Design and implementation of a digital control IC for driving multiple cold cathode fluorescent lamps

Abstract

This study designs and develops a digital control integrated circuit (IC) for driving circuits operating multiple cold cathode fluorescent lamps (CCFLs). The control IC adopts an external crystal oscillator for the IC's external frequency to provide the driving circuits a fixed frequency. Inside the IC, two control loops are designed, under synchronized operation frequencies, for a boost regulator and an inverter. The main function of the boost regulator control loop is to supply a steady DC voltage for the inverter. In designing the inverter's control circuit, an adjustable-frequency adjustable-voltage soft-start technique is used to start the lamps. We also use burst mode digital dimming technique to achieve synchronized dimming for the parallel-connected lamp-ignition circuits. The feedback voltage from the CCFLs can determine if any lamp is abnormal via a proposed lamp abnormality detection circuit. To deal with the equivalent-circuit's component parameter differences among various manufacturers' and brands' piezoelectric transformers (PTs), the inverter's operation frequency is designed fine-tunable in this study. Finally, the proposed design concept was implemented with an actual control IC and a driving circuit for CCFLs. The measured data and waveforms from our test circuitry are presented, which verifies the validity of the miniaturized controller proposed in this study. Copyright (C) 2008 John Wiley & Sons, Ltd.