JPS635417A - Protecting circuit for over-voltage of ac power source - Google Patents

Abstract

PURPOSE:To cope with momentary and continuous high voltage generated in an AC power source by short-circuiting a thyristor connected to output side of a full wave rectifier circuit and cut off a fuse when high voltage is generated in an AC power source. CONSTITUTION:When surge voltage is applied to the output terminal 1 of an AC power source and the surge voltage exceeds breakdown voltage of a Zener diode, large current flows in the gate 4a of a thyristor 4 from the anode of the diode 5 through a resistor R, and the thyristor 4 becomes the state of conduction. Consequently, the positive pole and negative pole are short-circuited temporarily, and accordingly, a fuse 2 is cut off immediately. By setting time constant of a CR integrating circuit properly, futile blowing of the fuse 2 can be prevented. In the case where high voltage is applied to the terminal 1 of the AC power source continuously, the high voltage flows in the cathode of the diode 5, the thyristor 4 is made to the state of conduction. Accordingly, the positive pole and negative pole of DC voltage are short-circuited and the fuse 2 is cut off.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to the destruction of various electric circuit devices when a high voltage is momentarily or continuously applied to the power input terminals of the electric circuit devices from an AC power source. This relates to an overvoltage protection circuit that does not cause any damage.

[Conventional technology]

Generally, the power input terminals of various electric circuit devices are provided with a fuse that disconnects when an overcurrent is applied from an AC power source to prevent overcurrent from being applied to the electric circuit device.

Furthermore, as a measure against overvoltage in an AC power source, there is known a method of shutting down the overvoltage by inserting a Zener diode having specific breakdown voltage characteristics between the positive and negative electrodes of the AC power source.

[Problems to be solved by the present invention]

The above-mentioned conventional means using a fuse has the problem of being able to deal with overcurrent from the power supply, but not being able to deal with the application of overvoltage.

On the other hand, with the conventional means using a Zener diode, overvoltage can be shut down when a momentary high voltage, commonly known as a surge voltage, generated by an AC power source is applied, but when a high voltage is continuously applied from an AC power source, However, when this happens, the high voltage is not shut down and is input to the electric circuit device as it is.

Therefore, the present invention solves the problems of such conventional overvoltage protection means in various electric circuit devices, and
The object of the present invention is to provide an overvoltage protection circuit capable of dealing with instantaneous or continuous high voltage generated by an AC power source and preventing the high voltage from being applied to an electric circuit device.

[Means for solving the above problems]

The present invention provides a fuse connected to one pole of an AC power source, a full-wave rectifier circuit inserted between the fuse and a power input terminal of an electric circuit device to convert an AC voltage into a DC voltage, and a full-wave rectifier circuit for converting an AC voltage into a DC voltage. A thyristor having an anode connected to a positive pole and a cathode connected to a negative pole, a Zener diode having a cathode connected to the positive pole of the DC voltage, and a CR integration circuit interposed between the anode of the Zener diode and the gate of the thyristor. The circuit is configured to short-circuit the thyristor and disconnect the fuse when a momentary or continuous high voltage is generated in the AC power source.

[Operation of the present invention]

When a momentary high voltage is generated in an AC power source, a large current flows through the Zener diode when this high voltage exceeds the breakdown voltage value of the Zener diode.

Even if the time during which the high voltage is generated is extremely short, CI'
A large current flows through the branch of the l1 circuit to the gate of the thyristor, and the thyristor becomes conductive. Therefore, the positive and negative poles of the DC voltage are momentarily short-circuited, the fuse connected to one pole of the AC power source is disconnected, and the power supply from the power source is stopped.

In addition, if continuous high voltage occurs in the AC power supply,
This high voltage causes a large current to flow through the Zener diode, and this large current is immediately applied to the gate of the thyristor, so that the thyristor becomes conductive and the fuse can be blown in the same manner as described above.

[6 Embodiments of the Present Invention] Hereinafter, an embodiment of the overvoltage protection circuit for an AC power supply according to the present invention will be described with reference to the attached drawings.

In the configuration shown in FIG.
is connected. Reference numeral 3 is a complete rectifier circuit formed by bridging four diodes, and converts the AC voltage of the AC power supply into DC voltage. Reference number 4 is a thyristor, and the anode of this thyristor 4 is connected to the positive pole (plus) of the DC voltage.
Further, the cathode of the thyristor 4 is connected to the negative electrode (minus).

Furthermore, the cathode of a Zener diode 5 is connected to the positive electrode of the DC voltage, and the Zener diode 5
The anode of is connected to the gate 4a of the thyristor 4 via the resistor R.
It is connected to the. Further, a capacitor C is inserted between the intermediate point 6 between the resistor R and the gate 4a and the negative electrode of the DC voltage.

The resistor R and capacitor C form a CR integration circuit 7 for supplying current to the gate 4a of the thyristor 4.

