Ultrahigh Step-down Converter Research Articles

Low Output Current Ripple Ultra High Step-Down Two-Phase Buck Converter With Low Switching Losses

Low Output Current Ripple Ultra High Step-Down Two-Phase Buck Converter With Low Switching Losses

Light-Load Efficiency Improvement for Ultrahigh Step-Down Converter Based on Skip Mode

In this paper, two light-load efficiency improvement methods are presented and applied to the ultrahigh step-down converter. The two methods are both based on skip mode control. Skip Mode 1 only needs one half-bridge driver integrated circuit (IC) to drive three switches, so it has the advantages of easy signal control and lower cost, whereas Skip Mode 2 requires one half-bridge driver integrated circuit IC, one common ground driver IC, and three independent timing pulse-width-modulated (PWM) signals to control three switches, so the cost is higher and the control signals are more complicated, but Skip Mode 2 can obtain slightly higher light-load efficiency than Skip Mode 1. Although the switching frequency used in these methods are reduced, the transferred energy is unchanged, but the output voltage ripple is influenced to some extent.

Interleaved Ultrahigh Step-Down Converter With Low Component Count

An ultrahigh step-down converter with a low number of semiconductor devices is presented in this article. Important features of this converter are simple structure with low size and cost, low voltage and current stress on components, low output current ripple, and low conduction and switching losses. In this converter, the power switches are turned on under zero current switching (ZCS) condition, whereas the output diodes commutate under ZCS condition without any auxiliary circuit. Thereby, in addition to the converter efficiency improvement, the diodes reverse recovery problem is alleviated. The proposed topology has employed a two-phase interleaved structure to reduce current stress, three windings coupled inductors to further decrease the voltage gain, and two series capacitors to diminish the voltage stress on the semiconductors elements and recover the leakage inductances energy. The experimental results of an implemented prototype are provided to evaluate the effectiveness of the proposed topology at 100 kHz and 200 W, which converts a 400-V input voltage into a 12-V output voltage.

Improvement in Voltage Conversion Ratio of Ultrahigh Step-Down Converter

A modified step-down converter is presented herein, which is mainly based on one coupled inductor and several energy-transferring capacitors to improve the voltage conversion ratio as well as to reduce the switch voltage stress. In addition, the portion of the leakage inductance energy can be recycled to the input via the active clamp circuit during the turn-off period and the switches have zero-voltage switching (ZVS) during the turn-on transient. In this paper, the basic operating principles of the proposed converter are firstly described and analyzed, and its effectiveness is finally demonstrated by experiment based on a prototype with input voltage of 60 V, output voltage of 3.3 V and rated output power of 33 W.

An Interleaved Nonisolated ZVS Ultrahigh Step-Down DC–DC Converter With Low Voltage Stress

This paper presents a nonisolated ultrahigh step-down dc-dc converter for low-voltage high-current applications. The converter provides extended duty cycle for all power switches while low voltage and current stresses are imposed on semiconductor devices that cause low conduction losses and low output current ripple. In addition, soft-switching condition is achieved for all semiconductor devices without adding any active element. To achieve the improved voltage conversion ratio, a pair of coupled inductors and series capacitors is used in the interleaved step-down structure. The two auxiliary inductors provide zero-voltage zero-current switching turn on for all switches and zero-current switching turn on and turn off for all diodes. Thus, the losses associated with semiconductor components are reduced impressively and the overall efficiency of the proposed converter is improved considerably. The accuracy of the converter operation is confirmed by a 450-W laboratory prototype operating at 400-V input, 12-V output, and 100 kHz switching frequency.

Voltage Gain Improvement of a High-Step-Down Converter With Coupled-Inductor Core Size Reduction Based on Flux Linkage

As compared with the buck converter, the ultrahigh step-down converter can achieve a much higher step-down gain, which can be determined by not only the duty cycle, but also the turns ratio of the coupled inductor. However, this converter suffers from some problems, such as pulsating output current and large dc magnetizing inductance current, which will degrade the core utilization. As compared with the ultrahigh step-down converter, the coupled-inductor-based high step-down converter features a nonpulsating output current and a zero dc magnetizing inductance current. Therefore, the output current ripple is lower and the core utilization can be upgraded. Since the core size is proportional to the square of the applied flux-linkages, an improved coupled-inductor-based high step-down converter is presented herein. By employing an auxiliary circuit, consisting of a small capacitor and a mosfet , the flux linkage of the coupled inductor can be decreased, and hence the required core size can be reduced. In addition, due to the auxiliary circuit, the voltage spike across the tapped switch can be reduced. Above all, the step-down gain can be improved. Finally, detailed theoretical analyses and experimental results are provided to verify the feasibility and effectiveness of the proposed converter.

