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Dynamic behaviour of double-interdigitated (TIL) GTOthyristors under resistive-inductive loadsANDREI SILARD a & BARNA KOSA ba Department of Electronics , Polytechnic Institute, Bucharest , O.P. 16, 76206, Romaniab Research & Development Institute , Metalotehnica, Tirgu-Mures, 4300, RomaniaPublished online: 06 Jul 2010.

To cite this article: ANDREI SILARD & BARNA KOSA (1985) Dynamic behaviour of double-interdigitated (TIL) GTO thyristorsunder resistive-inductive loads, International Journal of Electronics, 58:2, 295-305, DOI: 10.1080/00207218508939023

To link to this article: http://dx.doi.org/10.1080/00207218508939023

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INT. J. ELECTRONICS, 1985, VOL. 58, No.2, 283-294

Dynamic behaviour of double-interdigitated (TIL) GTOthyristors under resistive-inductive loads

ANDREI SILARDt and BARNA KOSAt

The paper focuses on the peculiar dynamic behaviour of the recently developed8 mm', TO-220-packaged, high-voltage, double-interdigitated (or two interdigi­tation levels-TIL) GTO thyristor. This novel power device was rated under bothslightly and heavily inductive resistive loads, i.e. close to the real conditionsencountered in practical power circuits employing GTO thyristors. Emphasis islaid on the ability of TIL GTOs to switch safely, with minimum power losses, acertain amount of anode current under high.voltage conditions and high com­mutation frequencies. The merits of TIL GTO thyristors are analysed in terms oftheir reliability and switching efficiency, which include the total power losses(conduction and switching losses), turn-on and turn-off gains and the switchingspeed. It is shown that thanks to their built-in self-protective features, these novelGTOs possess an enhanced current-handling capability at commutation fre­quencies up to 50kHz under extremely tough load conditions. The main implica­tions of the results for power applications are outlined.

1. Introduction

The double-interdigitated or two interdigitation levels (TIL) gate turn-off (GTO)thyristor (Fig. I) is a recent innovation in the area of power semiconductor devices(Silard 1983, Silard and Rusu 1983 a, b, Silard et al. 1984). This novel power switchcombines the advantages of a simple structure (Fig. I) with a series of improvedfeatures in comparison with identical, yet conventionally interdigitated GTO thyris­tors (Silard et al. 1984, Silard 1984 a, b, c). All the reported unique features withwhich the GTO thyristor is endowed are dictated by the double-interdigitated gate­cathode pattern, which actually subdivides the vertical structure of the device intoseveral elementary thyristors (Figs. I and 2). Each of these mini-thyristors contains astandard pnpn elementary section adjacent to an apparently non-regenerative pnpnsection, the latter having a thick p-type base and a thin n + -type emitter. The mainfunctional role of the shallow-diffused n + -type cathode zones belonging to thequasi-non-regenerative pnpn sections is to provide low p-type base resistance pathsfor the anode current removal via the gate during the transient turn-off process. Allthe opportunities the novel TIL gate-cathode pattern opens for significant improve­ment of GTO performances stem from the peculiar way by which wide interdigi­tated fingers actually produce all the beneficial effects typical of narrow-fingerdesign, without having the disadvantages of the latter (Silard et al. 1984). It shouldbe noted that the wide fingers of the TIL gate-cathode configuration inherentlyeliminate the difficulties currently encountered in conventional GTOs while con­tacting extremely narrow stripes.

The research presented in this work was focused on the peculiarities of thedynamic behaviour of the 4 x 4mm, TO-220-packaged, high-voltage TIL GTOs

Received 30 July 1984;accepted 20 August 1984.t Department of Electronics, Polytechnic Institute, Bucharest, O.P. 16, 76206 Romania.t Research & Development Institute, Metalotehnica, Tirgu-Mures, 4300 Romania.

