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Summary: In this paper, a novel two‐stage solution based on a 1‐MHz high step‐down hybrid LLC converter is proposed for low‐power 48 V voltage regulator modules (VRM). Since the hybrid LLC DCX converter with high step‐down ability is employed as the first‐stage, lower bus voltage can be obtained with the same transformer turns, which contributes to enhancing the duty cycle and efficiency of the second‐stage multi‐phase buck converter. Thus, an overall efficiency improvement can be achieved in the proposed two‐stage system, especially in low‐power applications. To further improve efficiency and power density, a novel integrated planar transformer is adopted for the double resonant tanks of the hybrid LLC converter. To validate the analysis, a 150‐W hardware prototype of the hybrid LLC converter is constructed in the laboratory. To ensure a fair comparison with existing LLC DCX designs, the output voltage is set at 6 V. The measured efficiency results of the first‐stage demonstrate an efficiency advantage at low power output levels compared to the similar full bridge LLC designs, especially at an output of around 100 W. Under the nominal 48‐V input, the first‐stage achieves a peak efficiency of 98.5% and a full load efficiency of 94.62%. Furthermore, a 4‐phase buck converter with nominal 6‐V input and 1.6‐V output is constructed to evaluate the efficiency performance of the overall system. When the second stage operates at 500 kHz, the proposed two‐stage system achieves a peak efficiency of 93.2% at 40A load, while maintaining an efficiency of 91.2% at 65A output. The calculated efficiency of the proposed two‐stage solution exhibits higher performance compared to the majority of single‐stage schemes. [ABSTRACT FROM AUTHOR]

Summary: By integrating the four switch buck–boost (FSBB) PFC and full‐bridge LLC resonant converter, a novel single‐stage FSBB‐LLC AC‐DC converter is proposed. Meanwhile, the corresponding PFM/PWM hybrid modulation is put forward. The proposed solution employs a dual‐loop feedback control strategy based on PFM/PWM hybrid modulation to obtain the desired bus voltage and stable output voltage. The bus voltage feedback loop is mainly used to smoothly determine the boost or buck–boost mode of FSBB PFC cell for regulating the bus voltage; the output voltage feedback loop is in charge of stabilizing the output voltage by adjusting the switching frequency or phase shifting angle. Furthermore, an optimal parameter design based on power balance principle is also derived. The experimental results of an 85 ~ 300 V input, 12V/25A output prototype demonstrate that (1) low and narrow bus voltage of 240 ~ 340 V is achieved under the entire input and output condition; (2) the LLC cell operates at DCX mode over the whole load range as the input voltage exceeds 120 V; (3) the output voltage is well regulated even under the no‐load condition; (4) ZVS feature for the shared switches is still maintained; and (5) a peak efficiency of 90.9% and PF values above 0.987 are achieved. [ABSTRACT FROM AUTHOR]

Conventional half‐bridge (HB) LLC converters have been a good candidate for the first stage in the two‐stage conversion structure because of its high conversion efficiency and high frequency operation ability. However, the voltage gain is only 0.5 exclusive of the transformer, resulting in the reduced efficiency for high step‐down applications. In order to solve this issue, in this paper, a novel hybrid HB LLC converter with double resonant tanks is firstly presented for high step‐down ratio applications. The distinctive features of the proposed converter are as follows: (1) the voltage gain of 0.25 is achieved by incorporating the switched capacitor circuit. Thus, the primary turns number for the transformer is halved compared with conventional HB LLC converters. Correspondingly, the smaller primary side winding losses and transformer volume can be implemented. (2) The power splitting and low input current ripple can be obtained due to the employed double resonant tanks. Thus, the uniform thermal distribution and low input filter capacitance are the second advantage for the proposed converter. (3) Soft switching over the entire operation range still can be maintained with larger magnetics inductance. The detailed operation principles, circuit analysis, and resonant tank design for the proposed converter are introduced and presented. A hardware prototype with 36–60 V input, 3 V/50 A‐output is built to demonstrate the declared features of the proposed hybrid converter. [ABSTRACT FROM AUTHOR]

Summary: Inductive power transfer (IPT) technology has become popular in wireless charging applications. Compared with the traditional 3‐kW wireless charging application, the diameter for the primary coil and the secondary coil in this special design are required to be smaller than 260 and 110 mm, respectively. In order to achieve this target, an approach to design and optimize the loosely coupled transformer (LCT) is proposed to match the strict geometry limitation, while achieving the high conversion efficiency. Different from the traditional design method, the low resonant current and voltage stress are considered as the input of the design flowchart, especially the LCT. Thus, the overall conversion efficiency can be improved. Based on series–series (S–S) compensation topology, the parameter range of the LCT is determined by analyzing transformer‐based equivalent model. To achieve the desired coil size, an asymmetric LCT with single‐layer primary coil and three‐layer secondary coil is designed and optimized by the proposed approach. Furthermore, the closed‐loop controller with narrow frequency variation range is design to realize constant current (CC) charge and constant voltage (CV) charge. A 3‐kW IPT charging prototype is built to demonstrate the validity of the proposed method. Experimental results show that the peak efficiency from input to battery load is 95.69% at 3‐kW output power in the transition point from CC mode to CV mode. [ABSTRACT FROM AUTHOR]