• 한국정보통신학회논문지
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• 제11권5호
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• pp.949-954
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• 2007

본 논문에서는 CMOS 공정을 이용하여 동작온도에 무관한 FVC(Frequency-to-Voltage Convener) 회로를 제안한다. FVC는 FLL(Frequency Locked Loop)의 핵심 회로로서 주파수 신호를 전압신호로 변환하는 회로이다. FLL 회로는 PLL(Phase-Locked Loop) 회로 같이 고정된 주파수 신호를 생성하는 회로지만, PLL과는 달리 위상비교기, charge pump, 저역 필터 등이 필요치 않아 간단히 회로를 구성할 수 있다. FVC 회로의 설계는 $0.25{\mu}m$ CMOS 공정을 이용하였다. 설계되어진 회로의 입력 주파수는 70MHz에서 140MHz를 사용하였다. 회로의 시뮬레이션 결과 동작 온도가 $0^{\circ}C$에서 $75^{\circ}C$까지 변화할 때 변환된 출력 전압의 변화는 상온에 비하여 ${\pm}2%$이내였다.

• Journal of Power Electronics
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• 제3권2호
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• pp.139-144
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• 2003

In this paper, 11 and 13 layered step-down piezoelectric transformers were fabricated and their electrical characteristics have been analyzed for AC-adapter. When the voltage is applied to the driving piezoelectric vibrator polarized in the longitudinal direction, the output voltage is generated at the generating piezoelectric vibrator polarized in the thickness direction due to the piezoelectric effects. From the piezoelectric direct and converse effects, symbolic expressions between the electric inputs and outputs of the step-down piezoelectric transformer are derived with an equivalent circuit model. With those expressions, load and frequency characteristics are discussed through the simulations. Output voltage and current from a 11-layered and a 13-layered piezoelectric transformers were measured under the different load and frequency conditions. First we measured resonant frequency from impedance curve and got equivalent impedance value of the piezoelectric transformer from admittance plot. It was shown from experiments that output voltage increase s and resonant frequency changes according to the various resistor loads. Output current decreases inversely proportional to the change of loads. Moreover, the measured output voltage and current are well matched with the simulated results obtained from the proposed equivalent circuit model. Furthermore, a new step-down piezoelectric transformer has been suggested to Increase the output power based on a simulation result having a driving piezoelectric vibrator polarized thickness direction.

• 한국산학기술학회논문지
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• 제7권2호
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• pp.157-162
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• 2006

본 논문에서는 오존발생시스템의 전원으로 사용하는 단상 풀브리지 인버터를 ATmega128을 이용하여 위상 변위제어 방식에 의해 출력 주파수와 전압을 제어하였다. 또한, 사용자가 오존발생 시스템에서 키패드를 사용하여 출력 주파수와 전압값을 설정할 수 있게 하였고, 사용자가 설정한 값을 LCD를 이용하여 디스플레이 하였다. 실제로 전원 시스템을 설계하여 제작하였으며, 오존발생시스템에서의 실험을 통해서 출력 전압과 주파수 제어의 성능을 검증하였다.

• 산업기술연구
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• 제32권A호
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• pp.115-118
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• 2012

Recently, there are a lot of papers in order to replace the electrolytic capacitor into the film capacitor in output of PFC(Power Factor Correction). However, the film capacitor, which has capacitance of low values, causes a large ripple voltage in output of PFC. The LED drivers are connected series in the output of PFC and affected by the magnitude of voltage ripple. In this paper, we have compared the fixed frequency method with the variable frequency for the constant-current control and propose the control method to avoid the sub-harmonic oscillation in the variable input voltage. An 80W PFC, using film capacitors instead of electrolytic capacitors, and LED driver has been built and compared the fixed frequency control method with the variable frequency control method.

• Journal of Power Electronics
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• 제14권3호
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• pp.531-540
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• 2014

A novel carrier-based PWM (CBPWM) strategy of a three-level NPC converter is proposed in this paper. The novel strategy can eliminate the low-frequency neutral point (NP) voltage oscillation under the entire modulation index and full power factor. The basic principle of the novel strategy is introduced. The internal modulation wave relationship between the novel CBPWM strategy and traditional SPWM strategy is also studied. All 64 modulation wave solutions of the CBPWM strategy are derived. Furthermore, the proposed CBPWM strategy is compared with traditional SPWM strategy regarding the output phase voltage THD characteristics, DC voltage utilization ratio, and device switching losses. Comparison results show that the proposed strategy does not cause NP voltage oscillation. As a result, no low-frequency harmonics occur on output line-to-line voltage and phase current. The novel strategy also has higher DC voltage utilization ratio (15.47% higher than that of SPWM strategy), whereas it causes larger device switching losses (4/3 times of SPWM strategy). The effectiveness of the proposed modulation strategy is verified by simulation and experiment results.

