ON AND OFF DETECTING CIRCUIT

PROBLEM TO BE SOLVED: To provide a inexpensive on/off detecting circuit which hardly receives the influence of a leakage current. SOLUTION: The circuit is provided with the serial body of voltage dividing resistances 5 and 6 which are connected to a semiconductor switch 7 in parallel and decide the on/off threshold of a semiconductor switch 7, a detector 3 for detecting the on/off state of the switch 7 by the voltage of a connection point between the resistances 5 and 6 and a current limit resistance 4 which is serially connected to the parallel body of the serial body with the switch 7 and limits the current flowing through the switch 7. The serial body of a photocoupler 2 for transmitting the on/off state of the semiconductor switch 7 with the detector 3 is connected to the serial body of the resistances 4, 5 and 6 in parallel.