JPH09318680A - Power supply cut detecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply cut detecting circuit capable of highly accurately detecting the reduction of a voltage with little influence of variance in photocoupler characteristic at low costs. SOLUTION: A power supply cut detecting circuit includes a power source device 2 for converting an AC current from an AC input power source 1 into a direct current and supplying this, a resistor 5 disposed in series to the AC input power source 1, to which the photocoupler light emitting element of a photocoupler 4 is connected via a voltage dependent element 6, and an integrating circuit 8 and a logic IC 9 provided for the output of the photocoupler 4. When the peak voltage of the AC input power source 1 is higher than a voltage provided for by the voltage dependent element 6, the photocoupler light emitting element is lit, the integrating circuit 8 is charged and, when the peak voltage of the AC input power source 1 is lower than the voltage provided for by the voltage dependent element 6, the photocoupler light emitting element is turned off, electricity is discharged from the integrating circuit 8 and, when the output voltage of the integrating circuit 8 is lower than the threshold voltage level of the logic IC 9, power supply cut or voltage reduction is determined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power failure detection circuit for detecting a voltage drop and a power failure of a device such as a facsimile machine, a personal computer and an electronic device which uses an AC power supply.

[0002]

2. Description of the Related Art Conventionally, there has been the following power failure detection circuit. (1) In the power cutoff detection circuit, the AC full-wave rectified voltage is directly input to the photocoupler, and the power cutoff detection circuit has a relatively simple circuit configuration for detecting the cutoff of the input voltage (for example, Japanese Patent Laid-Open No. -106844).

(2) An AC power supply voltage is rectified by a rectifier circuit, and the rectified voltage is smoothed by a smoothing circuit,
A power failure detection circuit that reduces the ripple of the voltage smoothed by the peak hold circuit (for example, Japanese Patent Laid-Open No. 60-666).
No. 18).

(3) A photo coupler consisting of a light emitting element and a light receiving element is connected to an AC input power source, and the photo coupler is connected to A
A power-off detection circuit connected to a timer circuit that generates a power failure detection output by time-up after a time longer than half the cycle of the C input power supply (for example, Japanese Patent Laid-Open No. 1-210869).
Reference).

[0005]

However, (1)
In the power-off detection circuit, the full-wave rectified voltage of the AC input is directly input to the photocoupler, and the circuit configuration is relatively simple for detecting the interruption of the input voltage. However, there was a problem that the cost was very high due to the large number of items. Further, there is also a problem that the detection accuracy becomes low with respect to the decrease of the input voltage.

Further, the photocoupler is an element having a large variation in the characteristics of the current conversion rate, and cannot be stably operated without adjustment. Therefore, there is also a problem that the cost becomes high because the adjustment is performed using a variable resistor or the like.

Further, in the power failure detection circuit of (2), if the detection accuracy is low, adjustment by the characteristic variation of the photocoupler is not necessary, but a peak hold circuit, a smoothing circuit, a voltage comparator (comparator), etc. are required. Therefore, there is a problem that the number of parts is large and the cost is very high.

Further, the power failure detection circuit of (3) is a very simple and low cost circuit specialized only for the function of detecting a power failure, but the influence of the characteristic variation of the photocoupler is large and the input voltage is lowered. However, there is a problem that it cannot be used when it is desired to design a system that has a low detection accuracy and reliably detects a voltage drop as well as a power failure and guarantees a stable power supply.

The present invention has been made in view of the above points, and it is an object of the present invention to provide a power failure detection circuit which can detect a voltage drop with high accuracy at a low cost and which is less affected by characteristic variations of photocouplers. With the goal.