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284 A. Silard and B. Kosa

Figure 1. Cross-sectional viewof the TIL GTO thyristor.

under resistive-inductive load conditions. The device ratings reported in this workare close to those encountered in practical power circuits employing GTO thyristors(switched-mode power supplies, motor speed control systems, various types of pulsewidth modulation inverters, horizontal TV deflection systems, etc.). Emphasis is laidon the ability of TIL GTOs to safety switch a certain amount of load current underhigh-voltage conditions at high commutation frequencies. The TIL GTO devicemerits are discussed in terms of switching efficiency, which includes the total powerlosses (conduction and commutation) in these thyristors at various commutationfrequencies. The implications of the results obtained are also outlined.

Ylb

G R0 1AT cE

R0 2

X0 a

Figure 2. Top view of an elementary thyristor with two interdigitation levels (TIL pattern),whose vertical structure consists of a standard pnpn section adjacent to a quasi-non­regenerative pnpn section. a is the half-width of the cathode, b is the length of anelementary thyristor, c is the length of the shallow-diffused cathode zone in an elemen­tary thyristor. Ro I and R0 2 are the sheet resistances of the p-type base under the deepand shallow n +-type layers, respectively.

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TIL GTO thyristors with resistive-inductive loads 285

2. Device fabrication and structure

The test TTL GTO devices were fabricated on 360 JIm-thick, n-type Wackersilicon wafers with a starting resistivity in the 85-90 n em range following theprocess flow detailed elsewhere (Silard et al. 1984). It is worth noting that the stan­dard technological process for conventional thyristors was followed as closely aspossible. The sole distinctive fabrication feature was the two-step phosphorus diffu­sion process, aimed at forming at different depths the corresponding n + -type zonesof the cathode (Fig. I). The implemented ratio of the sheet resistances in the p-typebase under the deep (Ro [) and shallow (Ro ') n +-type cathode diffusions, respec­tively, was ROllR 02 "" 25. The n-type base thickness was Wn = 250 JIm. The ratio ofthe cathode half-width a to the length b of an elementary thyristor was 4. Theimplemented ratio of b]c = 2 (Fig. 2) ensured an even distribution of the two typesof elementary pnpn sections (standard and quasi-non-regenerative) over the cathodearea. The gold diffusions from the anode side of the wafers were performed at 851°Cand 868°C, respectively, in order to reach a trade-off between the on-state losses andthe switching times of the devices. The two sets of TIL GTOs (hereafter: IF and 2Fdevices, respectively) had a measured (cf. Dean and Nuese, 1971) n-type base lifetimeof 4 JlS and 2 JlS, respectively. The entire cathode area A (8 mm ') of the finisheddevices consisted of 216 mini-thyristors, each of them having an elementary area ofabo The total area of the deep-diffused n + -type cathode zones was A [ = 3·5 mm".The off-state voltages (VORM = VRRM) ranged from 1000 V to 1500V, according to thedevice class. The nominal average anode currents of the TO-220-packaged IF and2F TIL GTO thyristors were lOA and 7 A, respectively. The tests at 1j = 25°Cyielded the following values of the forward voltage drop VT at a peak anode currentof lOA: VT ~ 2 V for IF devices; VT ~ 2·8 V for 2F devices; VT ~ 1-4V for control,i.e. not gold-diffused, units.

3. Experimental results

3.1. Preliminary considerations

A specially devised chopper-type circuit (Silard et al. 1984, Silard and Kosa1984) was used in the dynamic evaluations of the TTL GTOs under resistive­inductive load conditions. The devices were mounted on an alumina heatsink withthe thermal resistance R'hhs = 0·5°C/W, The TIL GTOs were subjected to rectangu­lar anode (load) current pulses with a 50% duty cycle (when not stated otherwise).Comparisons of TIL GTOs under various ratings were performed on an equalfooting, i.e. either under the same average anode current IT(Av) conditions (for exam­ple, 2 A or 5 A), or at a particular operational turn-off gain

(I)

which is the ratio of the output (anode) current to be switched to the peak input(gate) current.

