Jeong-il Kang

High efficiency voltage-clamped coupled-inductor boost converter

In this paper, a low voltage stress and high efficiency voltage-clamped coupled-inductor boost converter is proposed. The conventional coupled-inductor boost converter has a serious drawback of high voltage stresses across all power semiconductors due to the high surge voltage caused by the resonance between leakage inductor of coupled-inductor and stray capacitors. Therefore, the conventional converter must be equipped with the dissipative snubber for absorbing this surge voltage, which will degrade the overall power conversion efficiency. To overcome these drawbacks, the proposed converter employs the diode-clamping circuit instead of the dissipative snubber. Proposed clamping circuit can clamp voltages across the power switch and output diode on the link capacitor voltage and output voltage, respectively. In addition, the leakage inductor energy is stored in the link capacitor, and then transferred to the output side together with the input energy. Therefore, the proposed converter can achieve the higher efficiency than the conventional coupled-inductor boost converter. The proposed converter is expected to be well suited to various applications demanding the high efficiency and high-voltage gain. To confirm the validity of the proposed circuit, the theoretical analysis and experimental results of the proposed converter are presented.

High efficiency and high power factor single-stage balanced forward-flyback converter

In this paper, a high efficiency and high power factor single-stage balanced forward-flyback converter merging a foward and flyback converter topologies is proposed. The conventional AC/DC flyback converter can achieve a good power factor but it has a 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 on and 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.

Lossless Snubber with Minimum Voltage Stress for Continuous Current Mode Tapped-Inductor Boost Converters for High Step-up Applications

To invigorate the tapped-inductor boost (TIB) topology in emerging high step-up applications for off-grid products, a lossless snubber consisting of two capacitors and three diodes is proposed. Since the switch voltage stress is minimized in the proposed circuit, it is allowed to use a device with a lower cost, higher efficiency, and higher availability. Moreover, since the leakage inductance is fully utilized, no effort to minimize it is required. This allows for a highly productive and cost-effective design of the tapped-inductor. The proposed circuit also shows a high step-up ratio and provides relaxation of the switching loss and diode reverse-recovery. In this paper, the operation is analyzed in detail, the steady-state equation is derived, and the design considerations are discussed. Some experimental results are provided to confirm the validity of the proposed circuit.

High Efficiency Lossless Snubber for Photovoltaic Maximum Power Point Tracker

A new passive lossless snubber for boost converter based on magnetic coupling is proposed. It is composed of a winding coupled with boost inductor, one snubber inductor, two snubber capacitor and three additional diodes. Especially, the snubber inductor can not only limit the reverse recovery current of output diode but also minimize switch turn-on losses greatly. Moreover, all of the energy stored in the snubber is transferred to the load in the manner of resonance. To confirm the validity of proposed system, theoretical analysis, design consideration, and verification of experimental results are presented.

Lossless snubber for tapped-inductor boost converter for high step-up application

In order to suppress the switch voltage spike in the tapped-inductor boost (TIB) converter, a passive lossless snubber with minimum voltage stress is proposed. It consists of two capacitors and three diodes and takes advantage of the leakage inductance of the tapped-inductor. Moreover, it can readily be incorporated into an existing system since it does not modify the original TIB topology. The TIB converter employing the proposed snubber features zero current soft-switching of the switching devices, significantly relieved diode reverse-recoveries, and higher step-up ratio than the original TIB converter without a snubber. The proposed circuit is analyzed in detail, and some experimental results are also presented.

Cost-effective single switch multi-channel LED driver

In this paper, a cost-effective single switch multi-channel LED (light emitting diode) driver is proposed. While conventional LED drivers require as many non-isolated DC/DC converters as the number of LED channels, the proposed LED driver needs only one power switch and several balancing capacitors instead of expensive non-isolated DC/DC converters. Therefore, the proposed driver features a simpler structure, with a lower cost and a higher efficiency. Because its power switch can be turned off under the zero current switching condition, it has very desirable advantages such as improved electromagnetic interference characteristics and high efficiency. Moreover, it uses only a small number of DC blocking capacitors with no additional active devices for the current balancing of multi-channel LEDs. As a result, the proposed driver exhibits high reliability and is cost effective. To confirm the validity of the proposed driver, a theoretical analysis is performed, and design considerations and experimental results obtained from a prototype that is applicable to a 46” LED-TV are presented.

Analysis and Design of a High-Efficiency Boundary Conduction Mode Tapped-Inductor Boost LED Driver for Mobile Products

For low-power high-frequency LED driver applications in small form factor mobile products, a high-efficiency boundary conduction mode tapped-inductor boost converter is proposed. In the proposed converter, the switch and the diode achieve soft-switching, the diode reverse-recovery is alleviated, and the switching frequency is very insensitive to output voltage variations. The circuit is quantitatively characterized, and the design guidelines are presented. Experimental results from an LED backlight driver prototype for a 14 inch notebook computer are also presented.

LED Driver Compatible with Both Electronic and Magnetic Ballasts

Light-emitting diode (LED) drivers are recently replacing fluorescent lamps; these drivers can operate adaptively with various ballasts without modifying and removing such ballasts. To satisfy these trends, a LED driver that is compatible with both electronic and magnetic ballasts is proposed in this study. Unlike conventional LED drivers, the proposed driver has a ballast recognition circuit and a mode selection circuit to operate ballasts at optimal conditions. Therefore, it features low voltage stress, high efficiency, and good compatibility with both electronic and magnetic ballasts. Moreover, it can be compatible with a wide selection of ballasts from various manufacturers. To confirm the validity of the proposed LED driver, results of the theoretical analysis and experimental verification performed on a 15 W-rated prototype are presented.

Power Factor Correction LED Driver with Small 120Hz Current Ripple

Recently, the LED(Light Emitting Diode) is expected to replace conventional lamps including incandescent, halogen and fluorescent lamps for some general illumination application, due to some obvious features such as high luminous efficiency, safety, long life, environment-friendly characteristics and so on. To drive the LED, a single stage PFC(Power Factor Correction) flyback converter has been adopted to satisfy the isolation, PFC and low cost. The conventional flyback LED driver has the serious disadvantage of high 120Hz output current ripple caused by the PFC operation. To overcome this drawback, a new PFC flyback with low 120Hz output current ripple is proposed in this paper. It is composed of 2 power stages, the DCM(Discontinuous Conduction Mode) flyback converter for PFC and BCM(Boundary Conduction Mode) boost converter for tightly regulated LED current. Since the link capacitor is located in the secondary side, its voltage stress is small. Moreover, since the driver is composed of 2 power stages, small output filter and link capacitor can be used. Especially, since the flyback is operated at DCM, the PFC can be automatically obtained and thus, an additional PFC IC is not necessary. Therefore, only one control IC for BCM boost converter is required. To confirm the validity of the proposed converter, theoretical analysis and experimental results from a prototype of 24W LED driver are presented.

Analysis and Design of Continuous Current Mode Tapped-Inductor Boost Converter

As the turns ratio of the tapped-inductor contributes to the step-up ratio, the tapped-inductor boost (TIB) converter has significantly increased level of difficulties in its analysis and design compared to the conventional boost converter where the duty ratio is the sole factor affecting the step-up ratio. In this paper, the operation of the continuous current mode TIB converter is briefly reviewed, the characteristics are analyzed in detail, and a design guideline optimizing the loss in the tapped-inductor is presented with a practical design example. Finally, experimental results from a 12V/120V prototype for 0.25A LED driver application are also presented to confirm the design.