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A step-up converter with tapped inductor is analyzed. Compared to the classical boost converter, the structure has been slightly modified which offers the advantage of reduced voltage stress across the buffer capacitor and reduced current stress through a possibly needed input filter capacitor when designed properly. The common boost converter uses a simple inductor leading to the disadvantage of low duty cycles when very low step-up ratios are needed. To overcome such restrictions, a tapped inductor (autotransformer) can be used instead of the ordinary inductor thus avoiding low duty ratios. After basic analysis in continuous inductor current mode, important data for the dimensioning of the components, like the voltage and the current stress, and the equations for the component values are given. Moreover, a state space model and linearized transfer functions for the control of the converter are derived. When transformed into a bidirectional converter, it can be used for coupling two voltage links. To verify the proper function of this modified boost topology, a small test converter has been designed. Measurement results and a more precise model are given in the appendix.