• ETRI Journal
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• v.42 no.5
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• pp.790-798
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• 2020

Herein, a low-ripple coarse-fine digital low-dropout regulator (D-LDO) without ringing in the transient state is proposed. Conventional D-LDO suffers from a ringing problem when settling the output voltage at a large load transition, which increases the settling time. The proposed D-LDO removes the ringing and reduces the settling time using an auxiliary power stage which adjusts its output current to a load current in the transient state. It also achieves a low output ripple voltage using a comparator with a complete comparison signal. The proposed D-LDO was fabricated using a 65-nm CMOS process with an area of 0.0056 μ㎡. The undershoot and overshoot were 47 mV and 23 mV, respectively, when the load current was changed from 10 mA to 100 mA within an edge time of 20 ns. The settling time decreased from 2.1 ㎲ to 130 ns and the ripple voltage was 3 mV with a quiescent current of 75 ㎂.

• Proceedings of the KIEE Conference
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• 1999.11a
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• pp.13-15
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• 1999

The zero voltage and zero current switching(ZVZCS) full bridge (FB) PWM converter using secondary active clamp is characterized by high efficiency, good ZVZCS characteristic, simple topology and low cost. But at the period for discharge of the secondary clamp capacitor, peak pulses and ringing pulse occur in rectified secondary side of the converter. In this paper, a novel secondary active clamp circuit for the ZVZCS FB PWM converter is proposed and a 50 kHz, 500 W prototype converter was experimented for verification of the converter characteristics. It was verified that high voltage peak pulses and ringing pulse on secondary rectified waveforms of the converter are decreased effectively.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.761-767
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• 2001

In this paper, filtering techniques to reduce the adverse effects of motor leads on high-frequency PWM inverter fed AC motor drives will be examined. The filter was designed to keep the motor terminal from the cable surge impedance to reduce overvoltage reflections, ringing, and the dv/dt, di/dt. Therefore, filtering techniques are investigated to reduce the motor terminal overvoltage, ringing, and EMI noise in inverter fed ac motor drive systems. The output filter is used to limit the rate of the inverter output voltage and reduce EMI(common mode noise) to the motor. The performance of the output filter is evaluated through simulations (PSIM) and experiment on PWM inverter-fed ac motor drive(3phase, 3hp(2.2kw), input voltage 220/380V, induction motor). An experimental PWM drive system reduction of conducted EMI was implemented on an available TMS320C31 microprocessor control board. Finally, experimental results showed that the inverter output filter reduces more CM noise than the LPF(low pass filter) and reduce overvoltage and ringing at the motor terminal.

• ETRI Journal
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• v.37 no.5
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• pp.961-971
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• 2015

This paper proposes a 250 mV supply voltage digital low-dropout (LDO) regulator. The proposed LDO regulator reduces the supply voltage to 250 mV by implementing with all digital circuits in a$0.11{\mu}m$ CMOS process. The fast current tracking scheme achieves the fast settling time of the output voltage by eliminating the ringing problem. The over-voltage and under-voltage detection circuits decrease the overshoot and undershoot voltages by changing the switch array current rapidly. The switch bias circuit reduces the size of the current switch array to 1/3, which applies a forward body bias voltage at low supply voltage. The fabricated LDO regulator worked at 0.25 V to 1.2 V supply voltage. It achieved 250 mV supply voltage and 220 mV output voltage with 99.5% current efficiency and 8 mV ripple voltage at $20{\mu}A$ to $200{\mu}A$ load current.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.53 no.1
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• pp.14-21
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• 2004

Most adjustable-speed drives (ASDs) designed to operate low voltage induction motors incorporate voltage-source inverters (VSIs), which create motor voltages at high switching frequencies. The motor leads used to connect an ASD to a motor can behave like transmission lines for voltage pulses, which can be reflected at the motor terminals. The resulting oscillatory transient, known as the long-lead effect, can stress and consequently degrade the stator insulation system of a motor. This paper describes the results of tests to 1) determine the correlation between peak motor voltage and the length of motor leads and 2) determine the correlation between peak motor voltage and the switching frequency of the ASD Insulation failures like this usually are caused by voltage surges. Voltage surges are often the result of switching power circuits, lightning strikes, capacitor discharges and solid-state power devices.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2005.11a
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• pp.399-403
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• 2005

