Chapter 4: Switch realization

Transcription

1 Chapter 4. Switch Realizatio 4.1. Switch applicatios Sigle-, two-, ad four-quadrat switches. Sychroous rectifiers 4.2. A brief survey of power semicoductor devices Power diodes, MOSFETs, BJTs, IGBTs, ad thyristors 4.3. Switchig loss Trasistor switchig with clamped iductive load. Diode recovered charge. Stray capacitaces ad iductaces, ad rigig. Efficiecy vs. switchig frequecy Summary of key poits 1

2 SPST (sigle-pole sigle-throw) switches SPST switch, with voltage ad curret polarities defied 1 i V g with SPDT switch: 1 2 Buck coverter L i L C R V v All power semicoductor devices fuctio as SPST switches. with two SPST switches: i A A v A V g v B i B B L i L C R V 2

3 Realizatio of SPDT switch usig two SPST switches A otrivial step: two SPST switches are ot exactly equivalet to oe SPDT switch It is possible for both SPST switches to be simultaeously ON or OFF Behavior of coverter is the sigificatly modified discotiuous coductio modes (ch. 5) Coductig state of SPST switch may deped o applied voltage or curret for example: diode 3

4 Quadrats of SPST switch operatio 1 i switch o-state curret A sigle-quadrat switch example: v ON-state: i > OFF-state: v > switch off-state voltage 4

5 Some basic switch applicatios Siglequadrat switch switch o-state curret switch off-state voltage Curretbidirectioal two-quadrat switch switch o-state curret switch off-state voltage switch o-state curret switch o-state curret Voltagebidirectioal two-quadrat switch switch off-state voltage Fourquadrat switch switch off-state voltage 5

6 Sigle-quadrat switches v 1 i Active switch: Switch state is cotrolled exclusively by a third termial (cotrol termial). Passive switch: Switch state is cotrolled by the applied curret ad/or voltage at termials 1 ad 2. SCR: A special case tur-o trasitio is active, while tur-off trasitio is passive. Sigle-quadrat switch: o-state i ad off-state v are uipolar. 6

7 The diode 1 i v Symbol i o off v istataeous i-v characteristic A passive switch Sigle-quadrat switch: ca coduct positive ostate curret ca block egative offstate voltage provided that the iteded o-state ad off-state operatig poits lie o the diode i-v characteristic, the switch ca be realized usig a diode 7

8 The Bipolar Juctio Trasistor (BJT) ad the Isulated Gate Bipolar Trasistor (IGBT) BJT C IGBT C 1 i 1 i v v i o off v istataeous i-v characteristic A active switch, cotrolled by termial C Sigle-quadrat switch: ca coduct positive ostate curret ca block positive off-state voltage provided that the iteded o-state ad off-state operatig poits lie o the trasistor i-v characteristic, the switch ca be realized usig a BJT or IGBT 8

9 The Metal-Oxide Semicoductor Field Effect Trasistor (MOSFET) A active switch, cotrolled by termial C C 1 i v i o off v o (reverse coductio) Normally operated as siglequadrat switch: ca coduct positive o-state curret (ca also coduct egative curret i some circumstaces) ca block positive off-state voltage Symbol istataeous i-v characteristic provided that the iteded ostate ad off-state operatig poits lie o the MOSFET i-v characteristic, the switch ca be realized usig a MOSFET 9

10 Realizatio of switch usig trasistors ad diodes Buck coverter example V g i A A v A v B i B B L i L C R V Switch A: trasistor Switch B: diode i A i B SPST switch operatig poits switch A o i L switch B o i L switch A off switch B off V g v A V g v B Switch A Switch B 1

11 Realizatio of buck coverter usig sigle-quadrat switches V g i A v A v B L v L i L i B i A i B switch A o i L switch B o i L switch A off switch B off V g v A V g v B 11

12 Curret-bidirectioal two-quadrat switches C 1 i v BJT / ati-parallel diode realizatio i o (trasistor coducts) off o (diode coducts) istataeous i-v characteristic v Usually a active switch, cotrolled by termial C Normally operated as twoquadrat switch: ca coduct positive or egative o-state curret ca block positive off-state voltage provided that the iteded ostate ad off-state operatig poits lie o the composite i-v characteristic, the switch ca be realized as show 12

13 Two quadrat switches v 1 i i o (trasistor coducts) off o (diode coducts) v switch o-state curret switch off-state voltage 13