The overall power loss P in devices during commutation was determined from(Skanadore 1978, Adler and Westbrook 1982)

(2)

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286 A. Silard and B. Kosa

where Po is the on-state power loss, Eon and Eorr are the switching energies associ­ated with the devices turn-on and turn-off, respectively, and f is the commutationfrequency.

The determination of switching energies Eon and Eorr was based on the measure­ment of corresponding values of dissipated power from the current and voltagewaveforms during the rise-time t, and fall-time tr , respectively. Under heavily induc­tive resistive loads (clamped inductive switching), the switching energies Eon and Eorrwere taken as one-half the product of the voltage and current being switched andthe rise-time t, or the fall-time t r , respectively (Adler and Westbrook 1982). Thefactor of 1/2 accounts for an average value of the load current being switched: underclamped inductive load conditions during, for example, the turn-on, the currentquickly climbs to a value pre-established by external circuitry, while the value of theanode-eathode voltage Vo remains unchanged during the load current rise. Simi­larly, during the transient turn-off, Vo quickly rises to its clamp value and onlyafterwards does the anode current fall actually begin (Skanadore 1978, Adler andWestbrook 1982).

The determinations of P according to (2) were checked by direct measurement ofthe overall dissipated power which was performed as follows. The case temperaturesTc of the devices were monitored during ratings at an ever-increasing commutationfrequency f Under steady-state conditions the case temperature difference 6 Tc isinduced precisely by the increment 6P of the overall dissipated power while makingthe transition from a lower to a higher switching frequency f Since the thermalresistance junction-to-case Rth j-c of TO-220-packaged devices is known, the powerP could be easily inferred from the case temperature measurements. The differencebetween these two methods does not exceed 8%.

3.2. Behaviour under slightly inductive resistive loads

The dynamic evaluations were performed under a typical load of RL = 50n inseries with an inductance L = 20IlH. The time constant of the resistive-inductiveload '1. = LIR L = 0-4 us was of the same order of magnitude as the main com­ponents of the turn-on and turn-off times, respectively, over the entire range ofswitched anode currents (see Table I).

Anode current iT (A)

2 5 to 15

Fall time 1, at Ko" = 5 (Jls) IF 0·15 0·30 0·60 1·2 1·72F 0·12 0·25 0·55 1·1 1·6

Fall time Ir at Ko" = 10 (Jls) IF 0·2 0·4 0·8 1·3 1·82F 0·18 0·35 0·7 1·2 1·7

Rise time It at Ko• = 5 (Jls) IF 0·27 0·45 0·9 1·3 1·62F 0·3 0·55 1·0 1-4 1·7

Rise time I, at Ko• = 10 (Jls) IF 0·3 0·5 1·0 1·4 1·72F 0·33 0·6 1·1 1·5 1·8

Table 1. Typical values of switching times for IF and 2F TIL GTOs at several relevantvalues of anode current, turn-olf(K.,,) and turn-on (Kon) gains. Test conditions: VD =800V; duration of conduction In = 50Jls; repetition frequencyf= 500Hz; I" = I" =10Jls; Tc = 25°C; diG.ldl = 15AlliS; RL = 500; L = 20JlH.

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TIL GTO thyristors with resistive-inductive loads

ITlAVlIA!1Sr'-,-Tc-=SO-It;--------------,

" ,,,,,\

\\

\\ ,,

287

Figure 3. Typical experimental dependences of the average anode current on commutationfrequency for IF (dashed lines) and 2F (solid lines) TIL GTOs for three characteristicvalues of the case temperature, at an anode-cathode voltage Vo = 100V. Test condi­tions: 50% duty cycle: diG.Jdr = l5A/ps; IGFM = 500mA.

