JP7437252B2 - protection device - Google Patents

Description

TECHNICAL FIELD This disclosure relates to protective devices.

As one type of communication equipment placed indoors, there is communication equipment that is connected to a communication line brought in from outdoors. When a lightning strike occurs near a communication line placed outdoors, an overvoltage whose absolute value exceeds a predetermined voltage, a so-called surge voltage, may temporarily occur in the communication line. In the case where a communication line is simply connected to a communication device, when an overvoltage occurs, the overvoltage is applied to the communication device via the communication line, and there is a possibility that the communication device breaks down.

A protection device that protects communication equipment from application of overvoltage is disclosed in Patent Document 1. This protection device is placed near the communication device on the propagation path of the communication signal from the outdoors to the communication device, and is electrically connected to the ground. When the absolute value of the voltage applied to the communication line reaches a predetermined voltage, the protection device discharges through the ground and prevents the voltage applied to the communication line from becoming an overvoltage.

Japanese Patent Application Publication No. 2012-161137

A differential signal represented by a difference between two voltages may be used as a communication signal. In this case, the differential signal propagates through a pair of signal lines included in the communication line. A differential signal is expressed by the difference between two voltages applied to a pair of signal lines. In a protection device disposed on a differential signal propagation path, a pair of signal lines are provided on a substrate, and the differential signal is propagated via the pair of signal lines.

A limiting circuit that limits the absolute value of the applied voltage to a predetermined voltage or less is connected to the pair of signal lines. The limiting circuit is further connected to ground. When the absolute value of the voltage on the signal line reaches a predetermined voltage, discharge occurs via the limiting circuit and the ground, thereby preventing the voltage applied to the signal line from becoming an overvoltage.

When a pair of signal lines through which a differential signal propagates and a limiting circuit are provided on a single substrate, many long wiring lines that require detours are required, so a substrate with a large area is used. If the area of the board is large, the size of the protection device is large. When constructing a building, the location of protective devices is not usually considered. For this reason, it is preferable that the protection device be small so that it can be installed in various locations.

The present disclosure has been made in view of such circumstances, and its purpose is to provide a small-sized protection device that protects communication equipment from the application of overvoltage.

A protection device according to one aspect of the present disclosure is arranged in a propagation path of a differential signal represented by a difference between two voltages, and protects a communication device that transmits and/or receives the differential signal by an absolute value. is a protection device for protecting against the application of an overvoltage exceeding a predetermined voltage, the first substrate being provided with a pair of signal lines through which the differential signal propagates; a limiting circuit that limits the absolute value of the voltage applied to each of the pair of signal lines to below the predetermined voltage; a second substrate on which circuit elements included in the limiting circuit are arranged; , a plurality of support members that support the second substrate so as to overlap with the first substrate at intervals.

In the above embodiment, the first substrate and the second substrate are spaced apart and overlapped. Therefore, the connection from the signal line to the circuit element of the limiting circuit is realized by short wiring, and the number of long wiring that requires detours is small. Therefore, the total area of the first substrate and the second substrate is small, and a compact device can be realized.

In the protection device according to one aspect of the present disclosure, the pair of signal lines are arranged in parallel, and the lengths of the pair of signal lines are the same.

In the above embodiment, since the pair of signal lines are arranged in parallel and have the same length, the pair of signal lines is arranged in parallel depending on the location in the differential signal propagation path. The variation range of characteristic impedance is small. Therefore, while the differential signal is propagating through the pair of signal lines, the number of times the differential signal is reflected is small, and the reflectance of each reflection is small. Therefore, the waveform of the differential signal is less likely to be distorted, and communication quality is less likely to deteriorate.

In the protection device according to one aspect of the present disclosure, the plurality of support members include a second circuit element included in the restriction circuit.

In the above embodiment, since the second circuit element included in the limiting circuit is used as the support member, the number of parts of the device is small. As a result, an even smaller device can be realized and the manufacturing cost is low.

A protection device according to an aspect of the present disclosure includes a conductor, and the limiting circuit includes two first diodes each having an anode connected to each of the pair of signal lines, and a cathode connected to each of the pair of signal lines. connected to the two second diodes, the cathodes of the two first diodes, the anodes and conductors of the two second diodes, and the absolute value of the voltage applied to each of the pair of signal lines is equal to or less than the predetermined voltage. when the absolute value of the voltage applied to one of the pair of signal lines reaches the predetermined voltage, the current flows through the pair of first diodes and the pair of second diodes. The current flows through one of the diodes, the restrictor, and a conductor, and the plurality of support members includes the first diode or the second diode.

