FREQUENCY CONTROL CIRCUIT OF DC-DC CONVERTER FOR LIQUID CRYSTAL DISPLAY DEVICE USAGE

摘要

PURPOSE: A frequency control circuit of a DC-DC converter for liquid crystal display device usage is provided to have high stability for a loading change by adding a frequency control function to a pulse width modulation method. CONSTITUTION: The DC-DC converter comprises: a loading electric current detecting part(100) for detecting the loading current of a liquid crystal display device and for generating a first or a third electric current level signal according to the perceived current; a first and a second control signal for controlling upward and downward the frequency about a change of the loading current according to the screen display condition of the liquid crystal display device; a control part(200) generating a third or a fifth control signal for frequency changeable use at the same time in the blank section of a vertical locked signal; and a frequency changeable part(300) changing the frequency according to the loading change by inputting the control signal generated from the control part.