IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 47, NO. 4, AUGUST 2000 809 High-Power-Factor Electronic Ballast Based on a Single Power Processing Stage Márcio Almeida Có, Student Member, IEEE, Domingos S. L. Simonetti, Member, IEEE, and José Luiz F. Vieira, Member, IEEE Abstract—A new high-power-factor (HPF) electronic ballast is introduced in this paper. The proposed topology is based on a single power processing stage, and provides a high-frequency voltage to the fluorescent lamps in addition to presenting an HPF to the utility line. The power processing stage is formed by a half-bridge circuit operating above the resonant frequency, thus providing zero-voltage switching. The self-oscillating technique is employed, which increases the converter reliability with great simplicity. HPF is achieved by using a nonconventional boost stage operating in discontinuous conduction mode, which results in a lower dc-bus voltage than that produced by the conventional boost. Theoretical analysis and experimental results have been obtained for two 40-W fluorescent lamps operating at 40-kHz switching frequency and 220-V line voltage. Index Terms—Lighting, power-factor correction, soft switching. I. INTRODUCTION A RTIFICIAL lighting is responsible for the consumption of a significant portion of the overall generated electricity. Much effort has been devoted to the search for more efficient lighting sources to replace incandescent lamps. The gas dis- charge lamp technology has been of relevance for this purpose, particularly, the most popular of all is the fluorescent lamp. It is usually preferred because it inherently has longer lifetime and higher efficiency, when compared to the incandescent lamp. All gas discharge lamps have negative impedance character- istics that require some form of current-limiting control to pre- vent their destruction by excessive current. This problem has been solved by means of a magnetic ballast, composed by a se- ries inductor. In spite of their low cost, magnetic ballasts present the following problems, mainly associated with their operation at line frequency (50 or 60 Hz): flickering, high size and weight, and low power factor. These problems can be eliminated with the use of electronic ballasts, which have become cost competitive with conventional ballasts, particularly when overall costs are considered (the ini- tial cost plus increase in lifetime and energy savings) [1]–[5]. Electronic ballasts based on self-oscillating technique pos- sess inherent current-limiting control to the lamps, usually op- erate at high resonant frequency, and yield high striking voltage. Manuscript received August 17, 1998; revised April 9, 2000. Abstract pub- lished on the Internet April 21, 2000. An earlier version of this paper was pre- sented at the 1995 IEEE Power Electronics Specialist Conference, Atlanta, GA, June 12–15, 1995. The authors are with the Departamento de Engenharia Elétrica, Univer- sidade Federal do Espírito Santo, Vitória, ES 29060-970, Brazil (e-mail: j.vieira@ele.ufes.br). Publisher Item Identifier S 0278-0046(00)06823-4. They can also provide shutdown protection in the event of a lamp failure or lamp removal. A self-oscillating half-bridge parallel resonant converter has been an attractive choice for this application, due to its com- petitive cost and high reliability [1], [6]. The resonant converter is fed by a dc voltage source generated from the ac mains by a diode bridge rectifier, as shown in Fig. 1. It operates above the resonant frequency to provide zero-voltage switching (ZVS). However, from the ac line viewpoint, it absorbs a current with a low power factor and high harmonic distortion. High power factor (HPF) and low total harmonic distortion (THD) are features specified by international regulations and also required by utility companies. The advantages of HFP include a reduction in the line current harmonics and, consequently, in the rms line current. In this way, the utility line is more efficiently utilized [7]. The use of a continuous conduction mode (CCM) boost power factor corrector (PFC) is possible but not useful, because it requires two processing stages [2], [8] which reduces the reliability and increases the overall cost. Therefore, a single power processing stage has been the preferred option [7], [9]–[16]. In this way, this paper proposes an HPF electronic ballast operating in discontinuous conduction mode (DCM) that results in a high-performance, reliable solution. An additional feature of the proposed topology is that it presents input–output galvanic isolation. II. CONVERTER TOPOLOGY The power stage diagram of the proposed HPF electronic bal- last is shown in Fig. 2, and is described as follows: • input voltage ; • input diode bridge rectifier – ; • MOSFET half-bridge – ; • three-winding high-frequency transformer with the turns ratio: ; • boost inductor ; • high-frequency diode ; • parallel resonant circuit formed by , and ; • dc-link capacitor ; • blocking capacitor ; • self-oscillating gate-drive transformer ; • high-frequency input filter and , which eliminates switching frequency harmonic current. A nonconventional boost stage operating in DCM is formed by the boost inductor and the transformer secondary , 0278–0046/00$10.00 © 2000 IEEE