JPS5829323A - Power interruption detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-speed power failure detection device suitable for computer systems having volatile memory.

Conventional power failure detection devices generally perform full-wave rectification of the AC power supply voltage, smooth the output using an integrating circuit, etc., and cause a power outage when the voltage drops below a certain level. This has the disadvantage that detection is delayed due to the time required.Also, for high-speed detection, the AC power supply voltage is input to a comparator after full-wave rectification, and this comparison is set in multiple stages. A method of detecting by combining the outputs has been used, but this has the disadvantage that the circuit becomes complicated.The object of the present invention is to achieve high-speed detection with a simple circuit by using a monostable circuit with a retrigger function. The object of the present invention is to provide a power failure detection device that can detect power failures.

The present invention resets the oscillator using the output of a comparator that compares the full-wave rectified power supply voltage with a comparison voltage, and inputs the output pulse of this oscillator to the trigger terminal of a monostable circuit having a retrigger function. A power outage is detected by the interruption of the pulse output during the metastable time of the monostable circuit, which occurs continuously as long as the output of the monostable circuit is generated.

Hereinafter, the present invention will be explained in detail using Examples.

FIG. 1 is a circuit diagram showing an embodiment in which the present invention is applied to a microcomputer system.

In the figure, 1 is a diode bridge that performs full-wave rectification of AC power supply voltage, 2 is a system power supply connection terminal, 3 is a comparator, 4 is a variable resistor that sets the operating voltage of comparator 3, 5 is an oscillator, and 6 is a A monostable circuit with a retrigger function, 7 is a microcomputer. Here, the output of the diode bridge 1 is connected to the system power supply connection terminal 2 via a resistor 8 and a diode 9, and one of the comparator 3. Connected to the input terminal. Comparator 3
A variable resistor 4 is connected to the other input terminal of the variable resistor 4. Further, the output of the comparator 3 is connected to the reset terminal of the oscillator 5 to control the timing of the oscillation output. The output of the oscillator 5 is connected to a trigger terminal of a monostable device 6, which outputs a pulse signal of the metastable time formed by a resistor 10 and a capacitor 11 to a microcomputer 7.

Next, in FIG. 2, the operation of the power failure detection device having the above configuration will be explained using the time chart of FIG.
a), Φ), (C), (d), (e), and (f) are AC power supply, system power supply, output of diode bridge 1, output of comparator 3, output of oscillator 5, and monostable, respectively. 0 showing the waveform of the output of the device 6. In the figure, when the AC power is turned on at time s'O, the system power is turned on and a diode bridge output is also generated. The comparator 3 generates an output when the diode bridge output is equal to or higher than the voltage value set by the variable resistor 4. At this time, the oscillator 5 also generates an output and the monostable circuit 6
to drive. In this case, since the output period of the oscillator 5 is set shorter than the output pulse width of the monostable device 6, the output of the monostable device 6, which has a retrigger function, has a DC-like continuous waveform during normal operation. However, when the AC power supply is cut off at time tf, the output of the 1 oscillator 5 stops. Therefore, since the trigger is no longer input to the monostable device 6, the quasi-stable state formed by the last trigger is exhausted. At time point 12, the monostable device output is turned off, and information about the power outage is sent to the microcomputer 7.

As described above, according to this embodiment, a power outage can be detected in a short time that is shorter than the metastable time of the monostable device 6 determined by the resistor 10 and the capacitor 11.

As described above, according to the present invention, since an integrating circuit or the like is not used, it is possible to detect a power outage in less than 10 milliseconds after the AC power supply stops. Furthermore, since only one comparator is used, one circuit does not become complicated. Therefore, it is extremely effective when applied to computer systems such as microcomputers that require high-speed operation.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a timing chart for explaining its operation. 1... diode bridge, 3... comparator, 5...
・Start No. l Figure Z m Time →

Claims (1)

[Claims] 1. A diode bridge circuit that full-wave rectifies the AC power supply voltage, a comparator that compares its output with a preset operating voltage, and an oscillator that outputs an oscillation signal only when the output of this comparator is being generated. A power outage detection device comprising a monostable device having a retrigger function using this oscillation signal as a trigger input.