| 摘要 |
PURPOSE:To save power consumption by varying voltage supply to a backlight in accordance with the brightness of a detected periphery. CONSTITUTION:A signal corresponding to the quantity of peripheral light is outputted from a photodetector 1 and inputted to respective comparators 3 to 7 through an amplifier 2. Voltages V1 to V4 obtained by dividing a reference voltage V0 generated from a reference voltage generating circuit 8 by resistors R0 are respectively inputted to the other inputs of respective comparators 3 to 7. The outputs C3 to C7 of respective comparators 3 to 7 are encoded by an electro-luminescence (EL) voltage generating circuit 9 and a lighting voltage for an EL backlight 10 is outputted from the circuit 9. When only the comparator 7 is ON, i.e. the periphery is dark, the output of the circuit 9 is also downed, and when the comparators 6 to 4 are successively turned on, the output voltage of the circuit 9 is increased in stages. Consequently, the backlight is automatically turned on and off and its power consumption is saved. |
