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Till now, various types of current fed converters utilizing multiple devices have been developed. These converters exhibit good performance in high power step-up applications. However, they have a common limitation that the duty cycle be larger than 0.5 to maintain a conducting path for the boost inductor current. Although an auxiliary circuit that is magnetically coupled to a boost inductor can be a solution for below 0.5 duty cycle, it increases size and complexity. To relieve this problem, a new two transformer current-fed (TTCF) converter, which can be operated along a wide duty cycle with a simple structure, is proposed in this paper. In the TTCF converter, the magnetizing inductor of the transformer acts as a boost inductor, thus no additional boost inductor is needed. Moreover, only one auxiliary diode is employed for below 0.5 duty cycle operation. Therefore, the proposed converter can be promising for high power step-up applications with a simple structure.

In designing a LLC resonant converter, the ratio of magnetizing inductance (LM) to resonant inductance (LM), the inductor ratio (K) is usually considered. In high power density adapter, both adapter size and efficiency are important factors. considering the size of adapter, high K design can be more attractive. But, wide frequency variation of high K design results in design difficulty of magnetic elements and decrease in efficiency. To solve these drawbacks, an adaptive link voltage variation (ALVV) control is proposed. With the proposed control method, the LLC resonant converter can be operated at the resonant frequency despite the output voltage variation. The control strategy and schematics are presented, and verified experimentally.

Conventional single-stage power-factor-correction (SS-PFC) AC/DC converter has a link capacitor voltage problem at high line input and low load condition. In this paper, this problem is analyzed by using voltage conversion ratio of the DC/DC conversion cell. Based on this analysis, a new SS-PFC AC/DC converter with boost PFC cell integrated with voltage-doubler rectified asymmetric half-bridge (VDRAHB) is proposed. The proposed converter features good power factor correction, low current harmonic distortions, tight output regulations and low voltage of link capacitor. An 85 W prototype was implemented to show that it meets the harmonic requirements and standards satisfactorily with nearly unity power factor and high efficiency over universal input.

A conventional active-clamp forward converter is a favorable candidate in low-to-medium power applications. However, the switches suffer from high voltage stress, i.e., sum of the input voltage and the reset capacitor voltage. Therefore, it is not suitable for high input voltage applications such as a front-end converter of which the input voltage is about 400-Vdc. To solve this problem, a new multi-level active-clamp forward converter is proposed in this paper. In the proposed converter, the voltage stresses on switches are clamped to either the input voltage or the reset capacitor voltage by simply utilizing one clamping diode and adjusting gate signals. Utilizing low-voltage rated switches, the proposed converter features high efficiency and low cost for high input voltage applications. The operational principle and design consideration of the proposed converter are presented, and verified experimentally.