14 MOSFET body diode i o (trasistor coducts) off v C 1 i v o (diode coducts) Power MOSFET characteristics Power MOSFET, ad its itegral body diode Use of exteral diodes to prevet coductio of body diode 14

15 A simple iverter i A Q 1 V g D 1 v A v =(2D1)V g L i L V g D 2 C R Q 2 v B v i B 15

16 Iverter: siusoidal modulatio of D v =(2D1)V g v Siusoidal modulatio to produce ac output: V g D =.5 D m si (ωt).5 1 D The resultig iductor curret variatio is also siusoidal: V g i L = v R =(2D1)V g R Hece, curret-bidirectioal two-quadrat switches are required. 16

17 The dc-3øac voltage source iverter (VSI) i a V g i b i c Switches must block dc iput voltage, ad coduct ac load curret. 17

18 Bidirectioal battery charger/discharger D 1 L v bus Q 1 spacecraft mai power bus Q 2 D 2 v batt v bus > v batt A dc-dc coverter with bidirectioal power flow. 18

19 Voltage-bidirectioal two-quadrat switches Usually a active switch, cotrolled by termial C C i 1 BJT / series diode realizatio v off (diode blocks voltage) i o off (trasistor blocks voltage) istataeous i-v characteristic v Normally operated as twoquadrat switch: ca coduct positive o-state curret ca block positive or egative off-state voltage provided that the iteded ostate ad off-state operatig poits lie o the composite i-v characteristic, the switch ca be realized as show The SCR is such a device, without cotrolled tur-off 19

20 Two-quadrat switches 1 v i i o switch o-state curret v i 1 off (diode blocks voltage) off (trasistor blocks voltage) switch off-state voltage C v 2

21 A dc-3øac buck-boost iverter i L v ab φ a V g v bc φ b φ c Requires voltage-bidirectioal two-quadrat switches. Aother example: boost-type iverter, or curret-source iverter (CSI). 21

22 Four-quadrat switches switch o-state curret switch off-state voltage Usually a active switch, cotrolled by termial C ca coduct positive or egative o-state curret ca block positive or egative off-state voltage 22

23 Three ways to realize a four-quadrat switch 1 1 i 1 i 1 i v i v v v 23

24 A 3øac-3øac matrix coverter 3øac iput 3øac output i a v a v b i b v c i c All voltages ad currets are ac; hece, four-quadrat switches are required. Requires ie four-quadrat switches 24

25 Sychroous rectifiers Replacemet of diode with a backwards-coected MOSFET, to obtai reduced coductio loss v 1 i v 1 i C 1 i v off i o (reverse coductio) v o ideal switch covetioal diode rectifier MOSFET as sychroous rectifier istataeous i-v characteristic 25

26 Buck coverter with sychroous rectifier V g i A Q 1 v A C C Q 2 i B v B L i L MOSFET Q 2 is cotrolled to tur o whe diode would ormally coduct Semicoductor coductio loss ca be made arbitrarily small, by reductio of MOSFET oresistaces Useful i lowvoltage high-curret applicatios 26

27 4.2. A brief survey of power semicoductor devices Power diodes Power MOSFETs Bipolar Juctio Trasistors (BJTs) Isulated Gate Bipolar Trasistors (IGBTs) Thyristors (SCR, GTO, MCT) O resistace vs. breakdow voltage vs. switchig times Miority carrier ad majority carrier devices 27

28 { Power diodes A power diode, uder reverse-biased coditios: v low dopig cocetratio p - E v { depletio regio, reverse-biased 28

29 Forward-biased power diode i v coductivity modulatio { p - miority carrier ijectio 29

30 Typical diode switchig waveforms v t i di dt t r t area Q r (1) (2) (3) (4) (5) (6) 3

31 Types of power diodes Stadard recovery Reverse recovery time ot specified, iteded for 5/6Hz Fast recovery ad ultra-fast recovery Reverse recovery time ad recovered charge specified Iteded for coverter applicatios Schottky diode A majority carrier device Essetially o recovered charge Model with equilibrium i-v characteristic, i parallel with depletio regio capacitace Restricted to low voltage (few devices ca block 1V or more) 31

