Abstract— DC-DC converters are electronic circuit elements that are frequently used to change the direct current (DC) level. This paper presents a hybrid buck-boost converter – with constant modulation index – that can change a DC voltage at two directions compared to the conventional buck-boost DC-DC converters. First, the circuit structure and operation are given. Then, the performance of the proposed converter is tested on resistive and inductive loads, and compared with that of conventional buck-boost converters. The obtained results demonstrate the effectiveness of the proposed converter. They unveil that the proposed converter – compared to the conventional buck-boost converters – produces a higher and flexible rate of conversion without changing the operating ratio of the switches. Moreover, the proposed converter is able to change the voltage on double way on load for a constant operating ratio, while the traditional converters provide a one-way conversion.