JPS6436251A - Line closing control circuit - Google Patents

Abstract

PURPOSE:To prevent a malfunction due to noise in a location with deteriorated line state by comparing a line voltage from a telephone circuit with a reference voltage periodically, setting a new reference voltage based on the result of comparison and applying switching control of the telephone circuit based on the comparison output between the new reference voltage and the line voltage from the telephone circuit. CONSTITUTION:A line control section 6 applying switching control of a telephone circuit, a voltage comparison section 2 comparing the line voltage from the telephone circuit with a reference voltage from a reference voltage setting section 3 and a control section 4 are provided. Then the control section 4 is started periodically by the output from a timer section 7, a reference voltage of a reference voltage setting section 3 is adjusted for plural number of times based on the comparison output from the voltage comparison section 2, a voltage control signal is outputted to the section 3 to set a new reference voltage and the new reference voltage is stored in a memory section 5 and the control section 4 controls the line control section 6 based on the comparison output obtained from the voltage comparison section 2 operated by the new reference voltage to apply closing control of the telephone circuit.