In the above embodiment, since the first diode or the second diode is used as the support member, the number of parts of the device is small. As a result, an even smaller device can be realized and the manufacturing cost is low.

In the protection device according to one aspect of the present disclosure, the plurality of support members are removably attached to the first substrate.

In the above aspect, the second substrate can be removed from the first substrate by removing the plurality of support members from the first substrate. For example, in a case where a limiting circuit is realized by circuit elements arranged on the second board, if the limiting circuit is malfunctioning, the second board can be replaced with a new one that is equipped with a normally operating limiting circuit. The device can be easily repaired by replacing it with the second board.

According to the above aspect, a small-sized protection device that protects communication equipment from application of overvoltage is realized.

FIG. 3 is a cross-sectional view of the protection device in Embodiment 1. It is a circuit diagram of a protection device. FIG. 2 is a cross-sectional view of the protection device taken along line AA in FIG. 1; FIG. 3 is a plan view of the first substrate. FIG. 3 is a cross-sectional view of a protection device in Embodiment 2. It is an explanatory view of the exchange of the 2nd board. It is an explanatory view of the exchange of the 2nd board. FIG. 7 is a circuit diagram of a protection device in Embodiment 3.

Hereinafter, the present disclosure will be described in detail based on drawings showing embodiments thereof.
(Embodiment 1)
FIG. 1 is a sectional view of a protection device 1 in the first embodiment. The protection device 1 includes a storage box 10 . The storage box 10 is provided with a plurality of openings. A first connector 11 and a second connector 12 are arranged in each of the two openings. One end portions of a first cable 21 and a second cable 22 for communication are detachably connected to the first connector 11 and the second connector 12, respectively. For example, the protection device 1 is placed indoors. The first cable 21 is, for example, a cable drawn indoors from outdoors. The other end of the second cable 22 is connected to communication equipment located indoors. The first cable 21 and the second cable 22 are, for example, cables for LAN (Local Area Network).

Each of the first cable 21 and the second cable 22 includes a plurality of communication lines. Each communication line includes a pair of conductive signal lines. Differential signals are propagated through a pair of signal lines included in each communication line. In a differential signal, one of a plurality of values is indicated every clock (certain period). Each of the plurality of values indicated by the differential signal is represented by a difference between two voltages applied to a pair of signal lines.

The communication device transmits and receives differential signals according to, for example, a LAN communication standard. In this case, the communication standard is, for example, 1000BASE-TX. When the communication standard is 1000BASE-TX, the number of communication lines included in each of the first cable 21 and the second cable 22 is four. Further, the number of values shown in one clock is 4, and 2-bit data is transmitted in one clock. The communication frequency expressed as the reciprocal of the length of one clock period is 250 MHz. Therefore, the communication speed is 500 Mbps.

The length of the second cable 22 is short, and the protection device 1 is placed near the communication equipment. The communication device transmits the differential signal via the protection device 1 and receives the differential signal propagated via the protection device 1. The protection device 1 is placed on the differential signal propagation path. When the communication standard is 1000BASE-TX, the communication device transmits two differential signals via two communication lines and receives two differential signals via the remaining two communication lines. A communication device transmits or receives differential signals via one communication line, ie, a pair of signals.
Note that the communication device may transmit and receive differential signals via one communication line, that is, a pair of signal lines.

In the protection device 1, a plate-shaped ground conductor 13 is provided. Most of the ground conductor 13 is arranged inside the storage box 10. A portion of the ground conductor 13 is exposed to the outside of the storage box 10 through an opening provided in the storage box 10. On the outside of the storage box 10, the ground conductor 13 is fixed to a conductive member (not shown) with a screw 14. The ground conductor 13 is electrically connected to the ground via a conductive member.

An example in which the first cable 21 is led indoors from outdoors will be described below. When a lightning strike occurs around the first cable 21, an overvoltage whose absolute value exceeds a predetermined voltage, a so-called surge voltage, may temporarily occur in the communication line within the first cable 21. If an overvoltage occurs, voltage is applied to the communication device via the second cable 22. The predetermined voltage is a constant voltage. The predetermined voltage is sufficiently larger than the signal voltage applied to the signal line to transmit the differential signal. The overvoltage, the predetermined voltage, and the signal voltage are voltages whose reference potential is the potential of the ground conductor 13, that is, the earth.

