Isolated, Zero-Voltage-Switching (ZVS) dc-dc converter topologies represent attractive solutions in the continuous run towards higher switching frequencies, allowing more compact power supplies. Among them, the Asymmetrical Half-Bridge Flyback Converter (AHBFC) represents an interesting option, featuring simple duty-cycle control at constant switching frequency, as opposed to the popular LLC converter. The majority of papers dealing with this topology consider an approximated voltage gain similar to that of an isolated Buck converter operating in CCM, i.e. proportional to the duty-cycle, and, practically, load independent. On the contrary, the true voltage gain is non monotonic at high duty-cycle values. Anytime the converter is designed for a resonant operation, as is advisable to eliminate any reverse recovery problem of the rectifier diode, the voltage gain not only increases, but becomes a function of the switching frequency. This paper investigates the converter's voltage gain in detail, deriving a theoretical framework capable of capturing its real behavior and dependencies. The proposed analytical model has been verified through simulations as well as experimental measurements taken on a 160 W prototype working at 400 kHz.
Extended Analysis of The Asymmetrical Half-Bridge Flyback Converter
Spiazzi G.
;Buso S.
2020
Abstract
Isolated, Zero-Voltage-Switching (ZVS) dc-dc converter topologies represent attractive solutions in the continuous run towards higher switching frequencies, allowing more compact power supplies. Among them, the Asymmetrical Half-Bridge Flyback Converter (AHBFC) represents an interesting option, featuring simple duty-cycle control at constant switching frequency, as opposed to the popular LLC converter. The majority of papers dealing with this topology consider an approximated voltage gain similar to that of an isolated Buck converter operating in CCM, i.e. proportional to the duty-cycle, and, practically, load independent. On the contrary, the true voltage gain is non monotonic at high duty-cycle values. Anytime the converter is designed for a resonant operation, as is advisable to eliminate any reverse recovery problem of the rectifier diode, the voltage gain not only increases, but becomes a function of the switching frequency. This paper investigates the converter's voltage gain in detail, deriving a theoretical framework capable of capturing its real behavior and dependencies. The proposed analytical model has been verified through simulations as well as experimental measurements taken on a 160 W prototype working at 400 kHz.
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