Circuit for creating a variable LCD contrast voltage under computer control
Pat. No.:
Country/Region:
U.S.
Abstract:
A method and circuit for controlling the contrast of a liquid crystal display (LCD). The circuit includes a switching regulator circuit which generates a negative voltage at the output thereof, with the switching regulator circuit having a feedback node therein and also having a voltage regulator with a control input therein. An injected current coupled to the feedback node and the control input to the voltage regulator is used to provide a changed negative voltage at the output of the regulator circuit. Control values stored in the memory of a controller are used to select the injected current. The changed negative voltage at the output of the regulator circuit is used to control the contrast of the LCD.