[0010]

In order to achieve the above object, the present invention provides a power supply device for converting an AC input power supply into a direct current and supplying the same, a resistor arranged in series with the AC input power supply, and voltage dependence. A light emitting element of a photocoupler is connected via an element, an integrating circuit and a logic IC are provided at the output of the photocoupler, and the peak voltage of the AC input power source is equal to or higher than the voltage specified by the voltage dependent element. The light emitting element is turned on to charge the integrating circuit, the light emitting element is turned off and the integrating circuit is discharged when the peak voltage of the AC input power source is less than the voltage specified by the voltage dependent element, and the integrating circuit is discharged. There is provided a power failure detection circuit provided with means for determining power failure or voltage drop when the output voltage of the logic IC becomes equal to or lower than the threshold voltage level of the logic IC.

Further, it is preferable that the AC input power source is divided by a resistor and the voltage-dependent element and the light emitting element of the photocoupler are connected to the dividing point.

Further, it is preferable that the AC input power source is rectified by a bridge rectifier, and its output terminal is connected to the light emitting element side of the photocoupler via a resistor and a Zener diode.

The photocoupler may be an AC input type photocoupler, and the voltage-dependent element may be a varistor, a bidirectional Zener diode, or a Zener diode arranged in resistance.

Further, the time constant of the integrating circuit may be set to be smaller than 1/2 cycle of the AC input power source at the time of charging and larger at the time of discharging.

Furthermore, a rectifier composed of a bridge rectifier and two diodes of the power supply device may be provided, and the output terminal of the rectifier may be connected to the light emitting element side of the photocoupler via a resistor and a Zener diode.

According to the power failure detection circuit of the first aspect of the present invention, since the voltage-dependent element is inserted between the AC input power source and the photocoupler, the peak voltage of the AC input power source is accurately detected. Therefore, it is possible to prevent the accuracy of the detection voltage from being lowered due to the characteristic variation such as the current conversion rate of the photocoupler. Further, the cost can be reduced by using an inexpensive integrating circuit as the means for determining the voltage drop. Therefore, it is possible to detect the voltage drop with high accuracy by reducing the number of parts and keeping the cost of parts low.

Further, according to the power failure detection circuit of the second aspect of the present invention, since the voltage of the AC input power source is divided by the resistor, the detection point of the voltage drop can be finely adjusted, and the voltage drop can be further reduced. It can be performed with high accuracy.

Further, according to the power failure detection circuit of the third aspect of the present invention, since the AC input power is rectified, an inexpensive direct current type photocoupler can be used as the photocoupler, and the voltage-dependent element is further used. Since an inexpensive zener diode can be used, the number of parts is slightly increased, but an even cheaper circuit can be obtained.

Further, according to the power failure detection circuit of the fourth aspect of the present invention, by making the voltage-dependent element and the photocoupler the AC input type, the circuit is operated in both positive and negative phases of the AC input power. AC is possible because
It is possible to detect a power failure (instantaneous interruption) of 1/2 cycle of the input power supply.

Further, according to the power failure detection circuit of the fifth aspect of the present invention, the time constant of charging the integration circuit is made small and the time constant of discharging is made large so that the voltage of the AC input power supply is normal. The output of the integrating circuit can be made sufficiently high, and the margin for malfunction due to external noise such as AC line noise can be increased.

Furthermore, according to the power-off detection circuit of claim 6 of the present invention, by providing a rectifier circuit composed of a bridge rectifier and two diodes of a power supply device to be mounted at the same time, the full-wave by the two diodes is provided. Rectification becomes possible, and a highly accurate and inexpensive circuit can be made with a small number of parts.

[0022]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a power failure detection circuit according to the first embodiment of the present invention. The power-off detection circuit is mounted on a device such as a facsimile machine, a personal computer, or an electronic device that uses an alternating current (AC) power supply.

As shown in FIG. 1, this power interruption detection circuit includes an AC input power source 1, a DC power source device (hereinafter referred to as "power source device").
2, load section 3, photocoupler 4, photocoupler light emitting element 41, photocoupler light receiving element 42, resistor 5
81 and 82, the voltage-dependent element 6, the level conversion circuit 7,
It is composed of an integrating circuit 8, a capacitor 83, a logic IC 9, a control circuit DC power supply (Vcc) 10 and the like, and is configured as shown in FIG.

The arrangement of the photocoupler 4, the resistor 5, and the voltage-dependent element 6 can be interchanged.

