• 한국멀티미디어학회논문지
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• 제25권8호
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• pp.1022-1037
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• 2022

It is important to develop a transducer that generates uniform output power through frequency control of the HIFU at 4 MHz frequency for the high intensity focused ultrasound (HIFU) skin diseases treatment. In this paper, a 4 MHz frequency band HIFU system for skin disease treatment was designed, manufactured and developed. In HIFU, even for the ultrasonic vibrator in the 4 MHz frequency band, the characteristics of the output power of the HIFU are different depending on the difference in the thickness of the PZT material. Through the development of a system amplifier, the sound output of the HIFU transducer was improved to more than 48 W and uniform output power control was possible. And, it is possible to control the output power even in a frequency band of 4.0 to 4.7 MHz, which is wider than 4.0 MHz, and shows the resonance frequency of the transducer. The maximum output power for each frequency was 49.969 W and the minimum value was 48.018 W. The maximum output power compared to the minimum output power is 49.969 W, which is uniform within 4.1%. It was confirmed that the output power of the HIFU through the amplifier can be uniformly controlled in the 4 MHz frequency band.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2003년도 ICCAS
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• pp.1836-1840
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• 2003

This paper, we propose a new phase-locked loop (PLL) system with the controllable output phase, independent from the output frequency, and lock-up time. This PLL system has a dual control loop is described, the inner loop greatly improved VCO characteristic such as faster speed response as well as higher operation bandwidth, to minimize the effect of the VCO noise and the power supply variation and also get better linearity of VCO output. The main loop is the heart of this PLL which greatly improved the output frequency instability due to the external high frequency noise coupling to the input reference frequency also the main loop can control the output phase, independent from the output frequency, and reduce the lock-up time of the step frequency response. The experimental results confirm the validity of the proposed strategy.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 하계종합학술대회 논문집(2)
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• pp.193-196
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• 2000

In this work, I propose a temperature stable voltage-to-frequency converter in which the output frequency is directly proportional to the input voltage. The output frequency range is from 20㎑ to 60㎑ 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$^{\circ}C$.

• 한국통신학회논문지
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• 제24권9B호
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• pp.1683-1689
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• 1999

VCO의 표류성분 제거기와 빗쌀 하모닉 발생기를 이용하여 주파수를 상향 변환하면서 동시에 주파수 대역폭을 확장하는 시스템을 구현하였다. 출력 주파수 범위가 220∼280MHz, 분해능이 5MHz인 저주파수 합성기의 출력을 1660∼2140MHz의 광대역 주파수로 확장한다. 최종출력의 위상 잡음 상태는 저주파수 합성기와 빗쌀 하모닉 발생기에 의해 결정되며 VCO의 표류성분은 최종 출력에 나타나지 않는다. 필터 뱅커처럼 VCO의 조절로 주파수가 60MHz의 단위로 가변되는데 이때의 가변시간은 3usec이하이며, 스퓨리어스는 -55dBc이하이다. VCO의 출력 주파수 범위를 확장하면 쉽게 출력 대역폭을 추가로 확장할 수 있으며, 빠른 스위칭 시간을 요구하는 광대역 초고주파 합성기에 응용될 수 있다.

• Journal of Power Electronics
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• 제8권1호
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• pp.60-73
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• 2008

In this paper a three-phase ac-to-dc resonant converter with high input power factor and isolated output is proposed. To improve the input power factor of the converter, high frequency current is injected into the input of the three-phase diode bridge rectifier. It is injected through an impedance network consisting of a series of L-C branches from the output of the high frequency three-phase inverter. A narrow switching frequency variation is required to regulate the output voltage. A design example with different design curves is illustrated along with the component ratings. Experimental verification of the converter is performed on a prototype of 3 kW, 1000 V output, operating above 300 kHz. Experimental results confirm the concept of the proposed converter. Narrow switching frequency variation is required to regulate the output voltage.

• 전기학회논문지
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• 제56권5호
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• pp.892-897
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• 2007

This paper presents the output filter design and the output characteristic analysis by cut-off frequency set up of the LCR filter on NPC multi-level inverter with trap-filter. The single-phase NPC three-level inverter operates at low switching frequency. The proposed LC trap filter is comprised of a conventional LCR output filter, by using LC trap filter the need for high damping resistor and low LC cut-off frequency is eliminated. Also. low damping resistor is increased the output filter system. The multilevel inverter system used NPC type inverter in proper system for high power application and controller is used DSP(TMS320C31). The effectiveness of proposed system confirmed the validity through SPICE simulation and experimental results.

• Current Optics and Photonics
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• 제2권5호
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• pp.443-447
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• 2018

We propose a diode-pumped cesium laser using frequency locking of a pump laser that can effectively increase the maximum output power of the cesium laser. We simultaneously monitored the absorption spectrum of cesium and the laser output power, and the frequency of pump laser was locked at the center of the $D_2$ absorption line of the cesium atom to obtain an effective gain enhancement. Using this scheme, we have achieved output power increase of ~0.1 W compared to when frequency locking was not applied. Furthermore, by optimizing the temperature of the cesium cell and the reflectivity of the output coupler, we successfully achieved an output power of 1.4 W using the pump power of 2.9 W, providing a slope efficiency of 61.5% and optical-to-optical efficiency of 49%.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1995년도 Proceedings of the Korea Automation Control Conference, 10th (KACC); Seoul, Korea; 23-25 Oct. 1995
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• pp.87-90
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• 1995

When the ultrasonic transducer operating at l MHz for use in cleaning semiconductor wafers or other industsrial materials is driven from the MOS-FET DC-to RF inverter, the output power severely depends on the frequency of operation since the quality factor of the transducer is high. In order to tune to the eresonating frequency of the ultrasonic transducer, the drive signal frequency of the MOS-FET power inverter is automatically scananed until the frequency is set at the resonating frequency of the ultrasonic transducer is maximized. The control circuit consists of an output power sensing circuit, a PLL controller, a frequency standard, and other peripheral circuits. The operation was satisfactory when the transducer having an output of 600 W at 1 MHz was used.

• KEPCO Journal on Electric Power and Energy
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• 제7권2호
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• pp.255-261
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• 2021

This paper proposes impedance-based stability analysis of DC-DC boost converters, where a harmonic state space (HSS) modeling technique is used. At first, the HSS model of the boost converter is developed. Then, the closed-loop output impedance of the converter is derived in frequency domain using small signal modeling including frequency couplings, where harmonic transfer function (HTF) matrices of the open-loop output impedance, the duty-to-output, and the voltage controller are involved. The frequency response of the output impedance reveals a resonance frequency at low frequency region and frequency couplings at sidebands of switching frequency which agree with the simulation and experimental result.

• Journal of Power Electronics
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• 제9권3호
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• pp.396-402
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• 2009

A DC/DC converter generally needs to work under high switching frequency when used as an adjustable power supply to reduce the size of magnetic elements such as inductors, transformers and capacitors, but with the rising of the switch frequency, the switch losses will increase and the efficiency will reduce. Recently, to solve these problems, research is actively being done on a soft switching method that can be applied under high frequency and on a PWM converter that can be applied under low frequency such as a multi-level topology. In this paper a novel DC-DC conversion method for reducing the ripple of output voltage is proposed. In the proposed converter, buck converters are connected in series to generate the output voltage. By using this method, the ripple of output voltage can be reduced compared to a conventional buck converter. Particularly when output voltage is low, the number of acting switching elements is less and the result of ripple reduction is more obvious. It is expected that the converter proposed in this paper could be very useful in the case of wide-range output voltage.