Stability of cold cathode fluorescent lamps driven by piezoelectric transformers

The concept of envelope impedance (El) was used to develop a systematic and simple approach for studying the conditions for stability of PT-CCFL systems. It was found that the EI of PTs includes minimum points at low frequency when the EI of the CCFL is negative. This causes the loop gain of the system to encircle the -1 point, making the system unstable. The proposed analytical approach could be helpful in sorting out possible remedies for the PT-CCFL instability problems.