It has been a common practice to charge batteries with pure a DC current. Thus, chargers require a large electrolytic capacitor bank to suppress the low frequency components from entering into the battery. However, according to recent studies a pure DC charging current is not a mandatory requirement for high battery-lifetime and efficiency. This allows to omit the bulky and fast-aging electrolytic capacitors and its input PFC-rectifier. This paper presents the concept of a single-stage battery charger based on a LLC resonant converter. Component stresses are reduced by utilizing a minimized input voltage range. The LLC resonant tank is designed using an improved time-domain-analysis which considers major losses. This facilitates a higher degree of accuracy in determining the range and the modes of operation, which in turn helps in developing an optimized design. An experimental lab prototype achieves a peak efficiency of 97.0% and a calculated PFC-efficiency of 96.6%.
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