| 摘要 |
PURPOSE:To control the pulse width of a pulse current, and to make a current exceeding a constant value not flow and control the total quantity of light emission by detecting a current supplied to a light emission diode and varying the time rate of the current supplied to the light emitting diode according to the detected current value. CONSTITUTION:The anodes of light emitting diodes L1 - L54 are connected to a current detector CS through current limiting resistances R1 - R54 respectively. A pulse generator PG voltage control terminal VI is connected to the detected voltage output terminal SO of a current detector CS. The current detector CS detects the current flowing out of a power source PS and outputs a high voltage when the current is large or a low voltage when the current is small to the detected voltage output terminal SO. Further, a pulse generator PG makes the pulse width narrow when the input voltage at the voltage control terminal VI is high or wide when low and outputs pulses to the output terminal CP at a constant period. Therefore, the pulse width of the pulse current flowing to the light emitting diodes is controlled according to the value of the power source current and consequently while a current exceeding the constant value does not flow, the total quantity of light emission is controlled.
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