A New Family of Full-Bridge ZVS Converters

Transcription

1 New Famly of Full-rdge ZV Converers ungaek Jang and Mlan M. Jovanovć Power Elecroncs Laboraory Dela Producs Corporaon P.O. ox 7, 50 Davs Dr. Research Trangle Park, NC 7709, U... bsrac famly of sof-swched, full-brdge (F) pulsewdh-modulaed (PWM) converers ha feaures zero-volageswchng (ZV) of all brdge swches over a wde range of npu volage and oupu load wh mnmal duy cycle loss and crculang curren s descrbed. The Zf he prmary swches s acheved by employng wo magnec componens whose vol-second producs change n he oppose drecons wh a change of phase shf beween he wo brdge legs. One magnec componen s a ransformer whle he oher magnec componen s eher a coupled nducor or a sngle-wndng nducor. The ransformer s used o provde solaed oupu(s), whereas he nducor s used o sore energy for ZV. I. INTRODUCTI The F ZV-PWM converer shown n Fg. s he mos wdely used sof-swched crcu n hgh-power applcaons, []-[5]. Ths consan-frequency converer employs phaseshf conrol and feaures Zf he prmary swches wh a relavely small crculang energy. However, full ZV operaon can only be acheved n a lmed load and npuvolage range, unless a relavely large nducance s provded n seres wh he prmary wndng of he ransformer whch can be mplemened as, eher ncreased leakage nducance of he ransformer, and/or by addng an exernal nducor. Ths ncreased nducance has a dermenal effec on he performance of he converer snce causes an ncreased loss of duy cycle on he secondary sde, as well as severe volage rngng across he secondary-sde oupu recfers due o he resonance beween he nducance and he juncon capacance of he recfer. everal echnques have been proposed o exend he ZV range of F ZV converers whou loss of duy cycle and secondary-sde rngng [6]-[8]. Generally, hese crcus acheve Zf all prmary swches n an exended load and npu-volage range by ulzng energy sored n nducve componens of an auxlary crcu. In he approach descrbed and analyzed n [6] and [7], he auxlary crcu comprses a par of nducors ha are conneced beween he md-pon of he brdge legs and a md-pon of an npu-volage capacve dvder, whereas n he approach descrbed n [8], he energy sored n he magnezng nducance of an auxlary ransformer s used o exend he ZV range. Whle n he proposed F ZV-PWM converers he energy avalable for ZV ncreases as he npu volage ncreases, whch s he desrable drecon of change snce more energy s requred o acheve ZV a hgher npu volages, he sored energy n he proposed F ZV converers s ndependen of load. s a resul, he proposed F ZV-PWM converers canno opmally resolve he rade-off beween power-loss savngs brough abou by a full-load-range ZV and power losses of he auxlary crcu. Ideally, he auxlary crcu needs o provde very lle energy, f any, a full load because he fullload curren sores enough energy n converer s nducve componens o acheve a complee Zf all swches. s he load curren decreases, he auxlary crcu needs o provde progressvely more ZV energy, wh he maxmum energy requred a no load. F ZV-PWM converer ha feaures hs knd of adapve energy sorage n he auxlary V P V D D P L LK D/ C C V - D/ C LLK TR Deff / Fg.. Convenonal F ZV-PWM converer and s key waveforms. N N D R DR V O V - C F D D I O R L C C /0/$7.00 (C) 00 IEEE

2 crcu has been nroduced n [9]. The crcu mplemens adapve energy sorage usng a coupled nducor conneced beween he brdge legs. In hs paper, he concep nroduced n [9] s generalzed. The generalzed F ZV-PWM crcu s hen used o derve a famly of F ZV-PWM converers ha acheve a fullrange ZV wh vrually no secondary-sde duy-cycle loss and parasc rngng. II. NEW FMIL OF F ZV-PWM CVERTER Fgure shows he generalzed, solaed, phase-shfconrolled F ZV-PWM converer. The crcu n Fg. employs wo ransformers T and T ha have her respecve secondary oupus conneced o wo oupu crcus and. In dc-dc mplemenaons, each oupu crcu ncludes a recfer, low-pass fler, and load. Two consan volage sources V and V, conneced n seres wh he prmary wndng of ransformer T, are employed o provde he vol-second balance on he wndngs