JPH0782041B2 - Power supply abnormality detection method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply abnormality detection circuit, and more particularly to a power supply abnormality detection circuit that detects an abnormality when a commercial power supply fails.

[Conventional technology]

FIG. 4 shows an example of a power supply abnormality detection circuit conventionally used. This figure shows a circuit used for detecting a power failure of a commercial power source, 1 is a commercial power source, 2 is a rectifier circuit, 3 is a zener diode, 4 is a transistor, and 5 is a power failure display terminal.

When the power supply 1 is in the normal state, the DC voltage Vc is higher than the Zener voltage of the Zener diode 3, and therefore the resistance R
A voltage drop occurs at both ends of the transistor due to the current flowing through the Zener diode 3, and the transistor 4 is turned on by this voltage drop so that the voltage at the terminal 5 becomes zero and no abnormality is displayed.
When a power failure occurs here, the voltage Vc drops, so the current flowing through the Zener diode 3 is not zero, and therefore the resistance R
Since the voltage drop of 0 becomes zero, the transistor 4 is turned off. When the transistor 4 is turned off, the voltage Vc is applied to the terminal 5 and the power failure is displayed.

Even if a power failure occurs in this circuit, the transistor 4 operates because a large capacitance is connected to the rectifier circuit 2 and holds the DC voltage Vc for a certain time even during a power failure.

[Problems to be Solved by the Invention]

As described above, the circuit shown in FIG. 4 has an advantage that the number of components is relatively small and one power source is sufficient, but on the other hand, the fact that the DC power source voltage is maintained even if a power failure occurs is, for example, 1 to 2 cycles.
Or if a device that malfunctions even for short-term power outages of less than that is connected to an AC power source, this power failure detector is unreliable, and rather a failure even when investigating the cause of a device malfunction. I hate it.

An object of the present invention is to provide a power supply abnormality detection circuit that has excellent detection accuracy and greatly improves reliability.

[Means for Solving the Problems]

The present invention, in a power supply abnormality detection circuit for detecting abnormality of an AC power supply, sets thresholds for positive and negative voltages of the AC power supply, and operates a pair of switchings that operate corresponding to positive and negative voltages of the AC power supply having the thresholds. Element, a counter that inputs the rising and falling signals of the switching element and counts the operating period of the switching element using the reference clock pulse, and this counting operation is performed continuously for each cycle of the power supply, and the respective count values are calculated. It is characterized in that the circuit is composed of a control means that stores the time, calculates the time, obtains the deviation from the reference value, compares the deviation with a constant value, and determines the abnormality of the power supply according to the magnitude of the deviation, and is highly accurate. , We are trying to achieve the purpose by providing a highly reliable power failure detection circuit.

[Action]

In the power supply abnormality detection circuit of the present invention, when a power supply abnormality such as a power failure is detected, a threshold value is provided for each of the positive and negative voltages of the power supply and a pair of switching elements are connected in succession to the circuit, and this switching element is a positive or negative voltage of the AC voltage. Corresponding to, the period of turning on is counted by the reference pulse, this count value is input to, for example, a microcomputer to determine the time to, and this operation is performed continuously for each cycle of the power supply frequency, and changes from the normal value to. The difference tp from the value tx is calculated, and when tp is larger than tp for a constant value γ, it is determined that an abnormality has occurred in the power supply. If the threshold is approached, then tx
Since tx <to and tp <γ, it is possible to reliably detect an abnormal drop in the power supply voltage or a short power failure.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram showing an embodiment of the power supply abnormality detection circuit of the present invention. In the figure, 1 is an AC power supply, 6 is a resistor,
7 and 8 are photocouplers, 9 is a resistor, and 10 is a photocoupler 7.
And 8 output amplifiers, 11 counters, 12 clock circuits, 13 microcomputers, 14 internal registers, 15
Is a bus line for transmitting and receiving signals, Es is a power supply voltage, Ep is a phototransistor output side voltage, Eo is an amplifier output side voltage, Vc
Indicates a DC voltage.

When the voltage Es of the AC power supply 1 is applied to the photocouplers 7 and 8, the photocouplers 7 and 8 emit light corresponding to the positive and negative voltages of the voltage Es to generate the output voltage Ep. Voltage Ep is an amplifier
A voltage Eo which is amplified by 10 and whose waveform is inverted from the voltage Ep is generated.

Since the counter 11 is supplied with the voltage Eo and the reference pulse of the clock circuit 12, the counter 11 receives the voltage Eo based on these signals.
Count the number of pulses in the rising and falling periods of
This is input to the microcomputer 13. The microcomputer 13 stores this count value in the internal register 14, determines whether or not there is an abnormality, resets the counter 11 if there is no abnormality, and further issues an instruction to count for each cycle of the voltage Eo. The power supply abnormality is determined by comparing the current value with the subsequent value.

