Setting the Preheating and Steady-State Operation of Electronic Ballasts, Considering Electrodes of Hot-Cathode Fluorescent Lamps

Abstract

This paper presents a new methodology for the adjustment of the preheating process and steady-state operation of electronic ballasts intended for hot-cathode fluorescent lamps. The classical series-resonant parallel-loaded half-bridge inverter is the power stage analyzed in this paper. In addition, the preheating process is based on the imposition of a constant rms current through the electrodes, in order to provide a proper value of the ratio before the lamp start. According to the proposed methodology, it is possible to set suitable operating points for the electronic ballast, considering optimal conditions for the lamps electrodes. Therefore, the proposed methodology for setting the preheating and steady-state operation is a complete platform to the design of electronic ballasts for hot-cathode fluorescent lamps.

UV dose investigation for imersed lamp purifier for electronic ballast UV lamps design

“…[5] a) Preheat: At this stage the lamp filaments are heated in a controlled manner over a given time, allowing the released electrons to move between the ends of the lamp, what products a small current known as glow current, which one is responsible for the ionization of the glass bulb inert gas (usually argon) [5] [4].…”

“…According to that, as presented in [4], a good preheating process, what happens between 700°C and 1000°C guarantees adequate gas ionization and maximizes the lamp life. In this context, for temperatures under 700°C, a phenomenon called sputtering is increased, where stronger collisions between electrons and the emissive coating of the filaments accelerate its deterioration, while temperatures higher then 1000°C can cause filaments emissive coating evaporation [5] [4]. b) Steady State: Shortly after ignition the gas is fully ionized and a larger current appears due to electron flow between the electrodes.…”

“…Thus, in view of the temperature range suggested by [4] the relation between HR and RC is defined in (2).…”

“…In order to increase the structure efficiency, new ballast for the same lamp was developed, ensuring the correct startup operation with filaments preheating and capable to maintain the lamp nominal power in steady state [4]. This fraction of the work has demonstrated that the germicidal action increased when the UV lamp operated properly, what was verified with 25 times of fecal coliforms reduction with the commercial ballast and 50 time reduction with the laboratory one [5].…”

Evaluation of heat transfer coefficient of tungsten filaments at low pressures and high temperatures

“…The discharge is usually attained after a small period of preheating the electrodes. This time ranges from 0.5 to 2 s. Preheating the electrodes to a temperature of 1000 K or higher, prior to ignition, initiates the discharge and protects the electrodes from losing their emitter mixture [2,3,4]. During the preheating period, the electrodes are heated and the acquired temperature depends on the heat transfer from the filaments to the gas mixture into the bulb.…”