32 Characteristics of several commercial power rectifier diodes Part umber Rated max voltage Rated avg curret V F (typical) t r (max) Fast recovery rectifiers 1N3913 4V 3A 1.1V 4s SD453N25S2PC 25V 4A 2.2V 2µs Ultra-fast recovery rectifiers MUR815 15V 8A.975V 35s MUR156 6V 15A 1.2V 6s RHRU112 12V 1A 2.6V 6s Schottky rectifiers MBR63L 3V 6A.48V 444CNQ45 45V 44A.69V 3CPQ15 15V 3A 1.19V 32

33 The Power MOSFET Gate Source Gate legths approachig oe micro p - p Cosists of may small ehacemetmode parallelcoected MOSFET cells, coverig the surface of the silico wafer Vertical curret flow -chael device is show Drai 33

34 MOSFET: Off state source p- - juctio is reverse-biased p p off-state voltage appears across - regio depletio regio - drai 34

35 MOSFET: o state source p- - juctio is slightly reversebiased p p positive gate voltage iduces coductig chael chael - drai curret flows through - regio ad coductig chael drai drai curret o resistace = total resistaces of - regio, coductig chael, source ad drai cotacts, etc. 35

36 MOSFET body diode source p- - juctio forms a effective diode, i parallel with the chael p Body diode p egative drai-tosource voltage ca forward-bias the body diode drai - diode ca coduct the full MOSFET rated curret diode switchig speed ot optimized body diode is slow, Q r is large 36

37 Typical MOSFET characteristics I D 1A 5A A off state V DS = 2V V DS = 1V o state V DS = 2V V DS = 1V V DS =.5V V 5V 1V 15V V GS Off state: V GS < V th O state: V GS >> V th MOSFET ca coduct peak currets well i excess of average curret ratig characteristics are uchaged o-resistace has positive temperature coefficiet, hece easy to parallel 37

38 A simple MOSFET equivalet circuit D C gs : large, essetially costat C gd : small, highly oliear G C gd C gs C ds C ds : itermediate i value, highly oliear switchig times determied by rate at which gate driver charges/ discharges C gs ad C gd S C ds (v ds )= C 1 v ds V C ds(v ds) C V v ds = C ' v ds 38

39 Characteristics of several commercial power MOSFETs Part um ber R ated m ax voltage R ated avg curret R o Q g (typical) IRFZ48 6V 5A.18Ω 11C IRF51 1V 5.6A.54Ω 8.3C IRF54 1V 28A.77Ω 72C APT1M25BNR 1V 75A.25Ω 171C IRF74 4V 1A.55Ω 63C MTM15N4E 4V 15A.3Ω 11C APT525BN 5V 23A.25Ω 83C APT11RBNR 1V 11A 1.Ω 15C 39

40 MOSFET: coclusios A majority-carrier device: fast switchig speed Typical switchig frequecies: tes ad hudreds of khz O-resistace icreases rapidly with rated blockig voltage Easy to drive The device of choice for blockig voltages less tha 5V 1V devices are available, but are useful oly at low power levels (1W) Part umber is selected o the basis of o-resistace rather tha curret ratig 4

41 Bipolar Juctio Trasistor (BJT) Base Emitter Iterdigitated base ad emitter cotacts Vertical curret flow p p device is show miority carrier device - o-state: base-emitter ad collector-base juctios are both forward-biased Collector o-state: substatial miority charge i p ad - regios, coductivity modulatio 41

42 BJT switchig times v s V s2 V s1 V CC v BE.7V R L v s i B R B i C v BE v CE V s1 i B v CE I B1 I B2 V CC I Co R o i C I Co (1) (2) (3) (4) (5) (6) (7) (8) (9) t 42

43 Ideal base curret waveform i B I B1 I Bo t I B2 43

44 Curret crowdig due to excessive I B2 Base Emitter I B2 p p - ca lead to formatio of hot spots ad device failure Collector 44

45 BJT characteristics I C 1A 5A slope = β active regio quasi-saturatio saturatio regio V CE = 2V V CE = 2V V CE = 5V V CE =.5V Off state: I B = O state: I B > I C /β Curret gai β decreases rapidly at high curret. Device should ot be operated at istataeous currets exceedig the rated value cutoff V CE =.2V A V 5V 1V 15V I B 45

46 Breakdow voltages I C icreasig I B BV CBO : avalache breakdow voltage of base-collector juctio, with the emitter ope-circuited I B = BV CEO : collector-emitter breakdow voltage with zero base curret BV sus ope emitter BV CEO BV CBO V CE BV sus : breakdow voltage observed with positive base curret I most applicatios, the offstate trasistor voltage must ot exceed BV CEO. 46