The high-frequency switching characteristics of IF and 2F TIL GTOs underhigh-voltage conditions are shown in Figs. 3 and 4. The average anode currentITIAvl-frequency characteristics were measured at a constant case temperature: withthe increase of commutation frequency the value of ITIAvl was progressively reducedso as to match the pre-established value of Tc . The dependence of IT\Av) on theoff-state anode-cathode voltage at several relevant values of low and high fre­quencies is shown in Fig. 4. The overall power losses in IF and 2F TIL GTOsduring these ratings at average anode currents of 2 A and 5 A are shown in Fig. 5 forseveral relevant values of Va.

The fall of lTIAVl with frequency at Tc = const. (Fig. 4) occurs especially for theIOD-500 V range of the off-state voltage Va. With increase of Va over 500 V, the rateof fall of the average anode current with the frequency at higher values of the latter(~20k Hz) and constant case temperature diminishes. This rate of lTIAv) reductionbecomes even less important for Va exceeding 800 V and for frequencies higher than20 k Hz. The explanation of this behaviour is the following. At the lower values of Vathe load current is relatively large and the contributions of t, and tr (Table I) to theenergy dissipation are substantial. To match the pre-established value of Tc with theincrease of Va in the IOD-500 V range, the load current level and, hence, the switch­ing times t, and ts' should be properly adjusted at each variation of Va in order tomaintain the energy loss at a stable value. Starting with a threshold of ITIAvl = 2-3A at higher frequencies, the overall energy loss tends to remain almost constantowing to the diminution of switching times and of the on-state power losses (Silardet al. 1984). In other words, the decreases of r., tr and on-state voltage drop VT atlower current levels make the overall energy loss less sensitive with regard to varia­tions of the anode voltage Va.

Under high-voltage ratings, the current-handling capability of IF TIL GTOs atfrequencies up to 20 kHz is better than that of 2F devices. At frequencies exceeding20 kHz, there is no substantial difference between the current-handling capabilitiesof the two sets of TIL GTOs. The explanation is that the overall power dissipation

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288 A. Silard and B. Kosa

UKHz

................., , , ,

" , ,-,

5KHz

100 200 30J 400 500 600 700 800 900 1lOO Ve[yl(a)

InAV}[Arl----,,---.------r---.-----,-,..------,-,----.-,-----,15

U.

13

12

11

10

9

87

6

5I,':---,-',-------,-L--"l-_'c-~-----,-'--------'------,-'-------'-.=",-'-----,.___,Jo

'"="a,-=~_--_50KHz

- - - - --_'OOKHz

200KHz

ITIAV}[ArJ----r-...,--------,-,-----,-----r-.,.----.,--,----.--------,

10

9

87

6

5

4

3

2

1

o '00 200 30J 400 500 600 700 800 900 1000 Ve(y)(b)

Figure 4. Typical experimental dependences of the average anode current on the off-stateanode voltage Vo for IF (dashed lines) and 2F (solid lines) TIL GTOs at several rele­vant values of (a) lower and (b) higher commutation frequency and constant case tem­perature Tc = 50°C. Test conditions: same as for Fig. 3.

over a wide range of frequencies is almost identical for the two sets of GTOswitches: the 2F devices have larger on-state losses and somewhat longer turn-ontimes, yet possess lower turn-off losses owing to shorter turn-off times, while for 1FGTO thyristors the opposite is true (Table I, and Silard et al. 1984).

For an average anode current of 2 A (Fig. 5 (a)) the drives of TIL GTOs atturn-off gains Korr of 5 and 10, respectively, produce no substantial differences in theoverall power losses up to a frequency of 20 kHz, regardless to the anode--eathodevoltage. At higher frequencies the peak difference in power P for Korr = 5 and 10,respectively, amounts to 15%. Consequently, it is advantageous to drive the TILGTOs with a higher gain Kor~ even at higher frequencies, i.e. to increase the effi­ciency of the gate control. At an average current of 5 A, the difference in power loss

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TIL GTO thyristors with resistive-inductive loads 289

for gains Korr = 5 and 10, respectively becomes perceptible at a frequency of about5 kHz; yet even at higher frequencies this difference does not exceed 15%. However,at an average current rating of 5 A, the absolute level of overall dissipated power isquite large (Fig. 5 (b)). Consequently, the choice of the gate drive, and hence of thegain Korr , should be made with a view attaining the overall objectives.

