IRVINE, Calif., Nov. 29 -- Microsemi Corp. said it has added a backlight controller IC patent to its portfolio, for a total of four backlight patents for driving fluorescent lamps in PDA, notebook, automotive and flat panel TV applications. Its patent US6307765 describes Microsemi's technique of counting lamp current cycles to ensure smooth brightness control at low levels. This patent will be used in the company's automotive backlight products, where automatic dimming and low-light-level control is critical for nighttime or tunnel driving.