47 Darligto-coected BJT D 1 Q 1 Q 2 Icreased curret gai, for high-voltage applicatios I a moolithic Darligto device, trasistors Q 1 ad Q 2 are itegrated o the same silico wafer Diode D 1 speeds up the tur-off process, by allowig the base driver to actively remove the stored charge of both Q 1 ad Q 2 durig the tur-off trasitio 47

48 Coclusios: BJT BJT has bee replaced by MOSFET i low-voltage (<5V) applicatios BJT is beig replaced by IGBT i applicatios at voltages above 5V A miority-carrier device: compared with MOSFET, the BJT exhibits slower switchig, but lower o-resistace at high voltages 48

49 The Isulated Gate Bipolar Trasistor (IGBT) Emitter A four-layer device Gate Similar i costructio to MOSFET, except extra p regio p - p Collector p miority carrier ijectio O-state: miority carriers are ijected ito - regio, leadig to coductivity modulatio compared with MOSFET: slower switchig times, lower o-resistace, useful at higher voltages (up to 17V) 49

50 The IGBT Symbol collector gate Locatio of equivalet devices emitter Equivalet circuit C p i 2 i 1 p G - i 1 i 2 p E 5

51 Curret tailig i IGBTs C IGBT waveforms i L v A i A curret tail diode waveforms } V g i L t G i B v B t i 1 i 2 V g E p A = v A i A V g i L area W off t t 1 t 2 t 3 t 51

52 Characteristics of several commercial devices Part umber R ated m ax voltage R ated avg curret V F (typical) t f (typical) Sigle-chip devices HGTG32N6E2 6V 32A 2.4V.62µs HGTG3N12D2 12V 3A 3.2A.58µs Multiple-chip power modules CM4HA-12E 6V 4A 2.7V.3µs CM3HA-24E 12V 3A 2.7V.3µs 52

53 Coclusios: IGBT Becomig the device of choice i 5-17V applicatios, at power levels of 1-1kW Positive temperature coefficiet at high curret easy to parallel ad costruct modules Forward voltage drop: diode i series with o-resistace. 2-4V typical Easy to drive similar to MOSFET Slower tha MOSFET, but faster tha Darligto, GTO, SCR Typical switchig frequecies: 3-3kHz IGBT techology is rapidly advacig ext geeratio: 25V 53

54 Thyristors (SCR, GTO, MCT) The SCR costructio symbol Aode (A) equiv circuit Aode K G K Gate (G) Q 2 Q 1 p - Q 2 Cathode (K) Q 1 Gate p Cathode A 54

55 The Silico Cotrolled Rectifier (SCR) Positive feedback a latchig device A miority carrier device i A forward coductig Double ijectio leads to very low o-resistace, hece low forward voltage drops attaiable i very high voltage devices Simple costructio, with large feature size reverse blockig icreasig i G forward blockig i G = v AK Caot be actively tured off A voltage-bidirectioal two-quadrat switch reverse breakdow 5-6V, 1-2A devices 55

56 Why the covetioal SCR caot be tured off via gate cotrol K Large feature size Negative gate curret iduces lateral voltage drop alog gate-cathode juctio Gate-cathode juctio becomes reverse-biased oly i viciity of gate cotact G i G p - p i A K A 56

57 The Gate Tur-Off Thyristor (GTO) A SCR fabricated usig moder techiques small feature size Gate ad cathode cotacts are highly iterdigitated Negative gate curret is able to completely reverse-bias the gatecathode juctio Tur-off trasitio: Tur-off curret gai: typically 2-5 Maximum cotrollable o-state curret: maximum aode curret that ca be tured off via gate cotrol. GTO ca coduct peak currets well i excess of average curret ratig, but caot switch off 57

58 The MOS-Cotrolled Thyristor (MCT) Still a emergig device, but some devices are commercially available Gate Aode p-type device p A latchig SCR, with added built-i MOSFETs to assist the tur-o ad tur-off processes Q 3 chael Q 4 chael p - Small feature size, highly iterdigitated, moder fabricatio Cathode 58

59 The MCT: equivalet circuit Gate Q 4 Cathode Q 1 Q 2 Q 3 Negative gate-aode voltage turs p-chael MOSFET Q 3 o, causig Q 1 ad Q 2 to latch ON Positive gate-aode voltage turs -chael MOSFET Q 4 o, reversebiasig the base-emitter juctio of Q 2 ad turig off the device Aode Maximum curret that ca be iterrupted is limited by the o-resistace of Q 4 59

