Digital CCFL Drive System using Individual Current Modulation for LCD-TV

Current balance system using MCU (micro controller unit) which controls the individual lamp current is implemented in this paper. The system consists of a ballast capacitor for parallel lighting, an amplitude modulator switching between the on-state and the off-state for regulating the lamp current, a gate driver to shift a voltage level, and a current sensor to send a feedback signal to the MCU. Each lamp current is compared with a reference and appropriate gate signal is generated to balance the lamp current. The MCU controls lamp currents individually by changing the PWM duty cycle of a switch series connected with a lamp. An amplitude modulator using a junction capacitance as an off-state parallel impedance to control the lamp current is a switch having an anti-parallel body diode. Series connected ballast capacitor and off-state parallel capacitance play a role of a bidirectional current amplitude modulation with a switch regardless of the anti-parallel body diode. By employing only one switch for each lamp, the number of power supplies isolated from the system for driving gate signal can be minimized. The specified circuit configuration, analysis, balance principles, and experimental results of the proposed system will be presented for 46 inch LCD-TV.