JPS59144221A - Alternating current switch circuit - Google Patents

Abstract

PURPOSE:To turn on an AC voltage by one pulse and to hold this on state by holding enough charges to trigger a thyristor until a next half wave arrives from a rectifier. CONSTITUTION:The thyristor has a period wherein its current decreases below a holding current until the next half wave arrives after the 1st half wave arrives, but charges accumulated in a capacitor 17 supply a voltage and a current which are enough to trigger the thyristor 12 until the next half wave arrives from the rectifier 11. A resistance 14 for discharging accumulated carriers has a much less value than a resistance 15, so carriers accumulated in a voltage drop element 13 and a fine current flowing reversely from the capacitor 17 are discharged speedily. Therefore, while the current of the thyristor 12 decreases below the holding current, the gate-cathode voltage of this thyristor 12 is held above a trigger voltage. Thus, an alternating current flows through a load 10 for reception continuously once the thyristor 12 is triggered. Namely, the alternating current is turned on by one pulse and this ''on state'' is held.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit that turns on an alternating current with one pulse and maintains this on state.

Generally, alarm control devices, measuring devices, and the like of disaster prevention equipment may have their control functions and measuring functions deteriorate or malfunction due to a drop in power supply voltage.

In order to detect this drop in power supply voltage in advance, the device is often equipped with a voltage drop detection circuit.

Conventionally, a voltage drop detection circuit operates by constantly supplying current to a signal load when the power supply voltage is normal, and operates the signal load when the power supply voltage drops. A drop in power supply voltage was detected by the inability to supply sufficient current. For example, as shown in FIG. 1, when the power supply voltage is normal, the power supply voltage V is the Zener voltage VZ of the Zener diode 1 and the transistor 2.
The value of VZ is determined so that it is larger than the sum of the base-emitter voltage VBE. That is, V>VZ+
At VBE, transistor 2 turns on and operates signal load 3. The power supply voltage decreases and V<VZ+VB
When the voltage reaches E, no current flows to the base of the transistor 2, and the transistor 2 is turned off. Here, if the current amplification factor HFE of the transistor 2 is sufficiently large and the resistance value of the resistor 4 connected between the base of the transistor 2 and the power supply is much larger than the resistance value of the signal load 3, then the transistor 2 The active area can be practically ignored. If a relay is used for the signal load 3 and the contacts of the relay are used, direct current or alternating current can be turned on.
・Can be turned off. However, this method is uneconomical because power is constantly consumed inside the meter when the meter is in normal operation.

In order to solve the above problem, a circuit as shown in FIG. 2 was disclosed in Japanese Patent Application No. 57-034536.

In this circuit, since transistor 7 is in the ON state when the power supply voltage is normal, the base potential of transistor 8 cannot turn on the transistor 8. When the power supply voltage V drops, the transistor 7 is turned off, and the base potential of the transistor 8 rises, turning the transistor 8 off.
N and the signal load 6 is operated. Here, even though 5 is an element with a fairly large resistance value, when transistor 7 is OFF, it can flow enough base current to turn on transistor 8, so the power consumption when the power supply voltage V of the meter is normal is reduced. You can hold it down as much as possible. However, with such a method, the power supply voltage may drop suddenly and the signal load 6 may not be able to operate, or even if it is able to operate, it may not be recognized because it is only for a short time.

The problem currently required is that when the power supply voltage of the meter is normal, power is not consumed, and when the power supply voltage of the meter drops, even if the power supply voltage becomes OV, the power supply voltage is not consumed on the receiving side. It is to transmit a signal of decline.

The present invention was made in view of the above problem, and even if the time from when the power supply voltage of the meter starts to drop until it reaches OV is short, a single pulse is generated using the small amount of power left at the end. This pulse turns on the current on the receiving side and maintains this ON state. If the receiving load is operated by direct current, this can be easily achieved by applying a single pulse to the gate of a thyristor, but in general, commercial power is often used on the receiving side. . The present invention turns on not only direct current but also alternating current with one pulse, and
The present invention aims to provide a circuit for maintaining this ON state.

Hereinafter, the configuration of the present invention will be explained in detail with reference to the drawings.

