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1、Asymmetrical Half Bridge Converter based on L6591,Scott Han-Application EngineerI&PC Division STMicroelectronicsSept2010,Review of Switching Characteristics,The requirements of power converter include small size,light weight,high efficiency and high power density.Hard-switching PWM converters suffer
2、 from high switching losses,high switching stresses and high EMI noise.Soft-switching PWM converters can alleviate these problems in which a high switching frequency operation can be achieved.,2,3,Soft-switching converter configurations,AHB,MOSFET Switching losses,4,Turn-off transition waveforms of
3、a MOSFET.,Turn-on transition waveforms of a MOSFET.,Principle of zero-voltage switching,5,The Block of Asymmetrical Half-bridge,6,Lout current,D1 current,ASIMMETRIC,Hysteresis loop,Q1 current,HB midpoint voltage,Tank circuit current,Q1,Q2,D2,D1,Np,Ns1,Ns2,Iload,Iload,Iload,Ca,Ip,It,Lm,Im,Vp,Lo,L6591
4、,7,Switching process,Waveforms for switching process,8,AHB steady-state analysis(1),9,The following assumptions are made:The output filter inductance is high enough and the filter inductor operates in continuous conduction mode.The transformer leakage inductance is negligible and magnetizing inducta
5、nce is referred to the primary.The parasitic capacitances of the switches do not depend on voltage and are considered to be constant.All elements of circuit are lossless.The capacitor Ca is large enough.The dead time between the conduction interval is negligible.In steady state,zero volt-second inte
6、gral across the transformer primary winding,so Vca=Vin*D then the voltage transfer ratio of converter could be derived from volt balance of output choke Lo:Vo=Vin*D*(1-D)*(N1+N2)where N1=Ns1/Np,N2=Ns2/Np,AHB steady-state analysis(2),10,AHB,LLC(contiguous sine shaped hypothesis),AHB steady-state anal
7、ysis(3),Based on above analysis,comparing to LLC,we can take its advantage that smaller current stress at input&output side,especially to output capacitor,and simple circuit to implement synchronous rectification,take into account the more uneven voltage stress of output rectifier AHB is a good choi
8、ce for low output voltage and high output current application.,11,12,L6591:HB ZVS PWM Primary Controller,t,Typical Applications High Power Adapters/Chargers 90W ATX Desktop PCs(80+,85+initiative)Telecom SMPS Audio Applications Printers,L6591:NEW High Performance PWM Controller,L6591:NEW High Perform
9、ance PWM Controller,13,L6591:MOSFET DRIVERS,14,L6591:NEW High Performance PWM Controller,L6591:HIGH VOLTAGE START-UP&Vcc,15,ICHARGE=0.85 mA Typ.MINIMUM START VOLTAGE:80V Typ.HV GENERATOR RESTART VOLTAGE:5V/13V(DIS TRIPPING)VCC_ON/OFF:14V/10.5V TypADAPTIVE UVLO:2V SHIFTVcc CLAMP:25V,L6591:NEW High Pe
10、rformance PWM Controller,16,MINIMUM DEAD-TIME:200nSCF TYPICAL VALUE:100 1000 PFPAY ATTENTION TO PCB LAYOUT OF OSCILLATOR COMPONENTSUP TO 500KHz OPER.FREQ,L6591:OSCILLATOR,L6591:NEW High Performance PWM Controller,17,SOFT START,SOFT START IS INVOKED AT START-UP OR VCOMP=HIGH TEMPORARY OVERLOAD DELAY
11、PROGRAMMABLE BY USERCONNECTING A SMALL SIGNAL DIODE TO PIN#6(VREF)A LATCH OR AUTORESTART MODE IN CASE OF OVERLOAD CAN BE OBTAINED,L6591:NEW High Performance PWM Controller,18,OPEN-DRAIN PIN DEDICATED TO ON/OFF CONTROL OF PFC CONTROLLERUSED DURING BURST MODE OPERATION FOR MINIMIZING PFC LOSSES OR FOR
12、 PROTECTION PURPOSEACTIVATED(LOW)IF DIS4.5 V,ISEN1.5 V,SS5 V and COMP1.75VIF FUNCTION IS NOT USED LEAVE PIN OPEN,I/F WITH A GENERIC PFC CONTROLLER,EASY I/F WITH DAP005 PFC CONTROLLER,L6591:PFC_STOP FUNCTION,L6591:NEW High Performance PWM Controller,19,20,AHB Architecture with Synchronous Rectificati
13、on,AHB topology key features,21,CONTROLPWM fixed frequency(Dmax=50%)Dead time between HG and LG to allow ZVSHALF BRIDGEZVS operation:Soft Switching-No switching losses turn-onSECONDARY SIDEBalanced or unbalanced(Ns1Ns2)transformerOutput inductor neededCan be coupled for multiple outputsTRANSFORMERUn
14、balanced transformer:no need of high Llk to obtain ZVS,22,90W-12V/7.5A Adapter with PFC using L6591+L6563(1),23,115Vac,230Vac,90W-12V/7.5A Adapter with PFC using L6591+L6563(2),24,90W-12V/7.5A Adapter with PFC using L6591+L6563(3),Detailed ZVS switching at full load,Detailed ZVS switching at half lo
15、ad,Secondary side Key waveforms at full load,ZVS behavior the most critical transition is the one between LVG turn-off and HVG turn-on.In fact it is visible that the current available to move the half-bridge point is less with respect to the other transitionThe ZVS condition is harder to meet as the
16、 load increases,so full load is the worst condition to have for a correct ZVS operation,25,SAMPLES:AVAILABLE NOW(PRODUCTION PHASE)DATASHEETs:AVAILABLE UPON REQUESTDEMO BOARDS:EVL6591-90WADP12V/90W AC-DC ADAPTER WITH PFC USING L6563+L6591 EVL6591-400WATX(IN PROGRESS)12V and 5V outputs 400W ATX,85+COM
17、PLIANT,based on L6591 ZVS AHB and L6563 PFC,L6591:Promotional Tools,Power MOSFETs basics,RDS(on):the weight of each single contribution change with the BVDSS,confidential,HV Power MOSFETs Roadmap,MDmesh V series shows more than 35%RDS(on)improvement vs.MDmesh II series and extremely low FOM RDS(on)*
18、Qg allowing excellent conduction and switching performances,MDmesh V:Best on-state resistance,-Older competitor technology:VDSS 600 V,-Best competition:VDSS 600 V,Tj=25 C,MDmesh V:Product Family Availability,MDmesh V:WW best RDS(on)*Area,Coming up next:550V devices in the most popular packages.,31,M
19、Dmesh II Products Range enlargement,32,MDmesh II Products Range enlargement,STW55NM60ND Source Drain Diode parameters:Qrr=1.6uCTrr=200nsIrm=16A,STW55NM60ND vs STW55NM60N:Diode reverse recovery,Reduced carrier lifetime decreases the amount of stored charge,drastic reduction of trr and Qrr,Indicated for ZVS bridges,STW55NM60ND vs Direct Competitor,Fast Diode MDmesh II,34,35,Thank you for your attention,
