R. W. Erickson. Department of Electrical, Computer, and Energy Engineering University of Colorado, Boulder

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1 R. W. Erickso Deparme of Elecrical, Compuer, ad Eergy Egieerig Uiversiy of Colorado, Boulder

2 The Power MOSFET Gae Source Gae leghs approachig oe micro p - p Cosiss of may small ehacememode parallelcoeced MOSFET cells, coverig he surface of he silico wafer Verical curre flow -chael device is show Drai 46

3 MOSFET: Off sae source p- - jucio is reverse-biased p p off-sae volage appears across - regio depleio regio - drai + 47

4 MOSFET: o sae source p- - jucio is slighly reversebiased p p posiive gae volage iduces coducig chael chael - drai curre flows hrough - regio ad coducig chael drai drai curre o resisace = oal resisaces of - regio, coducig chael, source ad drai coacs, ec. 48

5 MOSFET body diode source p- - jucio forms a effecive diode, i parallel wih he chael p Body diode p egaive drai-osource volage ca forward-bias he body diode drai - diode ca coduc he full MOSFET raed curre diode swichig speed o opimized body diode is slow, Q r is large 49

6 Typical MOSFET characerisics I D 1A 5A A off sae V DS = 2V V DS = 1V o sae V DS = 2V V DS = 1V V DS =.5V V 5V 1V 15V V GS Off sae: V GS < V h O sae: V GS >> V h MOSFET ca coduc peak curres well i excess of average curre raig characerisics are uchaged o-resisace has posiive emperaure coefficie, hece easy o parallel 5

7 A simple MOSFET equivale circui D C gs : large, esseially cosa C gd : small, highly oliear G C gd C gs C ds C ds : iermediae i value, highly oliear swichig imes deermied by rae a which gae 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 51

8 Swichig loss caused by semicoducor oupu capaciaces Buck coverer example C ds V g + + C j Eergy los durig MOSFET ur-o rasiio (assumig liear capaciaces): W C = 1 2 (C ds + C j ) V g 2 52

9 MOSFET oliear C ds Approximae depedece of icremeal C ds o v ds : V C ds (v ds ) C v = C ' ds v ds Eergy sored i C ds a v ds = V DS : V DS W Cds = v ds i C d = 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 capacior havig value 4 3 C ds(v DS ) 53

10 Characerisics of several commercial power MOSFETs Par umber Raed max volage Raed avg curre R o Q g (ypical) 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 54

11 MOSFET: coclusios A majoriy-carrier device: fas swichig speed Typical swichig frequecies: es ad hudreds of khz O-resisace icreases rapidly wih raed blockig volage Easy o drive The device of choice for blockig volages less ha 5V 1V devices are available, bu are useful oly a low power levels (1W) Par umber is seleced o he basis of o-resisace raher ha curre raig 55

12 Bipolar Jucio Trasisor (BJT) Base Emier Ierdigiaed base ad emier coacs Verical curre flow p p device is show mioriy carrier device - o-sae: base-emier ad collecor-base jucios are boh forward-biased Collecor o-sae: subsaial mioriy charge i p ad - regios, coduciviy modulaio 56

13 BJT swichig imes 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) 57

14 Ideal base curre waveform i B I B1 I Bo I B2 58

15 Curre crowdig due o excessive I B2 Base Emier I B2 p + + p - ca lead o formaio of ho spos ad device failure Collecor 59

16 BJT characerisics I C 1A 5A slope = β acive regio quasi-sauraio sauraio regio V CE = 2V V CE = 2V V CE = 5V V CE =.5V Off sae: I B = O sae: I B > I C /β Curre gai β decreases rapidly a high curre. Device should o be operaed a isaaeous curres exceedig he raed value cuoff V CE =.2V A V 5V 1V 15V I B 6

17 Breakdow volages I C icreasig I B BV CBO : avalache breakdow volage of base-collecor jucio, wih he emier ope-circuied I B = BV CEO : collecor-emier breakdow volage wih zero base curre BV sus ope emier BV CEO BV CBO V CE BV sus : breakdow volage observed wih posiive base curre I mos applicaios, he offsae rasisor volage mus o exceed BV CEO. 61