In this paper, we analyze on the effect of RC filter to mitigate transient overvoltage on the high voltage induction motor fed by H-bridge cascaded 7-level inverter. The switching surge voltage becomes the major cause to occur the insulation failure by serious voltage stress in the stator winding of high voltage induction motor. The effect of switching surge appears more serious in high voltage induction motor than low voltage induction motor. Consequently, we demonstrated that the RC filter connected to the motor terminals greatly reduces the transient voltage stress md ringing. The results of simulation show the suppression of transient overvoltage at the motor end of a long cable. using EMTP

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.4
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• pp.351-355
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• 2016

Welding machines are high-capacity systems used in a low-frequency range using IGBT. As their system is similar to a large transformer, most welding machines suffer a great loss because of hard switching and vast leakage inductance. A voltage-balancing circuit is designed to overcome these shortcomings. This circuit can reduce the transformer size by making it into a high frequency and reducing the input voltage by half and by adopting a serial structure that connects two full-bridges in a series to use a MOSFET with a good property at high frequency. In addition, a Schottky diode is used in the primary rectifier to overcome the low efficiency of most welding machines. To use the Schottky diode with a reliably relatively low withstanding voltage, an active snubber is adopted to effectively limit the ringing voltage of the diode cut-off voltage.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.6
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• pp.546-555
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• 2001

In this paper filtering techniques to reduce the adverse effects of motor leads on high-frequency PWM inverter fed AC motor drives are presented. The filter was designed to keep the motor terminal from the cable surge impedance to reduce overvoltage reflections ringing and the dv/dt, di/dt, at the motor terminals. Specially the output filter is used to limit the rate of the inverter output voltage and reduce common mode noise to the motor, The performance of the output filter is evaluated through simulations and experiment on PWM inverter-fed AC motor drive. An experimental PWM drive system reduction of conducted EMI was implemented on an available TMS320C31 microprocessor control board Finally, experimental result shows inverter output filter reduces more common mode voltage than low pass filter also reduce overoltage and ringing at the motor terminal.

• Proceedings of the KIPE Conference
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• 2004.07a
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• pp.341-345
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• 2004

A high efficiency and low device stress voltage and current clamping BVS PWM asymmetrical half bridge converter is proposed in this paper. To achieve the ZVS of power switches along the wide load range, the transformer leakage inductor $L_{Ikg}$ is increased. Then, to solve the problem related to ringing in the secondary rectifier caused by the resonance between $L_{Ikg}$ and rectifier junction capacitors, the proposed converter employs a voltage and current clamping cell, which helps voltages and currents of rectifier diodes to be clamped at the output voltage and output current, respectively. Therefore, no RC-snubber for rectifier diodes is needed and a high efficiency as well as low noise output voltage can be realized. In addition, since all energy stored in $L_{Ikg}$ is transferred to the output side, the circulating energy problem can be effectively solved and duty loss does net exist. The operational principle, theoretical analysis, and design considerations are presented. To confirm the operation, validity, and features of the proposed circuit, experimental results from a 425W, 385-170Vdc prototype are presented.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.5
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• pp.587-592
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• 2018

Because the brightness of an AMOLED is determined by the flowing current, each pixel of AMOLED operates via A current driving method. Therefore, it is necessary to supply power to adjust the amount of current according to THE user's requirement for AMOLED driving. In this study, an IP driver block was designed and a simulation was conducted for an AMOLED display, which supplies power as selected by users. The IP driver design focused on regulating the output power due to the OLED characteristics for the diode electric current according to the voltage to be activated by pulse-skipping mode (PSM) under low loads, and 1.5 MHz pulse-width modulation (PWM) for medium/high loads. The IP driver was designed to eliminate the ringing effects appearing from the dis-continue mode (DCM) of the step-up converter. The ringing effects destroy the power switch within the IC, or increase the EMI to the surrounding elements. The IP driver design minimized this through a ringing killer circuit. Mobile applications were considered to enable true shut-down capability by designing the standby current to fall below $1{\mu}A$ to disable it. The driver proposed in this paper can be applied effectively to the same system as the AMOLED display dual power management circuit.