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USN 06EC73
Seventh Semester B.E. Degree Examination, Dec.20L3 tJan.2ol,A
Power Electronics
E11o.td-E Lcon A*r\3
Note: Answer FIVEfull questions, selectingat least TWO questionsfrom each part.
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Fig.Qa(a)
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=.'1.,. =, Time: 3 hrs.
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Max. Marks:10O!'-,,,_il
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i c. Th; #t#; j;;"ii9, temperature of a transistor is T.1 :..-11f0'c and the ambientg temperatur6,isla:25oC. If the thermal impedance are &c :O,$,?.bW, &A: 0.1oC/W and
E s l(sa : O.S"Ci*;tplculate: '.r !B'= ;i the maximum p,ower dissipationo'=
i 5 ii) The case tempefurre. u '-,,1
JhE l,' ur) Also draw the th6r ! equivalent circuit of a transistor. (04 Marks)aT Lal
E i 2 a. Explain switching charactetistics of BJT with models. (06 Marks)E B' b. Explain working with basic-$bflrtur. of OexitdtiOn type n and p channel MOSFETs with
tg ,.f"r"rr..totran-sfercharacteristie." *""' Jr----
(0gMarks)
.g % PARr_Afi I a. Eyl"]ain control characteristic features of the following power devices: (3 ifSqB.. ii) MCT iii) IGBT (r2 Marks)! u lpfueperipheral effects of converters. .,.._''*, 1o+ lvtarhsy
E I c. The base drive circuit in Fig.e2f.)=fruiqt. : 100 V, %, :2.ty, %,: 0.9V, VBE : 0.7y,
= o \/ - 1<\r ^.^l o - 1z n^l^--t^r^-; € VB: 15V and B: 16. Calculate:
H + i) The collector current withMeldmping -=do
= t iil The collector-emitter c$nnu,e voltage Vi".g € vr vrurlrvr v[q*!y}}r6 vvrlqSw y utsi;. ,4,,
F^ = iii) The collector current wglh clamping.&"8E€ # #r; 5 Fig.Q2(c) (06 Marks)bEA f; 3 a. Elpltin turn-on mechanism of a thyristor using two transistor ana{5gy= and derive an
i E rcx@ssion for the anode current in terms of transistor parameters. .. (0s Marks)
iE 9,-.'With the help of neat circuit diagram and waveforms, explain the UJT-triggeri5rg circuit.g ry
': Also mention its advantages over RC triggering. - rio Marks)
* t c. If the latching current for SCR iruerted in between a dc voltage source of 100 V and an=()H f . ut inductance load L:0.1 H is 4 mA. Calculate the minimum width of gate pulse'cfubnt,,1-^-l +^ :------- ^,- -^--^
- - '" rrr vYrsrrr vr bqlw yqrr
5 5; required to turn-on SCR. (02 Marmi==
i"- 4 a. If a converter shown in Fig.Q4(a) has a purely resistive load of R and the delay angle isE .:_r .-
2 a: xl2. Determine: i) 11, ii) Form factor, iii) Ripple factor, iv) TUF, v) PIV ofthyristor.
Fig.Q2(c)
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4 b' Explain the working of dual converter with a neat circuit diagram. Also obtain waveform forvoltage generating circulating current. (10 Marks)
'':':j - -- .:- 1 r PART-B*oi;rr,,.. 5 ?. MenJion drawbacks of self commutation (any three). (03 Maffir,
" ""','"'"'\, ... b. Explain the operation of complementary commutation with neat circuit and wavefor*r.rffi'':i'" ,. -' , *dy.. equation of c for design consideration. (rlMarks)
'";;'+c' Find the value of C for the commutation circuit shown in Fig.e5(c). Given Ir.*. :t0 A, ton.::::'.,|'': f'of SCRI : 30 psec, E4. : 50 V. Assume 50oZ tolerance on turn-off time. =
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"'...,,ri ,''., ., t\L/ ':rN
' I LVt I Ii * I IlrnllIil. t\,r'I lr.u,.;.,.*'1.-U:--l-.,:;',r,,,:.:ittA-l.""';.--r,-,,,,.€)t I f o.,,u'
tt" +, Fig.Q5(c) .j"'r' (05 Marks)
6 a' Explain the working of sirigfu phase bidirectional AC voltage controller for RL loadconsidering discontinuous current flow tlrough load with a nJat circuit and waveforms.Derive equation for vor,or.
,ii:::::::: :: (r0 Marks)b. An ac voltage controller has a resistive igad of R: 10 e and %*": I20y,60 Hz. Thethyristors switch is on for n ; 25 cycles apd off for m : 75 cycles. Determirre: i) Vo.*,,ii) load power, iii) input po-ei factor, iv) Ir"_, .v) Ir*, (10 Marks)
7 a' Explain the principle cf operation of step-down "n"fi$;ti
with a neat circuit and waveform.Derive the equationl&t %"" , %-,, input power * r"nT effective resistance. (10 Marks)
b. Find the *"YI:l efficiency if the load resistance R : i0 Q,lnput supply dc voltage is 220,duty cycle is 50% and chopper voltage drop V.6 :2y. (Converter is ,t.p_ao*r, choiper).
f-rl'. -. (06Marks)c. Draw-1.]i..:'oircuit diagram and waveforms for step-up chopper. -i'-i,,:
(04 Marks)''ttt''"8 ? .E"xqpin current source inverter circuit with waveform. .::..,.!j. (10 Marks)b' .,4"{10 full bridge inverter has resistive load R:2.4 e the dc input voltpge n;":';;Determine: -r --- e -
' .," il RMS output voltage at fundamental frequency.ii) The output power. n't":..\: '':':::: 'irll
'::i
iii) The average and peak current of each transistor. :: ::.'(10 Mrir[q),,.
! .: .,ji::,::::.... -|F
:.t,ir-^, - ru psec, D4s : )U v. Assume )u7o tolerance on turn-off time. t':
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