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Power Failure Detector Circuit

IP.com Disclosure Number: IPCOM000046647D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 45K

Publishing Venue

IBM

Related People

Orengo, G: AUTHOR [+2]

Abstract

The circuit of the present disclosure is supplied by power supplies, e.g., + 8.5 V and - 8.5 V, to be checked, and therefore avoids the use of auxiliary supplies or batteries. If one (or both) power supplies fail, the failure is detected by this circuit which, in turn, energizes an alarm-emitting circuit in order to warn, for example, a user. The basic principle of operation of such circuits may be understood from Fig. 1. When the power supplies (+ VF = + 8.5 V and - VF = -8.5 V, operate normally, switches SW1 and SW2 are controlled by the circuit 10 through additional logic circuitry (not shown). Capacitor C between the two power supplies is then charged. As soon as a failure is detected, the switches are opened by inputting an appropriate logic level at output 1.

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Power Failure Detector Circuit

The circuit of the present disclosure is supplied by power supplies, e.g., + 8.5 V and - 8.5 V, to be checked, and therefore avoids the use of auxiliary supplies or batteries. If one (or both) power supplies fail, the failure is detected by this circuit which, in turn, energizes an alarm-emitting circuit in order to warn, for example, a user. The basic principle of operation of such circuits may be understood from Fig. 1. When the power supplies (+ VF = + 8.5 V and - VF = -8.5 V, operate normally, switches SW1 and SW2 are controlled by the circuit 10 through additional logic circuitry (not shown). Capacitor C between the two power supplies is then charged. As soon as a failure is detected, the switches are opened by inputting an appropriate logic level at output 1. This results in isolating capacitor C from the supplies, preventing it from discharging. In addition, output 2 is forced to a level which allows circuit 20 to emit an alarm signal, for the time interval it is powered by the charge stored in capacitor C, acting as an auxiliary power supply. Circuit 10 is basically comprised of a voltage reference circuit 11 of the bandgap type, two comparators 12 (C1) and 13 (C2), a validation circuit 14 and additional circuitry including an interface circuit 16. Active circuits which are supplied between +
8.5 V and ground may normally operate in the voltage range : 4 - 8.5 V . Failure threshold is 7.225 V which corresponds to a change of 15% of the nominal voltage. In the range 4 - 7.225 V the active circuits must generate a failure signal to the validation circuit, the role of which is to check if the power supply voltage falls under 4 volts, and then sets an appropriate level at output 2 to confirm that a failure has been detected. For VF > 4 V, Vref is equal to
2.59 V and is stable, below 4 V, Vref is indefinite. Comparator C...