JPS6455018A - Power source off detector - Google Patents

Abstract

PURPOSE:To reduce the capacity of a capacitor by employing an interlocking switch through which the switching timings of first and second switches become constant. CONSTITUTION:The contact S2 of a first switch 11 is connected to an input terminal 13, and the contact S1 is connected through a power circuit 15 to an output terminal 14. The power source 15 has a rectifier 19, a smoothing capacitor 20 and a voltage generator 21. The contact S5 of a second switch 12 is grounded, a contact S4 is connected to the input terminal of an inverter 17 together with a pull-up resistor 16, and its output terminal is connected to a power source information output terminal 18. The contacts S1, S2 and S4, S5 are conducted when the switches 11, 12 are ON. When they are turned OFF, the contacts S4, S5 are interrupted, and the contacts S5, S6 are conducted. Then, the contacts S1, S2 are interrupted, and the contacts S2, S3 are conducted. That is, after the second switch 12 is first turned OFF, the switch 11 is turned OFF. Thus, the load of the potential holding time of the capacitor 20 can be alleviated.