of boh ransformers so ha he ransformers do no saurae. v 0 v CO 0 V = / V = / C T T n n O Fg.. Generalzed F ZV-PWM converer. D/ D/ v IN v IN -v IN (-D)/ D/ v - IN T 0 T T T T (-D)/ Fg.. Conrol mng dagrams of swches and volages across prmary wndngs of ransformers T and T (volages v and v CO, respecvely). Generally, he vol-second producs of he wndngs of ransformers and shown n Fg. are dependen on he phase shf beween he urn-on nsances of he correspondng swches n brdge legs - and -, as llusraed n Fg.. Namely, for zero phase shf,.e., when swches and and her correspondng swches and are urned on and off n unson (D = 0 n Fg. ), volage v across he prmary of ransformer T s zero so ha he vol-second produc of he prmary wndng of ransformer T s also zero. he same me, snce volage v C across wndng C and volage v C across wndng C mus have equal polary and snce v = v C v C = 0, follows ha v C = v C = 0. s a resul, volage v CO across he prmary wndng of ransformer T s /,.e., he vol-second produc of he prmary wndng of ransformer T s maxmal. mlarly, when swches and and her correspondng swches and are urned on and off n anphase,.e., wh a 80 phase shf (D = n Fg. ), he vol-second produc on he prmary of ransformer T s maxmal, whereas he vol-second produc of he prmary wndng of ransformer T s zero (mnmal). ecause he oupu volages of oupu crcus and are drecly proporonal o he vol-second producs of he correspondng prmary wndngs, he crcu n Fg. delvers power o oupus and n a complemenary fashon. pecfcally, for zero phase shf (D = 0), maxmum power s delvered o oupu, whereas no power (or mnmal power) s delvered o oupu. For 80 phase shf (D = ), maxmum power s delvered o oupu, whereas no power s delvered o oupu. ecause he ncremenal changes of he delvered power o oupus and wh phase-shf changes are n oppose drecons, he crcu n Fg. canno smulaneously regulae boh oupus f consan-frequency conrol s employed. Neverheless, he propery of he crcu o delver power o oupus and n he complemenary fashon makes he crcu deal for mplemenng Zf he prmary swches n a wde range of npu volage and load curren. Namely, f n he converer n Fg. one oupu s regulaed, he energy n ha oupu's fler nducor wll decrease as he load decreases. he same me, he energy sored n he magnezng nducance of he correspondng ransformer wll also decrease because a lgher load requres a smaller volsecond produc on he prmary wndng of he ransformer. However, he fler-nducor energy n he oher, unregulaed, oupu crcu and n he magnezng nducance of he correspondng ransformer wll ncrease because of an ncreased vol-second produc on he prmary of he ransformer. Ths ncreased energy n he oupu-fler nducor of he unregulaed oupu and n he magnezng nducance of s ransformer can be used o creae he ZV condon for he prmary swches a lgher loads, ncludng no load. To faclae he analyss of he operaon of he crcu n Fg., Fg. shows s smplfed crcu dagram when /0/$7.00 (C) 00 IEEE

3 oupu s regulaed. In he smplfed crcu n Fg., s assumed ha only energy sored n he magnezng nducance of ransformer T of he unregulaed oupu s used o creae he ZV condon. ecause no energy sored n he oupu fler nducor of oupu crcu s used o creae he ZV condon, oupu crcu and he assocaed secondary of ransformer are no shown n Fg.. Generally, hs smplfcaon does no have a sgnfcan effec on he operaon of he crcu snce he only effec of C C T V L V = / N V = / P P P C P O Fg.. mplfed crcu dagram of converer n Fg. when oupu s regulaed. v v v v v v P P v T C V V P N V V C V n = I n T 0 T T T T T 5 T 6 T 7 T 8 T 9 T 0 T T T = P / = P / - L D/ _ = -I n Fg. 5. Key waveforms of crcu n Fg.. oupu crcu s o ncrease he oal avalable energy ha can be used for creang he ZV condon. However, due o a reduced componen coun, he mplemenaon n Fg. s preferred n pracce. ecause only he prmary wndngs of ransformer T are used n he crcu n Fg., ransformer T operaes as a coupled nducor. To furher smplfy he analyss, s assumed ha he ressance of he conducng semconducor swches s zero, whereas he ressance of he non-conducng swches s nfne. In