The operations of both sets of TIL GTO devices at frequencies up to hundredsof kilohertz (Figs. 3 and 4) under high-voltage conditions and with a load currentamounting 10-30% of its nominal value (10 A and 7 A for IF and 2F devices,respectively) testify that the TIL pattern performs its main duties well, by (a) keeping

10

01 2 5 10 20 50 'OJ f[KHz]

(a)

,,f I

/ /f I

/ /

Koff=5 / /, ,, /

" ,.....Koff=5/ I , '~1O,' ,.

,

';'/, ,,/ ,, ,

.' ,Yo/ /

/ .' • l00V/ /

// / o500v»:.>

/

'" "",-'" x~V

51 2 5 10 20

(b)

P[wl/,0 Vo

• 100V0 SOOVx ~V

30

20

Figure 5. Overall power loss versus commutation frequency for IF (dashed lines) and 2F(solid lines) TIL GTOs for two relevant values of the turn-off gain Korr and threecharacteristic values of the anode voltage at rated average anode current of (a) 2 A and(b) 5 A. Test conditions: same as for Fig. 3.

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290 A. Silard and B. Kosa

the commutation losses within reasonable limits even at higher frequencies, i.e., byreducing the switching times which, at the load current levels encountered at highfrequencies, are anyway a decreasing function of the current (Table I); and (b) ensur­ing a uniform extraction of the current from the devices, i.e. by preventing anodecurrent crowding during transient turn-off into one or several interdigitated fingers,a phenomenon usually leading to the electrothermal failure of GTOs (Silard 1983,Silard 1984 c).

3.3. Behaviour under moderately and heavily inductive loads

The operation of TIL GTOs under moderate-to-heavy inductive loads, whosetime constants 'L are larger (or much larger) than the device switching times, is closeto typical ratings of these power thyristors in many real applications. The switchingefficiency and reliability of TIL GTOs are tightly interwoven with the frequency­dependence of overall power losses P and the latter's composition under theseratings (Baliga 1981, Adler and Westbrook 1982).

The behaviour of a sample of TIL GTOs under heavily inductive resitive loads(L = 2 mH, R,. = 2000) is given in Fig. 6. The ratio PolP of the on-state powerlosses Po to the total power losses P is also shown as a function of frequency f Thetime constant of the load 'I. = LIR L = lO)!s is much larger than the switching timesI r and t, of IF and 2F devices (Table 1) at the rated average anode current of 2A. Itis obvious from the experimental plots that under a high-voltage rating and fairgate-control efficiency (Korr = Kon = 5), both sets of TIL GTOs exhibit moderatepower losses even at frequencies around 50 kHz. At 10 kHz, there is an even split ofthe total power losses between the on-state Po and switching (Pon + Porr) power

p ---- ------2 5 1) 20

Figure 6. Overall power loss and the ratio PolP versus commutation frequency for tF(dashed Jines) and 2F (solid Jines) TIL GTOs at an average anode current of 2A andan anode voltage of 800Y. The on-state power losses Po at 2A current level are 2·6Wand 2·9W for IF and 2F devices, respectively. Test conditions: 50% duty cycle;L = 2mH; R = 2000; Korr = Kon = 5; diGJdt = 15AI/ls; 7j = 125°C.