The protection device 1 discharges through the ground conductor 13 when the absolute value of the voltage applied to the signal line included in the second cable 22 reaches a predetermined voltage, and the voltage of the signal line becomes a predetermined voltage. Prevent overvoltage from exceeding the voltage. As a result, the protection device 1 protects the communication equipment from application of overvoltage. When the communication device is a device that performs communication according to a LAN communication standard, the protection device 1 protects the LAN communication device from application of overvoltage.

FIG. 2 is a circuit diagram of the protection device 1. FIG. 2 shows an example of a protection device 1 in which four differential signals propagate. Hereinafter, any integer between 1 and 4 will be expressed as k. Therefore, k may be any integer from 1 to 4. In addition to the first connector 11, the second connector 12, the ground conductor 13, and the screw 14, the protection device 1 includes eight signal lines W1a, W1b, W2a, W2b, W3a, W3b, W4a, and W4b, and a shield conductor W5. and has. The signal lines Wka and Wkb form a set, and the pair of signal lines Wka and Wkb are included in one communication line. When the first connector 11 and the second connector 12 are respectively connected to the first cable 21 and the second cable 22, the pair of signal lines Wka and Wkb are connected to the pair of signal lines in the first cable 21 and the second cable 22, respectively. electrically connected to the line. A differential signal is propagated via a pair of signal lines Wka and Wkb.

Note that the number of differential signals propagating within the protection device 1 is not limited to 4, and may be 1, 2, 3, or 5 or more. The number of signal lines that the protection device 1 has varies depending on the number of differential signals. Furthermore, the numbers of first diodes Dc and second diodes Dd, which will be described later, also differ depending on the number of differential signals. When the number of differential signals propagating in the protection device 1 is expressed as N, the number of signal lines is (2・N), and the numbers of communication lines, first diodes Dc, and second diodes Dd are as follows. There are N pieces. "・" represents a product. When the number of differential signals is N, k is any integer from 1 to N.
In the following, an example in which the number of differential signals propagating within the protection device 1, that is, N is 4, will be explained.

In the first cable 21 and the second cable 22, four communication lines pass through a cylindrical shield conductor. When the first connector 11 and the second connector 12 are connected to the first cable 21 and the second cable 22, respectively, the shield conductor wire W5 is electrically connected to the shield conductor of the first cable 21 and the second cable 22.

The protection device 1 further includes a limiting circuit 15 . The limiting circuit 15 includes eight first diodes Dc, eight second diodes Dd, a first discharger 31, and a second discharger 32. Each of the first discharger 31 and the second discharger 32 is a so-called arrester, and has two discharge electrodes and a ground electrode. Each of the pair of signal lines Wka and Wkb is connected to the anode of the first diode Dc and the cathode of the second diode Dd. The cathodes of the eight first diodes Dc are connected to one discharge electrode of the first discharger 31. The anodes of the eight second diodes Dd are connected to the other discharge electrode of the first discharger 31.
Note that, in FIG. 2, the four first diodes Dc and the four second diodes Dd connected to the signal lines W2a, W2b, W3a, and W3b are omitted.

The shield conducting wire W5 is connected to one discharge electrode of the second discharger 32. The other discharge electrode of the second discharger 32 is open. Ground electrodes of the first discharger 31 and the second discharger 32 are connected to the ground conductor 13. As mentioned above, the ground conductor 13 is connected to the earth.

The limiting circuit 15 limits the absolute value of the voltage applied to each of the pair of signal lines Wka and Wkb to a predetermined voltage or less. Specifically, when the absolute value of the voltage of the signal line Wka whose reference potential is the potential of the ground conductor 13 becomes a predetermined voltage, in the first discharger 31, the voltage between one of the two discharge electrodes and the ground electrode A discharge occurs. When the voltage of the signal line Wka is a positive voltage, the current flows in the order of the first diode Dc, the first discharger 31, the ground conductor 13, and the earth. When the voltage of the signal line Wka is a negative voltage, the current flows through the earth, the ground conductor 13, the first discharger 31, and the second diode Dd in this order. Thereby, the absolute value of the voltage of the signal line Wka does not exceed a predetermined voltage.
When the absolute value of the voltage of the signal line Wka is less than a predetermined voltage, no current flows through the first diode Dc or the second diode Dd connected to the signal line Wka.

The voltage of the signal line Wkb is limited in the same way as the voltage of the signal line Wka, and the voltage of the signal line Wkb does not become an overvoltage. As a result, no overvoltage is applied to the communication equipment via the pair of signal lines Wka, Wkb and the pair of signal lines of the second cable 22, and the protection device 1 protects the communication equipment from application of overvoltage.

