| 摘要 |
PURPOSE:To extend the range of a phase detection voltage, by connecting resistance and a capacitor among input terminals R, S, and T into a shape like a star and comparing the voltage drop of the resistance with a reference voltage corresponding to the line voltage. CONSTITUTION:A series circuit of resistances R1 and R2, a resistance R3, and a capacitor C1 are connected to the first phase input terminal R, the second phase input terminal S, and the third phase input terminal T into a shape like a star. A reference voltage generating circuit generates a reference voltage corresponding to the voltage applied across input terminals S and T, and a comparing circuit 2 compares this reference voltage with the voltage drop of the resistance R2 to generate a regular phase detection signal or an opposite phase detection signal, and a regular phase display equipment 3 or an opposite phase display equipment 4 is driven. A sound production control circuit 5 responds to the regular phase detection signal to apply a continuous sound production control signal to a sound producing circuit 7, and a sound production control circuit 6 responds to the opposite phase detection signal to generate an intermittent sound production control signal from the circuit 5. Thus, when the line voltage is changed, the reference voltage is changed in accordance with this change, thereby extending the range of a phase detection voltage. |
