• JSTS:Journal of Semiconductor Technology and Science
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• v.14 no.5
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• pp.682-687
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• 2014

We have performed reverse gate bias stress tests on AlGaN/GaN-on-Si Heterostructure FETs (HFETs). The shift of threshold voltage ($V_{th}$) and the reduction of on-current were observed from the stressed devices. These changes of the device parameters were not permanent. We investigated the temporary behavior of the stressed devices by analyzing the temperature dependence of the instabilities and TCAD simulation. As the baseline temperature of the electrical stress tests increased, the changes of the $V_{th}$ and the on-current were decreased. The on-current reduction was caused by the positive shift of the $V_{th}$ and the increased resistance of the gate-to-source and the gate-to-drain access region. Our experimental results suggest that electron-trapping effect into the shallow traps in devices is the main cause of observed instabilities.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.11
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• pp.1625-1633
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• 2012

In the lighting industry, a Lighting Emitting Diode (LED) is increasingly used because of many advantages and a eco-friendly product comparing with the conventional lighting. However, the LED lighting has to include various AC/DC converters because the direct current is used for the LED lighting. Among a lot of power converters, the flyback converter is widely used for the LED lighting and includes some electrolytic capacitors for the voltage regulation. But the electrolytic capacitor has shorter lifetime than the LED element. It makes the expected life-time of the converter having the electrolytic capacitor shorter than the LED element. This paper proposes the single-stage PFC flyback converter without electrolytic capacitors. To verify the performance of the proposed converter, simulated and experimental works were carried out.

• Journal of Power Electronics
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• v.11 no.1
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• pp.37-44
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• 2011

In this paper, a four-phase 8/6-pole 4-kW SR motor drive model is presented. Based on experimental data, the model allows an accurate simulation of a drive in dynamic operation. Simulations are performed and a laboratory type set-up is built based on a TI TMS320F2812 platform to experimentally verify the theoretical results obtained for a SR motor. To reduce acoustic noise and to correct the power factor of this drive, a two-stage power converter is proposed that uses a current source rectifier (CSR) as the input stage for the asymmetrical converter of the studied SRM. Employing the space-vector modulation (SVM) method in matrix converters, the CSR switching allows the dc link's capacitors to be eliminated and the power factor of the SRM drive to be improved. As the electrical motive force (emf) is directly proportional to the rotor speed, the input voltage to the machine can be programmed to be a function of the speed with the modulation index of the CSR, leading to a reduction in the acoustic noise of the SRM drive. Simulation of the whole SRM drive system is performed using MATLAB-Simulink. The results fully comply with the required conditions such as power factor correction with an improvement in the THD.

• Journal of Power Electronics
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• v.19 no.3
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• pp.637-644
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• 2019

Wireless power transfer (WPT) technology with various transfer mechanisms such as inductive coupling, magnetic resonance and capacitive coupling is being widely researched. Until now, power transfer efficiency (PTE) and power transfer capability (PTC) have been the primary concerns for designing and developing WPT systems. Therefore, a lot of studies have been documented to improve PTE and PTC. However, power consumption in the standby mode, also defined as the no-load mode, has been rarely studied. Recently, since the number of WPT products has been gradually increasing, it is necessary to develop techniques for reducing the standby power consumption of WPT systems. This paper investigates the standby power consumption of commercial WPT products. Moreover, a standby power reduction technique for WPT systems via magnetic resonance coupling (MRC) with a parallel resonance type resonator is proposed. To achieve a further standby power reduction, the voltage control of an AC/DC travel adapter is also adopted. The operational principles and characteristics are described and verified with simulation and experimental results. The proposed method greatly reduces the standby power consumption of a WPT system via MRC from 2.03 W to 0.19 W.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.3
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• pp.223-227
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• 2016

Power supplies make the load compatible with its power source. DC power supplies are extensively used with most electrical and electronic appliances such as computers, television, and audio sets. The presence of non-linear loads results in a low power factor and higher harmonics in the power system. Several techniques for power-factor correction and harmonic reduction have been reported in the literature. This paper proposes a bridgeless boost converter that improves the power factor and reduces the harmonic content in input line currents as compared to full-bridge rectifiers. This bridgeless boost converter eliminates the need of a line-voltage bridge rectifier in conventional boost converter and thereby reduces conduction losses. The effectiveness of the proposed scheme is verified by computer simulations by using the PSIM software.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.5
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• pp.416-422
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• 2001

The BLDC(Brushless DC) Motor is characterized by linear torque to current and speed to voltage. It has low acoustic noise and fast dynamic response. Moreover, it has high power density with high proportion of torque to inertia in spite of small size drive. However, when armature current is commutated, the current ripple is generated by the motor inductance components in stator windings and back-EMF. This current ripple caused to torque ripple. Therefore, it is difficult to apply the BLDC motor to a precision servo drive system. In this paper, a new current control algorithm using fourier series coefficients is proposed. This proposed algorithm can minimize torque ripple due to the phase current commutation of BLDC motor. Simulation and Experimental results prove the effectiveness at the Proposed algorithm through comparison with the conventional unipolar PWM method.

