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- 1. Power Semiconductor Switches Pekik Argo Dahono
- 2. Power Semiconductor Switches • Diodes (Uncontrolled switches) • Thyristors (Controllable at turn-on but uncontrolled at turn-off or commonly called as latched devices). Triac is under the same category. • BJT, MOSFET, IGBT, GTO, MCT etc. are fully controllable switches.
- 3. Power Diodes A A i AK i AK A P P N− v AK v AK N N K K K
- 4. Reverse Recovery Problems VFD S t rr I FD Ed FD Io IS Io
- 5. Power diodes Diodes are classified as: - general purpose or line-frequency diodes - Fast recovery diodes - Schottky diodes
- 6. Schottky Diode • The schottky diode has a smaller voltage drop compared to conventional diodes (about 0.3 V). • The schottky diode has a smaller voltage breakdown than conventional diodes (less than 200 V).
- 8. Thyristor A iA iA P N v AK G P N K
- 9. Thyristor Model I A = I E1 I B1 Q1 I C1 = −α1I E1 + I C 01 I C 2 = −α 2 I E 2 + I C 02 IC 2 I C1 IG α 2 I G + I C 01 + I C 02 IA = Q2 1 − (α1 + α 2 ) I B2 IE2
- 10. Thyristor Classification • Phase control thyristors • Inverter-grade or fast-type thyristors • Light activated thyristors • Reverse conducting thyristors
- 11. Thyristor Features • Latching devices • Double carrier devices • Having forward and reverse blocking capabilities • Very high gain (IA/Ig) • Low on-state voltage • Can be protected by fuse
- 14. Snubbers for Diodes and Thyristors • Maximum dv/dt across diodes or thyristors must be limited and can be done by using an RC snubber that is connected in parallel to the devices. • Maximum di/dt through diodes or thyristors must be limited and can be done by using an inductor that is connected in series to the devices.
- 15. Switching Characteristics Gate signal vT iT Io Transistor voltage & Ed Io Ed iT current tdon tdoff vT t fv t fi t ri t son = tri + t fv trv t soff = t rv + t fi 1 1 Transistor Wson = Ed I ot son Wsoff = Ed I ot soff 2 2 power Pcd
- 16. Desired Switch Characteristics • Small leakage current in the off state • Small on-state voltage • Short turn-on and turn-off times • Large forward and reverse blocking voltage capabilities • High on-state current rating • Positive temperature coefficient of on-state resistance • Small control power • Wide Safe Operating Area • Large dv/dt and di/dt ratings
- 17. Safe Operating Area i turn - on turn - off v
- 18. Losses Switching losses : ( Ps = 1 E d I o f s t son + t soff 2 ) fs is switching frequency. Conduction losses : TON Pcd = Von I o Ts Ts is switching period.
- 19. Bipolar Junction Transistor iC iB 5 iC iB 4 C iB 3 C iC iB 2 iB iB1 = 0 N B vCE vCE B P N E iB 5 > iB 4 > iB 3 > iB 2 > iB1 E
- 20. VI characteristics of BJT Hard - saturation Quasi - saturation Second breakdown IC I B5 Primary I B4 breakdown I B3 I B2 I B1 IB < 0 vCE BVSUS BVCB 0 I B0 = 0
- 21. Operating region • Hard-saturation provides low voltage-drop but a large storage time (turn-off time) • Quasi-saturation provides high voltage-drop but a small storage time. • Second breakdown must be avoided by using a snubber and proper base current control. • Negative base current results in higher voltage breakdown.
- 22. Antisaturation circuit C D1 B B' D2 D3 E
- 23. BJT Features • Current controlled devices • Double carrier devices • No reverse blocking capability • Low gain (Ic/Ib) • Low on-state voltage • Can not be protected by fuse • Second breakdown problem
- 25. MOSFET iD vGS 5 iD vGS 4 D vGS 3 iD vGS 2 vGS1 = 0 G vDS v DS S vGS 5 > vGS 4 > vGS 3 > vGS 2 > vGS1
- 26. MOSFET Features • Voltage controlled devices • Single carrier devices • High on-state voltage • Very high gain • No reverse blocking capability • No second breakdown problem • Can not be protected by fuse
- 28. Gate-Turn-Off (GTO) Thyristor iA Blocking condition v AK
- 29. GTO switching characteristic Anode voltage Anode IA current Vd Spike voltage Tail current 0 Time IGR (b)
- 30. GTO Features • Controllable at turn-on and turn-off • High-voltage capability • Can be designed with reverse blocking capabilty • Low gain at turn-off • Low on-state voltage • High turn-off losses
- 31. Insulated Gate Bipolar Transistors (IGBTs) iC vGE 5 C vGE 4 iC vGE 3 vGE 2 vGE1 = 0 G vCE E vGE5 > vGE 4 > vGE3 > vGE 2 > vGE1
- 32. IGBT Features • Combining the advantages of BJT and MOSFET • No reverse blocking capability • No second breakdown • High gain at turn on and turn off
- 33. Other Switching Devices • Static Induction Transistor and Static Induction Thyristor. The main problems are normally-on and high conduction loss. The advantage is that the speed is very high. • MOS Controlled Thyristor. Combining the advantages of MOSFET and Thyristor. Still under development. • IGCT (Integrated Gate Controlled Thyristor). This is further development of GTOs.
