Power Semiconductor Switches

Transcription

1 Power Semiconductor Switches Pekik Argo Dahono 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. Pekik A. Dahono -- Elektronika Daya 2 1

2 Power Diodes A A i AK i AK P N P N N A K v AK v AK K K Pekik A. Dahono -- Elektronika Daya 3 Reverse Recovery Problems V FD S I FD t rr Ed FD I o I S I o Pekik A. Dahono -- Elektronika Daya 4 2

3 Power diodes Diodes are classified as: - general purpose or line-frequency diodes - Fast recovery diodes - Schottky diodes Pekik A. Dahono -- Elektronika Daya 5 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). Pekik A. Dahono -- Elektronika Daya 6 3

4 Sample of diodes Pekik A. Dahono -- Elektronika Daya 7 Thyristor A i A i A P N v AK G P N K Pekik A. Dahono -- Elektronika Daya 8 4

5 Thyristor Model I B1 Q1 I I C2 C 1 I G Q2 I A = I E1 I B2 I I I C1 C2 A = α I 1 E1 = α I 2 E2 + I + I ( α + ) 1 C01 C02 α2ig + IC01 + I = 1 α 2 C02 I E2 Pekik A. Dahono -- Elektronika Daya 9 Thyristor in Simple Circuit For successful turn-off, reverse voltage required for an interval greater than the turn-off interval Pekik A. Dahono -- Elektronika Daya 10 5

6 Thyristor Classification Phase control thyristors Inverter-grade or fast-type thyristors Light activated thyristors Reverse conducting thyristors Pekik A. Dahono -- Elektronika Daya 11 Latching devices Thyristor Features Double carrier devices Having forward and reverse blocking capabilities Very high gain (I A /I g ) Low on-state voltage Can be protected by fuse Pekik A. Dahono -- Elektronika Daya 12 6

7 Sample of thyristors Pekik A. Dahono -- Elektronika Daya 13 Thyristor Modules Pekik A. Dahono -- Elektronika Daya 14 7

8 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. Pekik A. Dahono -- Elektronika Daya 15 Switching Characteristics Gate signal Ed i T I o Transistor voltage& current E d v T i T I o v T Transistor power t don t ri t t fv doff t fi t t rv son = tri + t fv t soff = trv + t fi 1 Wson = Ed Iotson Wsoff 2 1 = Ed Iotsoff 2 P cd Pekik A. Dahono -- Elektronika Daya 16 8

9 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 Pekik A. Dahono -- Elektronika Daya 17 Safe Operating Area i turn - on turn - off Pekik A. Dahono -- Elektronika Daya 18 v 9

10 Losses Switching losses : 1 P = 2 E I f t + t f s is switching frequency. Conduction losses : T s is switching period. s P = V cd d on I o o T s ( ) ON T s son soff Pekik A. Dahono -- Elektronika Daya 19 Bipolar Junction Transistor B C N P N B i B C i C i C i B i 5 i B4 i B3 B2 i = 0 B1 v CE i C v CE E E i > i > i > i > i B5 B4 B3 B2 B1 Used commonly in the past Now used in specific applications Replaced by MOSFETs and IGBTs Pekik A. Dahono -- Elektronika Daya 20 10

11 VI characteristics of BJT Hard- saturation Quasi- saturation Second breakdown I C I B5 I B4 I B3 I B2 I B1 I B0 = 0 Primary breakdown < 0 I B BVSUS BV CB 0 v CE Pekik A. Dahono -- Elektronika Daya 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. Pekik A. Dahono -- Elektronika Daya 22 11

12 Antisaturation circuit D 1 C B' D 2 B D 3 E Pekik A. Dahono -- Elektronika Daya 23 BJT Features Current controlled devices Double carrier devices No reverse blocking capability Low gain (I c /I b ) Low on-state voltage Can not be protected by fuse Second breakdown problem Pekik A. Dahono -- Elektronika Daya 24 12