• Journal of the Korean Institute of Telematics and Electronics C
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• v.34C no.11
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• pp.1-11
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• 1997

The transient current components of the dRAM are analyzed and the sensing current, data path operation current and DC leakage current are revealed to be the major curretn components. It is expected that the supply voltage of less than 1.5V with low VT MOS witll be used in multi-giga bit dRAM. A low voltage dual VT self-timed CMOS logic in which the subthreshold leakage current path is blocked by a large high-VT MOS is proposed. An active signal at each node of the nature speeds up the signal propagation and enables the synchronous DRAM to adopt a fast pipelining scheme. The sensing current can be reduced by adopting 8 bit prefetch scheme with 1.2V VDD. Although the total cycle time for the sequential 8 bit read is the same as that of the 3.3V conventional DRAM, the sensing current is loered to 0.7mA or less than 2.3% of the current of 3.3V conventional DRAM. 4 stage pipeline scheme is used to rduce the power consumption in the 4 giga bit DRAM data path of which length and RC delay amount to 3 cm and 23.3ns, respectively. A simple wave pipeline scheme is used in the data path where 4 sequential data pulses of 5 ns width are concurrently transferred. With the reduction of the supply voltage from 3.3V to 1.2V, the operation current is lowered from 22mA to 2.5mA while the operation speed is enhanced more than 4 times with 6 ns cycle time.

• Progress in Superconductivity
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• v.13 no.1
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• pp.1-6
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• 2011

Measurement of magnetic signals generated from electric activity of myocardium provides useful information for the functional diagnosis of heart diseases. Key technical component of the magnetocardiography (MCG) technology is SQUID. To measure MCG signals with high signal-to-noise ratio, sensitive SQUID magnetic field sensors are needed. Present magnetic field sensors based on Nb SQUIDs have field sensitivity good enough to measure most of MCG signals. However, for accurate measurement of fine signal pattern or detection of local atrial fibrillation signals, we may need higher field sensitivity. In addition to field sensitivity, economic aspect of the SQUID system is also important. To simplify the SQUID readout electronics, the output voltage or flux-to-voltage transfer of SQUID should be large enough so that direct measurement of SQUID output can be done using room-temperature preamplifiers. Double relaxation oscillation SQUID (DROS), having about 10 times larger flux-to-voltage transfers than those of DC-SQUIDs, was shown to be a good choice to make the electronics compact. For effective cancellation of external noise inside a thin economic shielded room, first-order axial gradiometer with high balance, simple structure and long-baseline is needed. We developed a technology to make the axial gradiometer compact using direct bonding of superconductive wires between pickup coil and input coil. Conventional insert has mechanical support to hold the gradiometer array, and the dewar neck has equal diameter with the dewar bottom. Boiling of the liquid He can generate mechanical vibrations in the gradiometer array due to mechanical connection structure. Elimination of the mechanical support, and direct mounting of the gradiometer array into the dewar bottom can reduce the dewar neck diameter, resulting in the reduction of liquid He consumption.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.6
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• pp.497-504
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• 2021

This paper presents improvement of the reception noise suppression method during formation flights of aircraft. Since aircraft communication equipment is very important for flight mission and safety to perform the functions of internal/external communications, it is required to implement noise-free, clean communication quality, and transmitting/receiving functions. Therefore, the FTA (Fault Tree Analysis) analysis and failure search were performed on the reception noise, and the internal noise of the intercom that affected the reception noise and the none-transmition phenomenon was identified. We changed the multiple grounds of the intercom to a single ground and applied an improved method of filtering the DC Offset voltage. As a result, the voice quality of the communication system of the aircraft was improved through the reduction of the reception noise during formation flights, and it was verified by ground and flight tests.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.9
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• pp.1-7
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• 2014

Brushless Direct Current(BLDC) Motor is essential to measure a rotor position because of that this motor type needs to synchronize the rotor's position and changeover phase current instead of a brush and commutator used on the existing dc motor. Recently, many researches have studied on sensorless control drive for BLDC motor. The conventional control methods are a compensation value dq, Kalman filter, Fuzzy logic, Neurons neural network, and the like. These methods has difficulties of detecting BEMF accurately at low speed because of low BEMF voltage and switching noise. And also, the operation is long and complex. So, it is required a high-performance microprocessor. Therefore, it is not suitable for a small BLDC motor sensorless drive. This paper presents control methods suitable for economic small BLDC motor sensorless drive which are an improved design of the BEMF detection circuit, simplifying a complex algorithm and computation time reduction. The improved motor sensorless drive is verified stability and validity through being designed, manufactured and analyzed.