addon, he leakage nducances of boh ransformers are negleced snce her effec on he operaon of he crcu s no sgnfcan. Fnally, he magnezng nducance of ransformer T of he regulaed oupu s also negleced snce does no have a sgnfcan effec on he operaon of he crcu. However, he magnezng nducance of ransformer T, whch operaes as a coupled nducor, and oupu capacances of prmary swches C C are no negleced n hs analyss because hey play a major role n he operaon of he crcu. Consequenly, n Fg., ransformer T s modeled as an deal ransformer wh magnezng nducance L conneced across he seres connecon of prmary wndngs, whereas ransformer T s modeled only by an deal ransformer wh urns rao n. I should be noed ha magnezng nducance L of ransformer T represens he nducance measured beween ermnals and. Wh reference o Fg., he followng relaonshps beween currens can be esablshed: =, () P P P N = N, () P P P P =, () =. () nce he number of urns of wndng C and wndng C of ransformer T are he same, mus be ha P = P. (5) ubsung Eq. (5) no Eqs. ()-() gves P = P =, (6) n n =, (7) =, (8) n where n = / N s he urns rao of ransformer T. s can be seen from Eqs. (7) and (8), currens of boh brdge legs and are composed of wo componens: loadcurren componen /n and magnezng-curren componen. The load-curren componen s drecly depended on he load curren, whereas he magnezng curren does no drecly depend on he load, bu raher on he vol-second produc across he magnezng nducance. Namely, a change of he magnezng curren occurs only f he phase shf s changed o manan he oupu regulaon /0/$7.00 (C) 00 IEEE

4 Generally, a change of phase shf wh a load change s greaer a lgher loads han a heaver loads because as he load decreases oward no load he converer eners dsconnuous conducon mode. nce n he crcu n Fg. he phase shf ncreases as he load approaches zero, he vol-second produc of L also ncreases so ha he crcu n Fg. exhbs he maxmum magnezng curren a no load, whch makes possble o acheve ZV a no load. ecause magnezng curren does no conrbue o he load curren, bu flows beween he wo brdge legs, represens a crculang curren as seen n Fg.. Generally, hs crculang curren and s assocaed energy should be mnmzed o reduce losses and maxmze he converson effcency. Due o an nverse dependence of he vol-second produc of L on he load curren, he crcu n Fg. crculaes less energy a full load han a lgh load, and, herefore, feaures ZV n a wde load range wh a mnmum crculang curren. To furher undersand he operaon of he crcu n Fg., Fg. 5 shows s key volage and curren waveforms when he crcu s mplemened as a dc-dc converer. The waveforms n Fg. 5 are obaned based on analyss whch assumes ha oupu crcu comprses a low-pass LC fler, whch has a large fler nducance so ha durng a swchng cycle he refleced load curren no he prmary of ransformer T s consan, as shown n Fg. 5. s can bee seen from waveforms n Fg. 5, for all four prmary swches hrough he magnude of he curren flowng rough he swch a he urn-off momen s he same,.e., P (T ) = (T ) = (T7 ) = (T0 ) = I, (9) where, I s he amplude of he magnezng curren. ccordng o Eq. (9), commuaon of he swches n boh legs s done by he energy sored by prmary curren P and magnezng curren durng he perod when he capacance of he urned-off swch s chargng (volage across he swch s ncreasng) and he capacance of he swch ha s abou o be urned on s dschargng (volage across he swch s decreasng). Whle he commuaon energy conrbued by magnezng curren s always sored n magnezng nducance L of ransformer T, he commuaon energy conrbued by curren P s sored eher n he fler nducance of oupu crcu, or leakage nducances of ransformers T and T. pecfcally, for leadng-leg swches and, he commuaon energy conrbued by P s sored n oupu-fler nducor, whereas for laggng-leg swches and s sored n he leakage nducance of he ransformers. nce s desrable o mnmze he leakage nducance of ransformer T o mnmze he secondary-sde parasc rngng, he energy sored n s leakage nducances s relavely small,.e., much smaller han he energy sored n he oupu-fler nducance. s a resul, n he crcu