LLC的原理与应用

Vin
n:1:1 D1 Cout
Coss2 Lp
Q2
Vout
D2
Q1 is OFF, Q2 is ON D1 is OFF, D2 is ON Lp is dynamically shorte Output energy comes from Cr and Ls Phase ends when I(Ls)=0
•Q2先流过反向电流，再流正向电流， 工作模式与Q1相同
Product Department/ Advance team
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LLC拓扑形式
※ 分体电容 ※ 分体电容&绕组 ※ 原边全桥 ※ 副边全桥 ※ 多路输出
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LLC的工作模式分析
※ 谐振区、Buck区、Boost区
❖ 波形 ❖ 分段介绍 ❖ 特点 ❖ 等效电路 ❖ 总结
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Operating Sequence at resonance (Phase 1/6)
Vg Q1 OFF Q2 ON
Vc
I(lp) I(ls)
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LLC简介-10
※ 工作波形（谐振区）
流过Lr的电流
•Q1导通时，Lr、Lm电流上升；
•Q1关断时，Lr电流恰好等于Lm电 流过Lm的电流 流，D1 ZCS；
Q1电流 D1电流
•死区时间内Im对Q1的结电容充电， 对Q2的结电容放电；
•Q2的体二极管会续流直到Q2被驱动 导通,Q2 ZVS开通。
to Vout
Phase ends when Q1 is switched
off
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Operating Sequence at resonance (Phase3/6)
Vg Q1 OFF Q2 ON
Vc
I(lp) I(ls)
Imos
• 需要限制最低频率
❖ 空载时，增益无法降得更低
• 用跳周期解决
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LLC简介-7
※ MOSFET ZVS的实现
❖ 在死区时间内需要有足够的电流抽取MOSFET结电 容上的能量；
❖ 死区时间结束时，电流不能过零； ❖ 即使在无负载的情况下也能零电压开关；
Vin
n:1:1 D1 Cout
Coss2 Lp
Q2
Vout
D2
Q1 and Q2 are OFF (dead-time) D1 and D2 are OFF transformer’s secondary is open I(Ls+Lp) charges COSS2 and discharges COSS1, until V(COSS2)=Vin; Phase ends when Q1 is switched on
Product Department/ Advance team
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Operating Sequence at resonance (Phase 4/6)
Vg Q1 OFF Q2 ON
Vc
I(lp) I(ls)
Imos
Id
Q1 ON Q2 OFF
4/6
Q1 OFF Q2 ON
Q1 Coss1
Cr Ls
※ λ的含义
❖ 谐振电感与励磁电感的比值：Lr/Lm ❖ λ越大，调节能力越强，增益曲线越陡峭 ❖ λ越大，增益范围越大
Product Department/ Advance team
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9
LLC简介-8
※ λ不同时增益曲线的变化（图中k＝1/ λ ）
Product Department/ Advance team
Q1 is OFF, Q2 is ON D1 is OFF, D2 is ON Lp is dynamically shorted Cr resonates with Ls, fr1 appears Output energy comes from Cr and Ls Phase ends when Q2 is switched off
Reverse Recovery
Y Y
Y
Bridge rectifier FB/HB
Y
Center-tap LLC
N
Bridge rectifier LLC
N
Voltage stress for Diode >4Vo >4Vo
>4Vo
2Vo 2Vo Vo
DC gain
M 2M
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Operating Sequence at resonance (Phase 6/6)
Vg
6/6
Q1 OFF Q2 ON
Vc
Q1 ON Q2 OFF
I(lp) I(ls)
Imos
Id
Q1 OFF Q2 ON
Q1 Coss1
Cr Ls
Cr Ls
Vin
n:1:1 D1 Cout
Coss2 Lp
Q2
Vout
D2
Q1 is OFF, Q2 is ON D1 is OFF, D2 is ON Lp is dynamically shorted Output energy comes from Cr and Ls Phase ends when Q2 is switched off
LLC的原理与应用
Index
❖ LLC简介 ❖ 工作模式分析 ❖ LLC的特点 ❖ 3K LLC Demo Board介绍 ❖ 设计步骤 ❖ 与Push-pull的对比 ❖ 损耗分析 ❖ 效率优化
Product Department/ Advance team
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LLC简介-1
※ LLC：三元件谐振半桥/全桥
❖ 线路图
❖ 变频工作，电压反馈
❖ 50％Duty驱动
❖ 副边不需电感
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3
LLC简介-2
※ SRC电路与增益曲线
❖ SRC电路的直流增益总是小于1
❖ 轻载调整率，高的谐振能量，以及高输入电压时的较 大关断电流
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realize (integration)
Product Department/ Advance team
5
5
LLC简介-4
※ 工作在谐振频率时等效电路分析
❖ 副边电阻折算到原边 ❖ Lm被输出电压箝位 ❖ 电流滞后于电压 ❖ 电容直流偏压Vin-nVo=Vin/2
❖ FHA approach (first harmonic approximation)
Imos
Id
1/6
Q1 ON Q2 OFF
Q1 OFF Q2 ON
Q1 Coss1
Cr Ls
Vin
n:1:1 D1 Cout
Coss2 Lp
Q2
Vout
D2
Q1 is ON, Q2 is OFF
D1 is ON, D2 is OFF
Lp is dynamically shorted.