FIG. 3 shows an embodiment of an AC switch circuit according to the present invention. In the figure, 9 is a commercial power supply, 10 is a reception load, 1
1 is a rectifier, 12 is a thyristor, 13 is a voltage drop element,
14 is a resistor for discharging the storage carrier of the voltage drop element 13, 15 is a resistor for charging the capacitor 17, and 16 is a resistor for supplying the appropriate gate trigger voltage and gate trigger current to the thyristor 3 from the charge charged in the capacitor 17. 19 is a pulse generating circuit. Next, the operation of the AC switch circuit of the present invention will be explained based on FIG. 3. In the same figure, a capacitor 17 is charged by a pulse generated from a pulse generating circuit 19, and a voltage is applied to the gate of a thyristor 12 through a resistor 16, triggering the thyristor 12 and connecting the anode and cathode of the thyristor 12. is conductive. At this time, the current from the first half wave of the rectified commercial power supply flows through the voltage drop element 13, and at the same time, the capacitor 17 is charged via the resistor 15 due to the voltage drop of the voltage drop element 13. There is a time when the thyristor 12 becomes below the holding current from the first half wave to the arrival of the next half wave,
The charge stored in capacitor 17 provides sufficient voltage and current to trigger thyristor 12 until the next half-wave arrives from rectifier 11. Also, since the resistor 14 has a sufficiently smaller value than the resistor 15, the voltage drop element 1
The small current flowing back from the storage carrier 3 and the capacitor 17 is quickly discharged. Therefore, while the thyristor 12 is below the holding current, the voltage between the gate and cathode of the thyristor 12 is kept above the trigger voltage.In this way, once the thyristor 12 is triggered, an alternating current is applied to the receiving load 10. Keep flowing. That is, it is possible to turn on alternating current with one pulse and maintain this on state.

Next, an embodiment of the present invention including a pulse generation circuit is shown in FIG. In the figure, reference numeral 20 denotes a detected voltage source from which a drop in power supply voltage or a failure is detected. When this voltage source 20 becomes lower than the sum of the Zener voltage of the Zener diode 21 and the base-emitter voltage VBE of the transistor 22, the transistor 22 is turned off and current flows through the photocoupler 23. Furthermore, if the detected voltage source 20 fails and becomes OV in an instant, the capacitor 24
This is because the charges stored in the transistor 22 are discharged through the photocoupler 23 after being discharged through the transistor 22. During this time, the phototransistor 25 of the photocoupler remains in the ON state and becomes conductive. At this time, the rectified commercial power supply is charged to the capacitor 28 via the resistor 26, the Zener diode 27, and the phototransistor 25, and a voltage is applied to the gate of the thyristor 29, causing the thyristor 29 to turn off.
Become N. Once turned ON, the thyristor 29 remains in the ON state as explained in FIG. 3, and the receiving load 30 maintains the operating state. To turn off the thyristor 29 again,
After returning the detected voltage source to normal, turn on the commercial power switch S3.
1, or short-circuit between the gate of the thyristor 29 and the (-) terminal of the rectifier, or between the cathode of the thyristor 29 and the (-) terminal of the rectifier. Note that since the photocouplers 23 and 25 operate satisfactorily with an input of about 1 mA, resistors 33 and 34 can have large values, so power consumption during normal operation can be extremely reduced. In the embodiment shown in FIG. 4, there are many cases in which there is no problem in operation even if a resistor is used instead of a diode for the voltage drop element 32. Further, by connecting a diode from the cathode of the thyristor 29 to the positive side of the capacitor 28, it is possible to help charge the capacitor 28 after the thyristor 29 is turned on, and to ensure reliable operation.

As described above, the AC switch circuit according to the present invention operates the reception load 30 driven by the commercial power supply when the voltage of the detected voltage source 20 drops or when it malfunctions and instantly becomes OV. and can be retained. Further, the power source for operating the receiving load 30 of the present invention is not limited to a commercial power source, and may be any other AC power source or direct current power source. If a DC power supply is used for 32, the rectifier 35 is not necessary. Note that the circuit constants shown in FIG. 4 are only an example. Furthermore, it is easy to imagine that the AC switch circuit according to the present invention can be used as a non-contact interface circuit for controlling a large AC current with a small amount of current, such as in an elevator operated by a touch switch or the like. be.

[Brief explanation of drawings]

1 and 2 are voltage drop detection circuits according to the prior art. FIG. 3 shows an embodiment of an AC switch circuit according to the present invention. FIG. 4 shows an embodiment of an AC switch circuit according to the present invention. DESCRIPTION OF SYMBOLS 1... Zener diode, 2... Transistor, 3... Signal load, 4... Resistor, 5... Element having a large resistance value, 6
...Signal load, 7...Transistor 8...Transistor, 9
...Commercial power supply, 10...Receiving load, 11...Rectifier, 12...
Thyristor, 13... Voltage drop element, 14... Resistor for storage carrier discharge, 15... Resistor, 16... Resistor, 17... Capacitor, 18... Resistor, 19... Pulse generation circuit, 20... Voltage source to be detected, 21... Zener diode, 22... Transistor, 23... Photocoupler, 24... Capacitor, 25... Phototransistor of photocoupler, 26... Resistor, 27... Zener diode, 28... Capacitor, 29... Thyristor,
30...Reception load 31...Switch, 32...Commercial power supply, 3
3...Resistor, 34...Resistor, 35...Rectifier, Patent applicant Makoto Aso

Claims (1)

[Claims] Connect the anode and cathode of a thyristor and a voltage drop element in series between the (+) and (-) terminals of the rectifier, and if the thyristor turns on when a half wave arrives from the rectifier, the next An alternating current switch circuit characterized in that a capacitor charged by the voltage drop of the voltage drop element maintains a charge sufficient to trigger the thyristor until a half-wave of the voltage drop element arrives.