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TIL GTO rhyristors wirh resisrive-inducrive loads 291

losses. The switching losses tend to become dominant in the 20-50 kHz frequencyrange. Up to 20 kHz, the total power loss P of IF devices is smaller than that of 2FTIL GTOs, while at frequencies exceeding 20 kHz the opposite is ture. The ratioPolP is always smaller for IF devices than for 2F thyristors: at lower frequenciesowing to a somewhat smaller value of Po, and at higher frequencies owing to largervalues of the total power losses P. The components of the switching energy (Eon andEo,,) were confined to the 10- 5_10- 4 J range.

The behaviour of IF and 2F TIL GTOs at even higher load time constants andat an average anode current of 5 A is illustrated in Fig. 7 (a), and the corresponding

Yoo SOOVx BOOV

2010(aj

S2

1', =40jJs(L=2mH;RL =SOJ\.}

12 =2SjJs IL=2mH ;RL =80 J\.)

30

20

10

0~--7-------::--~-----::'::---------::!=--~~1

P[W]90

80

70

60

SO

40

100 ~[%Jp

Voo 500Vx BOOV

40

30

io101:----;2t-----=S---=1O:----=20:-------:::'::-:;,.."..,.....,.--J---

(h)Figure 7. (a) Overall power Joss and (h) ratio PolP versus commutation frequency under

heavily inductive resistive loads at an average anode current of 5 A and two character­istic values of the anode voltage. Test conditions: same as for Fig. 6.

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292 A. Si/ard and B. Kosa

Frequency j'{k l-lz)

2 5 10 20 50 100 200

Turn-on power IF 0·012 0·12 0·8 2-6 7'5 15 30loss r: (Wjt 2F 0·01 0·11 0·7 2·5 6·25 12·5 20

Turn-olT power IF 0·5 1·0 1·7 2·7 6·25 12·5 25loss r,« (Wlt 2F 004 0·9 1045 2·6 5·3 10·5 21·3

Overall power IF 8·51 9·12 10·5 13·3 21·75 35·5 63loss P (W)t 2F HI 10·01 11·15 14·1 20·55 31·5 50·3

Overall power IF 8·9 9·5 11·0 14·0 22·5 37·0 66loss P (W):t 2F s-s 10·2 11·6 15·0 21·5 32·7 47

t Determined from current-voltage waveformsand switching times.:t Determined from case temperature measurements.

Table 2. Typical values of the turn-on (Poo), turn-olT (Poff ) and overall (P) power losses(determined through two dilTerent methods) for 1F and 2F TIL GTOs as a function offrequency at an average anode current of 5 A under a heavily inductive load(L = 2mH; R = lOn, Te = 2001's). The on-state power losses Po at 5A current levelare 8 Wand 9 W for IF and 2F devices, respectively. Test conditions: 50% duty cycle;Va = 100V; Koff = Koo = 5; diGJdl = 15AIl's; Teat 200kHz is 85°C.

ratios PolP are shown as a function of frequency in Fig. 7 (b). The inductance waskept constant (L = 2 mH), i.e. different time constants were obtained through thevariation of ohmic resistances only. For the sake of clarity, only the IF curve isshown for Va = 800 V. The crossover point of power loss P for IF and 2F TILGTOs is around 10 kHz; beyond this frequency the 2Fs are the lowest loss devices.At frequencies exceeding 20 kHz, the overall power losses P tend to become substan­tial and the switching losses dominate the on-state losses Po. It is noteworthy thatthe TIL GTOs have the ability to switch safely a current of 5 A up to 50 kHz underhigh-voltage conditions. The typical recorded values of switching energy (Eon' Eoff)were of the order of 10- 4 1.

The behaviour of IF and 2F TIL GTOs under even more heavily inductiveloads (re = 200f/s, L = 2mH, R = IOn) is synthesized in Table 2 for [nAV) = 5Aand Va = 100 V. It is noteworthy that both sets of devices operated safely up to afrequency of 200 kHz (Tc = 85°C). The overall power loss becomes important at100kHz; the switching losses also become dominant around this frequency. Hereagain the 2F devices have lower power losses at higher frequencies; the crossoverpoint of total losses P for the two sets of devices is located in the 20-50 kHz range.The values of switching energies (Eon' Eorr) were in the 10-4_10- 5 J range. Theoverall power losses determined through both methods outlined in § 3.1 are shownin Table 2 as a matter of illustration only. It is obvious from the data presented inthe table that the two methods yield convergent results; the difference in the valuesof P is within the error margin of such measurements.

