JPH03853Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a lightning arrester circuit for a communication device that is connected to a communication line drawn in from outside and that uses commercial power.

[Summary] The present invention, in lightning protection circuits for communication equipment connected to communication lines and commercial power, allows the voltage limiting element inserted into the communication line to be grounded and the voltage limiting element inserted into the power line to be grounded in common. By connecting the power line and inserting a fuse with a current capacity smaller than that of the voltage limiting element into the power line, the inside of the communication device can be protected even if there is a difference in ground potential, and the lightning protection circuit can be protected. This makes it easy to identify failures.

[Conventional technology]

In recent years, in-home devices equipped with a simple extension switch, a keyboard, an image display, etc. have come into use, and most of these devices use commercial power as their power source. These devices use many semiconductor elements, and it is important to protect them from lightning strikes and surges.

Lightning arrester circuits protect electrical equipment by limiting shock overvoltages caused by lightning, switching surges, etc. A voltage limiting element is connected in series with a discharge gap, and when an overvoltage occurs, the gap discharges. When the discharge of the overvoltage is completed, the voltage limiting element cuts off the following current and returns the electric line to a normal state.

Conventionally, in such a lightning arrester circuit, a protector inserted into a communication line is grounded to a third-class earth, and a lightning arrester inserted into a commercial power source is connected to a second-class earth or an appropriate equipment earth. For this reason, when a lightning surge occurs on a communication line or commercial power supply, if a surge current flows through a protector or lightning arrester circuit in some system, the ground potentials of the two grounds will differ and the insulation inside the communication device will be destroyed. Sometimes. For this reason, a configuration in which two grounds are commonly connected inside the device has become known. With this configuration, even if there is a difference in ground potential due to lightning strikes, etc.,
The insulation inside the communication device will not be destroyed.

[Problem that the invention attempts to solve]

However, such conventional lightning arrester circuits have the disadvantage that even if a varistor element inserted into a power line is destroyed by a high voltage surge, the destruction is not visible from the outside and the circuit continues to be used. As a result, there is a problem in that the next time a high voltage surge occurs, the device will be damaged.

The present invention solves these conventional problems by providing a lightning protection circuit that can prevent dielectric breakdown inside a communication device caused by differences in ground potential, and can also recognize breakdown of a voltage limiting element on a power line. With the goal.

[Means for solving problems]

The present invention includes a first triode discharge tube connected between both lines of an external communication line terminal and ground, two varistor elements whose one end is connected to both lines of an external power line terminal, and In a lightning arrester circuit comprising a second triode discharge tube connected between each other end of the varistor element and ground, the first triode discharge tube is connected to the ground and the second triode discharge tube is connected to the ground. A fuse is connected to the current path of both lines between the external power line terminal and the varistor element, and the withstand current capacity of this fuse is set to be smaller than the withstand current capacity of the varistor element. It is characterized by having been done.

[Effect]

By commonly connecting the ground of the voltage limiting element inserted in the communication line and the ground of the voltage limiting element inserted in the power line, the present invention enables the internal connection of the communication device even if there is a difference in ground potential. can be protected.

In addition, by inserting a fuse in the power line whose withstanding current capacity is smaller than the voltage limiting element, even if the voltage limiting element inserted in the power line is shattered due to a high voltage surge, the communication line will not be connected to the power line because the fuse is blown. Since the fuse is not connected to the lightning protection circuit and the fuse is blown even in the event of an open circuit breakdown, it is easy to detect a failure in the lightning arrester circuit.

〔Example〕

Hereinafter, embodiments of the present invention will be explained based on the drawings.

The figure is a configuration diagram showing an embodiment of the present invention.
A triode discharge tube and a varistor element are used as voltage limiting elements. In the figure, external communication line terminal L ₁ ,
Connect triode discharge tube S ₁ between L ₂ and ground GND,
External power line terminal AC ₁ , AC ₂ has varistor element V ₁ ,
Connect one end of _V2 to each of this varistor element
A triode discharge tube S ₂ is connected between the other ends of V ₁ and V ₂ and the ground GND. Fuses F ₁ and F ₂ are inserted into the current paths of both lines between the external power line terminals AC 1 and AC ₂ and the varistor elements _{V 1} and V ₂ , respectively. The current capacity of the fuses F ₁ and F ₂ is smaller than that of the varistor elements V ₁ and V ₂ and larger than that of the device fuse (not shown).

In such a circuit, external communication line terminals L ₁ , L ₂
Or, if abnormal voltage occurs at the external power line terminals AC ₁ and AC ₂ due to a lightning strike, etc., the varistor elements V ₁ and
Fuses F ₁ and F ₂ blow before a sufficient current flows to open V ₂ . Also at this time,
If the varistor elements V ₁ , V ₂ are damaged in such a way that they become shot, the triode discharge tubes S ₁ , S ₂ must be grounded.
Since the GND is common, the external power line is connected to the communication line, but since the fuses F ₁ and F ₂ are blown, there is no problem, and the external communication line terminals L ₁ and L ₂ and the external power line terminal AC ₁ , No voltage exceeding the limit voltage will be generated between AC ₂ .

Therefore, insulation breakdown inside the communication device (not shown) is prevented, and the fuse
Since F ₁ and F ₂ are cut out first, failure can be easily detected.

In other words, when the fuses F ₁ and F ₂ are blown, the subscriber reports it as a malfunction, and a maintenance person goes to replace the fuse. During the fuse replacement work, the varistor elements V ₁ and V ₂ are inspected and if there is any abnormality. This can be replaced.

In addition, if the varistor elements V ₁ and V ₂ are open and destroyed, the subscriber must himself remove the fuses F _{1 and} V 2 .
By replacing the F ₂ , it will be possible to use a communication device for the time being, but its use will be limited to temporary use as it is not protected against lightning strikes.
However, it is effective in securing a means of communication in cases where the communication device is located in a remote location and it would take time for a maintenance person to visit. On the other hand, if the varistor elements V ₁ and V ₂ are short-circuited and destroyed, even if the fuses F ₁ and F ₂ are replaced, they will still be blown, so a maintenance person will have to come. Therefore, if communication becomes impossible due to a lightning strike or the like, the subscriber will notice the abnormality in either case, and the system will not continue to operate with damaged varistor elements V ₁ and V ₂ .

[Effect of idea]

As explained above, this invention does not destroy the insulation inside the communication device even if there is a difference in ground potential due to lightning strikes, etc., and it can be used with the voltage limiting element on the power line side destroyed. can be prevented from continuing.

[Brief explanation of the drawing]

The figure is a configuration diagram showing an embodiment of the present invention. L ₁ , L ₂ ... External communication line terminal, AC ₁ , AC ₂ ... External power line terminal, F ₁ , F ₂ ... Fuse, V ₁ , V ₂ ...
...varistor element, S ₁ , S ₂ ... triode discharge tube, GND
……ground.

Claims (1)

[Scope of claim for utility model registration] A first triode discharge tube connected between both lines of an external communication line terminal and the ground, and two varistors whose one end is connected to both lines of an external power line terminal. and a second triode discharge tube connected between each other end of the varistor element and the ground, wherein the first triode discharge tube is grounded and the second triode discharge tube is connected to the ground. A fuse is connected to the current path of both lines between the external power line terminal and the varistor element, and the withstand current capacity of this fuse is the same as the withstand current of the varistor element. A lightning protection circuit characterized by being set smaller than the capacity.