JPH02223864A - Power source abnormality detecting circuit - Google Patents

Abstract

PURPOSE:To detect with high accuracy abnormality when the power failure occurs at a commercial power source by detecting a range in which positive and negative voltages of AC exceed a threshold by a generation pulse of a switching element, and deriving the time between them by counting a reference clock pulse. CONSTITUTION:When a voltage ES of an AC power source 1 is inputted to photocouplers 7, 8, the couplers 7, 8 emit a light beam in accordance with positive and negative of the voltage ES, respectively, and output a voltage EP. The voltage EP is amplified by an amplifier 10, and a voltage EO whose waveform is inverted is generated. To a counter 11, the voltage EO and a reference pulse of a clock 12 are applied. Based on these signals, the counter 11 counts the number of pulses in rise and fall periods of the voltage EO, and inputs it to a microcomputer 13. The microcomputer 13 stores this value in an internal register 14, and also, discriminates whether abnormality exists or not. Unless abnormality exists, the counter 11 is reset and with regard to each cycle of the next voltage EO, the same operation as the foregoing is executed, and abnormality of the power source is decided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply abnormality detection circuit, and particularly to a power supply abnormality detection circuit that detects an abnormality during a power outage of a commercial power supply.

[Conventional technology]

Figure 4 shows an example of a conventional power supply abnormality detection circuit. The figure shows a circuit used to detect a power outage in a commercial power supply, where 1 is a commercial power supply, 2 is a rectifier circuit, 3 is a Zener diode, and 4 is a transistor. .

5 is a power failure display terminal.

When the power supply 1 is in a normal state, the DC voltage Vc is higher than the Zener voltage of the Zener diode 3, so a voltage drop occurs across the resistor R due to the current flowing through the Zener diode 3, and the transistor 4 is turned on due to this voltage drop. Then, the voltage at terminal 5 becomes zero and no abnormality is displayed. If a power outage occurs here, the voltage Vc decreases, so the current flowing through Zener diode 3 becomes zero, and therefore the voltage drop across resistor R becomes zero, so transistor 4 is turned off. becomes. When transistor 4 is turned off, voltage V is applied to terminal 5.
c will be applied and a power outage will be displayed.

Even if a power outage occurs in this circuit, the transistor 4 operates because a large capacitance is connected to the rectifier circuit 2, and the DC voltage Vc is maintained for a certain period of time even in the event of a power outage.

[Problem to be solved by the invention]

As mentioned above, the circuit shown in FIG. 4 has the advantage of having a relatively small number of parts and requiring only one power supply, but on the other hand, even if a power outage occurs, the DC power supply voltage can only be maintained for one to two cycles, for example.
If a device is connected to an AC power source that malfunctions even in the event of a short-term power outage, this power outage detector cannot be trusted, and the cause of the device malfunction may even be considered a failure when investigated. There is an inevitable dislike.

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 to solve the problem]

The present invention provides a power supply abnormality detection circuit for detecting an abnormality in an AC power supply, in which a threshold value is provided for each of the positive and negative voltages of the AC power supply, and a pair of switching devices that operate in response to the positive and negative voltages of the AC power supply having the threshold values are provided. A counter that inputs the rising and falling signals of the switching element and counts the operating period of the switching element using a reference clock pulse, and continuously performs this counting operation for each cycle of the power supply and calculates each count value. The circuit is characterized by a control means that memorizes and calculates the time to find the deviation from the reference value, compares the deviation with a fixed value, and determines whether there is an abnormality in the power supply based on the magnitude of the deviation, and is highly accurate. [Function] In the power supply abnormality detection circuit of the present invention, when detecting a power supply abnormality such as a power outage, the power supply abnormality detection circuit detects the positive and negative voltages of the power supply. At the same time, a pair of switching elements is connected to the circuit, the period during which this switching element is turned on in response to the positive and negative voltages of the AC voltage is counted using a reference pulse, and this count value is input into, for example, a microcomputer. This operation is performed continuously for each cycle of the power supply frequency, and the difference tp between the normal value to and the changed value tx is calculated. If tp is a constant value γ and tp>γ, then Since it is determined that an abnormality has occurred in the power supply, for example, if the power supply voltage decreases and the maximum value approaches the above threshold, then the current value X becomes tx(to, and tp<γ). It is also possible to reliably detect abnormal drops in power supply voltage and short-term power outages.

〔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 same figure, 1 is an AC power supply, 6 is a resistor,
7 and 8 are photocouplers, 9 is a resistor, 10 is an output amplifier for photocouplers 7 and 8, 11 is a counter, and 12 is a clock circuit.

