Relay restoration circuit for telephone set

Abstract

PURPOSE: To keep an ordinary operation, by restoring a latch relay automatically at the time of the voltage drop of an operating power source in a telephone set. CONSTITUTION: By depressing a button M on a keyboard 2. a negative pulse is sent from the port P1 of a microcomputer 3 to an inverter 4, and after a transistor Q1 is turned on, and a latch relay L is operated, a voltage VB drops, then no negative pulse is generated from the port P2 of the microcomputer 3 even by the second depression of the button M on the keyboard 2, and the latch relay b remains operating, and the telephone set is held at a state at that time, however, a restoring part 8 generates a positive pulse at the time of voltage drop of the voltage VB, and turns on a transistor Q2, and restores the latch relay L. In this way, since the latch relay L is restored automatically at the time of the drop of the voltage VB, the telephone set can be operated normally. 7: power source part. COPYRIGHT: (C)1988,JPO&Japio

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