LED DRIVE CIRCUIT DEVICE WITH GRADATION CONTROL

摘要

PURPOSE:To improve the quality of print without increasing a circuit scale of the device by controlling a lighting time of an LED based on a period of a clock signal. CONSTITUTION:The result of comparison between output data A of a counter 12 counting a clock signal and output data B of a latch circuit 2 at a comparator circuit 11 is fed to a gate of a MOS transistor(TR) 6. Then the TR 6 is turned on or off depending on the quantity of the comparison result and the operation of an LED 7 is controlled by controlling the flowing of a current from a power supply to the LED 7. Since the lighting of the LED is implemented by only an output of the comparator circuit 11 in this way, the count operation of the counter is quickened by decreasing the period of the clock signal at a portion with low gradation to control in details the operation of the LED 7 and the operating time is controlled to be extended by extending the period of the clock signal for a portion with high gradation. Thus, the lighting time of the LED is adjusted corresponding to the gamma characteristic with simple circuit configuration.