Automatic brightness control apparatus

Abstract

Automatic brightness control apparatus for providing real time control of the brightness of various types of displays while also providing ambient light compensation is disclosed which includes a photodiode for providing a current proportional to the ambient light level. Amplifiers, together with a load, change the photodiode current to a control voltage indicating the level of ambient light. The control voltage is provided as a reference input to a voltage comparator. The other input to the voltage comparator is the output of a free running ramp oscillator. The pulse width modulated logic signal comprising the output of the voltage comparator is provided as the input for an output driver whose pulse stream output is used to control the brightness of the designated display. The duty cycle of the pulse stream output varies with the ambient light level. Several logic gates are added to the free running ramp oscillator to provide synchronization capability and assure that the ramp output waveform of the ramp oscillator will always begin with an incoming synch pulse. The automatic brightness control apparatus is packaged as a monolithic integrated circuit on a single silicon chip which is housed in a clear plastic 8 pin DIP.

Dependencies are inferred from the claim text.