Small-signal analysis of the asymmetrical half-bridge converter with two transformers

Achieving soft switching in primary switches and reducing switching losses in the secondary ones make of the Asymmetrical Half Bridge (AHB) 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 for self-driven synchronous rectification. 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 is the difficult regulation due to a complex transfer function. The AHB with Two Transformers (AHBTT) solves the first problem. Nevertheless, the regulation of this converter is still very complex and, besides, the transfer functions of the standard AHB are not valid for the AHBTT. In this paper, the complete small-signal analysis of the AHBTT operating in Continuous Conduction Mode is provided. The validation of the resulting model is carried out by means of experimental results. The prototype is a 60-W AHBTT designed for an input voltage of 400 V and an output voltage of 48 V.