Table 3 presents the worst recorded experimental data for IF TIL GTOs ratedunder extremely tough load conditions: L = I mH, R = In (r L = I ms). These areextremely tough electrothermal ratings as well, because the devices are subjected tolarge current overshoots, especially during turn-on. The test devices exhibited a highdegree of reliability and ruggedness under these ratings, although the total powerlosses become important at commutation frequencies of about 5 kHz. The duty cycle

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TIL GTO thyristors with resistive-inductive loads

Frequency[(kHz)

2 3 4 5 6

Duty cycle (%) 2·5 5·0 7·5 10·0 12·5 15Turn-off energy Eoff (x 10- 4 J) 4·2 9·0 16·0 24·0 36·0 49·0Turn-on energy Eon ( x 10- 4 J) 1·1 2·6 8·2 15·8 25·0 33·0Total power loss P (W) 0·51 2·4 7-4 17·0 35·0 55·0

293

Table 3. Turn-on (Eoo) and turn-off (Eoff ) energy and the total power losses P as a functionof commutation frequency [for IF TIL GTOs (worst data) rated under inductive loadconditions (L = 1mH; R = 1n; TL = I ms). Test conditions: variable duty cycle; VD =150V; duration of conduction c. = 251's; t" = t,r = IOl's; K off = Koo = 5; diGlJdr =15AIl's.

of load current pulses during these testings was variable in a range typical of GTOapplications under such inductive loads.

4. Conclusions

The 1F and 2F TIL GTOs both possess good current-handling capabilities up toa frequency of 50 kHz under high-voltage conditions and with different types ofresistive-inductive loads. Of paramount importance is the fail-safe operation of TILGTOs under heavy load conditions.

The reliability of TIL GTOs implies that: (1) a fairly good and stable currentbalance between the interdigitated fingers is preserved during both turn-on andturn-off; (2) the temperature rise in the structure is kept within safe limits underhigh-voltagejhigh-current conditions; (3) the final dimensions of the anode currentcrowding zone are large enough, ihus limiting the density of power dissipated duringtransient turn-off. Thanks to these self-protective features, the 0·08 cm', TO-nO­packaged, high-voltage TIL GTOs developed here possess the highest value of thepeak interruptable anode current JATO (60 A) ever reported in the open literature forthis class of GTO, and they could safely operate at high commutation frequenciesunder tough load conditions.

At a rated average anode current of 5 A, the switching efficiency of these TILGTOs, defined primarily through reduced power losses P, is good up to a frequencyof 10kHz for both sets of devices under all tested typical resistive-inductive loadconditions. Thus the devices are particularly suitable for those applications (e.g.motor drives) where the maximum switching frequency is around 10 kHz or less.Usually in such applications involving a high-voltage line, the simplicity and effi­ciency of the drive, the ability to withstand different failure modes, rather than thevery fast switching speed, gain prominence. It is worth remembering that the peaknon-repetitive on-state current of TIL GTOs is large (ITSM = 50 A), which is animportant feature for fail-safe operation under inductive overshoots. Furthermore,TIL GTOs are low-power consuming devices, i.e. the gate pulses required forturn-on and turn-off are short, the turn-on and turn-off gains are relatively large,and there is no need to feed the gate in the on-state in order to reduce the on-statevoltage VT (Silard et al. 1984). These features are important whenever the gate driveconsiderations (signal amplitude and duration) are paramount. The 1F switches aremore suitable for this range of frequency than are the 2F devices, because up to10kHz the on-state losses still dominate the switching losses.