13 Darlington Configuration Pekik A. Dahono -- Elektronika Daya 25 MOSFET G D i D i D v GS5 v GS4 v GS v 3 GS2 v GS1 = 0 v DS i D v DS S v > v > v > v > v GS5 GS4 GS3 GS2 GS1 Pekik A. Dahono -- Elektronika Daya 26 13

14 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 Pekik A. Dahono -- Elektronika Daya 27 Integrated Power MOSFET Pekik A. Dahono -- Elektronika Daya 28 14

15 Gate-Turn-Off (GTO) Thyristor i A Blocking condition v AK Pekik A. Dahono -- Elektronika Daya 29 GTO switching characteristic Anode voltage Anode current I A V d Spike voltage Tail current 0 Time I GR (b) Pekik A. Dahono -- Elektronika Daya 30 15

16 Turn-Off Snubber for GTO Pekik A. Dahono -- Elektronika Daya 31 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 Pekik A. Dahono -- Elektronika Daya 32 16

17 GTO vs IGCT Pekik A. Dahono -- Elektronika Daya 33 GTO vs IGCT Pekik A. Dahono -- Elektronika Daya 34 17

18 Insulated Gate Bipolar Transistors (IGBTs) G C i C i C v GE5 v GE4 v GE3 v GE2 v GE1 = 0 v CE E v > v > v > v > v GE5 GE4 GE3 GE2 GE1 Pekik A. Dahono -- Elektronika Daya 35 IGBT Features Combining the advantages of BJT and MOSFET No reverse blocking capability No second breakdown High gain at turn on and turn off Pekik A. Dahono -- Elektronika Daya 36 18

19 IGBT vs IGCT Pekik A. Dahono -- Elektronika Daya 37 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. Pekik A. Dahono -- Elektronika Daya 38 19

20 Switching Device Development P (kva) THYRISTOR 10 3 GTO BPT HIGH POWER EASY DRIVE HIGH FREQUENCY P (kva) CONTROLLABLE POWER P (kva) GTO : GATE TURN-OFF THYRISTOR MCT : MOS CONTROLLED THYRISTOR THYRISTOR SI Thy : STATIC INDUCTION THYRISTOR BPT : BIPOLAR POWER TRANSISTOR 10 4 GTO IGBT : INSULATED GATE BIPOLAR TRANSISTOR MCT SI Thy THYRISTOR IGBT GTO BPT IGBT MOS BPT OPERATION FREQUENCY f (khz) MOS f (khz) f (khz) Pekik A. Dahono -- Elektronika Daya 39 Reverse Conducting and Reverse Blocking Switching Devices Reverse conducting Reverse blocking Pekik A. Dahono -- Elektronika Daya 40 20

21 Bidirectional Switches Pekik A. Dahono -- Elektronika Daya 41 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 controlledswitch Pekik A. Dahono -- Elektronika Daya 42 21

22 Properties and Rating of Semiconductor Power Switches Switch Control signal Control characteristic Switching frequency Voltage drop Maximum voltage rating Maximum current 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 Pekik A. Dahono -- Elektronika Daya 43 Properties of New Materials Property Si GaAs 3C-SiC 6H-SiC Diamond Bandgap at 300 K (ev) Relative dielectric constant Saturated drift velocity (cm/s) 1x10 7 2x x x x10 7 Thermal conductivity (W/cm/ o C Maximum operating temperature (K) Melting Sublime>1800 Sublime>1800 Phase change temperature (C) Electron mobility at 300 K (cm 2 /Vs) Breakdown electric field (V/cm) 3x10 5 4x10 5 4x10 6 4x10 6 1x10 7 Pekik A. Dahono -- Elektronika Daya 44 22

23 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. Pekik A. Dahono -- Elektronika Daya 45 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. Pekik A. Dahono -- Elektronika Daya 46 23

24 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. Pekik A. Dahono -- Elektronika Daya 47 Turn-ON and turn-off Snubbers Pekik A. Dahono -- Elektronika Daya 48 24

25 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. Pekik A. Dahono -- Elektronika Daya 49 The End 25