JPS58119727A - Power source malfunction detecting circuit - 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 power supply abnormality detection circuit for detecting AC power supply failure and voltage drop.

For example, many electronic devices using a μ-CPU (microcomputer) use a commercial power source to create a stabilized DC power source to operate the electronic circuit. In such electronic devices, if an abnormality in the power supply can be detected at the stage of commercial power supply or AC power supply, countermeasures can be taken against the power supply abnormality before its influence spreads to the DC power supply.

That is, for example, it is possible to protect the electronic device by switching the power source to a battery or temporarily storing data being processed in a non-volatile memory.

Typical alternating current power supply abnormalities that cause problems in electronic devices are failures (momentary power interruptions) or drops in power supply voltage. A conventional power supply abnormality detection circuit that detects these two abnormalities uses independent circuit parts to detect these abnormalities. Therefore, there is a problem in that it is difficult to reduce the number of circuit components, and it is difficult to reduce the cost and improve the reliability of the circuit.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a power supply abnormality detection circuit that can organically detect defects and voltage drops with one circuit.

The present invention includes a rectifying means for full-wave or half-wave rectification of AC voltage, a comparator for comparing the rectified voltage with a predetermined voltage serving as a reference for low voltage abnormality, and a comparator that is triggered by the output voltage of the comparator and at least the next trigger. The circuit is simplified by equipping the power supply abnormality detection circuit with a timer that outputs a pulse signal with a pulse width that is longer than the time that is likely to occur, and detecting defects and voltage drops based on the waveform of the timer's output signal. To achieve the above objectives.

The present invention will be described in detail below with reference to Examples.

FIG. 1 is a block diagram for explaining the operating principle of the power supply abnormality detection circuit of this embodiment. In this circuit, a full-wave rectified signal 3 of an input voltage 1 supplied from a commercial power source is supplied to a drop detection section 4. The drop detection section 4 compares the voltage level with the reference voltage signal 6 supplied from the reference voltage generator 5. The reference voltage signal 6 represents a DC voltage at a predetermined level that serves as a reference for determining whether there is an abnormality in voltage drop.

When an abnormal voltage drop is detected by the drop detector 4, a drop detection signal 7 is supplied to the detection signal generator 8. Based on this, the detection signal generator 8 outputs a signal (voltage drop signal) maintained at the L (low) level (OV) as shown in FIG. 2, for example, as the detection signal 9.

If the drop detection section 4 does not detect a voltage drop, its output signal 10 is supplied to the loss detection section 11 . The defect detection section 11 determines whether there is a defect or not, and supplies a discrimination signal 12 to the detection signal generator 8 .

In the detection signal generator 8, when there is a defect, the signal becomes H level (power supply voltage Vcc) in the vicinity of the defect, as shown in FIG.
) is output as the detection signal 10 (missing signal). In addition, in a normal case where there is no defect, a signal kept at the H level (normal signal) is outputted as the detection signal 10, for example, as shown in FIG. These detection signals 1
0 is supplied to the μ-CPU and the like, and abnormalities in the power supply are monitored.

FIG. 3 specifically shows this power supply abnormality detection circuit. The full-wave rectifier 2 performs full-wave rectification of the input voltage (FIG. 4a) (FIG. 4b). Two voltage dividing resistors 21 and 22 are connected in series on the output side of the full-wave rectifier 2, and a voltage-divided rectified signal 3 appears at a connection point 23 between them. The rectified signal 3 is supplied to the 0 input terminal of the comparator 25 via the overcurrent blocking resistor 24. The θ input terminal of the comparator 25 is connected to the cathode of a Zener diode 26 whose anode side is provided. The cathode of the Zener diode 26 is connected via a resistor 27 to a DC power supply (not shown) having a voltage Vcc. The θλ input terminal of the compare 25 is supplied with the reference voltage signal 6 by the Zener diode 26 .

Suppose now that the voltage 1 is abnormally low.

