| 摘要 |
PURPOSE:To uniform the quantity of light even if respective arrays have variance in characteristics during manufacture and to compensate even variance with time by converting the light emission output of each LED into the quantity of electricity, comparing the quantity of electricity with a reference voltage and generating a control signal, and controlling driving currents of respective LEDs. CONSTITUTION:The accumulated charge of an image sensor 6 is scanned and inputted as a DC signal voltage to a comparing circuit 7, which compares the input with the reference voltage VREF. The output signal 7a of the comparing circuit 7 is inputted to a shift register 8 and then led to the base of the FET4 of a drive control circuit 10 through a buffer 9 in synchronization with scanning pulses of the sensor 6. The current of the FET4 flows as the base current of a TR3 to control the driving current of each LED of the LED array 1. In this case, the FET4 and TR3 are connected so that negative feedback is provided through said feedback loop, and the light emission output of each LED is made constant and uniform. |