13 is a microcomputer, 14 is an internal register, 1
5 is a pass line for transmitting and receiving signals, Es is electric voltage, Ep
is the output side voltage of the phototransistor, Eo is the amplifier output side voltage, and Vc is the 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 correspond to the positive and negative voltages of the voltage Es, respectively. It emits light and generates an output voltage Ep. Voltage EP is amplified by amplifier 10 to generate voltage Eo whose waveform is inverted from voltage Ep.

Since the counter 11 is supplied with the voltage Eo and the reference pulse of the clock circuit 12, the counter 11 counts the number of pulses in the rising and falling periods of the voltage EO based on these signals, and inputs this to the microcomputer 13. The microcomputer 13 stores this count value in the internal register 14 and determines whether there is an abnormality. If there is no abnormality, the microcomputer 13 resets the counter 11 and instructs it to count each cycle of the voltage Eo, so that the count value is normal. A power failure is determined by comparing the current value with the subsequent value.

FIG. 2 shows an operating waveform diagram of each part, where the horizontal axis t represents time and the vertical axis represents voltages Es, Ep, and Eo. The voltage Vq indicates the forward voltage drop of the light emitting diode on the input side of the photocoupler 7.8, and the light emitting diode 7.8 emits light when the voltage Es exceeds the voltage vE. This voltage 7 isometrically represents the aforementioned threshold voltage, and in the case of this element, no particular threshold is set, but the output side voltage Ep is centered around the zero and π phase of the voltage Es. As a result, a pulse-like off period with a time width tp occurs.

Time ty is the on period corresponding to the light emitting period.

Voltage Eo is the amplified voltage Ep, so voltage EP
0 time to, which is an inverted waveform, is the time when the photocoupler 7.8 is turned on corresponding to time tN, and represents the case where the voltage Es is normal, and time tx is when the voltage Es decreases,
The time ty shows the case where it further decreases, and to)t
It becomes x. Therefore, if the value of to indicates a normal state of the power supply, it is possible to know whether the power supply is abnormal by determining 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, initial processing shown by the dotted line in the figure is performed.

In the initial process, the counter 11 is activated at the rise time tL of the voltage EO to start counting clock pulses, and the count is completed until the fall time t2. The count value NO at this time is stored in the internal register 14. Next, from time t to time t2, the power frequency (for example, 50Hz)
YE to find α≧to≧β whether it corresponds correctly to
If S, it is determined that the power supply is normal and the photocouplers 7 and 8 are operating normally, and the process proceeds to the next step. In the case of No, it is determined that the power supply is abnormal and the subsequent processing is canceled. In this case, α, β
If the power supply frequency is 50Hz, the value of is (1=10 (
m, s), β=8.5 (ms), if 60H, a
= 8.3 (ms) and β = 6.8 (ms), and the calculation is performed using these values.

After the initial processing is completed, the counter 11 is reset, and then counting of clock pulses is started again at time t4 when the voltage Eo rises, and ends at time t2. If the count number at this time is, for example, Nx, this Nx is stored in a register different from the register of No. in the internal register 14.

Next, convert these into times to and tx using No and NX to find the time t p = t o -t x, compare this with the constant value γ to find tp≧γ, and if YES, it is determined that the power supply is abnormal. It makes a judgment, outputs an alarm, and stops the device.

If No, it is determined that the power supply is normal and the counter 11 is
is reset, the rise and fall times of the voltage 'Eo are pulse-counted again, and the above judgment operation is repeated. In this case, γ
The determination is made using γ=2.5 (ms) as the value.

In this way, power outages and abnormal voltage drops can be detected with high accuracy and speed.

〔Effect of the invention〕

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

(1) Accidents such as instantaneous power outages and abnormal voltage drops in AC power supplies can be detected with high accuracy.

(2) Since the AC voltage of the power source 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 explanation of the drawing]

FIG. 1 is a system diagram showing an embodiment of the power supply abnormality detection circuit of the present invention, FIG. 2 is an operation waveform diagram of each part of FIG. 1, and FIG.
The 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, 7.8 is a photocoupler, 11 is a counter,
12 is a clock circuit, and 13 is a microcomputer. Patent Applicant Name Hitachi Koki Co., Ltd. Small 1 drawing vt L: / le torture width each 2nd appearance z - 1111111 drop t

Claims (1)

[Claims] 1. In a power supply abnormality detection circuit that detects an abnormality such as a power outage of an AC power supply, a threshold value is provided for each positive and negative voltage of the AC power supply, and the circuit operates in response to the positive and negative voltages having the threshold value. a pair of switching elements; a counter that receives rising and falling signals of the output voltage of the switching element and counts the operating period of the switching element using a reference clock pulse; The control means continuously stores each counted value, converts it into time, determines the deviation from the reference value, compares the deviation with a constant value, and determines whether there is an abnormality in the power supply based on the magnitude of the deviation. A power supply abnormality detection circuit characterized by: