Modeling of CCFL using lamp delay and stability analysis of backlight inverter for large size LCD TV

Cold cathode fluorescent lamps (CCFL) for LCD TVs have a special v-i characteristic, which can make the backlight inverter system unstable. In this paper, modeling of both the cold cathode fluorescent lamp and the backlight inverter is performed in terms of incremental impedance in the frequency domain. The stability analysis of the backlight inverter and the CCFL is presented using the derived models. It is concluded that the time delay, after which the lamp voltage responds to the lamp current change, contributes to the incremental impedance of the CCFL at the high frequency region, which may cause instability of the backlight inverter. The time delay is considered as a lamp characteristic. The effect of the inverter design parameters on the stability is also investigated. The lamp model and the stability analysis results are verified from experiments with a backlight inverter for 32-inch LCD TVs.