In lighting applications the electronic ballast is a unit which provides ignition and power supply for fluorescent tubes. More and more frequently, it becomes a substitute for the classical system consisting of an inductive ballast and a starter. Several reasons explain this evolution: better power factor, high frequency power supply of the tube, low heating, etc. Some electronic units are connected to the mains, others are powered by a DC voltage source. The electronic ballast considered in this paper is used in an emergency lighting unit where the DC voltage is provided by a battery. It consists of an lc oscillator and two transistors acting as DC-AC convertersbetween the source and the oscillator. The fluorescent tube is connected to the oscillator via a transformer. This type of electronic ballast stands out because of its simplicity and robustness which explains why it is particularly well suited for emergency lighting.
The paper starts with a detailed theoretical analysis of the electronic circuit, based essentially on the principle of harmonic balance and resulting in a set of mathematical expressions for the most important quantities such as currents and voltages in the oscillator and tube as well as oscillation frequency. These expressions are general in the sense that they hold independently of the specific values of the DC voltage source and the power of the fluorescent tube.
Relying on these expressions we give then to the designer a logical approach for choosing the correct values of the circuit components in order to satisfy the requirements concerning lighting intensity, oscillation frequency and autonomy of the unit.
Finally, we also provide an experimental verification of the results for specific case of a unit described for a 8 watt fluorescent tube. This verification confirms the soundness of the approach followed in the theoretical analysis.
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