• Journal of the Korean Society of Safety
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• v.12 no.1
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• pp.29-36
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• 1997

Precision electronic equipments for outdoor use are composed of sophisticated microcircuits that are extremely vulnerable to lightning-caused voltage spike. This transient voltage spike may cause upset, latent failure or Interference on electronic equipments. In order to develop efficient lightning protection measures on AC power lines of a road traffic controller as a electronic equipment for outdoor use, experimental surge immunity tests were conducted according to IEC standard 801-5. The combination of gas tube arrester and metal-oxide varistor was installed at the input of AC power lines and the silicon avalanche suppressor installed at the output of DC power supply for the lightning protection measures.

• Proceedings of the KIEE Conference
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• 2002.06a
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• pp.98-101
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• 2002

The switching-mode power converter has been widely used because of its features of high efficiency and small weight and size. These features are brought by the ON-OFF operation of semiconductor switching devices. However, this switching operation causes the surge and EMI(Electromagnetic Interference) which deteriorate the reliability of the converter themselves and entire electronic systems. This problem on the surge and noise is one of the most serious difficulties in AC-to-DC converter. In the case of carrier frequency selection, output-voltage of steady state and transient state is fully regulated. A RPWM control method was proposed in order to smooth the switching noise spectrum and reduce it's level. Experimental results are verified by converter operating at 300V/1kW with 5%${\sim}$30% white noise input. Spectrum analysis is performed on the Phase current and the CM noise voltage. The former is measured with Current Probe and the latter is achieved with USN. which are connected to the spectrum analyzer respectively.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.222-226
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• 2001

This paper compares three kinds of soft-switching circuits from viewpoints of surge suppression, load characteristic, and power efficiency for a tapped-inductor buck converter with low voltage and high current. As a result, these soft-switching techniques have achieved much higher efficiency of $80\%$ when compared with a hard-switching buck converter for the output condition of 1V and 20A.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.05a
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• pp.92-94
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• 2005

In this paper, when electric train is in dead-section the effect on electric train system was dealt. The feeding system of electrical railway is AC or DC. When the electric train is passed AC feeding system to DC, vice versa or phase is changed in between AC feeding systems, there is a dead section. A dead section usually makes the electrical system complex md may have an adverse effect on the electrical system inside the train. Accordingly, it is important to analyze the effect on trains in dead-section. Modeling an electric train and simulation using PSCAD/EMTDC was accomplished to analyze how power quality problem such as inverter switching surge is propagated to electric train through the feeding line, railway, pantograph.

• Journal of Power Electronics
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• v.5 no.3
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• pp.212-217
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• 2005

In order to correct the power boost topology has been used for easy control. But conventional boost topology has the following drawbacks: switching voltage surge, cross conduction current and right-half-plane zero of its control transfer function. Furthermore, in this topology the output voltage is always higher than the input voltage. As a result, a first-stage boost PFC converter needs to be connected with a second-stage DC-DC converter. A new topology which can be used as single stage PFC converter is proposed in this paper.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.3
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• pp.224-230
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• 2016

In this study, a single-power-conversion series-resonant ac-dc converter with high efficiency and high power factor is proposed. The proposed ac-dc converter consists of single-ended primary-inductor converter with an active-clamp circuit and a voltage doubler with series-resonant circuit. The active-clamp circuit clamps the surge voltage and provides zero-voltage switching of the main switch. The series-resonant circuit consists of leakage inductance $L_{lk}$ of the transformer and resonant capacitors $ C_{r1}$ and $ C_{r2}$. This circuit also provides zero-current switching of output diodes $D_1$ and $D_2$. Thus, the switching loss of switches and reverse-recovery loss of output diodes are considerably reduced. The proposed ac-dc converter also achieves high power factor using the proposed control algorithm without the addition of a power factor correction circuit and a dc-link electrolytic capacitor. A detailed theoretical analysis and the experimental results for a 1kW prototype are discussed.

