This paper introduces a modern, transformerless buck-boost dc-dc converter. In this topology, one active switch is used.The proposed buck-boost converter voltage gain is higher compared to the conventional buck-boost converter.With a moderate duty cycle, high voltage gain can be reached. The switch's voltage stress is minimal. As a consequence, the power switch's conduction loss is relatively low to improve efficiency. The converter is simple, hence it will be easy to control the proposed converter.