Since the plurality of first diodes Dc and the plurality of second diodes Dd are used, the number of first dischargers 31 required to protect the plurality of signal lines from application of overvoltage is one. If the first diode Dc and the second diode Dd are not used, a plurality of first dischargers 31 are required to protect the plurality of pairs of signal lines from overvoltage.
The first discharger 31 functions as a limiter that limits the absolute value of the voltage applied to each of the pair of signal lines Wka and Wkb to a predetermined voltage or less.

The second discharger 32 protects the shield conductor W5, ie, the shield conductor of the second cable 22, from application of overvoltage. Specifically, when the absolute value of the voltage of the shield conductor W5 whose reference potential is the potential of the ground conductor 13 reaches a predetermined voltage, the second discharger 32 causes a discharge between one of the discharge electrodes and the ground electrode. occurs. When the voltage of the shield conducting wire W5 is a positive voltage, the current flows in the order of the second discharger 32, the ground conductor 13, and the earth. When the voltage of the shield conductor W5 is a negative voltage, the current flows through the earth, the ground conductor 13, and the second discharger 32 in this order. This prevents the voltage of the shield conductor W5, that is, the shield conductor, from becoming an overvoltage. When the absolute value of the voltage of the shield conducting wire W5 is less than the predetermined voltage, no current flows through the second discharger 32.

Below, the arrangement of the components of the protection device 1 will be explained. FIG. 3 is a sectional view of the protection device 1 taken along line AA in FIG. As shown in FIGS. 1 and 3, a rectangular plate-shaped first substrate 16 is housed in the housing box 10 of the protection device 1. As shown in FIGS. On the front plate surface of the first substrate 16, the first connector 11 and the second connector 12 are arranged at the center of each of the two opposing sides. The first substrate 16 is, for example, a printed circuit board.

FIG. 4 is a plan view of the first substrate 16. As shown in FIGS. 3 and 4, each of the first diode Dc and the second diode Dd has a columnar shape. In the examples of FIGS. 3 and 4, a cylindrical first diode Dc and a second diode Dd are shown. For each of the first diode Dc and the second diode Dd, a cathode is provided at one end, and an anode is provided at the other end. The first diode Dc is attached to the front surface of the first substrate 16 such that the end surface on the anode side is in contact with the front surface of the first substrate 16 . The second diode Dd is attached to the front surface of the first substrate 16 such that the end surface on the cathode side is in contact with the front surface of the first substrate 16 . No circuit elements are arranged on the back surface of the first substrate 16.

As shown in FIG. 4, the eight first diodes Dc are arranged along the lateral direction of the first substrate 16. The eight second diodes Dd are arranged along the lateral direction of the first substrate 16. Each of the eight first diodes Dc faces eight second diodes Dd. The first diode Dc is arranged on the first connector 11 side of the second diode Dd.

As shown in FIG. 3, the lengths of the eight first diodes Dc and the eight second diodes Dd are substantially the same. As shown in FIGS. 1 and 3, a rectangular plate-shaped second substrate 17 is arranged on the cathode side end surfaces of the eight first diodes Dc and the anode side end surfaces of the eight second diodes Dd. There is. The second substrate 17 is also housed in the housing box 10. The back side plate surface of the second substrate 17 is opposed to the front side plate surface of the first substrate 16, and the first substrate 16 and the second substrate 17 overlap with each other with a gap between them. Each of the first diode Dc and the second diode Dd supports the second substrate 17 so as to overlap the first substrate 16 with a gap therebetween, and functions as a support member and also functions as a second circuit element. The second board 17 is, for example, a printed circuit board.
The ground conductor 13 is connected to wiring provided on the first substrate 16 by a conductive wire. Note that the connection destination of the ground conductor 13 is not limited to the wiring on the first substrate 16, and may be, for example, the wiring provided on the second substrate 17.

As shown in FIG. 4, eight signal lines W1a, W1b, W2a, W2b, W3a, W3b, W4a, and W4b and a shield conductive wire W5 are provided inside the first substrate 16. A pair of signal lines Wka and Wkb are arranged between the first connector 11 and the second connector 12. A shield conductive wire W5 is also arranged between the first connector 11 and the second connector 12.

A pair of signal lines Wka and Wkb are arranged in parallel. The length of the signal line Wka is the same as the length of the signal line Wkb. The width of the signal line Wka is the same as the width of the signal line Wkb. Therefore, in the propagation path of the differential signal propagating through the pair of signal lines Wka and Wkb, the range of variation in the characteristic impedance of the pair of signal lines depending on the location is small. Therefore, while the differential signal is propagating through the pair of signal lines Wka and Wkb, the number of times the differential signal is reflected is small, and the reflectance of each reflection is small. Therefore, the waveform of the differential signal is less likely to be distorted, and communication quality is less likely to deteriorate. The pair of signal lines Wka and Wkb are arranged in parallel, and the length of the signal line Wka is the same as the length of the signal line Wkb, so the insertion loss of the protection device 1 is small, and from one differential signal Crosstalk to other differential signals is also small.