18 Darligo-coeced BJT D 1 Q 1 Q 2 Icreased curre gai, for high-volage applicaios I a moolihic Darligo device, rasisors Q 1 ad Q 2 are iegraed o he same silico wafer Diode D 1 speeds up he ur-off process, by allowig he base driver o acively remove he sored charge of boh Q 1 ad Q 2 durig he ur-off rasiio 62

19 Coclusios: BJT BJT has bee replaced by MOSFET i low-volage (<5V) applicaios BJT is beig replaced by IGBT i applicaios a volages above 5V A mioriy-carrier device: compared wih MOSFET, he BJT exhibis slower swichig, bu lower o-resisace a high volages 63

20 The Isulaed Gae Bipolar Trasisor (IGBT) Emier A four-layer device Gae Similar i cosrucio o MOSFET, excep exra p regio p - p Collecor p mioriy carrier ijecio O-sae: mioriy carriers are ijeced io - regio, leadig o coduciviy modulaio compared wih MOSFET: slower swichig imes, lower o-resisace, useful a higher volages (up o 17V) 64

21 The IGBT Symbol collecor gae Locaio of equivale devices emier Equivale circui C p i 2 i 1 p G - i 1 i 2 p E 65

22 Curre ailig i IGBTs C IGBT waveforms i L v A i A curre ail diode waveforms } V g i L G i B v B i 1 i 2 V g E p A = v A i A V g i L area W off

23 Swichig loss due o curre-ailig i IGBT V g + i A physical IGBT v A + DT s + T s v B gae + driver i L ideal diode Example: buck coverer wih IGBT i B L rasisor ur-off rasiio IGBT waveforms diode waveforms i L v A i A curre ail } V g i B v B V g i L P sw = 1 T s swichig rasiios p A d =(W o + W off ) f s p A = v A i A V g i L area W off

24 Characerisics of several commercial devices Par umber Raed max volage Raed avg curre V F (ypical) f (ypical) Sigle-chip dev ices HGTG32N6E2 6V 32A 2.4V.62µs HGTG3N12D2 12V 3A 3.2A.58µs Muliple-chip power modules CM4HA-12E 6V 4A 2.7V.3µs CM3HA-24E 12V 3A 2.7V.3µs 68

25 Coclusios: IGBT Becomig he device of choice i 5 o 17V+ applicaios, a power levels of 1-1kW Posiive emperaure coefficie a high curre easy o parallel ad cosruc modules Forward volage drop: diode i series wih o-resisace. 2-4V ypical Easy o drive similar o MOSFET Slower ha MOSFET, bu faser ha Darligo, GTO, SCR Typical swichig frequecies: 3-3kHz IGBT echology is rapidly advacig: 33 V devices: HVIGBTs 15 khz swichig frequecies i 6 V devices 69

26 Thyrisors (SCR, GTO, MCT) The SCR cosrucio symbol Aode (A) equiv circui Aode K G K Gae (G) Q 2 Q 1 p - Q 2 Cahode (K) Q 1 Gae p Cahode A 7

27 The Silico Corolled Recifier (SCR) Posiive feedback a lachig device A mioriy carrier device i A forward coducig Double ijecio leads o very low o-resisace, hece low forward volage drops aaiable i very high volage devices Simple cosrucio, wih large feaure size reverse blockig icreasig i G forward blockig i G = v AK Cao be acively ured off A volage-bidirecioal wo-quadra swich reverse breakdow 5-6V, 1-2A devices 71

28 Why he coveioal SCR cao be ured off via gae corol K + Large feaure size Negaive gae curre iduces laeral volage drop alog gae-cahode jucio Gae-cahode jucio becomes reverse-biased oly i viciiy of gae coac G i G p - p i A + K A 72

29 The Gae Tur-Off Thyrisor (GTO) A SCR fabricaed usig moder echiques small feaure size Gae ad cahode coacs are highly ierdigiaed Negaive gae curre is able o compleely reverse-bias he gaecahode jucio Tur-off rasiio: Tur-off curre gai: ypically 2-5 Maximum corollable o-sae curre: maximum aode curre ha ca be ured off via gae corol. GTO ca coduc peak curres well i excess of average curre raig, bu cao swich off 73

