| 摘要 |
PURPOSE:To decide a current limiter only by one adjustment by inputting a current proportional to a constant current and a current proportional to an input current with reverse polarity respectively and deciding a point on which limiter characteristics appear. CONSTITUTION:Optical current radiated from a phototransistor (Tr) Q1 by photographing operation is changed at its direction by current mirrors Q2-Q4, Q7 and formed as a current having equal capacity and reverse direction to the collector current Ic1 of the Tr Q1 and the collector currents Ic4, Ic7 of the Trs Q4, Q7. On the other hand, a constant current formed by a constant current source circuit is changed at its direction by current mirrors Q18, Q19, Q9, Q11, Q16 and the constant currents Ic18, Ic16, Ic11, Ic9 having the same value are formed on respective Trs. Since the current mirror constitution is adopted, an integration current becomes the collector current Ic15 of a Tr Q15. When an input current entered the Tr Q1 is smaller than the constant current because of low intensity of illumination, a capacitor C is charged with a fixed current Ic15 and a limited output current is formed on an output terminal B.
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