FIG. 2 is a diagram showing operation waveforms in a main part of the power failure detection circuit shown in FIG. First, when the AC input power supply 1 is turned on and the input voltage is normal, the peak voltage of the input voltage is sufficiently large due to the specified voltage of the voltage-dependent element 6, and the photocoupler light-emitting element 41 of the photocoupler 4 is detected.
Lights up and the inter-terminal voltage of the photocoupler light receiving element 42 becomes low level. Then, the level converting circuit 7 inverts the signal level to charge the integrating circuit 8.

Here, resistor 81: Ra, resistor 82:
Assuming that Rb and capacitor 83 are CT, the charging-side time constant T1 of the integrating circuit 8 is determined by the following equation (1), and the discharging-side time constant T2 is determined by the following equation (2).

T1 = CT × {Ra × Rb / (Ra + Rb)} (1) T2 = Rb × CT (2)

The time constant T1 on the charging side is small and the time constant T2 on the discharging side is T2 based on the half cycle of the AC input power source.
Increase. For example, the charging side time constant T1 is set to approximately 1 ms or less,
It should be sufficiently smaller than 1/2 cycle of the AC input power supply. Further, the discharge side time constant T2 is set to approximately 20 ms or more,
It is set sufficiently larger than 1/2 cycle of the AC input power supply.

As a result, when the peak voltage of the AC input power supply 1 is higher than the specified voltage of the voltage-dependent element 6, the output voltage of the integrating circuit 8 is sufficiently higher than the threshold voltage level (high level voltage) L of the logic IC. It becomes a high voltage. When the peak voltage of the AC input power supply 1 is smaller than the specified voltage of the voltage-dependent element 6, the integrating circuit 8 discharges and the output voltage is sufficiently lower than the threshold voltage level (low level voltage) L of the logic IC 9. Become a voltage.

Then, this state is determined as the input voltage drop. Therefore, as shown in FIG. 2D, when the output voltage of the integrating circuit 8 becomes a voltage sufficiently higher than the threshold voltage level (low level voltage) L of the logic IC,
By detecting a normal AC input voltage, it is determined that the AC input power supply is normal.

Similarly, when the input voltage of the AC input power supply 1 is cut off, the integrating circuit 8 is similarly discharged without being charged, and its output voltage is sufficiently lower than the threshold voltage level L of the logic IC 9. become. Therefore, as shown in (d) of FIG. 2, the integrating circuit 8 is discharged to an output voltage that is sufficiently lower than the threshold voltage level L of the logic IC 9, and a power failure is detected to determine that the AC input power source is a power failure. .

FIG. 3 is a block diagram showing the configuration of a power-off detection circuit according to the second embodiment of the present invention, and the portions common to FIG. 1 are designated by the same reference numerals. In this power failure detection circuit, a resistor 11 is newly added to the power failure detection circuit shown in FIG. The power failure detection circuit operates similarly to the power failure detection circuit shown in FIG.

That is, in the power failure detection circuit of FIG. 3, the resistor 11 forms a series circuit with the resistor 5 to form the AC input power source 1
By dividing the voltage, the set value of the detection voltage when the voltage drops can be finely adjusted by the resistor 11.

FIG. 4 is a block diagram showing the configuration of a power failure detection circuit according to the third embodiment of the present invention.
The same parts as those of the above are denoted by the same reference numerals. This power failure detection circuit is provided with a bridge rectifier 12 for rectifying the AC input power source 1 in the power failure detection circuit shown in FIG. 3, and after the bridge rectifier 12 rectifies the voltage of the AC input power source 1, the resistor 5 And 11, the voltage-dependent element 6, and the photocoupler 4. The power failure detection circuit operates similarly to the power failure detection circuit shown in FIG.

That is, in the power failure detection circuit of FIG. 4, it is possible to use the DC type voltage-dependent element 6 and the photocoupler 4 which are highly accurate and inexpensive, and to detect a drop in the power supply voltage with a low cost circuit configuration. Can be performed with high precision.

