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Lecture-4 : Semiconductor Power Switching Devices-1

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Lecture-4 on Power Electronics. Describes ideal and practical power switches and power diodes.

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Lecture-4 : Semiconductor Power Switching Devices-1

  1. 1. Semiconductor Power Switching Devices-1 (Lecture-4) R S Ananda Murthy Associate Professor and Head Department of Electrical & Electronics Engineering, Sri Jayachamarajendra College of Engineering, Mysore 570 006 R S Ananda Murthy Semiconductor Power Switching Devices-1
  2. 2. Static i-v Characteristics of Ideal Switch + - (a) + - (b) ON OFF Fully Controlled ON OFF Fully Controlled (c) We use power semiconductor devices as switches in converters. R S Ananda Murthy Semiconductor Power Switching Devices-1
  3. 3. Properties of Ideal Switch When switch is OFF, i = 0 and −∞ ≤ v ≤ +∞ which implies that PON = 0 When switch is ON, v = 0 and −∞ ≤ i ≤ +∞ which implies that POFF = 0 It should be possible to easily turn the switch ON and OFF by applying an appropriate control signal. The power terminals of the switch should be electrically isolated from the control terminals. R S Ananda Murthy Semiconductor Power Switching Devices-1
  4. 4. Properties of Ideal Switch The power required to keep the switch in a particular state, or to switch it ON/OFF should be infinitesimally small. Should be able to change state instantaneously which implies that tON = 0, tOFF = 0 and PSW = 0. Should be able to withstand infinite temperature which means that its power handling capability is infinite, i.e., PHmax → ∞. Should be able to withstand infinite value of di/dt during turn ON and infinite value of dv/dt during turn OFF. R S Ananda Murthy Semiconductor Power Switching Devices-1
  5. 5. Static i-v Characteristics of Practical Switch −V1 +V2 Limit Power Limit Power III II I IV v i + Ito toOFF State close v − axis i − axis ON State close − I The switch is assumed to be bilateral while drawing this. R S Ananda Murthy Semiconductor Power Switching Devices-1
  6. 6. Classification of Power Semiconductor Devices Bipolar voltage blocking Pulse triggered (latched) Continuously triggered Unilateral Bilateral Semi−controlled Fully−controlledUncontrolled Unidirectional Power Semicondutor Switching Devices Unipolar voltage blocking R S Ananda Murthy Semiconductor Power Switching Devices-1
  7. 7. Classification of Power Semiconductor Devices Device Control Input Controllability Conduction Blocking Diode Nil Uncontrolled Forward Reverse SCR Pulse Can be turned on Forward Bipolar LASCR Pulse Can be turned on Forward Bipolar TRIAC Pulse Can be turned on Bilateral Bipolar BJT Continuous Fully-controlled Forward Forward MOSFET Continuous Fully-controlled Forward Forward IGBT Continuous Fully-controlled Forward Forward SITH Continuous Fully-controlled Forward Forward GTO Pulse Fully-controlled Forward Bipolar MCT Pulse Fully-controlled Forward Forward SITH – Static Induction Thyristor; MCT – MOS Controlled Thyristor. R S Ananda Murthy Semiconductor Power Switching Devices-1
  8. 8. Power Losses in a Switch t p = vi t p = vi i Turn−on time Turn−off time v i v The total average power loss over a time interval T is PD = PON +POFF +PG +PSW ≈ PON +PSW = 1 T ˆ T 0 pdt as POFF +PG is negligible as compared to PON +PSW . R S Ananda Murthy Semiconductor Power Switching Devices-1
  9. 9. Static Characteristics Power Diodes Reverse leakage current VBR VF ( ) Forward conduction drop A K Circuit symbol + − i v A K Structure p i n i v i v Linear Approximation i v Ideal Characteristics Avalanche breakdown VF = Vγ +IF RF where RF is the ON-state bulk resistance. R S Ananda Murthy Semiconductor Power Switching Devices-1
