Pwm illumination control circuit with low visual noise for driving led

Abstract

A pulse width modulation (PWM) illumination control circuit with low visual noise for driving a light-emitting diode (LED) is provided. An illumination control pulse-generating unit is used to generate an illumination control pulse signal according to an illumination-adjusting signal. The duty cycle or frequency of the illumination control pulse signal varies within a predetermined scope for controlling a DC/DC converter to drive the light-emitting diode so that overall visual noise level of the PWM illumination control circuit is improved.

1 . A pulse width modulation illumination control circuit for controlling the illumination of light-emitting diodes inside a liquid crystal display, comprising: 
 an illumination control pulse-generating unit, for receiving an illumination-adjusting signal and generating an illumination control pulse signal according to the illumination-adjusting signal, wherein a frequency of the illumination control pulse signal varies with time within a predetermined range; and    a DC/DC converter, coupled to the illumination control pulse-generating unit for driving the light-emitting diodes according to the illumination control pulse signal.    
   
   
       2 . The control circuit of  claim 1 , wherein the illumination control pulse-generating unit is implemented using a microprocessor.  
   
   
       3 . A pulse width modulation illumination control circuit for controlling the illumination of light-emitting diodes inside a liquid crystal display, comprising: 
 an illumination control pulse-generating unit, for receiving an illumination-adjusting signal and generating an illumination control pulse signal according to the illumination-adjusting signal, wherein a phase shift of the illumination control pulse signal varies with time within a predetermined range; and    a DC/DC converter, coupled to the illumination control pulse-generating unit for driving the light-emitting diodes according to the illumination control pulse signal.    
   
   
       4 . An illumination control pulse generating device for receiving an illumination adjusting signal, the illumination control pulse generating device comprising: 
 a random signal generating unit, for generating a random signal;    a combine unit, coupled to the random signal generating unit for combining the random signal with the illumination adjusting signal to form a random signal combining illumination adjusting signal; and    a comparator, coupled to the combine unit for comparing the random signal combining illumination adjusting signal with a comparing signal to produce a illumination control pulse signal, wherein a frequency of the illumination control pulse signal varies with time within a predetermined range.    
   
   
       5 . The illumination control pulse generating device of  claim 4 , wherein the random signal generating unit is a noise generator.  
   
   
       6 . The illumination control pulse generating device of  claim 4 , wherein the combine unit is an analogue adder.  
   
   
       7 . The illumination control pulse generating device of  claim 4 , wherein the comparing signal is a triangular wave.