Cr resonates with Ls, fr1 appears I(Ls) flows through Q1’s RDS(on) back to Vin (Q1 is working in the 3rd
Product Department/ Advance team
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Operating Sequence at resonance (Phase 5/6)
Vg 5/6
Q1 OFF Q2 ON Vc
I(lp) I(ls)
Imos
Id
Q1 ON Q2 OFF
Q1 OFF Q2 ON
Q1 Coss1
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LLC简介-9
※ Diode ZCS的实现
❖ 能量传递过程 ❖ Spike & Rating ❖ 损耗 ❖ 反向恢复
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11
LLC简介-9
※ 副边Diode耐压
Topology\Items Flyback Forward
Center-tap FB/HB
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Waveforms at resonance (fsw = fr1)
Vg Tank circuit current is sinusoidal
Dead-time
Gate-drive signals
Magnetizing current is triangular
Q1 OFF Q2 ON
Q1 Coss1
Cr Ls
Vin
n:1:1 D1 Cout
Coss2 Lp
Q2
Vout
D2
D1 is ON, D2 is OFF
Lp is dynamically shorted
Cr resonates wБайду номын сангаасth Ls, fr1 appears Energy is taken from Vin and goes
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Operating Sequence above resonance (Phase 2/6)
Vg
2/6
Q1 OFF Q2 ON
Vc
Q1 ON Q2 OFF
I(lp) I(ls)
Imos
Id
Q1 OFF Q2 ON
Q1 Coss1
HB mid-point Voltage
Resonant cap voltage
Transformer currents
CCM operation
Output current
Diode voltages
Diode currents
Product Department/ Advance team
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22
Id
3/6
Q1 ON Q2 OFF
Q1 OFF Q2 ON
Q1 Coss1
Cr Ls
Vin
n:1:1 D1 Cout
Coss2 Lp
Q2
Vout
D2
Q1 and Q2 are OFF (dead-time) D1 and D2 are OFF transformer’s secondary is open I(Ls+Lp) charges COSS1 and discharges COSS2, until V(COSS2)=0 Phase ends when Q2 is switched on
quadrant)
Phase ends when I(Ls)=0
Product Department/ Advance team
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Operating Sequence at resonance (Phase 2/6)
Vg Q1 OFF Q2 ON
Vc
I(lp) I(ls)
Imos
Id
2/6
Q1 ON Q2 OFF
Product Department/ Advance team
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6
LLC简介-5
※ 一些公式
❖ 存在2个谐振频率Fr1和Fr2
fr1 1/(2 LrCr )
fn f / fr1 ❖ 其余归一化参数
fr2 1/(2 (Lr Lm)Cr )
Zr Lr / Cr Q Zr / Re
Re 8a2Rout / 2
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LLC简介-3
※ Advantages of adding Lm
❖ Current Lag ❖ ZVS ❖ Boost ❖ Wide range ❖ Best use of resonant point ❖ High Efficiency
※ Drawbacks
❖ Increasing resonant tank circle current ❖ Additional magnetic component, but easy to
Lr / Lm M 2a Vout /Vin a n Vin / 2Vout
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LLC简介-6
※ 增益特性
Boost区
谐振区
Buck区
❖ 在谐振点Fr1，在所有负载条件下增益是固定的 ❖ 峰值增益在Fr2和Fr1之间 ❖ 存在ZCS区和ZVS区
Cr Ls
Vin
n:1:1 D1 Cout
Coss2 Lp
Q2
Vout
D2
Q1 and Q2 are OFF (dead-time) D1 and D2 are OFF transformer’s secondary is open V(D2) reverses as I(D2) goes to zero Phase ends when Q1 is switched on
Operating Sequence above resonance (Phase1/6)
Vg
1/6
Q1 OFF Q2 ON
Vc
Q1 ON Q2 OFF
I(lp) I(ls)
Imos
Id
Q1 OFF Q2 ON
Q1 Coss1
Cr Ls
Vin
n:1:1 D1 Cout
Coss2 Lp
Q2
Vout
D2