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This paper proposes a bidirectional low-voltage DC-to-DC converter for advanced fuel-cell electric vehicles (FCEVs). The proposed converter consists of two parallel-operated power converters driving the low-voltage output stage to reduce the size of the filter. Two power converters are internally connected in series with an isolated LLC resonant converter and a non-isolated buck/boost converter to achieve high efficiency in both directions while ensuring very wide input and output voltage ranges. The LLC resonant converter generates an input from a 12 V low-voltage battery to a non-isolated converter when starting an FCEV. Once the fuel-cell stack is activated, the power flow reverses, and the non-isolated buck/boost converter regulates the input voltage for the LLC resonant converter from the power generated in the fuel-cell stack. To validate the performance of the proposed converter, a prototype converter is designed, built, and tested with 2.0 kW in the forward powering mode, 4.5 kW in the reverse powering mode, a 260–430 VDC input, and a 10–15 VDC output. Experimental results demonstrate that the proposed converter achieves a power conversion efficiency of over 95.5% in both the forward and reverse powering modes, while ensuring stable bidirectional operation and much lower current and voltage ripples.