FIG. 2 is a diagram showing operation waveforms of each part. The horizontal axis t represents time, and the vertical axis represents voltages Es, Ep and Eo. The voltage V _F indicates the forward voltage drop of the input side light emitting diodes of the photocouplers 7 and 8, and the light emitting diodes 7 and 8 emit light when the voltage Es exceeds the voltage V _F. This voltage V _F equivalently represents the above-mentioned threshold voltage, and in the case of this element, no particular threshold value is provided, but the output side voltage Ep is centered around the zero and π phases of the voltage Es. A pulsed off period of time width t _F will occur. The time t _N is the ON period corresponding to the light emission period. Since the voltage Eo is the amplified voltage Ep, it has a waveform obtained by inverting the voltage Ep. The time to is the time when the photocouplers 7 and 8 are turned on corresponding to the time t _N and represents the case where the voltage Es is normal, and the time tx is the time ty when the voltage Es decreases.
Indicates the case of further decrease, and to> tx. Therefore, if the value of to indicates a normal state of the power supply, the abnormality of the power supply can be known by obtaining to-tx or to-ty.

FIG. 3 shows an operation flowchart of the microcomputer 13. In the figure, when the AC power supply 1 is applied and the apparatus enters the start state, the initial processing shown by the dotted line in the figure is performed.

Initial processing is counter the rising time t ₁ of the voltage Eo 11
Is started to start counting the clock pulse, count until the falling time t ₂ and end. The count value No at this time is stored in the internal register 14. Next, from time t _1, whether time t ₂ correctly corresponds to the power supply frequency (for example, 50 Hz) is obtained α ≧ to ≧ β, and if YES, the power supply is normal and the photocouplers 7 and 8 are operating normally. If it is determined that there is, proceed to the next. In the case of NO, it is determined that the power supply is abnormal and the subsequent processing is stopped. In this case, the values of α and β are α = 10 (ms), β = 8.5 (ms) when the power supply frequency is 50 Hz, and α when it is 60 Hz.
= 8.3 (ms) and β = 6.8 (ms), calculation is performed using these values.

When the initial process is completed, the counter 11 is reset, and then the counting of the clock pulse is started again from the rising time t _{1 of the} voltage Eo, and is finished at the time t ₂ . If the count number at this time is Nx, for example, this Nx is stored in a register other than the above No register in the internal register 14, and then
From No and Nx, these are converted into time to and tx, and time tp = to−
Calculate tx and compare it with a constant value γ to calculate tp ≧ γ
If it is S, it is determined that the power supply is abnormal, an alarm is output, and the device is stopped.

If NO, the power supply is determined to be normal, the counter 11 is reset, the rise / fall time of the voltage Eo is pulse counted again, and the above determination operation is repeated. In this case, the determination is performed using γ = 2.5 (ms) as the value of γ.

In this way, a power failure of the power supply and an abnormal voltage drop are required with high accuracy and high speed.

〔The invention's effect〕

As described above, according to the present invention, the following effects can be obtained.

(1) Accidents such as momentary power failure of AC power supply and abnormal voltage drop can be detected with high accuracy.

(2) Since the AC voltage of the power supply is directly detected, the detection circuit has no capacitance and can be detected at high speed.

(3) The reliability of the power supply abnormality detection device can be improved.

[Brief description of drawings]

FIG. 1 is a system diagram showing an embodiment of a power supply abnormality detection circuit of the present invention, FIG. 2 is an operation waveform diagram of each part of FIG. 1, and FIG.
FIG. 4 is an operation flowchart of the microcomputer used in the figure, and FIG. 4 is a conventional power failure detection circuit diagram. 1 is an AC power supply, 7 and 8 are photocouplers, 11 is a counter, 12
Is a clock circuit and 13 is a microcomputer.

Claims (1)

[Claims] 1. A pair of switching elements, which are provided with thresholds for positive and negative voltages of the AC power supply and operate in response to the positive and negative voltages having the thresholds, and an output voltage of the switching elements. And a counter for inputting the rising / falling signal of 1 to count the operation period of the switching element using a reference clock pulse, and means for continuously performing the counting operation for each cycle of the power supply and storing each count value. In the power supply abnormality detection method of detecting an abnormality at the time of power failure of the AC power supply, the first count value is stored in the storage means and then it is determined whether the first count value is within a predetermined range. When the first count value is within a predetermined range, the deviation between the count value from the next time onwards and the first count value is obtained, and the deviation is compared with a constant value to determine the abnormality of the power supply according to its magnitude. You Power failure detecting method, characterized in that.