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294 TIL GTO thyristors with resistive-inductive loads

When rated at an average anode current of 2 A the TIL GTOs possess a fairlygood switching efficiency up to a commutation frequency of 50kHz. The 2F devicesare more suitable for applications in the 10-50 kHz range of frequencies becausethese devices possess lower switching losses than the IFs at higher commutationfrequencies. The ability of TIL GTOs to be driven from low-energy sources makesthem particularly suitable for high-voltage/medium-current applications when thelow-cost gate drive is one of the sought-for objectives.

Although it is beyond the scope of the present paper to perform a comprehensivecomparison between the TI L GTO thyristors and other power switching devices(Baliga 1981, Adler and Westbrook 1982), several basic comparative remarks will bemadc taking into account the rated current densities. Since at load current levels upto lOA the anode current conduction in TIL GTOs in the on-state is primarilyassured by the standard pnpn sections, with a total cathode area of 0·035 em", thedevices rated at 2 A and 5 A have anode current densities of 55-60 A/cm 2 and 125­130 A/cm 2

, respectively (Silard et al. 1984). Compared on this basis with other novelpower switching devices, such as field-controlled thyristors (FCT) or static induction(SIT) thyristors, power bipolar Darlington transistors (DT), standard GTOs andMOSFETs (Baliga 1981, Adler and Westbrook 1982), it is obvious that the TILGTOs are the lowest loss devices up to a frequency of 1-2 kHz. Between 2 and10kHz the switching efficiencies of FCT(SIT) DT and TIL GTO are comparable.However, if a 'normally off' operation, high voltage and high degree of reliability arerequired, and if the simplicity of gate/base drive as well as the efficiency of gate/basecontrol rather than the switching speed are the primary objectives, then the TILGTO should be the first choice.

REFERENCESADLER, M. S., and WESTBROOK, S. R., 1982, Power semiconductor switching devices-A com­

parison based on inductive switching. I.E.E.E. Trans. Electron Devices, 29, 947-952.BALlGA, B. J., 1981, Switching lots of watts at high speeds. I.E.E.E. Spectrum, 18,42-48.DEAN, R. H., and NUESE, C. J., 1971,A refined step-recovery technique for measuring minority

carrier lifetimes and related parameters in asymmetric p-n junction diodes. I.E.E.E.Trans. Electron Devices, 18, lSI-ISS.

SILARD, A., 1983, New developments in the area of gate turn-off thyristors. Proc. FourthBrazilian Workshop 011 Microelectronics, pp. 371-378. PROMOCET, Carnpinas, SaoPaulo.

SILARD, A., 1984a,Increasing lATO in TIL GTO thyristors, Electron. Leu., 20,130-132.SILARD, A., 1984b, Switching characteristics of 45A double-interdigitated GTO thyristors.

I.E.E.E. Trans. Electron Devices, 31, 1230-1237.SILARD, A., 1984c, Electrothermal failure-safety of TIL GTO thyristors. I.E. E.E. Electron

Device Lett.; 5, 338-341.SILARD, A., and KOSA, B., 1984, A novel versatile control circuit for GTO thyristors, Electron.

Lett., 20 (to be published).SILARD, A., and Rusu, ~., 1983 a, A novel gate-cathode configuration with two interdigitation. levels for GTO thyristors. I.E.E.E. Electron Device Leit., 4,188-190.SILARD, A., and Rusu, ~., 1983b, The TIL GTO thyristor-A power switch with unique

turn-off features. I.E.E.E. Electron Device Lett., 4,347-349.SILARD, A., Rusu, S., TURTUDAU, F., and KOSA, B., 1984,A double-interdigitated GTO switch.

I.E.E.E. TrailS. Electron Devices, 31, 322-328.SKANADORE, W. R., 1978, Methods for utilizing high-speed switching transistors in high­

energy switching environments. General Semiconductor Industries Inc., Tempe,Arizona.

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