###### Abstract
Figure 1: Circuit diagram: (**a**) buck; (**b**) boost; (**c**) buck-boost. Figure 2: Circuit diagram of the conventional TSBB converter. New circuits are suggested in [5; 6] to prevent such a decrease in power efficiency. They demonstrated that power efficiency can be increased compared to those of the conventional TSBB converter by reducing the number of switching and conduction semiconductors in the current path. However, there is a trade-off between the number of semiconductors in the current path and the voltage stress. Therefore, in the new circuits of [5; 6], the voltage stress of the semiconductors in the boost and buck-boost topologies increases, and it will lower power efficiency above a specific power range. The experimental results confirm the efficiency based on changes in the output current; however, it is difficult to find the optimal power range according to the changes in the input voltage and duty that influence the voltage stress of the semiconductors. To solve this problem, this study proposed a new type of TSBB converter for improving power efficiency and analyzing the optimal power range that can improve power efficiency. The proposed TSBB converter can increase power efficiency in buck and buck-boost topologies by reducing conduction loss caused by the diode in the switch-off section while using the same number of semiconductors as that of the conventional TSBB converter. Moreover, the optimal power range of each topology is analyzed by evaluating the effect of an increase in the voltage stress of semiconductors. The contributions of this study are as follows:  
* We investigated related research about the TSBB converter and proposed a modified design of the TSBB converter to improve power efficiency using fewer conduction components in the current path. * We presented the optimal power range according to the buck, boost, and buck-boost topologies in CV and CC modes, and, in particular, divided into step-up/step-down sections in the buck-boost topology. * We analyzed the power dissipation of the three topologies and explained why the CC mode of the buck-boost step-up is less efficient than conventional converters over a certain power range through analytic and experimental diode stress analysis. The remainder of this paper is organized as follows. Section 2 describes the operation principle of the proposed TSBB converter. In Section 3, the power loss is compared between the proposed TSBB converter and the conventional TSBB converter in each topology by analyzing the switching and conduction losses. The experiment results are described in Section 4, and, finally, the conclusions are presented in Section 5. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Topology**} & \multirow{2}{*}{**Period**} & \multicolumn{4}{c}{**Component**} \\ \cline{3-6}  & & \(\mathbf{S_{1}}\) & \(\mathbf{S_{2}}\) & \(\mathbf{D_{1}}\) & \(\mathbf{D_{2}}\) \\ \hline \multirow{2}{*}{Buck} & Switch ON & ON & ON & \multirow{2}{*}{Always OFF} & OFF & \multirow{2}{*}{Always ON} \\  & Switch OFF & OFF & & & ON & \\ \hline \multirow{2}{*}{Boost} & Switch ON & \multirow{2}{*}{Always ON} & ON & \multirow{2}{*}{Always OFF} & OFF \\  & Switch OFF & & & OFF & ON & ON \\ \hline \multirow{2}{*}{Buck-Boost} & Switch ON & ON & ON & ON & OFF & OFF \\  & Switch OFF & OFF & OFF & ON & ON \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Switch operation of the conventional TSBB converter.