An Expandable Two-Phase Interleaved Ultrahigh Step-Down Converter With Automatic Current Balance

In the high step-down voltage applications, the dc–dc converter with a high step-down voltage conversion ratio is usually used. Recently, a high step-down converter, named ultrahigh step-down converter, has been presented. As compared with the nonisolated tapped-inductor buck converter, the ultrahigh step-down converter has not only a higher voltage step-down gain but also a lower voltage spike. On the other hand, in the high-current applications, a multiple phase structure is preferable. Therefore, in this paper, a novel expandable two-phase interleaved ultrahigh step-down converter with automatic current balance is presented, which is derived from the existing single-phase ultrahigh step-down converter. There are four main advantages of the proposed converter. First, the step-down voltage gain is improved. Therefore, the turns ratio of each phase can be decreased. Second, due to the charge balance of the energy-transferring capacitor, the proposed two-phase ultrahigh step-down converter possesses an automatic current balance. Third, as compared with a single-phase ultrahigh step-down converter, the output current ripple can be reduced. Fourth, the phase number of the proposed converter can be expanded. Finally, the basic operating principle of the proposed converter is analyzed, and a prototype is constructed to verify its effectiveness by some experimental results.

Ultrahigh Step-Down Converter With Wide Input Voltage Range Based on Topology Exchange

To overcome the traditional buck converter, which is difficult to achieve a high step-down gain with an appropriate duty cycle, a coupled-inductor-based step-down converter, named ultrahigh step-down converter, is proposed by Hwu et al. [11] . As compared with the buck converter, the ultrahigh step-down converter can achieve a much higher step-down gain, which can be determined by not only the duty cycle but also the turns ratio of the coupled inductor. However, the ultrahigh step-down converter is designed at a fixed input voltage of 48 V. In the telecommunication applications, the high dc bus voltage varies in a wide range, not kept at a fixed nominal voltage of 48 V. The experimental results show that as the input voltage increases, the efficiency of the ultrahigh step-down converter decreases. Therefore, in this paper, an improved ultrahigh step-down converter with a wide input voltage range is presented. According to the topology exchange, the voltage gain can be changed to a suitable one when the input voltage changes. By doing so, as compared with the ultrahigh step-down converter [11] , the duty cycle of the proposed converter can be extended, and hence the efficiencies of the proposed converter can be improved. The proposed converter is verified by a wide input voltage (18–54 V), with an output voltage of 1.2 V and a rated output current of 10 A.

Performance comparison between tapped-inductor buck converter and ultrahigh step-down converter

ABSTRACTIn this study, a detailed performance comparison between the tapped-inductor buck converter and the ultrahigh step-down converter is presented. The items used to compare include the voltage gain, DC magnetising inductance current, component voltage stress, coupled inductor size, output current ripple and efficiency. Moreover, the advantages and disadvantages are discussed herein. The experimental results with the same specifications are shown to compare.

Ultrahigh Step-Down Converter

In this paper, an ultrahigh step-down converter is presented, which combines one coupled inductor and one energy-transferring capacitor. The corresponding voltage conversion ratio is much lower than that of the traditional synchronously rectified (SR) buck converter, and the proposed converter can achieve extremely low output voltage with an appropriate duty ratio. Moreover, there are three major merits in the proposed converter. One merit is that the voltage conversion ratio of the proposed converter is linear, thereby making control quite easy. Another merit is that if one of the switches fails or is abnormally controlled, a high voltage does not appear in the output terminal, so the output load can be protected. The other merit is that the proposed converter can be driven using the existing SR buck pulse-width modulation control integrated circuit. In this study, brief theoretical deductions and some experimental results are given to verify the feasibility and effectiveness of the proposed converter.