| 摘要 |
PROBLEM TO BE SOLVED: To provide a back-light control device for a liquid crystal display, which secures a wide range of light modulation and a stable supply of a tube current and does not make uncomfortable audible sound. SOLUTION: This back-light control device reduces audible sound by superposing pulses outside of the audible sound range generated by an oscillation part during an ON-period of PWM pulses for light modulation outputted from a PWM generation part. Moreover, the control device varies a DC output voltage from a chopper part by varying an output pulse width from the oscillation part according to the results of the tube current detection, and supplies the voltage to an inverter circuit. In such a manner, it is possible to obtain a back- light control device for liquid crystal display permitting to secure a wide range of light modulation and stabilize the tube current. |