Reference numeral 8 in the figure indicates a DC voltage input terminal to various electric circuit devices not shown in the figure.

The operation of the overvoltage protection circuit of the present invention with such a configuration is as follows.

That is, under normal conditions, AC power supplied from the output terminal 1 is converted into DC by the full-wave rectifier circuit 3 and supplied from the input terminal 8 to various electric circuit devices.

Next, assume that a momentary high voltage, commonly known as a surge voltage, is applied to the output terminal l of the AC power supply for some reason. ``The above surge voltage first flows to the cathode side of the Zener diode 5. This Zener diode 5 is connected in the opposite direction between the positive and negative electrodes.

A large current flows through the anode when a preset breakdown voltage is exceeded. Therefore, when the surge voltage exceeds the breakdown voltage, the Zener diode 5
from the anode of the gate 4 of the thyristor 4 via the resistor R.
Since a large current flows through a, the thyristor 4 becomes conductive.

Therefore, the positive and negative electrodes of the DC voltage are temporarily short-circuited, so that the fuse 2 is immediately cut off and the supply of DC voltage to the input terminal 8 is stopped.

1. Normally, if the surge voltage occurs in an extremely short period of time, the anode current of the Zener diode 5 will not reach the current that turns on the gate of the thyristor 4, and the DC voltage will continue to be supplied. It is also possible to That is, by appropriately determining the time constant of the CRa circuit, it is possible to allow a short-term surge voltage that does not cause any trouble to various electric circuit devices, and to prevent the fuse 2 from blowing unnecessarily.

Next, assume that a continuous high voltage is applied to the output terminal 1 of the AC power supply for some reason.

In this case, since the above-mentioned high voltage flows to the cathode of the Zener diode 5, a large current waves to the anode of the Zener diode 5 in the same manner as described above, and the large current immediately flows to the gate of the thyristor 4 (4a). The current flows to the thyristor 4, thereby making the thyristor 4 conductive. Therefore, the positive and negative electrodes of the DC voltage are short-circuited and the fuse 2 is disconnected.

The above operation description can be summarized as follows.

In other words, even if the high voltage generated in the AC power supply is extremely instantaneous or continuous, by appropriately selecting the time constant of the CR integration circuit, the fuse can be removed even in the case of instantaneous or continuous high voltage. This means that it is possible to disconnect the electrical circuit and prevent the application of overvoltage to the electrical circuit device.

[Effects of the present invention]

As explained in detail above, according to the present invention, there is a fuse connected to one pole of an AC power source, and an aftereffect that is inserted between the fuse and the power input terminal of an electric circuit device to convert an AC voltage into a DC voltage. a rectifier circuit, a thyristor having an anode connected to the positive pole of the DC voltage and a cathode connected to the negative pole, a Zener diode having a cathode connected to the positive pole of the DC voltage, and between the anode of the Zener diode and the gate of the thyristor; An overvoltage protection circuit is constructed by the CR integration circuit inserted in the .

This brings about the effects described below.

That is, by appropriately selecting the time constant of the CRa circuit inserted between the anode of the Zener diode and the gate of the thyristor, it is possible to adjust the current value applied to the gate, which reduces the amount of current generated in the AC power supply. Whether the high voltage is instantaneous or continuous, the fuse can be cut to turn off the power.

Therefore, it is important to completely prevent the situation where high voltage is applied to various electric circuit devices and the electric circuit devices are destroyed.

- On the other hand, according to the device according to the present invention, by appropriately selecting the time constant of the CR integration circuit, it is possible to apply a high voltage for an extremely short period of time without adversely affecting the electric circuit device, Since the fuses can be replaced less frequently, it is possible to increase the versatility to a wide variety of electric circuit devices.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of an overvoltage protection circuit for an AC power supply according to the present invention. Symbol 1 in the diagram...Output terminal 2 (of AC power supply), Φ...φ fuse 3...Full-wave rectifier circuit 4...Thyristor 4 a* housing...(Thyristor ) Gate 51111
...Zener diode 6...Intermediate point (between resistor R and gate) 7...φ.
・CR integration circuit 8... (DC voltage) input terminal.

Claims (1)

[Claims] A fuse connected to one pole of an AC power supply, a full-wave rectifier circuit inserted between the fuse and a power input terminal of an electric circuit device to convert AC voltage into DC voltage, and an anode connected to the positive pole of the DC voltage. a thyristor connected to the thyristor and having a cathode connected to the negative electrode, a Zener diode having a cathode connected to the positive electrode of the DC voltage, and a CR interposed between the anode of the Zener diode and the gate of the thyristor.
1. An overvoltage protection circuit for an AC power supply, comprising an integrating circuit, and short-circuiting a thyristor and cutting a fuse when a momentary or continuous high voltage is generated in the AC power supply.