A Dimming Method for Hot Cathode Fluorescent Lamp Using a Resonant Inverter Operating at Fixed Switching Frequency

This paper describes a dimming method for hot cathode fluorescent lamp (HCFL) using a resonant inverter operating at fixed switching frequency. The proposed method is based on burst dimming and decreases the inverter output voltage during the burst-off period by changing the switching pattern of the inverter. Consequently, the lamp can be turned OFF, while the filaments of lamp are kept preheated without adding an inverter for preheating. Once the lamp is turned OFF, N-times resonant mode (where N means a natural number) occurs because the characteristic of the resonant circuit (which depends on lamp impedance) changes drastically. This mode keeps the root mean square of filament currents large enough to ensure long lamp life. Moreover, the inverter operates in zero-voltage-switching resonant mode during both the burst-on and burst-off periods. Experimental results showed that stable burst dimming and preheating characteristics were attained. The proposed method thus contributes to achieving long lifetime, small size, and low cost of lighting system for HCFLs.