| 摘要 |
PURPOSE:To provide a light emission diode drive circuit used for sensing a change in the light emission quantity of a light emission diode due to a change in ambient temperature or a secular change or the like so as to adjust automatically the light emitting quantity constant. CONSTITUTION:The light emission diode drive circuit applying a drive pulse to a light emission diode 1 to light it intermittently is provided with a clamp circuit 3, a photo diode 5 arranged closely to the light emission diode 1 to detect a light emitting output of the light emission diode 1, an AC amplifier 6 Ac-amplifying a detection output of the photodiode 5 and whose DC operating point is made stable by a DC negative feedback circuit 16, a shaping circuit 20 shaping an output amplified signal of the AC amplifier 6 and a comparator circuit 8 comparing a voltage of an output shaping signal of the shaping circuit 20 with a reference voltage, and an output of the comparator circuit 8 controls a clamp voltage of the clamp circuit 3 to make the light emitting output of the light emission diode 5 constant.
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