FIG. 5 is a block diagram showing the configuration of the power failure detection circuit according to the fourth embodiment of the present invention.
The same parts as those in FIG. 4 are designated by the same reference numerals. This power failure detection circuit is used in combination with the power supply device 2
The input voltage of the AC input power supply 1 is rectified by the rectifier circuit 13 and is output to the resistors 5 and 11, the voltage dependent element 6, and the photocoupler 4.

The power failure detection circuit operates in the same manner as the power failure detection circuit shown in FIG. That is, in the power failure detection circuit of FIG. 5, the parts can be shared with the power supply device 2, so that the cost of the circuit can be reduced.

The logic IC of the power failure detection circuit
Reference numeral 9 may be a detection means such as a comparator, or any element that can be constituted by a transistor (Tr) and a resistor and can be turned on / off at a certain voltage level can be used. Further, the voltage-dependent element 6 may be another element as long as it is a circuit component such as a varistor or a Zener diode capable of flowing a current at a certain voltage or more.

[0039]

As described above, according to the power-off detection circuit according to the present invention, it is possible to detect a voltage drop with high accuracy at a low cost and reduce the influence of the characteristic variation of the photocoupler. it can.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a power failure detection circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram showing operation waveforms in a main part of the power failure detection circuit shown in FIG.

FIG. 3 is a block diagram showing a configuration of a power failure detection circuit according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a power failure detection circuit according to a third embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a power failure detection circuit according to a fourth embodiment of the present invention.

[Explanation of symbols]

 1: AC input power supply 2: (DC) power supply device 3: Load section 4: Photo coupler 41: Photo coupler light emitting element 42: Photo coupler light receiving element 5, 11, 81, 82: Resistor 6: Voltage dependent element 7: Level conversion circuit 8: Integration circuit 83: Capacitor 9: Logic IC 10: Control circuit DC power supply (Vcc) 12: Bridge rectifier 13: Rectification circuit L: Threshold voltage level

Claims (6)

[Claims] 1. A light-emitting device of a photocoupler is connected via a power supply device that converts an AC input power supply to a direct current and supplies the light, and a resistor and a voltage-dependent element arranged in series with the AC input power supply, An integrating circuit and a logic IC are provided at the output of the photocoupler, and the light emitting element is turned on to charge the integrating circuit by lighting the light emitting element when the peak voltage of the AC input power source is equal to or higher than the voltage defined by the voltage dependent element. When the peak voltage of the input power supply is less than the voltage specified by the voltage dependent element, the light emitting element is turned off and the integrating circuit is discharged, and the output voltage of the integrating circuit becomes equal to or lower than the threshold voltage level of the logic IC. A power failure detection circuit, characterized in that it is provided with means for sometimes determining power failure or voltage drop. 2. The power-off detection circuit according to claim 1, wherein the AC input power is divided by a resistor, and the voltage-dependent element and the light-emitting element of the photocoupler are connected to the voltage dividing point. Characteristic power failure detection circuit. 3. The power failure detection circuit according to claim 1, wherein the AC input power is rectified by a bridge rectifier, and its output terminal is connected to the light emitting element side of the photocoupler via a resistor and a Zener diode. A power failure detection circuit characterized in that 4. The power failure detection circuit according to claim 1, wherein the photocoupler is an AC input type photocoupler, and the voltage-dependent element is arranged as a varistor, a bidirectional Zener diode, or a resistor. A power failure detection circuit, which is a Zener diode. 5. The power failure detection circuit according to claim 1, wherein a time constant of the integration circuit is set to be smaller than a half cycle of the AC input power supply during charging and a time constant during discharging. Power failure detection circuit characterized by increasing the size. 6. The power supply cutoff detection circuit according to claim 1, wherein a rectifier composed of a bridge rectifier and two diodes of the power supply device is provided, and the output terminal of the rectifier is provided with a resistor and a Zener diode. A power failure detection circuit characterized by being connected to the light emitting element side of a photocoupler.