A fixed frequency controlled half-bridge type resonant converter by reusing transformer is proposed. The transformer of this converter can work alternately in resonant mode and forward mode which improves core utilization. The output voltage can be regulated by adjusting the duty cycle of the forward circuit and the resonant circuit can still operate with a fixed switching frequency. lt is beneficial to design the magnetic components and the filter circuit with fixed frequency pulse width modulation (PWM) control which has more simple and reliable control features compared with frequency modulation. In addition, the resonant circuit achieves the benefits of zero-voltage-switching(ZVS) turn on and zero-current-switching (ZCS) turn off. ZCS turn off for the secondary diode can still be fulfilled and an additional reset circuit is not required for the transformer because of alternative operation mode. The operational principle and circuit topology of the proposed converter is analyzed. Superiority is verified by a 62～82 V input and 24 V/2. 5 A output prototype compared with traditional half bridge LLC resonant converter.%提出了一种定频调节的半桥式变压器复用型谐振变换器.该变换器使变压器交替工作于谐振模式与正激模式,提高了磁芯利用率.采用定频脉宽调制(PWM)控制方式,通过改变正激电路的占空比来实现输出电压调节.与传统调频控制方式相比,定频PWM控制更为简单可靠,有利于磁性元器件和滤波电路的设计.此外,该变换器的谐振电路部分具有开关管零电压开关(ZVS)开通和零电流开关(ZCS)关断,以及次级二极管ZCS关断等优点,且谐振电路与正激电路交替工作即可实现变压器复位,无需额外的复位电路,结构简单.详细分析了所提变换器的电路拓扑结构与工作原理,并搭建62～82 V输入,24 V/2.5 A输出的实验样机,最后与传统半桥LLC谐振变换器进行性能比较,实验结果验证了理论分析的正确性.
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