Patent ID: 6963329

Claim:
A portable computer system which includes a main body, a power supplying unit, and a liquid crystal display (LCD) apparatus having an LCD panel which is operated by electric power supplied by the power supplying unit and a back light which illuminates the LCD panel, said system further comprising: a direct current alternating current (DC/AC) inverter for supplying AC power to the back light; a contrast sensing part for sensing contrast of a video signal displayed on the LCD panel and outputting a pulse width modulation (PWM) signal; a DC converter for converting the PWM signal from the contrast sensing part into a DC signal; a voltage controller provided between an output of the DC converter and an input of the DC/AC inverter for providing the DC signal from the DC converter as an operating voltage to the DC/AC inverter; and a controller connected in series with the DC/AC inverter for sensing the operating voltage of the DC/AC inverter, and for controlling the voltage controller on the basis of the operating voltage of the DC/AC inverter.