| 摘要 |
PURPOSE:To simplify a level decision circuit so that it includes only one constant voltage circuit by making a level decision voltage independent of the variation in one of supply voltages of two supply power sources. CONSTITUTION:When the input voltage applied to the inverted input terminal of an operational amplifier 16 is lower than a decision voltage VL, the decision output of the amplifier 16 is a positive voltage, and when the voltage exceeds a decision voltage VH determined by constants of resistances 15, 12, and 13, and the output voltage of a constant voltage circuit 18 connected to a plus source voltage, the decision output is inverted into a negative voltage. Consequently, a diode 14 connected to the resistance 13 is biased reversely to cut off a feedback circuit, and the voltage VL is determined by the constants of the resistances 12 and 13 and the output voltage of the circuit 18; when the input voltage drops below the voltage VL, the decision output of the amplifier 16 is inverted into the positive voltage again. Therefore, there is no need to provide a constant voltage circuit on the minus source voltage side where there is no influence of the variation in supply voltage, and the constitution of the level decision circuit is simplified.
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