  10. 10. Reverse Recovery Characteristics of Power Diodes IR t1 t2 t3 VF IF QRR IRM t 3 t 2 SF = VR IRM dt diQRR QRR 2 di/dt trr = dt di < 0 Diode with snubber Turn OFF starts here turn OFF ends here v t t Area = RM V - E 0.25 IRM = 2 0 Reverse Recovery Charge Reverse Recovery Time is the time taken by the minority carriers in the diode to recombine when the diode is reverse biased R S Ananda Murthy Semiconductor Power Switching Devices-1
  11. 11. Important Specifications of Power Diodes Reverse Blocking Voltage (VRRM). Forward Average Current (IF(AVE)). Forward RMS Current (IF(RMS)). Surge Current Rating (IFSM). Maximum On-state Voltage Drop (VFM). I2t Rating. Reverse Recovery Time (trr ). The maximum allowable junction and case temperatures (θJM and θCM). Junction-to-case and case-to-sink thermal resistances (RθJC and RθCS). R S Ananda Murthy Semiconductor Power Switching Devices-1
  12. 12. Types of Power Diodes 1 Standard Recovery Diodes 2 Fast Recovery Diodes 3 Schottky Diodes 4 Silicon Carbide Diodes. R S Ananda Murthy Semiconductor Power Switching Devices-1
  13. 13. Standard Recovery Diodes trr ≈ 25µs. Leakage current in the OFF-state is of the order of few µA. Have lower ON-state voltage drop. Available with ratings of several kV and kA. Typically used in rectifiers at power frequencies i.e., at 50 Hz or 60 Hz. R S Ananda Murthy Semiconductor Power Switching Devices-1
  14. 14. Fast Recovery Diodes trr ≤ 5µs Have relatively higher ON-state voltage drop. Typically used in D.C.-to-D.C. converters and inverters operating at higher frequencies as freewheeling diodes. R S Ananda Murthy Semiconductor Power Switching Devices-1
  15. 15. Schottky Diodes A K Barrier Metal n−type silicon layer Heavily doped silicon substrate A K Barrier Metal n−type silicon layer Heavily doped silicon substrate n+ trr is typically around few ns. Have very low ON-state voltage drop of the order of 0.15-0.45 V and consequently very low PON. Typically available in voltage ratings in the range 50-200 V. Used in circuits having very low output voltages like switched mode power supplies. R S Ananda Murthy Semiconductor Power Switching Devices-1
  16. 16. Silicon Carbide Diodes These are Schottky diodes constructed from silicon carbide. Have very low power loss. Have extremely fast switching behavior with ultra-low trr . Can operate at junction temperatures > 225◦ C. Switching behavior is independent of ON-state forward current and temperature. Have much lower reverse leakage current than silicon Schottky diodes, and higher reverse voltage rating. Very expensive as compared to Si Schottky diodes. R S Ananda Murthy Semiconductor Power Switching Devices-1
  17. 17. Some Diode Packages Axial Pack Plastic Pack Plastic Pack Stud Type Stud Type Disc Type Source: www.irf.com R S Ananda Murthy Semiconductor Power Switching Devices-1
  18. 18. Some Diode Packages Stud type diodes (Source: www.china-rectifier.com) R S Ananda Murthy Semiconductor Power Switching Devices-1
  19. 19. Some Diode Packages Disc type diodes (Source: www.china-rectifier.com) R S Ananda Murthy Semiconductor Power Switching Devices-1
  20. 20. Some Diode Rectifier Modules Single-phase Diode Bridge Module (Source: www.china-rectifier.com) R S Ananda Murthy Semiconductor Power Switching Devices-1
  21. 21. Some Diode Rectifier Modules Three-phase Diode Bridge Module (Source: www.china-rectifier.com) R S Ananda Murthy Semiconductor Power Switching Devices-1
  22. 22. Next Lecture... In the next lecture we will discuss some more power semiconductor switching devices used in power electronics. Thank You. R S Ananda Murthy Semiconductor Power Switching Devices-1

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