IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 17, NO. 2, MARCH 2002 163 A Simple Single-Switch Single-Stage AC/DC Converter With Fast Output Voltage Regulation Oscar García, Member, IEEE, José A. Cobos, Member, IEEE, Pedro Alou, Roberto Prieto, Member, IEEE, and Javier Uceda, Senior Member, IEEE Abstract—In this paper, a simple single-stage ac/dc converter based on the flyback topology is presented. With a single switch, a fast-regulated output voltage is achieved and, although the line current is not sinusoidal, the converter complies with the Standard IEC 1000-3-2 about low frequency harmonics for a medium power range (50–500 W). The major advantages of this converter are the size and the efficiency. Design guidelines, analysis of the line cur- rent, and extensions to other topologies are analyzed. Experimental results are included in the paper. Index Terms—AC/DC converter, EN61000–3–2, power factor correction, single-stage. I. INTRODUCTION T RADITIONAL ac/dc schemes to comply low frequency harmonic regulations are composed by two cascaded dc/dc converters connected to ac mains. This scheme (see Fig. 1) has several important advantages such as high power factor, fast output voltage regulation, controlled voltage on the storage ca- pacitor, etc. On the other hand, it has disadvantages such as high cost and size, and the efficiency of the conversion is penalized because the output power is processed twice. Present Standard about low frequency harmonics (IEC 1000-3-2) does not force to obtain a unity power factor in the equipment connected to the utility, but limits the amplitude of the current harmonics. Therefore, since a sinusoidal input current is not required for ac/dc converters, more simple solutions can be used, compared with the two-stage approach. The first type of alternatives is the use of passive filters [1]–[3]. Some of them [1], [2] have been designed to meet the Regulation IEC 1000-3-2. As can be checked, those are simple alternatives since only a few components are required to shape the waveform in such a way that it is classify into Class A of the Regulation. Once this is done, it is easy to comply with the maximum harmonic limits for low power applications. Reference [3] describes the passive technique named valley-fill that is also valid to achieve the qualification of the equipment. Since passive solutions do not provide a fast output voltage regulation, it is necessary to add a cascade dc/dc converter. The second group of alternatives is based on active circuits. There are several interesting single-stage solutions in the state of Manuscript received June 12, 2000; revised October 10, 2001. Recommended by Associate Editor K. Ngo. This paper was presented in part at the IEEE Power Electronics Specialists Conference (PESC), Charleston, SC, June 1999 and at the IEEE Applied Power Electronics Conference (APEC), New Orleans, LA, February 2000. The authors are with the División de Ingeniería Electrónica, Universidad Politécnica de Madrid, Madrid 28006, Spain (e-mail: oscar@upmdie.upm.es). Publisher Item Identifier S 0885-8993(02)02253-6. Fig. 1. Classical two-stage approach. Fig. 2. General single-stage approach. the art [4]–[12]. A schematic representation of them is shown in Fig. 2. Single stage solutions supply the load with a constant and fast-regulated dc voltage, while in most cases, the line current is not sinusoidal. Compared with the two-stage approach, many strategies have been developed to reduce the size and the cost and to improve the efficiency, such as the following: • Improve the power processing: in these solutions, the ef- ficiency is the main target. These approaches are based on dividing the input power waveform trying to maximize the amount of power processed once [4], [5]. Several control loops are required but sinusoidal line current is obtained. • Reduce the number of switches: a method to reduce the number of switches is proposed in [6]. This means a re- duction of the cost and size due to the switch itself and the control circuit. Since there is one control loop, it is in charge of keeping the output voltage regulated with a high bandwidth. This technique can be applied to almost any cascade association of power factor correction and dc/dc converters. With a proper design, the line current can be almost sinusoidal. • Combine topologies: converters that perform both power factor correction (normative compliance) and output voltage regulation can be obtained combining known topologies and controlling only the output voltage [7]–[9]. This combination usually implies a reduction in the number of switches. The key is to obtain simple solutions although the line current is distorted. 0885–8993/02$17.00 © 2002 IEEE