Note that "parallel" regarding the pair of signal lines Wka and Wkb does not mean strictly parallel. The state in which the pair of signal lines Wka and Wkb are parallel includes the state in which the angle formed by the pair of signal lines Wka and Wkb falls within the allowable range of the specifications of the protection device 1. Similarly, regarding the length and width of the pair of signal lines Wka and Wkb, "same" does not mean strictly the same. The state where the lengths are the same includes a state where the difference in length between the pair of signal lines Wka and Wkb is within the allowable range of the specifications of the protection device 1. The state where the widths are the same includes a state where the difference in width between the pair of signal lines Wka and Wkb is within the allowable range of the specifications of the protection device 1.

For each of the first board 16 and the second board 17, wiring is provided on at least one of the front board surface, the inside, and the back board surface. Further, each of the first substrate 16 and the second substrate 17 is provided with various holes called through holes or vias for electronic components. The electronic component through hole is a hole for inserting electronic components such as the first diode Dc, the second diode Dd, the first discharger 31, or the second discharger 32. Vias are used to connect wiring on the front board to wiring on the back board, or to connect wiring on the front or back board of the board to wiring or signal lines existing inside the board. It is a hole where you can be exposed. The circuit of the protection device 1 shown in FIG. 2 is realized using wiring and holes.

As shown in FIGS. 1 and 3, eight first diodes Dc and eight second diodes Dd are arranged on the back surface of the second substrate 17, and first diodes Dc and eight second diodes Dd are arranged on the front surface of the second substrate 17. An electric appliance 31 and a second discharger 32 are arranged. Therefore, the limiting circuit 15 is realized by the circuit elements arranged on the second substrate 17.

In the protection device 1, the first substrate 16 and the second substrate 17 are overlapped with an interval. Therefore, the connection from the pair of signal lines Wka and Wkb to the limiting circuit 15 is realized by short wiring, and the number of long wiring that requires detours is small. Therefore, the total area of the first substrate 16 and the second substrate 17 is small, and a small box can be used as the storage box 10. As a result, a compact device is realized. Further, since the limiting circuit 15 is realized by circuit elements arranged on the second substrate 17, the pair of signal lines Wka and Wkb are parallel to each other on the first substrate 16, and the pair of signal lines Wka and Wkb are parallel to each other on the first substrate 16. , Wkb have the same length and width.

When the range of frequency components that make up the differential signal propagated through a pair of signal lines Wka and Wkb is narrow, for example, when the differential signal is made up of frequency components that belong to the range from 0 Hz to several hundred kHz. , the permissible variation range of characteristic impedance is large. When the pair of signal lines Wka and Wkb are not parallel, when the lengths of the pair of signal lines Wka and Wkb do not match, or when the widths of the pair of signal lines Wka and Wkb do not match, However, the deterioration in communication quality is small.

When the range of frequency components constituting the differential signal propagated through the pair of signal lines Wka and Wkb is wide, for example, when the upper limit of the frequency component range is a numerical value on the order of MHz, the allowable characteristic impedance The fluctuation range is small. In this case, it is required that the pair of signal lines Wka and Wkb are parallel and that the length and width of the pair of signal lines Wka and Wkb are the same. Therefore, the configuration in which the first substrate 16 and the second substrate 17 are overlapped with a certain interval is more effective as the maximum value of the range of frequency components constituting the differential signal is higher.

Further, as supporting members that support the second substrate 17, eight first diodes Dc and eight second diodes Dd included in the limiting circuit 15 are used. Therefore, the number of parts of the protection device 1 is small. As a result, an even smaller device can be realized, and the manufacturing cost of the protection device 1 is low.
Note that the locations where the first discharge device 31 and the second discharge device 32 are arranged are not limited to the front surface of the second substrate 17, but may be the back surface of the second substrate 17.

(Embodiment 2)
In the first embodiment, when the first diode Dc and the second diode Dd are fixed to the first substrate 16, when the limiting circuit 15 breaks down, it cannot be repaired and the entire device must be replaced. No. Embodiment 2 shows a configuration in which the limiting circuit 15 can be easily replaced.

