| 摘要 |
PROBLEM TO BE SOLVED: To prolong the service life of an EL element by driving an EL with a value found by comparing the output value of a light receiving element arranged in the vicinity of an EL element light emitting face with a reference value and controlling an EL element light emitting output to a predetermined value. SOLUTION: When a power source switch is turned on so as to actuate a drive part 3 for turning on an EL element 1, a light-receiving element 4 arranged in the vicinity of the EL element 1 generates an output corresponding to luminance of the EL element 1. In an impedance conversion part 5 which converts impedance to a lower one for avoiding noise influence, an impedance of the light-receiving element output is converted so as to be inputted to a comparison part 7. A constant reference voltage is always inputted into the comparison part 7 in spite of fluctuation in a supply voltage, and the reference voltage is subtracted from the input voltage inputted from the light-receiving element. When the difference is more than zero, a value corresponding to the difference value is outputted to the drive part 3, and when difference is less than zero, the output is set to zero. Therefore, if the EL element luminance is a predetermined value or higher, the driving part 3 controls the EL element luminance to a prescribed value.
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