1. Technique for LLC Series Resonant DC/DC Converter Low Power Group Technique for LLC Series Resonant DC/DC Converter

2. Low Power Group Contents: 1. Problems of Conventional DC/DC Converter 2. Principle of Proposed LLC-SRC 3. Experimental Verification 4. Application Examples 5. Conclusions

3. Technique for LLC Series Resonant DC/DC Converter Low Power Group S1 S2 Vin Vo Tr Cd D2 D1 Ld S1 S2 Tr Cd D2 D1 Ld S3 S4 Lr Vin Vo Forward Asymmetrical H/B Phase Shift F/B S n: 1 Vo Vin D2 D1 Ld Duty cycle Conversion efficiency Input voltage Low InputHigh Input Voltage spike di/dt iDiD Problems of Conventional PWM Converter Efficiency declines when high input Reverse recovery problem for rectifier

4. Technique for LLC Series Resonant DC/DC Converter Low Power Group Problems of Conventional Resonant Converter Large frequency variation Failure at no load Small frequency variation High circulation energy Lower circulation energy Efficiency optimized at low input Series resonant Parallel resonant LCC series parallel resonant

5. Technique for LLC Series Resonant DC/DC Converter Low Power Group Principle of LLC-SRC Ls Cs C1 S1 S2 Tr D1 D2 C2 Vin Vo Lm Proposed Half-bridge LLC Series Resonant Converter (LLC-SRC)

6. Technique for LLC Series Resonant DC/DC Converter Low Power Group Comparison with Conventional SRC 1 fsfs fmfm LLC-SRC (Lm=3~7Ls) Conventional SRC frequency Gain=OUT/IN Ls LLC-SRC IN Cs Load Lm OUT Conventional SRC Ls IN Cs Load OUT ZVS operation range: Conventional SRC: f>f s LLC-SRC: f>f m f m <f<f s ZCS for rectifiers

7. Technique for LLC Series Resonant DC/DC Converter Low Power Group Operation Waveforms : S1 S2 i Ls i Ld f m <f<f s imim ImIm v AB Ls Cs C1 S1 S2 Tr i C1 i Ls D1 D2 C2 i Ld Lm imim

8. Technique for LLC Series Resonant DC/DC Converter Low Power Group Operation Waveforms : S1 S2 i Ls i Ld f m <f<f s imim ImIm v AB Ls Cs C1 S1 S2 Tr i C1 i Ls D1 D2 C2 i Ld Lm imim

9. Technique for LLC Series Resonant DC/DC Converter Low Power Group Operation Waveforms : S1 S2 i Ls i Ld f=f s imim v AB Ls Cs C1 S1 S2 Tr i C1 i Ls D1 D2 C2 i Ld Lm

10. Technique for LLC Series Resonant DC/DC Converter Low Power Group Operation Waveforms : S1 S2 i Ls i Ld imim v AB Ls Cs C1 S1 S2 Tr i C1 i Ls D1 D2 C2 i Ld Lm f>f s

11. Technique for LLC Series Resonant DC/DC Converter Low Power Group Regulation Equation of LLC-SRC: Ls Cs nVo Vin/2 nVo Vin/2 nVo Vin/2 nVo Vin/2 R Lm f<f s f=f s f>f s

12. Technique for LLC Series Resonant DC/DC Converter Low Power Group Experimental Verification Ls Cs C1 S1 S2S2 Tr i C1 i Ls D1 D2 C2 i Lb S1, S2: IRF3710 D1& D2: 40CPQ60 Core EE32/16/9 n: 6 : 6 Cs: 1.6uF Ls: 1uH (leakage inductance) Lm: 6uH SPECIFICATIONS: INPUT: 40 V - 60 V OUTPUT: 24 V / 10 A Frequency: 75kHz Higher PARAMETER SELECTION: Test Circuit

13. Technique for LLC Series Resonant DC/DC Converter Low Power Group Driver signal of switch Vds of the switch Resonant Current Voltage of output diode Vin=40V f=94kHz < fs (125kHz) Measured operation waveforms

14. Technique for LLC Series Resonant DC/DC Converter Low Power Group Resonant Current is close to sine wave. Vin=50V f=112kHz ~ fs Measured operation waveforms

15. Technique for LLC Series Resonant DC/DC Converter Low Power Group Voltage overshot. ZCS condition was lost. Vin=60V f=133kHz > fs Measured operation waveforms

16. Technique for LLC Series Resonant DC/DC Converter Low Power Group Efficiency of test circuit : Vin = 40 ~ 60V, Vo = 24V @24V/10A Output

17. Technique for LLC Series Resonant DC/DC Converter Low Power Group Application for holdup time requirement Ls Cs C1 S1 S2 C3 Tr D1 D2 1kW, 400V input and 54V/20A output sever power S1,S2: IRFP37N50A D1,D2: 30CPQ150 Tr: EE42/20 – 3C85

18. Technique for LLC Series Resonant DC/DC Converter Low Power Group Input Range LsCsLmn A300~400V20uH88uF120uH20:5 B200~400V20uH108uH50uH17:5 Parameters of Two Designs:

19. Technique for LLC Series Resonant DC/DC Converter Low Power Group Tested Efficiency (1kW, 54V/20A) A: 300V~400V input design B: 200V~400V input design

20. Technique for LLC Series Resonant DC/DC Converter Low Power Group Frequency Variation Rang: @54V output

21. Technique for LLC Series Resonant DC/DC Converter Low Power Group 1kW, 400V input and 54V/20A output Transformer Primary switches Output Rectifier Output Capacitors

22. Technique for LLC Series Resonant DC/DC Converter Low Power Group Application for high power and high input voltage Full-Bridge Structure High input voltage

23. Technique for LLC Series Resonant DC/DC Converter Low Power Group Conclusions: Features of LLC-SRC: Simple and flexible structure ZVS for switches and ZCS for rectifiers Conversion efficiency optimized at high input Applications: High input voltage Higher output voltage Holdup time requirement