n Fg., s easy o acheve ZV of leadng-leg swches and n he enre load range, whereas Zf laggng-leg swches and requres a proper szng of magnezng nducance L snce a lgh loads almos enre energy requred o creae he ZV condon of laggng-leg swches and s sored n he magnezng nducance. smlar analyss can be performed by assumng ha oupu of he crcu n Fg. s regulaed. smplfed crcu dagram when oupu s regulaed s shown n Fg. 6. In he smplfed crcu n Fg. 6, s assumed ha only energy sored n he magnezng nducance of ransformer T of he unregulaed oupu s used o creae he ZV condon. ecause no energy sored n he fler-nducor of oupu crcu s used o creae he ZV condon, oupu crcu s no shown n Fg. 6, whch represens he preferred mplemenaon due o a mnmum componen coun. Furhermore, because of he absence of oupu crcu, ransformer T operaes wh he secondary wndng opened,.e., only he prmary wndng of he ransformer s nvolved n he operaon of he crcu. Therefore, n he crcu n Fg. 6, ransformer T operaes as an nducor. In he smplfed crcu n Fg. 6, hs nducor s modeled by nducance L M. lso, n Fg. 6, he magnezng nducance of ransformer T s negleced because has no mporan role n he operaon of he crcu. Wh reference o Fg. 6, he followng relaonshps beween currens can be esablshed: N N N 0, (0) P P = M =. () olvng Eqs. (0) and () for and gves M =, () n M =. () n where n = / N s he urns rao of ransformer T. s can be seen from Eqs. () and (), as n he case of mplemenaon n Fg., currens of boh brdge legs and are composed of wo componens: load-curren componen /n and magnezng-curren componen M /. The loadcurren componen s drecly depended on he load curren, whereas he magnezng curren does no drecly depend on he load, bu raher on he vol-second produc across he magnezng nducance. nce n he crcu n Fg. 6 he phase shf decreases as he load approaches zero, he volsecond produc of L M also ncreases so he crcu n Fg. 6 exhbs he maxmum magnezng curren a no load, whch makes possble o acheve ZV a no load. s can be seen from Fg. 6, magnezng curren M does no conrbue o he load curren because half of hs curren flows hrough prmary wndngs C and C of ransformer n oppose drecons. Therefore, curren M represens a crculang curren ha should be mnmzed. Due o an nverse dependence of he vol-second produc of L M on he load curren, he crcu n Fg. 6, lkewse he crcu n /0/$7.00 (C) 00 IEEE

5 Fg., crculaes less energy a full load han a lgh load, and, herefore, feaures ZV n a wde load range wh a mnmum crculang curren. Fgure 7 shows key curren and volage waveforms of he crcu n Fg. 6, when he crcu s mplemened as a dc-dc converer. The waveforms n Fg. 7 are obaned by assumng ha oupu crcu comprses a low-pass LC fler, whch has a large fler nducance so ha durng a swchng cycle he refleced load curren no he prmary of C C V C V OUTPUT CIRCUIT V N V = / V = / n T C O Fg. 6. mplfed crcu dagram of converer n Fg. when oupu s regulaed. v v v L M V P V C V M D/ ransformer T s consan, as shown n waveform n Fg. 7. s can be seen from waveforms n Fg. 7, for all four prmary swches hrough he magnude of he curren flowng hrough he swch a he urn-off momen s he same,.e., IM (T ) = (T ) = (T7 ) = (T0) =, () n where I M s he amplude of he magnezng curren M. However, should be noed ha oppose from he mplemenaon n Fg., n he mplemenaon n Fg. 6 he energy for creang he ZV condon of laggng-leg swches and s sored n he oupu fler nducor, whereas he energy for creang he ZV condon of leadng-leg swches and s sored n he leakage nducances of ransformer T and nducance L M. Therefore, n he crcu n Fg. 6, s harder o acheve Zf he leadng-leg swches han he laggng-leg swches. In fac, snce almos all energy for zerovolage commuaon of leadng-leg swches and s sored n nducance L M, o acheve Zf he leadng-leg swches n a wde load range a proper szng of he magnezng nducance L M s requred. From he generalzed crcu n Fg., a famly of F ZV- PWM crcus can be derved. Fgures 8 hrough 0 shows some examples of hese crcus mplemened as dc-dc converers. The crcu n Fg. 8 s derved from he crcu n Fg. by mplemenng oupu