• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.8
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• pp.423-429
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• 2006

Recently, the high frequency isolated boost DC/DC converter has been widely used for the PCS (Power Conditioning System) system because of its small size and low cost. However, the high frequency isolated boost DC/DC converters applied the conventional voltage-fed converter and current-fed converter have the problems such as the high conduction losses and the surge voltage due to the high circulating current and the leakage inductance, respectively. To overcome this problems, in this paper the secondary LLC resonant converter is proposed, and the experimental results of the secondary LLC series resonant converter for boost DC/DC converter are verified on the simulation based on the theoretical analysis and the 700W experimental prototype.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.6
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• pp.627-637
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• 2011

To cope with the high power density and low cost in switching power supply, this paper presents a novel planar transformer, which can regulate the leakage inductance of planar transformer used for LLC resonant converter. Modeling and analysis of a novel planar transformer are discussed in detail and a prototype 200W LLC resonant converter is tested to verify.

• Proceedings of the KIPE Conference
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• 2007.07a
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• pp.424-427
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• 2007

The LLC series resonant converter with a LLT (Inductor-Inductor-Transformer) transformer for PDP power supply is presented. LLT transformer used to combine the inductor and transformer into one unit has the increased leakage inductance in the primary and secondary due to the winding method and the use of the gaped core. The increased leakage inductance in the primary and secondary of LLT transformer can be impacted on the DC voltage gain characteristics of LLC series resonant converter. In this paper, DC gain characteristics and the experimental results of the LLC series resonant converter with a LLT transformer are verified on the Math-CAD simulation based on the theoretical analysis and the 600W experimental prototype.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.30 no.1
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• pp.79-86
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• 2016

In this paper, we propose a current-driven synchronous rectifier driver circuit for LLC resonant half-bridge converters. The proposed driver circuit detects a relatively low current in the primary side of the transformer although a large current is flowing in the secondary side. Due to this feature, the driver circuit has a simple circuit structure and stabilizes the switching operation with a logic-level switching voltages for the synchronous rectifier. The operation and performance of the proposed driver circuit are confirmed with a prototype of 1kW class LLC resonant half-bridge converter. The experimental results proved that the proposed synchronous rectifier driver method improves the power conversion efficiency by around 1% and reduces the internal power loss by 17W.

• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.2
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• pp.142-151
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• 2020

This paper presents a DC/DC LLC resonant converter with wide input/output voltage gain characteristics and its control method for efficiency improvement. For a wide input/output voltage gain characteristics without designing small transformer magnetization inductance, the proposed converter changes the topology into three modes of operation according to the main switch switching pattern. In each operating mode, variable LINK voltage modulation and frequency modulation were performed to control output voltage and improve operating efficiency. A prototype of a 5-kW DC/DC LLC resonant converter was built and tested to verify the validity and applicability of the proposed converter.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.1
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• pp.46-52
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• 2021

This study proposes a feedforward compensation control method to reduce 120 Hz output voltage ripple in a single-phase AC/DC rectifier system composed of PFC and LLC resonant converters. The proposed method compensates for the voltage ripple of the DC-link by using the AC input and DC output power difference, and then reduces the final output voltage ripple component of 120 Hz through feedforward compensation based on the linearized frequency gain curve of the LLC resonant converter. Through simulation and experimental results, the validity of the ripple reduction performance was verified by comparing the conventional PI controller and the proposed feedforward compensation method.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.7
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• pp.1366-1371
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• 2011

The resonant converter cause the high voltage stress according to the input voltage, which increases the conduction loss in converter power switches. The topology of LLC half bridge resonant converter provides ZVS characteristic and also the stress of voltage and current is smaller than that of the general resonant converters. So we can expect the higher efficiency. In this paper, the analysis of the characteristics of the converter efficiency and the best conditions for highest efficiency were investigated. As a result, the efficiency of utilizing up to 93% is achieved.

• The Transactions of the Korean Institute of Power Electronics
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• v.11 no.5
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• pp.409-416
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• 2006

Operating Characteristics of LLC Series resonant converter with a LLT(Inductor-Inductor-Transformer) transformer is presented. LLT transformer used to combine the inductor and transformer into one unit has the increased leakage inductance in the primary and secondary due to the winging method and the use of the gaped core. The increased leakage inductance in the primary and secondary of LLT transformer can be impacted on the DC voltage gain characteristics of LLC series resonant converter. In the paper, DC gain characteristics and the experimental results of the LLC series resonant converter with a LLT transformer are verified on the simulation based on the theoretical analysis and the 400W experimental prototype.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.47 no.5
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• pp.71-79
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• 2010

This paper presents a design of a LLC resonant controller IC. LLC resonant controller IC controls the voltage of the 2nd side by adjusting frequency the input frequency of the external resonant circuit. The clock generator is integrated to provide the pulse to the resonant circuit and its frequency is controlled by the external resistor. Also, the frequency of the VCO is adjusted by the feedback voltage. The protection circuits such as UVLO(Under Voltage Lock Out), brown out, fault detector are implemented for the reliable and stable operation. The HVG, and LVG drivers can provide the high current and voltage to the IGBT. The designed LLC resonant controller IC is fabricated with the 0.35 um 2P3M BCD process. The overall die size is $1400um{\times}1450um$, and supply voltage is 5V, 15V.

• Journal of Power Electronics
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• v.9 no.2
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• pp.215-223
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• 2009

A design methodology for transformers including integrated and center-tapped structures for LLC resonant converters is proposed. In the LLC resonant converter, the resonant inductor in the primary side can be merged in the transformer as a leakage inductance. And, the absence of the secondary filter inductor creates low voltage stress on the secondary rectifiers and is cost-effective. A center-tapped structure of the transformer secondary side is widely used in commercial applications because of its higher efficiency and lower cost than full-bridge structures in the rectifying stages. However, this transformer structure has problems of resonance imbalance and transformer inefficiency caused by leakage inductance imbalance in the secondary side and the position of the air-gap in the transformer, respectively. In this paper, gain curves and soft-switching conditions are derived by first harmonic approximation (FHA) and operating circuit simulation. In addition, the effects of the transformer including integrated and center-tapped structures are analyzed by new FHA models and simulations to obtain an optimal design. Finally, the effects of the air-gap position are analyzed by an electromagnetic field simulator. The proposed analysis and design are verified by experimental results with a 385W LLC resonant converter.