This paper investigates the integrated buck-flyback converter (IBFC) as a good solution for implementing low-cost high-power-factor ac-dc converters with fast output regulation. It will be shown that, when both buck and flyback semistages are operated in discontinuous conduction mode, the voltage across the bulk capacitor, which is used to store energy at low frequency, is independent of the output power. This makes it possible to maintain the bulk capacitor voltage at a low value within the whole line voltage range. The off-line operating modes of the IBFC are also investigated to demonstrate that the control switch of the proposed converter handles lower root-mean-square currents than those in similar integrated converters. The off-line operation of the IBFC is analyzed to obtain the design characteristics of the bulk capacitor voltage. Finally, the design and experimental results of a universal input 48 V-output 100 W ac-dc converter operating at 100 kHz is presented. Experiments show that the IEC-61000-3-2 input current harmonic limits are well satisfied and efficiency can be as high as 82%.

Integrated Buck-Flyback Converter as a High-Power-Factor Off-Line Power Supply

A single-switch nonisolated dc/dc converter for a stand-alone photovoltaic (PV)-battery-powered pump system is proposed in this paper. The converter is formed by combining a buck converter with a buck-boost converter. This integration also resulted in reduced repeated power processing, hence improving the conversion efficiency. With only a single transistor, the converter is able to perform three tasks simultaneously, namely, maximum-power-point tracking (MPPT), battery charging, and driving the pump at constant flow rate. To achieve these control objectives, the two inductors operate in different modes such that variable switching frequency control and duty cycle control can be used to manage MPPT and output voltage regulation, respectively. The battery in the converter provides a more steady dc-link voltage as compared to that of a conventional single-stage converter and hence mitigates the high voltage stress problem. Experimental results of a 14-W laboratory prototype converter with a maximum efficiency of 92% confirmed the performance of the proposed converter when used in a PV-battery pump system.

Design of a Single-Switch DC/DC Converter for a PV-Battery-Powered Pump System With PFM+PWM Control

Hybridizing power electronic systems using an energy storage unit has gained popularity in transportation and power system applications. This task has traditionally been performed by using several independent power electronic converters. Multi-input converters, due to their reduced part count and improved efficiency, seem to be an advantageous option to replace the conventional converters. A few multi-input converter topologies have been reported in the literature; however, there is not a systematic approach to derive them. Furthermore, all possible topologies are not completely explored and it is difficult to derive new converters from the existing topologies. Hence, in this paper, a systematic approach to derive multi-input converters by using single-pole triple-throw switches as building blocks is presented.

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Synthesis of double-input DC-DC converters using a single-pole triple-throw switch as a building block

There is currently a trend in power electronics to avoiding the use of electrolytic capacitors in LED drivers, provided that their expected life span is much lower than that of the LEDs, thus reducing the reliability of the entire LED fixture. This paper presents an optimization study about the determination of the minimal bus capacitance needed for reducing the power factor preregulator (PFP) stage dc-link capacitor down to values that are available in metalized-film technology. This optimization study will be applied to the buck converter, which is an interesting topology for high power factor (HPF) LED drivers due to its low component count, HPF, low output voltage, and lower voltage stress on semiconductors than the boost or buck–boost PFPs, which yields to lower efficiency decline under dimming operation. This way, a 70-W integrated buck–flyback converter is developed and proposed with an metalized-film polypropylene (MKP) dc-link capacitor, intended for outdoor applications where a high reliability is pursued, and capable of driving several LED lamps in different configurations. The experimental results show the accuracy of the theoretical predictions, confirming the feasibility of the buck converter as a high-performance PFP.

Optimization of a Front-End DCM Buck PFP for an HPF Integrated Single-Stage LED Driver

In known line-powered, phase control circuits, the middle point (b) of a serial connection between an inductance (1a) and a switch (T1) connected to the output (a) of the power line rectifier (BG) is connected by an inductance (D1) to a charging capacitor (Cb). The object of the invention is to reduce in such circuits the amplitude of the harmonic waves drawn from the power line. For that purpose; a second diode (D2) is arranged between the middle point (b) and the switch (T1), and the switch (T1) is connected by the primary winding (Lp) of a combinatorial circuit transformer (Tr) to the charging capacitor (Cb). The invention is particularly useful for television receivers or video-recorders.

Line-powered, phase-control circuit

It is difficult to obtain a large input/output voltage ratio with a DC-DC converter, because the duty factor d may not reach very small values. For the same reason, it is difficult to obtain an output voltage that is adjustable in a large range. A DC-DC converter circuit is proposed that overcomes this limitation by performing a voltage ratio d/sup 2//(1-d) in the best operating mode. Circuit operation is analyzed, operating modes are evidenced, and the voltage ratio is deduced in each operating mode as a function of output current, duty factor, and circuit component values. Boundary conditions between different operating modes are obtained; consequently, it is concluded that these conditions do not occur for some operating modes. Component ratings are summarized, to facilitate circuit design. The buck-flyback DC-DC converter is very suitable for low-voltage (e.g. computer) power supplies and for power supplies with the output voltage (adjustable in a large range) supplied from the mains without a mains voltage transformer. >

S. Birca-Galateanu

Papers

Buck-flyback DC-DC converter