llc电路基本原理分析及公式推导.pdf

I ZCS, then no recovery losses ?No output choke; cost saving ?Integrated magnetics: both L’s can be realized with the transformer. ?High efficiency: >96% achievableLLC tank circuitLsLpPreferably integrated into a single magnetic structureVoutCenter-tapped output with full- wave rectification (low voltage and high current)Single-ended output with bridge rectifiication (high voltage and low current)fr112 π⋅Ls Cr⋅⋅fr212 π⋅LsLp+() Cr⋅⋅3 reactive elements, 2 resonant frequenciesfr1fr2>Q1Q2I?Q, the quality factor, is related to load: Q=0 means Re=∞(open load), Q=∞means Re=0 (short circuit); one can think of Q as proportional to IoutI current lags voltage, so whenvS=0, iSis still >0: ZVS?Below fr2(xQm(x) it is capacitive ⇒ ZCS.?In general, the ZVS-ZCS borderline isdefined by Im(Zin(jω))=0?For x> |Zin(jω)| is concordant withthe load: the lower the load the lowerthe input current?For x0 have maximathat fall in the capacitive region.?Above resonance it is always M0.5 only below resonance?ZVS below resonance at a givenfrequency occurs if M> Mmin>0.5; ifM> Mmin>0.5 is fixed, it occurs ifQ>Qm.I each contributes for half cycle?Under no-load, rectifiers have low reverse voltage applied, Cj increases.?The parasitic tank has a high-frequency resonance that makes M increase at some point: feedback becomes positive, system loses control?Cure: minimize Cp and Cj, limit max fsw. 0.111000.511.522.53MM x kC,0,p,()MM x kC,0.05,p,()MM x kC,0.1,p,()MM x kC,0.2,p,()xqx41k λ2⋅λ λ λ λ =0.08VinVoutaM⋅=xMd d0regionI 450 V is the OVP theshold of the PFC pre-regulator320 to 450 VdcVin rangeELECTRICAL SPECIFICATIONI ZVS at light load difficult to achieve ?Diodes: high voltage stress ⇒ higher VF⇒ higher conduction losses; recovery losses ?Holdup requirements worsen efficiency at nominal input voltage?MOSFETs: low turn-off losses; ZVS at light load easy to achieve ?Diodes: low voltage stress (2·Vout) ⇒ lower VF⇒ low conduction losses; ZCS ⇒ no recovery losses ?Operation can be optimized at nominal input voltage0204060801001209292.59393.59494.59595.596Output Power (W)Efficiency (%)AHBLLC280300320340360380400420919293949596Input Voltage (V)Efficiency (%)AHBLLCNominal voltageAHB optimized for 400 V。