crcu wh a full-wave recfer. Transformer T of he unregulaed oupu s mplemened as coupled nducor L C, whereas volage sources V and V are mplemened wh capacors C and C, respecvely. Namely, f capacors C and C are large enough so ha he resonan frequency of he seres resonan crcu formed by hese capacors and he magnezng nducance of L C s much smaller han he swchng frequency han he volage across capacors s consan and equal o /. I also should be noed ha he crcu n Fg. 8 can be also mplemened wh oher ypes of he secondary-sde recfer crcu such as, for example, he v D D v C C C C v P P M n = I M M = M / P L M - = -I M M D C N C N C LC D TR C F D R L C = / - M P v n T 0 T T T T T 5 T 6 T 7 T 8 T 9 T 0 T T T Fg. 7. Key waveforms of crcu n Fg. 6 Fg. 8. Implemenaon of F ZV-PWM converer derved from crcu n Fg. when s regulaed oupu. N N D /0/$7.00 (C) 00 IEEE

6 D D C C NC C N C LC D D C C Fgure 0 shows he mplemenaon of he F ZV-PWM converer accordng o he crcu n Fg. 6 when s regulaed oupu. Ths converer employ capacors C and C o mplemen source V and V. I should be noed ha he crcus n Fg. 8 and 9 use coupled nducor L C o sore energy for ZV, whereas nducor L n he crcu n Fg. 0 s uncoupled. C NP NP TR Fg. 9. Implemenaon of F ZV-PWM converer derved from crcu n Fg. 6 when s regulaed oupu. D D L C C C TR Fg. 0. Implemenaon of F ZV-PWM converer derved from crcu n Fg. 6 when s regulaed oupu. curren-doubler recfer. Fgure 9 shows a opology derved from he crcu n Fg. 6. In hs opology, volage sources V and V are shfed from he respecve prmares of ransformer T no he prmary of ransformer T. nce hs crcu ransformaon does no change any of he crcu s branch currens and node volages, also does no change he waveforms of he crcu. s a resul, volage sources V and V are mplemened wh sngle capacor C n Fg. 9. However, o preven he sauraon of ransformer T when he swchng waveforms of he brdge legs are no dencal, capacor C s conneced n seres wh ransformer T,.e., coupled nducor L C. Generally, he volage across capacor C s small (close o zero) snce hs capacor only akes on he volage dfference caused by a msmachng of he brdge legs, whch s usually small. N N D D C N N D D CF C F D D RL R L C C III. DEIGN GUIDELINE To acheve Zf he converer shown n Fg., he sum of he energy sored n he leakage nducance of he ransformer n he regulaed oupu and he magnezng nducance of he ransformer n he unregulaed oupu mus be a leas equal o he energy requred o dscharge he capacances of he swches whch are abou o be urned on and off. heaver load currens, ZV s prmarly acheved by he energy sored n he resdual leakage nducances of he ransformers n he regulaed oupu. s he load curren decreases, he energy sored n he leakage nducances also decreases, whereas he energy sored n he magnezng nducance of he ransformer of he unregulaed oupu ncreases so ha a lgh loads hs magnezng nducance provdes an ncreasng share of he energy requred for ZV. In fac, a no load, he magnezng nducance provdes he enre energy requred o creae he ZV condon. Therefore, f he value of he magnezng nducance of he ransformer n he unregulaed oupu s seleced so ha ZV s acheved a no load and maxmum npu volage (max), ZV s acheved n he enre load and npu-volage range. Neglecng he capacances of he ransformer s wndngs, magnezng nducance L necessary o acheve Zf leggng-leg swches n he mplemenaons where oupu s regulaed s gven by L, (5) Cf whereas, magnezng nducance L M requred o acheve Zf leadng-leg swches n he mplemenaons where oupu s regulaed s gven by L M, (6) 8Cf where C s he oal capacance across he prmary swches (parasc and exernal capacance, f any) n he correspondng legs. The conrol of he proposed crcus s he same as ha of he convenonal consan-frequency F ZV-PWM converer. In fac, any of he negraed phase-shf conrollers avalable on he marke can be used o mplemen he conrol of he proposed crcu. However, should be noed ha n he crcus wh regulaed oupu, he maxmum oupu volage (vol-second produc) s obaned when he brdge legs are operaed n phase (0 phase shf), whereas he maxmum oupu volage (vol-second produc) for he crcus wh regulaed oupu occurs when he brdge legs /0/$7.00 (C) 00 IEEE