In this case, the peak voltage of the rectified signal 3 is lower than that of the reference voltage signal 6. Therefore con/<lator 25
is the drop detection signal 7 held at L level (Fig. 5 81
) is output. The drop detection signal 7 is supplied to the input terminal IN of the retrigger monostable multivibrator 28 . In this case, the retrigger monostable multivibrator 28 always outputs an L level signal as the output signal 29 from the output terminal OUT. Signal 29 is supplied to the base of transistor 32 via a current limiting resistor 31. The transistor 32 has a collector that outputs the detection signal 9 connected to the DC power supply via a resistor 33, and an emitter that is grounded. Therefore, when an L level signal is supplied as the output signal 29, the transistor 32 becomes conductive, and an L level voltage drop signal (FIG. 5 a2) is output from the collector as the detection signal 9.

Next, a case where input voltage 1 is normal will be explained.

In this case, the peak voltage of the rectified signal 3 is the reference voltage signal 6
It is higher than that of . Therefore, comparator 25
outputs a pulse voltage as the output signal 10 during a period in which the rectified signal 3 is higher than the voltage VR represented by the reference voltage signal (FIG. 5b1). This pulse voltage is generated regularly with a period of half a cycle of the commercial power supply. The output signal 10 is a retrigger monostable multivibrator 28
is supplied to the input terminal IN of. Retrigger monostable multivibrator 28 produces a pulse signal at a number of times determined by resistor 35 and capacitor 36 each time a pulse voltage is applied. This pulse signal has a pulse width of approximately 0.8 cycles, which is longer than a half cycle of the commercial power supply, and this pulse width is continuously extended by retriggering by the output signal 10. Therefore, when a regular pulse train with a period of half a cycle is supplied as the output signal 10, the output terminal 01JT of the retrigger monostable multivibrator 28 outputs a signal held at H level as the output signal 29. At this time, the transistor 32
A case will be explained in which there is a one-cycle loss in the input voltage 1 at the end of the positive and normal signal held at the power supply voltage Vcc as the output signal 9 at the collector of the output signal 9. As shown in FIG. 5 C1, the comparator 25 does not output a pulse voltage for the cycle in which the loss occurs. Therefore, the portion of the output signal 10 where the loss occurs is held at L level. This output signal 1o, tj retrigger monostable multivibrator 2
8, the output signal 2 is output at the part where the defect occurs.
9 drops to L level.

Therefore, at the collector of the transistor 32, a defective signal (C2 in FIG. 5) in which this portion similarly falls to the L level appears as the output signal 9.

As explained above, according to the present invention, a retriggerable timer is used to determine a power failure, so by appropriately adjusting the time constant of the timer, a loss that does not cause any trouble in the use of electronic equipment can be detected. You can prevent it from happening.

In the embodiment, a retrigger monostable multivibrator is used as the timer, but the timer is not limited to this.

[Brief explanation of the drawing]

The drawings are for explaining one embodiment of the present invention.
The figure is a block diagram for explaining the operating principle of the power supply abnormality detection circuit, Figure 2 is a diagram of various voltage waveforms of the output signals of this circuit, Figure 3 is a circuit diagram of the power supply abnormality detection circuit, and Figure 4 is the input voltage. Figure 5 is a voltage waveform diagram that appears on the output side of the comparator and transistor in each case. 1... Input terminal 2... Full wave rectifier 5
...Reference voltage generator 25 ... Comparator 26 ... Zener diode 28 ... Retrigger monostable multivibrator 3
2...Transistor 35...Resistor 3
6...Applicant for capacitor Umeo Yamauchi, patent attorney representing Fuji Xerox Co., Ltd.

Claims (1)

[Claims] 1. Rectifying means for full-wave or half-wave rectification of the voltage obtained from the AC power source for which abnormality detection is to be performed, and rectifying the voltage obtained by the means for abnormality judgment of power supply voltage drop. A comparator that compares with a standard reference voltage and generates a trigger pulse when the voltage after rectification is higher than this reference voltage, and a comparator that inputs the trigger pulse and generates a half cycle of the AC power supply if full-wave rectification is performed. It is equipped with a retriggerable timer that generates a pulse with a time width of 1 minute or more, or 1 cycle or more of the AC power supply when half-wave rectification is performed, and the waveform of the output signal of the timer is used to control the power supply. A power supply abnormality detection circuit characterized by detecting voltage drops and defects. 2. The power supply abnormality detection circuit according to claim 1, wherein the timer is a retrigger monostable multivibrator.