High-Efficiency Asymmetrical Half-Bridge Converter With Linear Voltage Gain

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 dc offset of magnetizing current, an unbalanced average current of the diode, and a nonlinear voltage gain 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 of magnetizing current. Due to the zero dc offset of magnetizing current, it has a small size transformer and improved zero-voltage switching 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 the 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.