| 摘要 |
PURPOSE:To obtain a circuit which is satisfactory in its answering characteristic and high in its reliability, by providing a phototransistor corresponding to each service current supervising circuit, and supervising an output state of each phototransistor respectively, and detecting a current of a service line. CONSTITUTION:Service current supervising circuits SUPA and SUPB are provided on each line of a service line respectively. The circuits SUPA and SUPB are connected to the service line by a bridge circuit consisting of diodes D1- D4. In this state, a Zener diode DZ and a photodiode DP are connected in parallel with an input resistance R1. Also, when phototransistors TRQA and QB corresponding to the supervising circuits SUPA and SUPB are provided and outputs of each TRQA and QB are supervised respectively, if a ground-fault is occurred, it is detected, and furthermore, this circuit is satisfactory in its answering characteristic, and a loss of the circuit is reduced. |