• Journal of Electrical Engineering and Technology
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• v.11 no.3
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• pp.644-652
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• 2016

This paper presents an improved single-stage ac-dc LED-drive flyback converter using the transformer-coupled lossless (TCL) snubber. The proposed converter is derived from the integration of a full-bridge diode rectifier and a conventional flyback converter with a simple TCL snubber. The TCL snubber circuit is composed of only two diodes, a capacitor, and a transformer-coupled auxiliary winding. The TCL snubber limits the surge voltage of the switch and regenerates the energy stored in the leakage inductance of the transformer. Also, the switch of the proposed converter is turned on at a minimum voltage using a formed resonant circuit. Thus, the proposed converter achieves high efficiency. The proposed converter utilizes only one general power factor correction (PFC) control IC as its controller and performs both PFC and output power regulation, simultaneously. Therefore, the proposed converter provides a simple structure and an economic implementation and achieves a high power factor without the need for any separate PFC circuit. In this paper, the operational principle of the proposed converter is explained in detail and the design guideline of the proposed converter is briefly shown. Experimental results for a 40-W prototype are shown to validate the performance of the proposed converter.

• Proceedings of the KIEE Conference
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• 2006.10b
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• pp.154-158
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• 2006

The switching-mode power converter has been widely used because of its features of high efficiency and small weight and size. These features are brought by the ON-OFF operation of semiconductor switching devices. However, this switching operation causes the surge and EMI(Electromagnetic Interference) which deteriorate the reliability of the converter themselves and entire electronic systems. This problem on the surge and noise is one of the most serious difficulties in AC-to-DC converter. Random Pulse Width Modulation (RPWM) is peformed by adding a random perturbation to switching instant while output-voltage regulation of converter is performed. RPWM method for reducing conducted EMI in single switch three phase discontinuous conduction mode boost converter is presented. The more white noise is injected, the more conducted EMI is reduced. But output-voltage is not sufficiently regulated. This is the reason why carrier frequency selection topology is proposed. In the case of carrier frequency selection, output-voltage of steady state and transient state is fully regulated. A RPWM control method was proposed in order to smooth the switching noise spectrum and reduce it's level. Experimental results are verified by converter operating at 300v/1kW with $5%{\sim}30%$ white noise input. Spectrum analysis is performed on the Phase current and the CM noise voltage. The former is measured with Current Probe and the latter is achieved with LISN, which are connected to the spectrum analyzer respectively.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.12
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• pp.1111-1116
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• 2005

ZnO varistor ceramics added a glass-frit 0.03 $wt\%$ were fabricated with variation of sintering temperature. The sintering temperature and time were $1125^{\circ}C\~1200^{\circ}C$ and 2 h. The average grain sizes increased and the varistor voltage decreased with increasing the sintering temperature. The values of the specimen sintered at $1200^{\circ}C$ were $23.7\;{\mu}m$ and 329 V, respectively. The leakage current of all specimens was less than $1\;{\mu}A$ at DC $82\%$ of varistor voltage. The clamping voltage ratio of the specimen sintered at $1175^{\circ}C$ was 1.37. The endurance of surge current and the deviation of varistor voltage of the specimen sintered at $1175^{\circ}C$ were 6400 $A/cm^2$ and ${\Delta}-2.81\%$, respectively. After the High Temperature Load Test(HTLT) at $85^{\circ}C$ for 1000 h, the specimen sintered at $1175^{\circ}C$ showed the lowest deviation of varistor voltage of ${\Delta}-1.92\%$.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.5
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• pp.857-864
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• 2020

The multi-functional VoIP phone supports the Ethernet protocol in the TIPS(: Tactical IP Switch), which is one of the sub-systems of the tactical information and communication system (TICN). It provides secured voice / video calls in conjunction with VoIP exchanges and supports differential services such as multi-party calls and command functions. In this paper, improving methods have been proposed to reduce power supply defects in the field of multi-functional VoIP phones. The power supply part was improved by applying TVS of the output voltage inlet of the dedicated adapter of the multi-functional VoIP phone, TVS of the PoE module input, adding blocking diodes, and adding DC / DC converters behind the poly-switch. Also, functional and environmental tests were performed to verify the validity of the proposed methods.