In the following, differences between the second embodiment and the first embodiment will be explained. The other configurations except those described later are the same as those of the first embodiment. Therefore, components common to those in Embodiment 1 are given the same reference numerals as in Embodiment 1, and their explanations are omitted. In the second embodiment as well, an example will be described in which the number of differential signals propagating within the protection device 1, that is, N is four.

FIG. 5 is a sectional view of the protection device 1a in the second embodiment. The protection device 1a similarly includes the components included in the protection device 1 in the first embodiment. The protection device 1a further includes 16 attachment members 18 (see FIG. 7). The 16 attachment members 18 are fixed to the front plate surface of the first substrate 16. Each of the eight first diodes Dc and the eight second diodes Dd is removably attached to the sixteen attachment members 18. The second substrate 17 can be replaced by removing the eight first diodes Dc and the eight second diodes Dd from the sixteen attachment members 18. As described in the description of the first embodiment, the limiting circuit 15 is realized by the circuit elements arranged on the second substrate 17.

6 and 7 are explanatory diagrams for exchanging the second board 17. FIG. 6 shows a state in which the second substrate 17 is removed from the first substrate 16. FIG. 7 shows the first substrate 16 on which sixteen attachment members 18 are arranged. As shown in FIG. 6, each of the first diode Dc and the second diode Dd has a columnar main body 41. As shown in FIG. A rod-shaped electrode 42 protrudes from the center of one end surface of the main body 41 along the axial direction of the main body 41 . The cross-sectional area of the electrode 42 is smaller than the cross-sectional area of the main body portion 41.

Regarding the first diode Dc, the electrode 42 is an anode, and the other end surface of the main body portion 41 is an end surface on the cathode side. Regarding the second diode Dd, the electrode 42 is a cathode, and the other end surface of the main body 41 is an anode side end surface. As in the first embodiment, the end surface of the main body 41 on the cathode side of the first diode Dc is arranged on the back surface of the second substrate 17. As for the second diode Dd, the anode-side end surface of the main body portion 41 is arranged on the back side of the second substrate 17.

As shown in FIGS. 6 and 7, the attachment member 18 has a columnar shape, and one end surface of the attachment member 18 faces the front plate surface of the first substrate 16. At the center of the other end surface of the attachment member 18, an insertion hole 18h recessed inside the attachment member 18 is provided. The area of the insertion hole 18h is slightly larger than the cross-sectional area of the electrodes of the first diode Dc and the second diode Dd, and the electrodes 42 of the first diode Dc and the second diode Dd are inserted into the insertion hole 18h.

Each of the 16 attachment members 18 is arranged on the front surface of the first substrate 16 at a position corresponding to the eight first diodes Dc and the eight second diodes Dd. The mounting member 18 is connected to each of the signal lines Wka and Wkb by wiring, vias, through holes, or the like.

The eight first diodes Dc and eight second diodes Dd are attached to the first substrate 16 by inserting the eight first diodes Dc and eight second diodes Dd into the 16 attachment members 18. It will be done. As a result, the limiting circuit 15 is connected to the eight signal lines W1a, W1b, W2a, W2b, W3a, W3b, W4a, and W4b, and the circuit of the protection device 1a is realized. At this time, the eight first diodes Dc and the eight second diodes Dd support the second substrate 17 so as to overlap with the first substrate 16 at intervals. By pulling out the eight first diodes Dc and eight second diodes Dd from the 16 attachment members 18, the eight first diodes Dc and eight second diodes Dd are removed from the first substrate 16. . In this way, the first diode Dc and the second diode Dd, which function as support members, are each removably attached to the first substrate 16.

When replacing the second substrate 17, the second substrate 17 is removed from the first substrate 16 by removing eight first diodes Dc and eight second diodes Dd from the 16 attachment members 18. Thereafter, the eight first diodes Dc and eight second diodes Dd provided on the new second substrate 17 are attached to the 16 attachment members 18. This completes the replacement of the second board 17.

As the number of discharges increases for each of the first discharger 31 and the second discharger 32, the electrical characteristics deteriorate, and a failure may occur. If the first discharger 31 or the second discharger 32 breaks down, the protection device 1a can be easily repaired by replacing the second board 17. The protection device 1a in the second embodiment has the same effects as the protection device 1 in the first embodiment.
In the first and second embodiments, the location where the pair of signal lines Wka and Wkb are provided is not limited to the inside of the first substrate 16, but may be on the front side plate surface or the back side plate surface of the first substrate 16. .

