Joong-Gi Kwon

Theoretical analysis and optimal design of LLC resonant converter

A LLC resonant topology is analyzed to derive efficiency and cost optimal design for wide input ranges and load variations. In the LLC converter, a wide range of output power is controlled with only a narrow variation in operating frequency since this converter is capable of both step-up and step-down. In addition, ZVS turn-on and ZCS turn-off of MOSFETs and diode rectifiers can be achieved over the entire operating range. Finally, the inductance of a resonant tank in the primary side can be merged in the main power transformer by resonant inductance and the absence of the secondary filter inductor makes low voltage stress on secondary rectifier and cost-effective property. DC characteristics and input-output response in frequency domain are obtained with the equivalent circuit derived by first harmonic approximation (FHA) method. In addition, operational principles are explained to show the ZVS and ZCS conditions of primary switches and output diode rectifiers, respectively. Efficiency and cost optimal design rules of the LLC resonant converter are derived by a primary resonant network, operating frequency, and dead time duration. Proposed analysis and designation are proved by experimental results with a 400 W LLC resonant converter.

Novel techniques of the reduction of standby power consumption for multiple output converters

Recently, the reduction of a standby power consumption is significantly issued in the electronic and electrical industry for the conservation of environment. In the case of a switched mode power supply (SMPS), it is demanded high efficiency at extremely low load conditions by consumers. However, it is very different from high efficiency techniques at full load conditions. In addition, many SMPSs are designed as a multi-output circuit for various loads because of the cost down. This circuit is difficult to implement both the high efficiency and good cross regulation performance, simultaneously. In this paper, novel secondary side post regulator (SSPR), current mode control method, and power sequence control technique are proposed to reduce standby power consumption and to improve the cross regulation performance of the multi-output SMPSs which consist of a single or multiple converter. The proposed methods are analyzed by their operational principles and optimal designs verified by experimental results with 110 W and 270 W SMPSs.

Asymmetrical ZVS PWM Flyback Converter with Synchronous Rectification for Ink-Jet Printer

This paper presents a novel asymmetrical half bridge flyback converter with synchronous rectifier. To achieve a higher efficiency and a lower switching stresses than a conventional topology, the proposed APWM flyback converter can achieve ZVS operation of the power switches, and ZCS operation on output rectifier using MOSFET switch. In addition, its simple configuration enables the cost to be reduced with the smallest number of components. In this paper, analytical approach and proposed design guide are also described. A 12V/20A prototype has been implemented to verify the proposed topology and theoretical operation under full load condition.

Soft switching and optimal resonance conditions of APWM HB flyback converter for high efficiency under high output current

The soft switching and optimal resonance conditions of the asymmetrical pulse-width modulated (APWM) half-bridge (HB) flyback converter for high efficiency under high output current are proposed. This converter can operate under high efficiency by using soft switching techniques such as the zero-voltage switching (ZVS) of primary power switches and the zero-current switching (ZCS) of output rectifiers. Under high output current condition, however, the converter satisfied with the ZCS of output rectifiers does not always have higher efficiency than no ZCS cases. The ZCS condition grows the rms value of the output rectifier current to finish its resonance operation transferring power from the primary side to the secondary. This high rms current increases the conduction loss of the transformerpsilas secondary wire and output rectifier, especially the synchronous rectifier (SR). Therefore, the resonance should be considered by several factors such as the conduction loss of the output rectifier and its reverse recovery loss. Experimental results using a 300 W APWM HB converter are obtained to verify the suggested efficiency-optimal conditions by demonstrating the efficiency data of the converter under load variations.

A Study on a Hybrid Induction Heating System for Laser Printer

Recently, the demand for the development of high quality and high-speed laser printers and efficient power utilization has required. Among complicated electro-mechanic devices in laser printers, the toner-fusing unit consumes above 90[%] of all electrical energy needed for printing devices. Therefore, the development of a more effective energy-saving toner fusing process becomes a significant task in great demand. Generally, there are several ways to implement a fusing unit. Among them this paper presents a new induction heating method. The proposed induction heating method enables the increase of coupling coefficient between heating coil and heat roller which also increases total energy transfer efficiency. Therefore, the proposed IH (Induction Heating) inverter system provides very fast W.U.T. (Warm UP Time) as well as higher efficiency. Through experimental results, the proposed control system is verified.