| 摘要 |
PURPOSE:To provide a snap characteristic and a hysteresis characteristic by employing simple constitution wherein a phototransistor with a base terminal and a normal transistor are combined. CONSTITUTION:The series circuit of voltage dividing resistances R1 and R2 and the series circuit of a resistance R3 and the phototransistor PT with the base terminal are connected in parallel to a transistor TR connected between the gate and source of an MOS transistor MT, and the voltage division point between the resistances R1 and R2 is connected to the base of the transistor PT, whose collector is connected to the base of the transistor TR. Consequently, the light excitation and base bias of the transistor PT are utilized to provide a negative resistance characteristic to the parallel circuit of the transistors PT and TR. Consequently, when light intensity reaches a certain value, the transistor MT turns on momentarily. The light intensity when a load current IL is in on operation and that when in off operation are different from each other and the hysteresis characteristic is obtained.
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