Small-Signal and Large-Signal Analysis of the Two-Transformer Asymmetrical Half-Bridge Converter Operating in Continuous Conduction Mode

The asymmetrical half-bridge converter (AHBC) has many advantages over other PWM converters. The possibility of soft switching in primary switches and reduced switching losses in the secondary ones implies that the AHBC is a suitable topology for many high-performance applications. Besides, the lack of dead times, except those needed for achieving soft switching, is a very interesting feature to implement self-driven synchronous rectification. Moreover, the small size of its output filter is also a remarkable advantage in some fields (e.g., LED lighting). On the other hand, it also has some disadvantages. One of them is the short range of the duty cycle (lower than 0.5) and the other one is the difficult regulation due to a complex transfer function. The two-transformer AHBC (TTAHBC) solves the first problem as it enlarges the duty cycle range making its top limit higher than 0.5. Nevertheless, the regulation of this converter is still very complex and, besides, the transfer functions of the standard AHBC are not valid for the TTAHBC. As a consequence, the small- and large-signal models have yet to be studied. In this paper, the complete small-signal and large-signal analysis of the TTAHBC operating in continuous conduction mode is provided. The large-signal and small-signal models are developed taking into account the main parasitic components that affect the transient response of this converter. The validation of the resulting model is carried out by means of both, simulation and experimental results. The prototype is a 60-W TTAHBC designed for an input voltage of 400 V and an output voltage of 48 V.