7 are operaed n anphase (80 phase shf). Ths dfference n he conrol characerscs of he wo crcu mplemenaons has a mnor effec on he conrol loop desgn snce a smple conrol-sgnal nverson n he volage conrol loop solves he problem. IV. EPERIMENTL REULT The performance of he proposed crcu shown n Fg. 8 was verfed on a 670-W expermenal prooype operang a khz, as repored n [9]. The expermenal converer was desgned o operae from 00-V dc npu and delver from a 8-upu. The phase-shf conrol crcu was mplemened usng a UC875 conroller. Fgure shows he measured waveforms of he proposed F ZV converer. s can be seen from he waveforms n Fg., he proposed converer has a very small duy cycle loss (< %), as well as a small parasc rngng because of a mnmzed leakage nducance of he ransformer ha s less han µh measured on he prmary sde. The proposed converer shows a converson effcency mprovemen n he enre measured power range as shown n Fg.. Generally, he effcency mprovemen s more pronounced a lgh loads where he convenonal F ZV V [00 V/dv] P [0 /dv] V [500 V/dv] V [500 V/dv] Fg.. Measured key waveforms a P O=670 W. From op o boom: secondary volage V ; prmary curren P dran-o-source volage V of ; dran-o-source volage V of. Tme base: µs/dv. Effcency Convenonal ZV Full-rdge Converer Duy Cycle Loss < % Proposed ZV Full-rdge Converer wh Coupled Inducor Inpu Volage = 00 V Oupu Volage = 8 V wchng Frequency = khz Oupu Power Fg.. Measured effcences of convenonal F ZV converer and proposed F ZV converer as funcons of oupu power [9] converer operaes wh hard swchng. pecfcally, he measured effcency s approxmaely 89% a 0% load and 95% a full load. V. CCLUI new famly of solaed, consan-frequency, phase-shf F ZV-PWM converers ha can acheve complee ZV n a wde range of load curren and npu volage s nroduced. The nroduced F ZV-PWM famly employs an auxlary crcu n whch he energy ha s used for creang he ZV condon s no only dependen on he npu volage, bu s also dependen on he load. pecfcally, he auxlary crcu provdes very lle energy a full load, whereas provdes maxmum energy for ZV a no-load. In he auxlary crcu n he proposed famly of F ZV-PWM converers, he energy-sorage componen s an nducor, eher coupled or uncoupled. nce hs nducor does no appear n he powerransfer pah,.e., does no carry he load curren, also does no cause a loss of duy cycle or volage rngng across he oupu recfers. REFERENCE [] O.D. Paerson and D.M. Dvan, Pseudo-resonan full brdge DC/DC converer, n Proc. IEEE PEC'87 Rec., pp. 0, 987. [] R.. Fsher, K.D.T. Ngo, and M.H. Kuo, 500 khz, 50 W DC-DC converer wh mulple oupus conrolled by phaseshfed PWM and magnec amplfers, Hgh Frequency Power Converson Proc., pp. 00-0, May 988. [] L.H. Mweene, C.. Wrgh, and M.F. chlech, kw, 500 khz fron-end converer for a dsrbued power supply sysem, n Proc. IEEE PEC'89 Rec., pp. -, 989. [] J.. abaé, V. Vlakovć, R.. Rdley, and F.C. Lee, Hghvolage, hgh-power, ZV, full-brdge PWM converer employng an acve snubber, n Proc. IEEE PEC'9 Rec., pp. 58-6, 99. [5] W. Chen, F.C. Lee, M.M. Jovanovć, and J.. abaé, comparave sudy of a class of full brdge zero-volageswched PWM converers, n Proc. IEEE PEC'95 Rec., pp , 995. [6] M. Nakaoka,. Naga,.J. Km,. Ogno, and. Murakam, The sae-of-he ar phase-shfed ZV-PWM seres & parallel resonan DC-DC power converers usng nernal parasc crcu componens and new dgal conrol, n Proc. IEEE PEC'9 Rec., pp. 6 70, 99. [7] P.K Jan, W. Kang, H. on, and., nalyss and desgn consderaons of a load and lne ndependen zero volage swchng full brdge DC/DC converer opology, IEEE Trans. Power Elecron., vol. 7, no. 5, pp , ep. 00. [8] R. yyanar and N. Mohan, Novel sof-swchng DC-DC converer wh full ZV-range and reduced fler requremen Par I: Regulaed-oupu applcaons, IEEE Trans. Power Elecron., vol. 6., no., pp. 8-9, Mar. 00. [9]. Jang and M.M. Jovanovć, new ZV-PWM full-brdge converer, IEEE Inernaonal Telecommuncaons Energy Conf. (INTELEC) Proc., pp. - 9, /0/$7.00 (C) 00 IEEE