• Journal of Power Electronics
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• 제15권1호
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• pp.10-17
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• 2015

A quasi-constant on-time controlled buck front end in combined discontinuous conduction mode and boundary conduction mode is proposed to improve power factor (PF).When instantaneous AC input voltage is lower than the output bus voltage per period, the buck converter turns into buck-boost converter with the addition of a level comparator to compare input voltage and output voltage. The gate drive voltage is provided by an additional oscillator during distortion time to eliminate the cross-over distortion of the input current. This high PF comes from the avoidance of the input current distortion, thereby enabling energy to be delivered constantly. This paper presents a series analysis of controlling techniques and efficiency, PF, and total harmonic distortion. A comparison in terms of efficiency and PF between the proposed converter and a previous work is performed. The specifications of the converter include the following: input AC voltage is from 90V to 264V, output DC voltage is 80V, and output power is 94W.This converter can achieve PF of 98.74% and efficiency of 97.21% in 220V AC input voltage process.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• 제24권8호
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• pp.632-635
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• 2011

Additions (ZnO, CuO) doped $0.98(Na_{0.5}K_{0.5})NbO_3-0.02Li(Sb_{0.17}Ta_{0.83})O_3$ (0.98NKN-0.02LST-x) lead free piezoelectric ceramics have been fabricated by ordinary sintering technique. The effects of additions doping on the dielectric, piezoelectric, and ferroelectric properties of the ceramics were mainly investigated. X-ray diffraction of the sample appeared orthorhombic phase. The specimen doped with additions exhibits enhanced electrical properties ($d_{33}$= 153 pC/N). These results indicate that the 0.98NKN-0.02LST-x ceramics is a promising candidate for lead-free piezoelectric ceramics for applications such as piezoelectric actuators, harmonic oscillator and so on.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• 제18권6호
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• pp.195-200
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• 2018

A W-band frequency octupler is implemented on 100-nm GaAs pHEMT process. The fabricated octupler can be used as a local oscillator or a signal source of W-band transceivers. Three common-source doublers are connected in cascade to multiply an input signal of 10.75 GHz to 83 GHz. A common-source amplifier is followed for each doubler to improve the conversion gain and suppress the unwanted harmonics. The fabricated octupler showes high output of more than 6 dBm in the 80 - 84 GHz band and achieved excellent spurious suppression performance over 20 dBc.

• The Transactions of the Korean Institute of Power Electronics
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• 제8권1호
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• pp.70-79
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• 2003

In this paper, T5 28-watt fluorescent lamp ballast using a piezoelectric transformer is fabricated and its characteristic is investigated. Developed electronic ballast is composed of basic circuits and blocks, such as rectifier part, active power factor corrector part, frequency oscillation part using microcontroller and feedback control, piezoelectric transformer and resonant half bridge inverters. The fabricated ballast uses to variable frequency methode in external so exciting that the frequency of piezoelectric transformer could be generated by voltage control oscillator using microcontroller(AT90S4433). The current of fluorescent lamp is detected by feedback control circuit. The signal of inverter output is received using Piezoelectric transformer, and then its output transmitted to fluorescent lamp. Traditional electromagnetic ballasts operated at 50-60Hz have been suffered from noticeable flicker, high loss, large crest factor and heavy weight. A new electronic ballast is operated at high frequency about 75kHz, and then Input power factor, distortion of total harmonic and lamp current crest factor are measured about 0.9!35, 12H and 1.5, respectively Accordingly, the traditional ballast is by fabricated electronic ballast using piezoelectric transformer and voltage control oscillator because of its lighter weight, high efficiency, economic merit and saving energy.

• Korean Journal of Optics and Photonics
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• 제19권3호
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• pp.229-236
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• 2008

The optimum conditions of second harmonic generation (SHG) can be successfully achieved experimentally using single pass and double pass methods of a pumping beam. The beam has a power of several Watts radiated by a DOFA (Diode Laser Oscillator & Fiber Amplifier) system, which is a high power CW wavelength tunable infrared laser system, in a PPLN (Periodically Poled MgO doped Lithium Niobate) nonlinear crystal. In the case of a single pass method, the parameters are the wavelength of 535 nm for SHG and the output power of 245 mW generated from the pumping input beam with wavelength of 1070 nm and the power of 2.45 W at phase matching temperature of $108.9^{\circ}C$. The conversion efficiency of SHG was 10%. In order to enhance the output of SHG, the double pass method of the SHG system of a PPLN using a concave mirror for the retroreflection and a pair of wedged flat windows for phase compensation was also presented. In this double pass system, we obtained the SHG output beam with the wavelength of 535 nm and the maximum power of 383 mW at optimum phase matching temperature of $108.5^{\circ}C$ by using an incident pumping beam with wavelength of 1070 nm and the power of 2.45 W. The maximum conversion efficiency is 15.6%, which is more than that of the single pass method.