60 Summary: Thyristors The thyristor family: double ijectio yields lowest forward voltage drop i high voltage devices. More difficult to parallel tha MOSFETs ad IGBTs The SCR: highest voltage ad curret ratigs, low cost, passive tur-off trasitio The GTO: itermediate ratigs (less tha SCR, somewhat more tha IGBT). Slower tha IGBT. Slower tha MCT. Difficult to drive. The MCT: So far, ratigs lower tha IGBT. Slower tha IGBT. Easy to drive. Secod breakdow problems? Still a emergig device. 6

61 4.3. Switchig loss Eergy is lost durig the semicoductor switchig trasitios, via several mechaisms: Trasistor switchig times Diode stored charge Eergy stored i device capacitaces ad parasitic iductaces Semicoductor devices are charge cotrolled Time required to isert or remove the cotrollig charge determies switchig times 61

62 Trasistor switchig with clamped iductive load V g i A physical MOSFET v A DT s T s v B gate driver i L ideal diode i B L trasistor waveforms diode waveforms i L v A i A V g i L t Buck coverter example v B =v A V g i A i B =i L trasistor tur-off trasitio i B v B V g t W off = 1 2 V gi L (t 2 t ) p A = v A i A V g i L area W off 62 t t 1 t 2 t

63 Switchig loss iduced by trasistor tur-off trasitio Eergy lost durig trasistor tur-off trasitio: W off = 1 2 V gi L (t 2 t ) Similar result durig trasistor tur-o trasitio. Average power loss: P sw = 1 T s switchig trasitios p A dt =(W o W off ) f s 63

64 Switchig loss due to curret-tailig i IGBT V g i A physical IGBT v A DT s T s v B gate driver i L ideal diode Example: buck coverter with IGBT i B L trasistor tur-off trasitio IGBT waveforms diode waveforms i L v A i A curret tail } V g i B v B V g i L t t P sw = 1 T s switchig trasitios p A dt =(W o W off ) f s p A = v A i A V g i L area W off 64 t t 1 t 2 t 3 t

65 Diode recovered charge V g i A fast trasistor v A v B i L silico diode i B L trasistor waveforms i A Q r V g v A i L t Diode recovered stored charge Q r flows through trasistor durig trasistor tur-o trasitio, iducig switchig loss diode waveforms i L area Q r i B v B V g t Q r depeds o diode o-state forward curret, ad o the rate-of-chage of diode curret durig diode tur-off trasitio p A = v A i A t r area ~Q r V g area ~i L V g t r 65 t t 1 t 2 t

66 Switchig loss calculatio Eergy lost i trasistor: W D = switchig trasitio v A i A dt With abrupt-recovery diode: W D switchig trasitio V g (i L i B ) dt trasistor waveforms diode waveforms V g i L v A area Q r i A Q r i B v B i L V g t t Soft-recovery diode: (t 2 t 1 ) >> (t 1 t ) Abrupt-recovery diode: (t 2 t 1 ) << (t 1 t ) = V g i L t r V g Q r t r Ofte, this is the largest compoet of switchig loss p A = v A i A area ~Q r V g area ~i L V g t r 66 t t 1 t 2 t

67 Device capacitaces, ad leakage, package, ad stray iductaces Capacitaces that appear effectively i parallel with switch elemets are shorted whe the switch turs o. Their stored eergy is lost durig the switch tur-o trasitio. Iductaces that appear effectively i series with switch elemets are ope-circuited whe the switch turs off. Their stored eergy is lost durig the switch tur-off trasitio. Total eergy stored i liear capacitive ad iductive elemets: 1 2 W C = Σ 2 C i V i capacitive elemets W L = 1 2 L j I j 2 Σ iductive elemets 67

68 Example: semicoductor output capacitaces Buck coverter example C ds V g C j Eergy lost durig MOSFET tur-o trasitio (assumig liear capacitaces): W C = 1 2 (C ds C j ) V g 2 68

69 MOSFET oliear C ds Approximate depedece of icremetal C ds o v ds : V C ds (v ds ) C v = C ' ds v ds Eergy stored i C ds at v ds = V DS : V DS W Cds = v ds i C dt = v ds C ds (v ds ) dv ds V DS W Cds = C ' (v ds ) v ds dv ds = 2 3 C 2 ds(v DS) V DS same eergy loss as liear capacitor havig value 4 3 C ds(v DS ) 69