30 Summary: Thyrisors The hyrisor family: double ijecio yields lowes forward volage drop i high volage devices. More difficul o parallel ha MOSFETs ad IGBTs The SCR: highes volage ad curre raigs, low cos, passive ur-off rasiio The GTO: iermediae raigs (less ha SCR, somewha more ha IGBT). Slower ha IGBT. Slower ha MCT. Difficul o drive. The MCT: So far, raigs lower ha IGBT. Slower ha IGBT. Easy o drive. Secod breakdow problems? Sill a emergig device. 76

31 4.3. Swichig loss Eergy is los durig he semicoducor swichig rasiios, via several mechaisms: Trasisor swichig imes Diode sored charge Eergy sored i device capaciaces ad parasiic iducaces Semicoducor devices are charge corolled Time required o iser or remove he corollig charge deermies swichig imes 77

32 Trasisor swichig wih clamped iducive load V g + i A physical MOSFET v A + DT s + T s v B gae + driver i L ideal diode i B L rasisor waveforms diode waveforms i L v A i A V g i L Buck coverer example v B =v A V g i A +i B =i L rasisor ur-off rasiio i B v B V g W off = 1 2 V gi L ( 2 ) p A = v A i A V g i L area W off

33 Swichig loss iduced by rasisor ur-off rasiio Eergy los durig rasisor ur-off rasiio: W off = 1 2 V gi L ( 2 ) Similar resul durig rasisor ur-o rasiio. Average power loss: P sw = 1 T s swichig rasiios p A d =(W o + W off ) f s 79

34 Swichig loss due o curre-ailig i IGBT V g + i A physical IGBT v A + DT s + T s v B gae + driver i L ideal diode Example: buck coverer wih IGBT i B L rasisor ur-off rasiio IGBT waveforms diode waveforms i L v A i A curre ail } V g i B v B V g i L P sw = 1 T s swichig rasiios p A d =(W o + W off ) f s p A = v A i A V g i L area W off

35 Diode recovered charge V g + i A fas rasisor v A + + v B + i L silico diode i B L rasisor waveforms i A Q r V g v A i L Diode recovered sored charge Q r flows hrough rasisor durig rasisor ur-o rasiio, iducig swichig loss Q r depeds o diode o-sae forward curre, ad o he rae-of-chage of diode curre durig diode ur-off rasiio diode waveforms 81 p A = v A i A i L area Q r i B v B r V g area ~Q r V g area ~i L V g r 1 2

36 Swichig loss calculaio Eergy los i rasisor: W D = swichig rasiio v A i A d Wih abrup-recovery diode: W D swichig rasiio V g (i L i B ) d rasisor waveforms diode waveforms V g i L v A area Q r i A Q r i B v B i L V g Sof-recovery diode: ( 2 1 ) >> ( 1 ) Abrup-recovery diode: ( 2 1 ) << ( 1 ) = V g i L r + V g Q r r Ofe, his is he larges compoe of swichig loss p A = v A i A area ~Q r V g area ~i L V g r

37 Device capaciaces, ad leakage, package, ad sray iducaces Capaciaces ha appear effecively i parallel wih swich elemes are shored whe he swich urs o. Their sored eergy is los durig he swich ur-o rasiio. Iducaces ha appear effecively i series wih swich elemes are ope-circuied whe he swich urs off. Their sored eergy is los durig he swich ur-off rasiio. Toal eergy sored i liear capaciive ad iducive elemes: 1 2 W C = Σ 2 C i V i capaciive elemes W L = 1 2 L j I j 2 Σ iducive elemes 83

38 Example: semicoducor oupu capaciaces Buck coverer example C ds V g + + C j Eergy los durig MOSFET ur-o rasiio (assumig liear capaciaces): W C = 1 2 (C ds + C j ) V g 2 84

39 MOSFET oliear C ds Approximae depedece of icremeal C ds o v ds : V C ds (v ds ) C v = C ' ds v ds Eergy sored i C ds a v ds = V DS : V DS W Cds = v ds i C d = 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 capacior havig value 4 3 C ds(v DS ) 85

40 Some oher sources of his ype of swichig loss Schoky diode Esseially o sored charge Sigifica reverse-biased jucio capaciace Trasformer leakage iducace Effecive iducaces i series wih widigs A sigifica loss whe widigs are o ighly coupled Iercoecio ad package iducaces Diodes Trasisors A sigifica loss i high curre applicaios 86