• Korean Journal of Optics and Photonics
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• 제7권3호
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• pp.251-259
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• 1996

Two-Photon Fluorescence (TPF) experiment measures temporal width of an amplified short laser pulse which has passed through a four-pass Nd: glass amplifier, after selecting a single pulse from pulse train Q-switched and mode-locked(QSML) in Nd:YLF master oscillator. Determination of pulsewidth and pulseshape was also made with detection of autocorrelation trace of CW mode-locked pulse train by using noncollinear type I Second Harmonic Generation (SHG) method. The observed TPF track showed various patterns, depending on pulse-selecting position in QSML pulse train. That is, autocorrelation of a pulse extracted at front of the train displayed smooth pulse shape, while one from the trailing part of the train created many sharp spikes and substructure in the pulse. By TPF method, pulsewidth was measured to be 44.4 ps with contrast ratio of 2.86 which enabled us to find out energy fraction of a pulse to total energy, (sum of pulse and background); we obtain the value of 0.62. Pulsewidth of 46.6ps was also acquired in another SHG experiment with the help of only mode-locked pulse train. On the other hand, we confirmed that shape of the pulse is close to $sech^2$ one as a result of fitting the SHG autocorrelation signal with various functions. With simulation using this $sech^2$ type of pulse, pulsewidth reduction of the beam, having passed through four-pass amplifier, was also verified.

• Journal of the Korean Institute of Telematics and Electronics
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• 제11권6호
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• pp.44-49
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• 1974

reactance modulator composed of multi-stage phase modulator utilizing VVC diodes as variable reactance elements and an oscillartor-modulator, utilizing a VVC diode as a tuning element, coupled to a crystal resonator through an artificial λ/4 network are introduced and their characteristics as FM modulator are compared mutually from the practical view points. especially, to get high modulation sensitivity of reactance modulators using VVC diodes, making a multi-stage modulation distortion characteristics of multi-stage modulator was necessary. The harmonic moj\dulationdistorion characteristics of multi-stage reactance modulator is analized in detall. Multi-stage reachance modulator is preferable to maintain sufficiently stable carrier frequency over the wide range of temperature and a mobile-transceiver was made through this method. On the other hand, FM-Quartz oscillator using a VVc diode is suitavle for handy-talkies of good quality were made through this method.

• Journal of Power Electronics
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• 제10권5호
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• pp.548-554
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• 2010

In this paper, a 1.5 kW Interior Permanent Magnet Synchronous Generator (IPMSG) with a power conditioner for the grid integration of a variable-speed wind turbine is developed. The power-conditioning system consists of a series-type 12-pulse diode rectifier powered by a phase shifting transformer and then cascaded to a PWM voltage source inverter. The PWM inverter is utilized to supply sinusoidal currents to the utility line by controlling the active and reactive current components in the q-d rotating reference frame. While the q-axis active current of the PWM inverter is regulated to follow an optimized active current reference so as to track the maximum power of the wind turbine. The d-axis reactive current can be adjusted to control the reactive power and voltage. In order to track the maximum power of the wind turbine, the optimal active current reference is determined by using a simple MPPT algorithm which requires only three sensors. Moreover, the phase angle of the utility voltage is detected using a simple electronic circuit consisting of both a zero-crossing voltage detecting circuit and a counter circuit employed with a crystal oscillator. At the generator terminals, a passive filter is designed not only to decrease the harmonic voltages and currents observed at the terminals of the IPMSG but also to improve the generator efficiency. The laboratory results indicate that the losses in the IPMSG can be effectively reduced by setting a passive filter at the generator terminals.

• Journal of the Institute of Electronics and Information Engineers
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• 제51권3호
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• pp.45-54
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• 2014

In this paper, We have designed and fabricated 20 InP Gunn diodes using a current limiting epitaxial structure by MINT's optimized fabrication processes. We have also packaged the fabricated InP Gunn diodes using our optimized packaging method, and then designed and fabricated a W-band waveguide FTO to measure characteristics of the packaged InP Gunn diodes. The packaged InP Gunn diode have a ceramic ring, a Au plated stud and a lid, and a Maltese cross. The fabricated InP Gunn diodes have good RF characteristics such as high output powers (11.8~17 dBm) and limiting low currents (less than 400 mA) between 92.9 and 94.78 GHz.

• Journal of the Korean Chemical Society
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• 제22권5호
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• pp.289-294
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• 1978

In this paper, for the purpose of studying the adsorbed states of benzene and p-xylene molecules on both of the Spheron 6(graphitized carbon) and the Alucer(aluminium oxides), we have calculated the differential molar entropies of adsorption in the Submonolayer region, by the use of statistical thermodynamics. The models we have adopted are two-dimensional gases and the harmonic oscillators. The values calculated in this way are compared with experimental values. As a result, it is believed that the adsorbed benzene molecules are localized on the Spheron 6, whereas on the Alucer it is nonlocalized. The molecular frequency, which is an adjustable parameter and is introduced as a result of oscillator model is $10^{11}\;sec^{-1}$ in the order of magnitude. For the case of p-xylene molecules adsorbed on these adsorbents, an abnormal result is obtained quite prior to the monolayer coverage, contrarily to the expectation of similar results as for the case of benzene.