A 97.3%-Peak-Efficiency Always-Dual-Path Buck-Boost Converter with Single-Mode Operation and Fast Transient Responses

In the mobile devices, a buck-boost converter is commonly used to obtain a fixed mid-3V voltage from a lithium-ion battery [1]–[6]. The conventional buck-boost converter [1] suffers from high conduction loss due to the large inductor current (IL) and the presence of two power switches connected in series with the inductor, resulting in low efficiency. Various hybrid buck-boost converters have been proposed to address this issue. In [2], a flying capacitor (CF) is introduced to eliminate a switch in the main current path, but
$\mathrm{l}_{\mathrm{L}}$
remains large, and high-voltage devices are required. Another approach, the charge pump-based converter [3], addresses voltage stress problems by connecting the inductor directly to the output capacitor in a manner similar to a buck converter. However, this design reduces IL only in boost mode, not in buck mode. The topology presented in [4] combines a dual-path buck with a dual-path boost to reduce I
L
in both modes, improving overall efficiency. Although the introduction of CF has enhanced efficiency, the mentioned topologies face challenges during mode transition.
$\ln$
[1] [3], triple-mode operation requires a complex control circuit, and in [2] [4], the discontinuous voltage across CF can cause large inrush currents during mode transition. To tackle this issue, single-mode buck-boost converters are proposed in [5]–[6]. However, in [5], I
L
is reduced only in buck mode, and both [5] and [6] encounter voltage stress problems.