LLC谐振分析.pdf

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Simplified Analysis and Design of Series- resonant LLC Half-bridge Converters resonant LLC Half-bridge Converters MLD GROUP INDUSTRIAL & POWER CONVERSION DIVISION Off-line SMPS BU Application Lab Claudio Adragna Application & Architecture Manager, System & Application Expert I&PC Div. - Off-line SMPS Appl. Lab

Presentation Outline • LLC series-resonant Half-bridge: operation and significant waveforms • Simplified model (FHA approach) • 300W design example • 300W design example I&PC Div. - Off-line SMPS Appl. Lab

Series-resonant LLC Half-Bridge Topology and features Vin e g d i r b - f l a H r e v i r D Q1 Cr Ls Q2 Lp LLC tank circuit LLC tank circuit Preferably integrated into a single magnetic structure 3 reactive elements, 2 resonant frequencies fr1 fr2 2 p 2 p 1 Ls Cr 1 Lp+ Ls ( ) Cr > f r1 f r2 Center-tapped output with full-wave rectification (low voltage and high current) Vout Vout Single-ended output with bridge rectifiication (high voltage and low current) Multi-resonant LLC tank circuit Variable frequency control Fixed 50% duty cycle for Q1 & Q2 Dead-time between LG and HG to allow MOSFET’s ZVS @ turn-on allow MOSFET’s ZVS @ turn-on fsw » fr, sinusoidal waveforms: low turn-off losses, low EMI Equal voltage & current stress for secondary rectifiers; ZCS, then no recovery losses No output choke; cost saving Integrated magnetics: both L’s can be realized with the transformer. High efficiency: >96% achievable I&PC Div. - Off-line SMPS Appl. Lab

LLC Resonant Half-bridge Waveforms at resonance (fsw = fr1) Dead-time Tank circuit current is sinusoidal Magnetizing current is triangular CCM operation Output current I&PC Div. - Off-line SMPS Appl. Lab Gate-drive signals HB mid-point Voltage Resonant cap voltage Transformer currents Diode voltages Diode currents

LLC Resonant Half-bridge Switching details at resonance (fsw = fr1) Dead-time ZVS ! Tank circuit current >0 Magnetizing current V(D1)<0 I(D1)=0 ZCS ! I&PC Div. - Off-line SMPS Appl. Lab Gate-drive signals HB mid-point Voltage Resonant cap voltage Transformer currents Diode voltages Diode currents

LLC Resonant Half-bridge Operating Sequence at resonance (Phase 1/6) 1/6 Q1 OFF Q2 ON Q1 ON Q2 OFF Q1 OFF Q2 ON Vin Q1 Q2 Coss1 Ls Cr Coss2 Lp Lp n:1:1 D1 Cout Vout D2 Q1 is OFF, Q2 is ON D1 is OFF, D2 is ON; V(D1)=-2·Vout Lp is dynamically shorted: V(Lp) =-n·Vout. Cr resonates with Ls, fr1 appears Output energy comes from Cr and Ls Phase ends when Q2 is switched off I&PC Div. - Off-line SMPS Appl. Lab

LLC Resonant Half-bridge Operating Sequence at resonance (Phase 2/6) 2/6 Q1 OFF Q2 ON Q1 ON Q2 OFF Q1 OFF Q2 ON Vin Q1 Q2 Coss1 Ls Cr Coss2 Lp Lp n:1:1 D1 Cout Vout D2 Q1 and Q2 are OFF (dead-time) D1 and D2 are OFF; V(D1)=V(D2)=0; transformer’s secondary is open I(Ls+Lp) charges COSS2 and discharges COSS1, until V(COSS2)=Vin; Q1’s body diode starts conducting, energy goes back to Vin I(D2) is exactly zero at Q2 switch off Phase ends when Q1 is switched on I&PC Div. - Off-line SMPS Appl. Lab

LLC Resonant Half-bridge Operating Sequence at resonance (Phase 3/6) 3/6 Q1 OFF Q2 ON Q1 ON Q2 OFF Q1 OFF Q2 ON Vin Q1 Q2 Coss1 Ls Cr Coss2 Lp Lp n:1:1 D1 Cout Vout D2 Q1 is ON, Q2 is OFF D1 is ON, D2 is OFF; V(D2)=-2·Vout Lp is dynamically shorted: V(Lp) = n·Vout. Cr resonates with Ls, fr1 appears I(Ls) flows through Q1’s RDS(on) back to Vin (Q1 is working in the 3rd quadrant) Phase ends when I(Ls)=0 I&PC Div. - Off-line SMPS Appl. Lab

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