(Embodiment 3)
In the first embodiment, each of the first discharger 31 and the second discharger 32 is a discharger having three electrodes. However, instead of a discharge vessel with three electrodes, a discharge vessel with two electrodes may also be used.

In the following, differences between the third embodiment and the first embodiment will be explained. The other configurations except those described later are the same as those of the first embodiment. Therefore, components common to those in Embodiment 1 are given the same reference numerals as in Embodiment 1, and their explanations are omitted. In the third embodiment as well, an example will be described in which the number of differential signals propagating within the protection device 1, that is, N is four.

FIG. 8 is a circuit diagram of the protection device 1b in the third embodiment. The protection device 1b in the third embodiment similarly includes the components other than the limiting circuit 15 among the components included in the protection device 1 in the first embodiment. The protection device 1b includes a limiting circuit 15b instead of the limiting circuit 15. The limiting circuit 15b in the third embodiment similarly has the constituent parts other than the first discharger 31 and the second discharger 32 among the constituent parts included in the limiting circuit 15 in the first embodiment. The limiting circuit 15b includes a first varistor 51 and a second varistor 52 instead of the first discharger 31, and a third varistor 53 instead of the second discharger 32.

When the voltage between the two electrodes of each of the first varistor 51, the second varistor 52, and the third varistor 53 becomes a constant voltage, a current flows through the two electrodes, and the voltage between the two electrodes becomes a constant voltage. will be maintained. If the voltage between the two electrodes is less than a certain voltage, no current will flow through the two electrodes.

One electrode of the first varistor 51 is connected to the cathodes of eight first diodes Dc. One electrode of the second varistor 52 is connected to the anodes of eight second diodes Dd. One electrode of the third varistor 53 is connected to the shield conducting wire W5. The other electrodes of the first varistor 51 , the second varistor 52 , and the third varistor 53 are connected to the ground conductor 13 . The first varistor 51 , the second varistor 52 , and the third varistor 53 are arranged on the front plate surface of the second substrate 17 .

The limiting circuit 15b also limits the absolute value of the voltage applied to each of the pair of signal lines Wka and Wkb to a predetermined voltage or less. Specifically, when the absolute value of the voltage of the signal line Wka whose reference potential is the potential of the ground conductor 13 becomes a predetermined voltage, when the voltage of the signal line Wka is a positive voltage, the voltage of the first varistor 51 is The voltage between the two electrodes becomes a constant voltage. As a result, current flows through the first diode Dc, the first varistor 51, the ground conductor 13, and the earth in this order.

In a similar case, when the voltage of the signal line Wka is a negative voltage, the voltage between the two electrodes of the second varistor 52 becomes a constant voltage. As a result, the current flows through the earth, the ground conductor 13, the second varistor 52, and the second diode Dd in this order. Thereby, the absolute value of the voltage of the signal line Wka does not exceed a predetermined voltage.
When the absolute value of the voltage of the signal line Wka is less than a predetermined voltage, no current flows through the first diode Dc or the second diode Dd connected to the signal line Wka.

The voltage of the signal line Wkb is limited in the same way as the voltage of the signal line Wka, and the voltage of the signal line Wkb does not become an overvoltage. Therefore, the first varistor 51 and the second varistor 52 act as a whole in the same manner as the first discharger 31 in the first embodiment, and function as a limiter.

The third varistor 53 protects the shield conductor W5, that is, the shield conductor of the second cable 22 from application of overvoltage. Specifically, when the absolute value of the voltage of the shield conductor W5 whose reference potential is the potential of the ground conductor 13 becomes a predetermined voltage, the voltage between the two electrodes of the third varistor 53 becomes a constant voltage, and the third varistor Current flows through 53. When the voltage of the shield conducting wire W5 is a positive voltage, the current flows in the order of the third varistor 53, the ground conductor 13, and the earth. When the voltage of the shield conducting wire W5 is a negative voltage, the current flows through the earth, the ground conductor 13, and the third varistor 53 in this order. This prevents the voltage of the shield conductor W5, that is, the shield conductor, from becoming an overvoltage. When the absolute value of the voltage of the shield conducting wire W5 is less than the predetermined voltage, no current flows through the third varistor 53. The third varistor 53 functions similarly to the second discharger 32 in the first embodiment.

The protection device 1b in the third embodiment has the same effect as the protection device 1 in the first embodiment.
Note that in the first and second embodiments, the first varistor 51 and the second varistor 52 may be used instead of the first discharger 31. Furthermore, the third varistor 53 may be used instead of the second discharger 32.

