A study on Dimming in Self・excited Electronic Ballast for Electrodeless Fluorescent Lamps

概要

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This paper presents a novel dimming circuit using intermittent oscillation in the self・excited electronic ballast for an electrodeless fluorescent lamp. A resonant half-bridge inverter with zero-voltage-switching is used for the electronic ballast. This self-excited electronic ballast satisfies technical conditions for intermittent oscillation. These conditions have been investigated by using separately-excited electronic ballast. Derived conditions are as follows. 1) Coil voltage must be over 600V at no-load to achieve a short enough striking time compared with the period (several milliseconds) of the dimming signal. 2) A fast-response control circuit is needed to achieve a short enough delay time at starting and stopping compared with the period of the dimming signal. Previous starting circuits using a voltage-breakover-type device (DIAC, Zener diode etc.) are not suitable for intermittent oscillation because the delay time is too longer. Our dimming circuit consists of an auxiliary switch for intermittent oscillation and the starting circuit consists of only resistance and capacitance. In an experiment at 2.65MHz, our circuit had a sufficiently short delay time below 100μs and controlled the illuminance of the electrodeless fluorescent lamp from 100% to under 5%.
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