• Proceedings of the KIPE Conference
• /
• 1997.07a
• /
• pp.256-260
• /
• 1997

To achieve high efficiency in high power and high frequency applications, reduction of switching losses and noise is very important. In this paper, an improved soft switching forward converter is proposed. The proposed converter is constructed by using non-dissipative snubbers in parallel with the main switch and output diode of the conventional forward converter. Due to the use of the non-dissipative snubbers in the primary and secondary, the proposed converter achieves zero-voltage and zero-current switching for all switching devices without switching losses and output diode recovery losses. The complete operating principles, theoritical analysis, experimental results will be presented.

• Proceedings of the KIPE Conference
• /
• 1998.07a
• /
• pp.409-412
• /
• 1998

In this paper, an improved soft switching forward dc/dc converter is proposed. The proposed converter is constructed by using non-dissipate snubbers in parallel with the main switch and output diode of the conventional forward converter. Due to use of the non-dissipative snubbers, the proposed converter achieves zero-voltage switching for all switching devices and output diodes without switching losses. The complete operating principles and experimental results will be presented.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.66 no.9
• /
• pp.1437-1443
• /
• 2017

Electric energy is consumed or regenerated according to an operation of electric rail cars in urban railway power substations. A thyristor dual converter system is used to deal with the electric energy. Since the AC input voltage of power substations is $22.9kV{\pm}10%$, the magnitude of the AC voltage fluctuates according to load conditions, so the secondary side voltage of the DDY transformer also fluctuates. In the thyristor dual converter, the response characteristics of the DC output voltage and the DC output current are changed based on an initial firing angle in the cross mode conversion between the forward mode and the reverse mode. Therefore, this paper proposes the initial firing angle tracking algorithm considering fluctuation of the AC input voltage. The effectiveness of the proposed algorithm is verified by a simulation compared with the conventional algorithm.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.18 no.5
• /
• pp.492-500
• /
• 2013

A balanced forward-flyback converter for high efficiency and high power factor using a foward and flyback converter topologies is proposed in this paper. The conventional AC/DC flyback converter can achieve a good power factor but it has the high offset current through the transformer magnetizing inductor, which results in a large core loss and low power conversion efficiency. And, the conventional forward converter can achieve the good power conversion efficiency with the aid of the low core loss but the input current dead zone near zero cross AC input voltage deteriorates the power factor. On the other hand, since the proposed converter can operate as the forward and flyback converters during switch turn-on and turn-off periods, respectively, it cannot only perform the power transfer during an entire switching period but also achieve the high power factor due to the flyback operation. Moreover, since the current balanced capacitor can minimize the offset current through the transformer magnetizing inductor regardless of the AC input voltage, the core loss and volume of the transformer can be minimized. Therefore, the proposed converter features a high efficiency and high power factor. To confirm the validity of the proposed converter, theoretical analysis and experimental results from a prototype of 24W LED driver are presented.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.22 no.2
• /
• pp.140-149
• /
• 2017

This study proposes a new type of active-clamp forward-flyback converter with two transformers that operate in forward and flyback modes during on and off times, respectively, instead of not using an output inductor. The main switch can be turned on with zero-voltage switching (ZVS) using the leakage inductance of the transformer and the output capacitor of the main switch. The leakage inductance should be increased to ZVS. However, the ringing between the leakage inductance of the transformer and the parasitic output capacitance of the secondary side rectifier switches results in a serious voltage spike. A forward-flyback converter employing auxiliary inductor and auxiliary diode is proposed to overcome the problem. The operational principles are analyzed in detail and validated through experiments with a 385 V-to-53 V/37 A prototype.

• Current Optics and Photonics
• /
• v.5 no.2
• /
• pp.173-179
• /
• 2021

The electroluminescence (EL) intensities of GaN-based light-emitting diodes (LEDs) are estimated based on their photoluminescence (PL) properties. The PL intensity obtained under open-circuit conditions is divided into two parts: the PL intensity under a forward bias lower than the optical turn-on voltage, and the difference between the PL intensities under open-circuit conditions and under forward bias. The luminescence induced by photoexcitation under a constant forward bias lower than the optical turn-on voltage is primarily the PL from the excited area of the LED. In contrast the intensity difference, obtained by subtracting the PL intensity under the forward bias from that under open-circuit conditions, contains the EL induced by the photocarriers generated during photoexcitation. In addition, a reverse photocurrent is generated during photoexcitation under constant forward bias across the LED, and can be correlated with the PL-intensity difference. The relationship between the photocurrent and PL-intensity difference matches well the relationship between the injection current and EL intensity of LEDs. The ratio between the photocurrent generated under a bias and the short-circuit current is related to the ratio between the PL-intensity difference and the PL intensity under open-circuit conditions. A relational expression consisting of the ratios, short-circuit current, and PL under open-circuit conditions is proposed to estimate the EL intensity.

• Proceedings of the KIEE Conference
• /
• 1992.07b
• /
• pp.992-994
• /
• 1992

Diode rectifier has many low order harmonics in line currents. So, power factor of input side is relatively low. Recently, PWM conveters have been actively studied in order to reduce the harmonics. This paper describes a voltage source PWM rectifier with feed-forward compensation of instantaneous load power. By adding feed-forward compensation to dc link voltage control loop, the fluctuation of dc link voltage at a sudden load change can be considerably suppressed. Simulation based on analytical approach Was performed and the results of it showed a good agreement with theory.

• 한국컴퓨터산업교육학회:학술대회논문집
• /
• 2003.11a
• /
• pp.95-98
• /
• 2003

Power semiconductors are being currently used as a application of intelligent power inverters to a refrigerator, a washing machine and a vacuum cleaner as well as core parts of industrial system. The rating of semiconductor devices is an important factor in decision on the field of application and the forward blocking voltage is one of factors in decision of the rating. The Power MOS device has a merit of high input impedance, short switching time, and stability in temperature as well known. Power MOS devices are mainly used as switches in the field of power electronics, especially the on-state resistance and breakdown voltage are regarded as the most important parameters. Power MOS devices that enable a small size, a light weight, high-integration and relatively high voltage are required these days. In this paper, we proposed the new lateral power MOS which has forward blocking voltage of 250V and contains trench electrodes and verified manufactural possibility by using TSUPREM-4 that is process simulator.

• Proceedings of the KIEE Conference
• /
• 1998.07f
• /
• pp.2042-2044
• /
• 1998

In this paper, we proposed the alternated forward multi-resonant converter. It can reduce the voltage stress due to the operation of two multi resonant switches and also provides a high frequency applications. The proposed circuit is verified through the PSpice simulation and the 50W experimental set with 2MHz maximum frequency. The measured voltage stress is up to 170V of 2.9 times the input voltage and the efficiency is about 81.66% at low line.

• Transactions on Electrical and Electronic Materials
• /
• v.2 no.3
• /
• pp.33-37
• /
• 2001

A vertical trench electrode type EST has been proposed in this paper. The proposed device considerably improves snapback which leads to a lot of problems of device applications. In this paper, the vertical dual gate Emitter Switched Thyristor (EST) with trench electrode has been proposed for improving snab-back effect. It is observed that the forward blocking voltage of the proposed device is 745V. The conventional EST of the same size were no more than 633V. Because the proposed device was constructed of trench-type electrodes, the electric field moved toward trench-oxide layer, and the punch through breakdown of the proposed EST is occurred at latest.