction conducts essentially no current until a critical breakdown voltage is reached. The breakdown voltage can range from 1V to 100V. Breakdown mechanisms include avalanche and zener tunneling. Prof. K. Adisesha
  • 16. • The forward bias current is closely approximated by where VT =kT/q is the thermal voltage (~25.8mV at room temp T= 300K or 27C ) k = Boltzman’s constant = 1.38 x 10-23 joules/kelvin T = absolute temperature q = electron charge = 1.602 x 10-19 coulombs n = constant dependent on structure, between 1 and 2 (we will assume n = 1) IS = scaled current for saturation current that is set by diode size – Notice there is a strong dependence on temperature – We can approximate the diode equation for vD >> VT , Diodes and Diode Circuits PN Junction Diode V-I Characteristic Diodes and Rectifiers )1()1(  T DD nV v s nkT qv sD eIeIi Current Equations T D V v SD eIi  Prof. K. Adisesha
  • 17. Diodes and Diode Circuits PN Junction Diode V-A Characteristic Diodes and Rectifiers Current Equations • In reverse bias (when vD << 0 by at least VT ), then • In breakdown, reverse current increases rapidly… a vertical line 0 SD Ii P5.1, PN Junction when T = 300K, Find iD whenAIS 14 10  VvD 70.0 mAeeIi T D V v sD 93.4)1(10)1( 026.0 7.0 14   AeeIi T D V v sD 14026.0 7.0 14 10)1(10)1(     Prof. K. Adisesha
  • 18. Diodes and Diode Circuits PN Junction Diode V-A Characteristic Diodes and Rectifiers Prof. K. Adisesha
  • 19. Diodes and Diode Circuits PN Junction Diode V-A Characteristic Diodes and Rectifiers P5.2, Look at the simple diode circuit below. E=1.5V D 100Ώ I 20 15 i D (mA) 1.0 10 0.5 1.5 vD(V) Q operating point Load line ID=7(mA), VD=0.8(V) Prof. K. Adisesha
  • 20. Diodes and Diode Circuits Diode Parameters Diodes and Rectifiers VR The maximum reverse DC voltage that can be applied across the diode. IR The maximum current when the diode is reverse-biased with a DC voltage. IF The maximum average value of a rectified forward current. fM The maximum operation frequency of the diode. Prof. K. Adisesha
  • 21. Diodes and Diode Circuits Diodes Diodes and Rectifiers Prof. K. Adisesha
  • 22. Diodes and Diode Circuits Light Emitting Diodes Diodes and Rectifiers • When electrons and holes combine, they release energy. • This energy is often released as heat into the lattice, but in some materials, they release light. • This illustration describes the importance of the plastic bubble in directing the light so that it is more effectively seen. Prof. K. Adisesha
  • 23. Diodes and Diode Circuits Diodes and Rectifiers Diode Models-- The Ideal Switch Model v (v) O iD (mA) When forward-biased, the diode ideally acts as a closed (on) witch. When reverse-biased, the diode acts as an open (off) switch. Prof. K. Adisesha
  • 24. Diodes and Diode Circuits Diodes and Rectifiers Diode Models-- The Offset Model Si diode：Von ≈ 0.7(V)（0.6～0.8） Ge diode：Von ≈ 0.2（V） vD (v) Von iD (mA) Von V  Von， closed switch V < Von， open switch Von iD Prof. K. Adisesha
  • 25. Diodes and Diode Circuits Diodes and Rectifiers Diode Models--The Small-Signal Model D T d I V r  Cj rd=rS+rj rj 频率不高时 rS id ＋ － vd Frequency is not high. Prof. K. Adisesha
  • 26. Diodes and Rectifiers Diode Circuits Application of Diode Radio Demodulation Power Conversion/ Rectifiers Over-voltage protection Logic gates Temperature measuring Current steering Musical Keyboards Prof. K. Adisesha
  • 27. Diode Circuits Diodes and Rectifiers Diode Limiter + + - vi vo vo - + R D t t Von vi vo When vi > Von , D on vo  vi； vi < Von， D off  vo = 0。 Prof. K. Adisesha
