LLC 电路基本原理分析及公式推导
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Simplified Analysis and Design of Series-resonant LLC Half-bridge Converters
MLD GROUP
INDUSTRIAL & POWER CONVERSION DIVISION
Off-line SMPS BU Application Lab
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
I&PC Div. - Off-line SMPS Appl. Lab
Series-resonant LLC Half-Bridge Topology and features
Q1
Cr
Ls
Vin
Q2 Lp
LLC tank circuit Preferably integrated into a single
magnetic structure
3 reactive elements, 2 resonant frequencies
1
f r1
2⋅π⋅Ls⋅Cr
f>f
r1r2Center-tapped output with full-
wave rectification
(low voltage and high current)
Vout
Vout
Single-ended output with
bridge rectifiication
(high voltage and low current)
Multiresonant LLCtank circuit
Variable frequency control
Fixed50%duty cycle for Q1&Q2
Deadtime between LGandHGto
allow MOSFET’s ZVS@turnon
fsw≈fr,sinusoidal waveforms:low
turnofflosses,low EMI
Equal voltage¤t stressfor
secondary rectifiers;ZCS,then no
recovery losses
Nooutputchoke;cost saving
Integrated magnetics:both L’scan
be realized with thetransformer.
Highefficiency:>96%achievable
fr2
1
2⋅π⋅(Ls+
Lp)⋅Cr
I&PC Div. - Off-line SMPS Appl. Lab
LLC Resonant Half-bridge
Waveforms at resonance (f sw = f r1)
Dead-time
Gate-drive
signals
HB mid-point
Voltage
Resonant cap
voltage Tank circuit current is sinusoidal Magnetizing current is triangular
Transformer
currents
Diode
voltages
Output current
CCM operation
Diode
currents
I&PC Div. - Off-line SMPS Appl. Lab
Switching details at resonance (f sw = f r1)
Dead-time Gate-drive
signals
ZVS !
HB mid-point
Voltage
Resonant cap
voltage
Tank circuit current >0
Magnetizing current Transformer currents
V(D1)<0
Diode
voltages I(D1)=0 ZCS !
Diode
currents
I&PC Div. - Off-line SMPS Appl. Lab
Operating Sequence at resonance (Phase 1/6) 1/6
Q Q Q1 ON
Q2 OFF
Q1 OFF
Q2 ON
Q1
Coss1
Vin
Ls
Cr n:1:1D1
Cout
Coss2
Vout
Lp
Q2
D2
Q1is OFF,Q2is ON
D1is OFF,D2is ON;V(D1)=2Vout
Lp is dynamically shorted:V(Lp)=nVout.
Cr resonates with Ls,f r1appears
Outputenergy comes from Cr andLs
Phase ends when Q2is switched off
I&PC Div. - Off-line SMPS Appl. Lab