- 34. Switching Device Development ER 2000 POW 105 GTO : GATE TURN-OFF THYRISTOR E IV DR MCT : MOS CONTROLLED THYRISTOR THYRISTOR H Y SI Thy : STATIC INDUCTION THYRISTOR NC HIG E SY BPT : BIPOLAR POWER TRANSISTOR QU 104 EA GTO E P (kVA) IGBT : INSULATED GATE BIPOLAR TRANSISTOR FR G H HI 1990 MCT SI Thy CONTROLLABLE POWER 103 104 THYRISTOR IGBT 102 103 GTO 1980 BPT P (kVA) 101 102 IGBT MOS 104 THYRISTOR BPT 101 10-1 -1 103 10 100 101 102 104 105 106 P (kVA) OPERATION FREQUENCY f (kHz) GTO MOS 102 -1 10 10-1 100 101 102 104 105 101 BPT f (kHz) 10-1 -1 10 100 101 102 104 f (kHz)
- 35. Reverse Conducting and Reverse Blocking Switching Devices Reverse conducting Reverse blocking
- 37. Switching devices Ideal Switch Unidirectional uncontrolled switch Unidirectional semicontrolled switch Bidirectional semicontrolled switch Reverse conducting fully controlled switch Reverse conducting fully controlled switch Reverse blocking fully controlled switch Bidirectional fully controlled switch
- 38. Properties and Rating of Semiconductor Power Switches Switch Control Control Switching Voltage Maximum Maximum signal characteristic frequency drop voltage current rating rating Diode medium 6.5 kV 5 kA SCR current trigger low medium 6 kV 4 kA TRIAC current trigger medium 1 kV 50 A GTO current trigger low medium 6.5 kV 4.5 kA BJT current linear medium low 1.5 kV 1 kA MOSFET voltage linear Very high high 1 kV 200 A IGBT voltage linear high medium 3.5 kV 2 kA
- 39. Properties of New Materials Property Si GaAs 3C-SiC 6H-SiC Diamond Bandgap at 300 K 1.12 1.43 2.2 2.9 5.5 (eV) Relative dielectric 11.8 12.8 9.7 10 5.5 constant Saturated drift velocity (cm/s) 1x107 2x107 2.5x107 2.5x107 2.7x107 Thermal 1.5 0.5 5.0 5.0 20 conductivity (W/cm/o C Maximum 400 460 873 1240 1100 operating temperature (K) Melting 1415 1238 Sublime>1800 Sublime>1800 Phase change temperature (C) Electron mobility 1400 8500 1000 600 2200 at 300 K (cm2 /Vs) Breakdown electric field 3x105 4x105 4x106 4x106 1x107 (V/cm)
- 40. Applications • Thyristor is only used for very large power applications. • Forced commutated thyristors are no longer used. • Bipolar junction transistors are no longer used. • MOSFET is commonly used in low-power applications. • IGBT is used from low-power up to medium power applications. • GTO is used for large power applications.
- 41. Loss Considerations • Conduction losses • Switching losses • The loss will determine the junction temperature and the heatsink and cooler required. • In many cases, the switching frequency is limited by the temperature instead of device speed.
- 42. Snubbers • Turn-off losses can be reduced by using a turn-off snubber. This snubber is also useful to limit high dv/dt across the device. • Turn-on losses can be reduced by using a turn-on snubber. This snubber is also useful to limit high di/dt through the device. • Snubbers are useful to reduce the switching losses on the switching devices. The total switching losses, however, may still the same or even increase.
- 43. Turn-ON and turn-OFF Snubbers
- 44. Reducing Switching Losses • Switching losses can be reduced by using lossless snubbers. These snubbers, however, may make the converter circuit became complicated. • IGBTs may operate without snubbers. • GTOs and IGCTs usually need a turn-off snubber because of high tail current. • Switching losses can be reduced or even eliminated by using soft-switching techniques. These methods, however, may increase the required voltage and/or current ratings.