However, whereas the LLC resonant converter works
fine for high voltage applications, its applicability for low
voltage and high power applications, such as server or
telecom power supplies, requires an enhancement of the
first order capacitive output filter. Because the output of
the LLC resonant circuit injects a sine wave of current into
the rectifier and output filter capacitor, there will be a
significant ac component at double switching frequency
superimposed on the dc output voltage due to the p.d. at
the ESR of the filter capacitor. As a common workaround,
adding an additional second order filter to the output may
eliminate the ac component of the output voltage but
efficiency and power density will suffer.