SELF-OSCILLATING ELECTRONIC BALLAST WITH LIGHTING INTENSITY CONTROL J. DE P. LOPES, M. F. DA SILVA, P. C. LUZ, V. BORIN, M. F. MENKE, F. E. BISOGNO, Á. R. SEIDEL AND R. N. DO PRADO Intelligence for Lighting Group (GEDRE), Federal University of Santa Maria Santa Maria, RS, 97105-900, Brazil pelegrinilopes@yahoo.com.br, fbisogno@gmail.com, arseidel@uol.com.br Abstract - This paper presents electronic ballast with dimming capability supplying a 32 W fluorescent lamp. The electronic ballast is a self-oscillating driving circuit with an additional circuit responsible for dimming the fluorescent lamp based on a signal from a lighting dependent resistor. This luminous sensor measures the luminous flux level and set the lamp power by the voltage gain variation of the resonant filter. Simulation and experimental results of the electronic ballast are presented to demonstrate the feasibility of the proposed system. Keywords – Electronic ballast, fluorescent lamps, self-oscillating, switching frequency. 1. Introduction The growing electric energy consumption worldwide, day by day, is stimulating research and development of energy efficiency technique. Considering that the artificial lighting systems represent a great amount of consumption (Hammer, 1985), the development in this field making possible saving energy to produce light. This will make a significant contribution on total electric energy consumption. This work propose a saving energy solution for lighting systems, using electronic ballast operating at high-frequency to supply fluorescent lamps. Some electric advantages can be observed in the use of high-frequencies electronic ballast comparing to electromagnetic one, like audible noise, flicker absence, and better lighting efficacy (lm/W). Moreover, electronic ballasts are lighter and smaller than electromagnetic ballasts. Self-oscillating electronic ballast (SOEB) has been used widely due to its simplicity. On the other hand its design has been reported in several papers due to its complexity (Chang, 2001; Seidel, 2003c; Seidel, 2007; Tao, 2001). These studies have shown that several applications were derived since SOEB behavior was understood as a nonlinear control system circuit (Dalla Costa, 2003; Seidel, 2003b). Thus, in this work is proposed one application involving the SOEB with dimming capability. The electronic ballast is formed by a self-oscillating driving circuit with an additional circuit that must control light intensity for the fluorescent lamp. The dimming capability is achieved by the switching frequency sweep that changes the resonant filter gain. The light intensity control is done through a lighting-dependent-resistor (LDR) that has a resistance proportional to the visual electromagnetic radiation spectrum applied. The LDR is responsible to measure the environment luminous flux level and set the luminous flux through the lamp power. The remainder of this paper is organized as follows; the proposed idea is shown in Section 2, the design synthesis and simulation results are shown in section 3 and 4, the experimental results are presented in section 5 and the final considerations are presented in the last section. 2. Proposed Self-Oscillating Electronic Ballast The proposed system is an application of the traditional SOEB with switching frequency sweep that allows for regulating the fluorescent lamp light intensity based on a feedforward control. Electronic ballast with dimming capability was proposed in (Seidel, 2003a; Seidel, 2003b). However, the circuit and the design methodology were different. Figure 1(a) shows the proposed circuit that is based on the universal SOEB (Lopes, 2009). However, in this paper the additional circuit is used to dimming the fluorescent lamp. Thus, the proposed work consists in controlling the fluorescent lamp power by the electronic ballast switching frequency (fs) as the LDR resistance changes, since the lamp power decreases (increases) as fs increases (decreases) if it is considered the LCC resonant filter voltage gain feature (Wakabayashi, 2005). Figure 1(b) shows the equivalent gate driver circuit and its waveforms. The behavior of the SOEB is based on the resonant current feedback i s from the LCC resonant filter through a current transformer (CT), which includes L S1 , L S2 and L P . The CT secondary side is connected to gate-source terminals of S 1 and S 2 with complementary polarity, which ensures S 1 turns on (off) and S 2 turns off (on). It is shown that when zener current i z crosses zero, the polarity over S 1 -S 2 gate-source changes. The i z current is the sum of i s and the CT magnetizing current i m as it is shown in the equivalent circuit. The f s is controlled through the series inductance L d and equivalent resistance R d provided by a bipolar transistor T SC . It is possible due to the insertion of a current path paralleled with i m and i s currents according points 1 and 2 in Figure 1(b). The rectifier bridge D 6 -D 9 allows flow the bidirectional i d current. Thus, the transistor T SC operates as a variable resistance which depends on T SC base current i b . The i b current controls i d and it is also controlled by means the voltage divider LDR+R 1 and R 2 . The zener 3681 XVIII Congresso Brasileiro de Automática / 12 a 16-setembro-2010, Bonito-MS