Design and implementation of an FPGA-based CCFL driving system with digital dimming capability

The proliferation of liquid-crystal display (LCD) monitors and notebook computers places an ever-increasing demand on display technology. The LCD with cold cathode fluorescent lamp (CCFL) best satisfies display performance, size, and efficiency. To operate the CCFL, a driving circuit is needed to light the lamp with a relatively high voltage and then stabilize the arc current. For minimizing the component count and size, a high-frequency zero-voltage switching (ZVS) resonant converter is preferred. In this paper, a field-programmable-gate-array-based ZVS resonant converter for driving CCFL with digital dimming capability is presented. The proposed digital controller utilizes the pulse density modulation technique to adjust the output power. A 3-W prototyping system is built and tested; experimental results show that the proposed system can reduce the voltage spike by more than 15%, compared to the low-frequency dimming methods. The overall system power efficiency is approximately 85%. The advantages of the proposed system include high efficiency, low output voltage and current spike, wide dimming range, flexibility, and compactness.