  • 28. Diode Circuits Diodes and Rectifiers Rectifier Circuits One of the most important applications of diodes is in the design of rectifier circuits. Used to convert an AC signal into a DC voltage used by most electronics. Prof. K. Adisesha
  • 29. Diode Circuits Diodes and Rectifiers Rectifier Circuits Simple Half-Wave Rectifier What would the waveform look like if not an ideal diode? Prof. K. Adisesha
  • 30. Diode Circuits Diodes and Rectifiers Rectifier Circuits Bridge Rectifier Looks like a Wheatstone bridge. Does not require a enter tapped transformer. Requires 2 additional diodes and voltage drop is double. Prof. K. Adisesha
  • 31. Diode Circuits Diodes and Rectifiers Rectifier Circuits Peak Rectifier To smooth out the peaks and obtain a DC voltage, add a capacitor across the output. Prof. K. Adisesha
  • 32. Diodes and Rectifiers Zener Diode Key Words: Reverse Bias Piecewise Linear Model Zener diode Application Prof. K. Adisesha
  • 33. Zener Diode Diodes and Rectifiers Reverse Bias Piecewise Linear Model z z z I V r    + - D2 VZ rZ D1 perfect Zener symbol (VBR) Prof. K. Adisesha
  • 34. Zener Diode Diodes and Rectifiers Zener diode Application 1.0k + 10V - Assume Imin=4mA, Imax=40mA, rz=0, What are the minimum and maximum input voltages for these currents? Solution: For the minimum zener current, the voltage across the 1.0k resistor is VR = IminR = 4(V) Since VR = Vin - Vz, Vin = VR + Vz=14(V) For the maximum zener current, the voltage across the 1.0k resistor is VR = ImaxR = 40(V) Therefore, Vin = VR + Vz = 50(V) Prof. K. Adisesha
  • 35. Zener Diode Diodes and Rectifiers Zener diode Application        k m R mIand m k I kmA VRIV R R BRzDD L 6646.3 )A(61.1 1.612 )A(61.1 )A(61.0 10 1.6 )V(1.661.01 Design forID=-1mA Prof. K. Adisesha
  • 36. Zener Diode Diodes and Rectifiers Zener diode Application Design Verification: Apply Thevinen’s Equivalent to simplifyCase study 1:       8.7818 2.6818K 0.1K 6V 1.000mA 1m 0.1K 6 6.1V th out V I I I V          =8.7818VthV  3.6646K 10K 3.6646K / /10K 2.6818K 3.6646K 10K thR      Prof. K. Adisesha
  • 37. Zener Diode Diodes and Rectifiers If VDD = 15 V instead of 12 what is Vout? Case study 2: Note that Vout only went from 6.1V to 6.1789V as VDD went from 12 to 15V.The circuit is a voltage regulator.  15 10K = 10.977V 3.6646K 10K thV    3.6646K 10K 2.6818K 3.6646K 10K thR        10.977 2.6818K 0.1K 6VthV I I       10.977 6 2.7818K 1.7891mAI     1.7891m 0.1K 6 6.17VoutV    Prof. K. Adisesha
  • 38. Zener Diode Diodes and Rectifiers Zener diode Application If RL = 8 KΩ instead of 10 KΩ; what is Vout?Case study 3: The circuit again shows voltage regulation .Vout only went from 6.1V to 6.0853V RTh=2.513KΩ Ri=0.1KΩ 6VVTh=8.23V               12 8K = 8.230V 3.6646K 8K 3.6646K 8K 2.513K 3.6646K 8K 8.230 2.513K 0.1K 6V 8.230 6 2.613K 0.8534mA 0.8534m 0.1K 6 6.0853V th th th out V R V I I I V                 Prof. K. Adisesha
  • 39. Zener Diode Diodes and Rectifiers Zener diode Application VI↑ → IR↑ → VL↑ → Iz↑↑→ IL↑→ ILRL↑→ VO↑ Case study 1、 2: RL have no changed: RL↓→IR↓→IL↓→ VO↓ Case study 1、 3: VI have no changed: Prof. K. Adisesha
  • 40. Zener Diode Diodes and Rectifiers Zener diode Application RR RV Vo L LI   LRZ III  R VV R V I LIR R   PZ＝IZVZ Prof. K. Adisesha
  • 41. iV oV Si VL=20V Zener Diode Diodes and Rectifiers Given a source voltage being with applying in this circuit: t 60V -60V Vi(t) iV oV 0.7V 20V Determine Vo When Vi>0, the equivalent circuit is: Vo=20V iV oV 0.7V 20V When Vi<0, the equivalent circuit is: Vo=0V Zener diode can be seen as a voltage regulator. Therefore: t 60V -60V Vi(t) 20V Vo Prof. K. Adisesha