Sin-Woo Lee

Single-Stage Bridgeless AC–DC PFC Converter Using a Lossless Passive Snubber and Valley Switching

A single-stage bridgeless ac-dc PFC converter using a lossless passive snubber and valley switching is proposed. The proposed converter is based on a two-stage bridgeless boost-flyback converter. In the proposed converter, the conduction losses are reduced by removing an input full-bridge diode rectifier. The boost inductor is designed to be operated in the discontinuous-conduction mode for achieving high power factor. In the flyback module, the couple inductor that provides input-output electrical isolation for safety is designed to be operated in the critical-conduction mode for low RMS current and low turn-on switching loss by using valley-switching operation. Because of the lossless snubber circuit, the voltage spike of switch is clamped, and the leakage inductor energy is recycled. The snubber capacitor is used as a dc-bus capacitor, which is divided into two capacitors. In addition, some input power is directly conducted to the output, and the remaining power is stored in dc-bus capacitor. So, low-voltage rating capacitors can be used as the dc-bus capacitor and power transfer efficiency is improved. The presented theoretical analysis is verified on an output 48-V and 60-Wexperimental prototype.

A Single-Switch AC–DC LED Driver Based on a Boost-Flyback PFC Converter With Lossless Snubber

A single-switch ac-dc light-emitting-diode (LED) driver based on boost-flyback power factor correction (PFC) converter with a lossless snubber is proposed. In the proposed LED driver, the boost PFC module is designed to be operated in the discontinuous-conduction mode to achieve a high power factor. The dc-dc flyback module is designed to provide input-output electrical isolation to improve safety. The lossless snubber circuit clamps the peak voltage spike of switch to a low voltage and the leakage inductor energy is recycled via the dc-dc flyback module. Additionally, a low-voltage-rating capacitor can be used as the dc-bus capacitor because some of the input power is directly conducted to the output; the remaining power is stored in the dc-bus capacitor. Therefore, the proposed LED driver can provide a high power factor and a high power conversion efficiency. These results are verified for an output of 48 V and 2 A for the experimental prototype.

Zero-Ripple Input-Current High-Step-Up Boost–SEPIC DC–DC Converter With Reduced Switch-Voltage Stress

This paper proposes a zero-ripple input-current high-step-up boost–single ended primary inductor converter (SEPIC) dc–dc converter with reduced switch-voltage stress to overcome some drawbacks of the conventional cascaded boost–SEPIC dc–dc converter. In the proposed converter, the input current ripple is significantly removed by the auxiliary circuit at the boost stage and the voltage gain is more increased by using turn ratio of a coupled inductor at the SEPIC stage. Additional, the switch-voltage stress is reduced due to the clamping circuit, and the reverse-recovery problem of the output diode is alleviated by the leakage inductor. Hence, the low-voltage-rating MOSFET, which has low

Boost-Integrated Two-Switch Forward AC–DC LED Driver With High Power Factor and Ripple-Free Output Inductor Current

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Efficient bridgeless PFC converter with reduced voltage stress

, can be utilized as a main switch device. Therefore, the total power efficiency is improved. The theoretical analysis of the proposed converter is verified on an output 200-V to 200-W prototype.

An isolated bridgeless AC-DC PFC converter using a LC resonant voltage doubler rectifier

This paper proposes a boost-integrated two-switch forward ac–dc light-emitting diode (LED) driver with a high power factor and ripple-free output inductor current. In the proposed LED driver, the maximum switch voltages are clamped to the voltage level of the dc-link capacitor without an RCD snubber circuit by adopting a two-switch forward structure, and the magnetizing inductor energy is restored in the dc-link capacitor to prevent the magnetizing inductor from saturating without a tertiary winding. Moreover, the relatively small capacitance can be utilized by the output capacitor, as the output inductor current ripple is significantly reduced by the additional circuit, unlike in the conventional LED driver. Hence, the LC filter at the output stage is simplified. The proposed LED driver has a high power factor and the power efficiency is improved. The theoretical analysis results of the proposed LED driver are verified on an output 24 [V]–1.4 [A] prototype.

High Step-Up Cascade Boost DC–DC Converter Using Coupled Inductor with Ripple-Free Input Current

Summary An efficient bridgeless power factor correction converter with reduced voltage stress is proposed. In the proposed converter, the input full-bridge rectifier is removed to reduce the conduction loss of rectification, and the voltage stress of switching devices is significantly reduced by utilizing the additional circuit composed of a capacitor and a diode. Therefore, low-voltage-rating diodes with less forward voltage drop and low-voltage-rating Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) with low RDS(on) is utilized. The proposed converter is based on the single-ended primary-inductor converter power factor correction operation in discontinuous conduction mode to achieve a high power factor with a simple control circuit. Consequently, the proposed converter can provide a high power factor and a high power efficiency, and it is also suitable for low-cost converter for high input/output voltage system. The operational principles, steady-state analysis, and design equations of the proposed converter are described in detail. Experimental results are verified for a 130 W prototype at a constant switching frequency 100 kHz. Copyright

High Step-Up Coupled-Inductor Cascade Boost DC–DC Converter With Lossless Passive Snubber

ABSTRACT This paper proposed an isolated bridgeless AC–DC power factor correction (PFC) converter using a LC resonant voltage doubler rectifier. The proposed converter is based on isolated conventional single-ended primary inductance converter (SEPIC) PFC converter. The conduction loss of rectification is reduced than a conventional one because the proposed converter is designed to eliminate a full-bridge rectifier at an input stage. Moreover, for zero-current switching (ZCS) operation and low voltage stresses of output diodes, the secondary of the proposed converter is designed as voltage doubler with a LC resonant tank. Additionally, an input–output electrical isolation is provided for safety standard. In conclusion, high power factor is achieved and efficiency is improved. The operational principles, steady-state analysis and design equations of the proposed converter are described in detail. Experimental results from a 60 W prototype at a constant switching frequency 100 kHz are presented to verify the performance of the proposed converter.

Isolated SEPIC DC–DC Converter With Ripple-Free Input Current and Lossless Snubber

Abstract This paper proposes a high step-up cascade boost DC–DC converter using a coupled inductor with ripple-free input current. The proposed converter is based on a conventional cascade boost converter for high step-up. In the proposed converter, the first boost cell cancels the input current ripple with a small auxiliary circuit, as well as increases the voltage gain. Therefore, the input current ripple is significantly removed by the ripple-free circuit. In the second boost cell, the turn ratio of a coupled inductor is utilized to further increase the voltage gain in comparison with the conventional cascade boost converter. The theoretical analysis and performance are proved by experimental results from an output 200-[V], 200-[W] prototype of the proposed converter.