Furthermore, instead of the first varistor 51, a Zener diode or a suppressor may be used. When using Zener diodes, the cathodes of the Zener diodes are connected to the cathodes of the eight first diodes Dc, and the anodes of the Zener diodes are connected to the ground conductor 13. The Zener diode and suppressor each function similarly to the first varistor 51.

Similarly, a Zener diode or a suppressor may be used instead of the second varistor 52. When using a Zener diode, the anode of the Zener diode is connected to the anodes of the eight second diodes Dd, and the cathode of the Zener diode is connected to the ground conductor 13. The Zener diode and suppressor each function similarly to the second varistor 52.

Furthermore, instead of the third varistor 53, a series circuit of two Zener diodes or a suppressor may be used. In a series circuit, the cathodes of two Zener diodes are connected to each other, or the anodes of two Zener diodes are connected to each other. Each of the series circuit and the suppressor functions similarly to the third varistor 53.

In the first to third embodiments, the second substrate 17 does not have to be supported by all eight first diodes Dc and eight second diodes Dd. A portion of the eight first diodes Dc and the eight second diodes Dd may support the second substrate 17. A portion of the eight first diodes Dc and the eight second diodes Dd may be only the eight first diodes Dc, only the eight second diodes Dd, or some of the first diodes Dc and some of the first diodes Dc. The second diode Dd, etc. Even in this case, the second substrate 17 is supported by the circuit elements arranged on the second substrate 17, so the number of parts of the device is small. In order to easily replace the limiting circuit 15, the remaining diodes are preferably provided on the second substrate 17.

Further, the member supporting the second substrate 17 is not limited to the first diode Dc or the second diode Dd. Another circuit element may support the second substrate 17, or a member different from the circuit element may support the second substrate 17. Even in this case, the remaining diodes are preferably provided on the second substrate 17 in order to easily replace the limiting circuit 15. Further, the configuration of the limiting circuit 15 is not limited to the configuration using the first diode Dc and the second diode Dd. For example, one end of the discharger may be connected to each of the pair of signal lines Wka and Wkb, and the other end of the discharger may be connected to the ground conductor 13. The discharger may be an arrester, a varistor, a suppressor or a series circuit of two Zener diodes. In this case, the discharger may support the second substrate 17.

The technical features (constituent features) described in Embodiments 1 to 3 can be combined with each other, and new technical features can be formed by combining them.
The disclosed embodiments 1 to 3 are illustrative in all respects and should not be considered restrictive. The scope of the present invention is indicated by the claims rather than the above-mentioned meaning, and is intended to include meanings equivalent to the claims and all changes within the scope.

1, 1a, 1b protection device, 13 ground conductor, 15, 15b limiting circuit, 16 first board, 17 second board, 31 first discharger (limiter), 51 first varistor (part of limiter), 52 Second varistor (part of limiter), Dc first diode (support member, second circuit element), Dd second diode (support member, second circuit element), W1a, W1b, W2a, W2b, W3a, W3b, W4a, W4b signal line

Claims (5)

Protecting a communication device that is placed in a propagation path of a differential signal represented by a difference between two voltages and that transmits and/or receives the differential signal from the application of an overvoltage whose absolute value exceeds a predetermined voltage. A protective device,
a first substrate provided with a pair of signal lines through which the differential signal propagates;
a limiting circuit that is connected to each of the pair of signal lines and limits the absolute value of the voltage applied to each of the pair of signal lines to below the predetermined voltage;
a second substrate on which circuit elements included in the limiting circuit are arranged;
A protection device comprising: a plurality of support members attached to the first substrate and supporting the second substrate so as to overlap with the first substrate at intervals. the pair of signal lines are arranged in parallel,
The protection device according to claim 1, wherein the pair of signal lines have the same length. The protection device according to claim 1 or 2, wherein the plurality of support members include a second circuit element included in the restriction circuit. Equipped with a conductor,
The limiting circuit is
two first diodes whose anodes are connected to each of the pair of signal lines;
two second diodes whose cathodes are connected to each of the pair of signal lines;
a limiter connected to the cathodes of the two first diodes, the anodes and conductors of the two second diodes, and limiting the absolute value of the voltage applied to each of the pair of signal lines to below the predetermined voltage. death,
When the absolute value of the voltage applied to one of the pair of signal lines reaches the predetermined voltage, the current flows through one of the pair of first diodes and the pair of second diodes and the limiter. , flows through the conductor and
The protection device according to any one of claims 1 to 3, wherein the plurality of support members include the first diode or the second diode. The protection device according to any one of claims 1 to 4, wherein the plurality of support members are removably attached to the first substrate.

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