70 Some other sources of this type of switchig loss Schottky diode Essetially o stored charge Sigificat reverse-biased juctio capacitace Trasformer leakage iductace Effective iductaces i series with widigs A sigificat loss whe widigs are ot tightly coupled Itercoectio ad package iductaces Diodes Trasistors A sigificat loss i high curret applicatios 7

71 Rigig iduced by diode stored charge v i i L L v L silico diode i B v B C v i i L V 1 V 2 t Diode is forward-biased while i L > Negative iductor curret removes diode stored charge Q r Whe diode becomes reverse-biased, egative iductor curret flows through capacitor C. v B area Q r t t Rigig of L-C etwork is damped by parasitic losses. Rigig eergy is lost. V 2 t 1 t 2 t 3 71

72 Eergy associated with rigig Recovered charge is Q r = t 3 i L dt v i V 1 Eergy stored i iductor durig iterval t 2 t t 3 : W L = v L i L dt t 3 t 2 t 2 i L V 2 t Applied iductor voltage durig iterval t 2 t t 3 : v L =L di L =V dt 2 Hece, t 3 W L = L di t L 3 i dt L dt = (V 2 )i L dt t 2 t 2 v B area Q r t t W L = 1 2 Li 2 L(t 3 )=V 2 Q r V 2 t 1 t 2 t 3 72

73 Efficiecy vs. switchig frequecy Add up all of the eergies lost durig the switchig trasitios of oe switchig period: W tot = W o W off W D W C W L... Average switchig power loss is P sw = W tot f sw Total coverter loss ca be expressed as P loss = P cod P fixed W tot f sw where P fixed = fixed losses (idepedet of load ad f sw ) P cod = coductio losses 73

74 Efficiecy vs. switchig frequecy 1% 9% 8% P loss = P cod P fixed W tot f sw dc asymptote f crit Switchig losses are equal to the other coverter losses at the critical frequecy f crit = P cod P fixed W tot η 7% 6% 5% 1kHz 1kHz 1MHz This ca be take as a rough upper limit o the switchig frequecy of a practical coverter. For f sw > f crit, the efficiecy decreases rapidly with frequecy. f sw 74

75 Summary of chapter 4 1. How a SPST ideal switch ca be realized usig semicoductor devices depeds o the polarity of the voltage which the devices must block i the off-state, ad o the polarity of the curret which the devices must coduct i the o-state. 2. Sigle-quadrat SPST switches ca be realized usig a sigle trasistor or a sigle diode, depedig o the relative polarities of the off-state voltage ad o-state curret. 3. Two-quadrat SPST switches ca be realized usig a trasistor ad diode, coected i series (bidirectioal-voltage) or i ati-parallel (bidirectioalcurret). Several four-quadrat schemes are also listed here. 4. A sychroous rectifier is a MOSFET coected to coduct reverse curret, with gate drive cotrol as ecessary. This device ca be used where a diode would otherwise be required. If a MOSFET with sufficietly low R o is used, reduced coductio loss is obtaied. 75

76 Summary of chapter 4 5. Majority carrier devices, icludig the MOSFET ad Schottky diode, exhibit very fast switchig times, cotrolled essetially by the chargig of the device capacitaces. However, the forward voltage drops of these devices icreases quickly with icreasig breakdow voltage. 6. Miority carrier devices, icludig the BJT, IGBT, ad thyristor family, ca exhibit high breakdow voltages with relatively low forward voltage drop. However, the switchig times of these devices are loger, ad are cotrolled by the times eeded to isert or remove stored miority charge. 7. Eergy is lost durig switchig trasitios, due to a variety of mechaisms. The resultig average power loss, or switchig loss, is equal to this eergy loss multiplied by the switchig frequecy. Switchig loss imposes a upper limit o the switchig frequecies of practical coverters. 76

77 Summary of chapter 4 8. The diode ad iductor preset a clamped iductive load to the trasistor. Whe a trasistor drives such a load, it experieces high istataeous power loss durig the switchig trasitios. A example where this leads to sigificat switchig loss is the IGBT ad the curret tail observed durig its tur-off trasitio. 9. Other sigificat sources of switchig loss iclude diode stored charge ad eergy stored i certai parasitic capacitaces ad iductaces. Parasitic rigig also idicates the presece of switchig loss. 77