(A) high-efficiency asymmetrical half-bridge converter with linear voltage gain

Abstract

A conventional asymmetrical half-bridge (AHB) converter is one of the widely used topologies in low to medium power applications. However, when it is designed in a wide input voltage range, it operates with a low duty ratio at nominal input voltage. In addition, it has disadvantages such as a non-linear voltage gain, a DC-offset current in the transformer, and an unbalanced average current of diode due to asymmetrical operation. To solve these disadvantages, an AHB converter with linear voltage gain is proposed. The proposed converter has a structure in which a capacitor is added as a voltage source to obtain a symmetrical operation by extending the commutation period. Therefore, it has a narrow range of operating duty ratio and a zero DC-offset current in the transformer. Due to zero DC-offset current, it has a small size transformer and improved ZVS conditions of the primary side switches. In addition, it has a low primary RMS current and a balanced average current of the diode. Consequently, the proposed converter has high efficiency under entire load conditions. A 300-400 V input and 48 V/400 W output prototype is tested to verify the feasibility of the proposed converter.