MHz High Efficiency High Power Density LLC Resonant Converters with SR (2005)

Performance per watt requirements are driving higher energy efficiency metrics in server and telecom equipment designs for both idle and active power states. Hence there is a large incentive to increase the overall efficiency of power delivery systems. Meanwhile, with the development of power conversion technology, power density becomes another challenge for DC/DC converters. On the other hand, to meet the holdup time requirement, bulky capacitors have to be used to provide the energy during holdup time, which is affected by DC/DC stage operation input voltage range. Apparently, wide operation range DC/DC stage can reduce the holdup time capacitance. Therefore, the size and cost of the bulky capacitors are reduced. Higher system power density is obtained. CPES developed MHz LLC resonant converters. LLC resonant converters can achieve very high efficiency at MHz switching frequency and very wide input voltage operation range. Thus, high efficiency and high power density can be accomplished. 

                                              Capacitance vs. Vin
                                   1MHz LLC resonant converter with SR
                             95.9% efficiency and 96W/in3 power density

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