41 Rigig iduced by diode sored charge v i + i L L + v L silico diode i B + v B C v i i L V 1 V 2 Diode is forward-biased while i L > Negaive iducor curre removes diode sored charge Q r Whe diode becomes reverse-biased, egaive iducor curre flows hrough capacior C. v B area Q r Rigig of L-C ework is damped by parasiic losses. Rigig eergy is los. V

42 Eergy associaed wih rigig Recovered charge is Q r = 3 2 i L d Eergy sored i iducor durig ierval 2 3 : W L = v L i L d 3 2 v i i L V 1 V 2 Applied iducor volage durig ierval 2 3 : v L =L di L =V d 2 Hece, 3 W L = L di L 3 i d L d = (V 2 ) i L d 2 2 v B area Q r W L = 1 2 Li 2 L( 3 )=V 2 Q r V

43 Efficiecy vs. swichig frequecy Add up all of he eergies los durig he swichig rasiios of oe swichig period: W o = W o + W off + W D + W C + W L +... Average swichig power loss is P sw = W o f sw Toal coverer loss ca be expressed as P loss = P cod + P fixed + W o f sw where P fixed = fixed losses (idepede of load ad f sw ) P cod = coducio losses 89

44 Efficiecy vs. swichig frequecy 1% 9% 8% P loss = P cod + P fixed + W o f sw dc asympoe f cri Swichig losses are equal o he oher coverer losses a he criical frequecy f cri = P cod + P fixed W o η 7% 6% 5% 1kHz 1kHz 1MHz This ca be ake as a rough upper limi o he swichig frequecy of a pracical coverer. For f sw > f cri, he efficiecy decreases rapidly wih frequecy. f sw 9

45 Summary of chaper 4 1. How a SPST ideal swich ca be realized usig semicoducor devices depeds o he polariy of he volage which he devices mus block i he off-sae, ad o he polariy of he curre which he devices mus coduc i he o-sae. 2. Sigle-quadra SPST swiches ca be realized usig a sigle rasisor or a sigle diode, depedig o he relaive polariies of he off-sae volage ad o-sae curre. 3. Two-quadra SPST swiches ca be realized usig a rasisor ad diode, coeced i series (bidirecioal-volage) or i ai-parallel (bidirecioalcurre). Several four-quadra schemes are also lised here. 4. A sychroous recifier is a MOSFET coeced o coduc reverse curre, wih gae drive corol as ecessary. This device ca be used where a diode would oherwise be required. If a MOSFET wih sufficiely low R o is used, reduced coducio loss is obaied. 91

46 Summary of chaper 4 5. Majoriy carrier devices, icludig he MOSFET ad Schoky diode, exhibi very fas swichig imes, corolled esseially by he chargig of he device capaciaces. However, he forward volage drops of hese devices icreases quickly wih icreasig breakdow volage. 6. Mioriy carrier devices, icludig he BJT, IGBT, ad hyrisor family, ca exhibi high breakdow volages wih relaively low forward volage drop. However, he swichig imes of hese devices are loger, ad are corolled by he imes eeded o iser or remove sored mioriy charge. 7. Eergy is los durig swichig rasiios, due o a variey of mechaisms. The resulig average power loss, or swichig loss, is equal o his eergy loss muliplied by he swichig frequecy. Swichig loss imposes a upper limi o he swichig frequecies of pracical coverers. 92

47 Summary of chaper 4 8. The diode ad iducor prese a clamped iducive load o he rasisor. Whe a rasisor drives such a load, i experieces high isaaeous power loss durig he swichig rasiios. A example where his leads o sigifica swichig loss is he IGBT ad he curre ail observed durig is ur-off rasiio. 9. Oher sigifica sources of swichig loss iclude diode sored charge ad eergy sored i cerai parasiic capaciaces ad iducaces. Parasiic rigig also idicaes he presece of swichig loss. 93

R. W. Erickson. Department of Electrical, Computer, and Energy Engineering University of Colorado, Boulder

R. W. Erickson. Department of Electrical, Computer, and Energy Engineering University of Colorado, Boulder R. W. Erickso Departmet of Electrical, Computer, ad Eergy Egieerig Uiversity of Colorado, Boulder 4.2.2. The Power MOSFET Gate Source Gate legths approachig oe micro p - p Cosists of may small ehacemetmode