• Journal of Electrical Engineering and Technology
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• 제6권6호
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• pp.842-848
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• 2011

The current study proposes the design of a hybrid series-parallel resonant converter (SPRC) and a three-stage Cockcroft-Walton voltage multiplier for precisely adjusting the power generated by a continuous wave (CW) $CO_2$ laser. The design of a hybrid SPRC, called LCC resonant converter, is described, and the fundamental approximation of a high-voltage and high-frequency (HVHF) transformer with a resonant tank is discussed. The results of the current study show that the voltage drop and ripple of a three-stage Cockcroft-Walton voltage multiplier depend on frequency. The power generated by a CW $CO_2$ laser can be precisely adjusted by a variable-frequency controller using a DSP (TMS320F2812) microprocessor. The proposed LCC converter could be used to obtain a maximum laser output power of 23 W. Moreover, it could precisely adjust the laser output power within 4.3 to 23 W at an operating frequency range of 187.5 to 370 kHz. The maximum efficiency of the $CO_2$ laser system is approximately 16.5%, and the minimum ripple of output voltage is about 1.62%.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 하계학술대회 논문집 B
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• pp.585-587
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• 1998

It is suggested that the PWM inverter is controlled by Digital Software Programming. VVVF(Variable Voltage Variable Frequency) inverter control being used by PWM control for driving the motor with speed-varying, makes the PWM pattern with calculating the output voltage and frequency, and with controlling the carrier and signal, so actually this method is difficult to correspond with driving the motor by using voltage-varying and frequency-varying. Therefore this research suggested the new algorithm controlled by micro processor which is already stored by various PWM form of output voltage by using fundamental data of the carrier and signal. The PWM wave can be controlled with real time by using extra hardware and digital software and to speed up program processing, the control signals to switch the power semi-conductor of three phase PWM inverter, simultaneously use the output signal by microprocessor and extra hardware, and control signal by software. In the end, this method was proved by applying to Three Phase Voltage-type Inverter.

• Journal of Electrical Engineering and Technology
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• 제2권1호
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• pp.29-34
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• 2007

The input and output impedances in a low voltage distribution system is one of the most important matters for power line communication because from the viewpoint of communication, the attenuation characteristic of the high frequency signals is greatly caused by impedance mismatch during sending and receiving. The frequency range is from 1MHz to 30MHz. Therefore, this paper investigates the input and output impedances in order to understand the characteristic of high frequency signals in the low voltage distribution system between a pole transformer and an end user. For power line communication, the model of Korea's low voltage distribution system is proposed in a residential area and then the low voltage distribution system is set up in a laboratory. In the low voltage distribution system, S parameters are measured by using a network analyzer. Finally, input and output impedances are calculated using S parameters.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제52권3호
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• pp.105-108
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• 2003

In this work, a Voltage-to-Frequency Converter(VFC) in which the output frequency is proportional to the input voltage is proposed. To obtain the temperature stable characteristics of the VFC circuit is designed by BiCMOS technology. The output frequency range is 24KHz to 65KHz and the difference between simulated and calculated values is less than about 5% for this range of output frequency. The temperature variation of sample output frequencies is less than $\pm$0.5% in the temperature range $-25^{\circ}C$ to 75$^{\circ}C$.

• Journal of Power Electronics
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• 제9권6호
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• pp.823-834
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• 2009

This paper proposes a high-efficiency single-stage ac/dc converter. The proposed converter features low voltage stresses and reduced switching losses. It operates at the boundary of discontinuous- and continuous-conduction modes by employing variable switching frequency control. The turn-on switching loss of the switch can be reduced by turning it on when the voltage across it is at a minimum. The voltage across the bulk capacitor is independent of the output loads and maintained within the practical range for the universal line input, so the problem of high voltage stress across the bulk capacitor is alleviated. Moreover, the voltage stress of the output diodes is clamped to the output voltage, and the output diodes are turned off at zero-current. Thus, the reverse-recovery related losses of the output diodes are eliminated. The operational principles and circuit analysis are presented. A prototype circuit was built and tested for a 150 W (50V/3A) output power. The experimental results verify the performance of the proposed converter.