Liquid crystal display back-lighting circuit

摘要

To provide a cold cathode tube lighting circuit which quickly and smoothly carries out lighting of a cold-cathode tube and prevents damage of a piezoelectric transformer as an inverter transformer in the lighting circuit, the lighting circuit is provided with a protection circuit for detecting a primary current of the piezoelectric transformer. When the cold-cathode tube is used as a backlight for a liquid crystal display driven by the use of a scanning frequency, a dimmer circuit is used for producing a dimmer signal with a dimmer frequency and a controlled duty ratio given by a manual selector for controlling start and stop of the oscillator according to a desired brightness of the backlight. The dimmer frequency is obtained from frequency division of the scanning frequency. The controlled duty ratio is also modified corresponding to the divided frequency.