JP3455457B2 - Communication line lightning surge current suppression circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication line lightning surge current suppressing circuit for suppressing a lightning surge current flowing into a communication line.

[0002]

2. Description of the Related Art FIG. 9 is a circuit diagram of a conventional lightning protection circuit for communication equipment. In FIG. 9, L1 and L2 are communication lines and 1
1 is a communication device, 12 is a ground wire of the communication device 11, 13 is a protector, ARR1 and ARR2 are lightning arresters, F1 and F2 are fuses, 14 is a ground wire of the protector 13, 15 is ground, 16 is insulation for communication line It is a transformer. V1 and V2 are lightning surge voltages generated on the communication lines L1 and L2, I1 and I2 are induced surge currents flowing from the communication lines L1 and L2 toward the communication device 11, and I4 is a lightning arrester ARR1 and AR.
The current flowing through the ground line 14 when R2 operates, I11,
I21 is a lightning surge current flowing into the communication device 11. Z is the impedance of the ground line 14 of the protector 13.

Conventionally, in order to protect the communication device 11 against a lightning surge current flowing from the communication lines L1 and L2, as shown in FIG. 9, a protector 13 incorporating a lightning arrester ARR1 and ARR2 is provided in the communication line lead-in portion. Mounted on the communication line 1 and the lightning surge voltages V1 and V2 generated on the communication lines L1 and L2 are
When the proof strength exceeds 1, the lightning arresters ARR1 and ARR2
Is made conductive so that the lightning surge current flows out to the protector ground wire 14. Furthermore, the communication device 11
If the grounding of the protector 13 and the grounding of the protector 13 are separate, the ground potential of the protector 13 rises due to the current flowing from the protector 13 to the ground.
There is a phenomenon that a lightning surge current intrudes into the communication device 1. In order to prevent this, the communication device 11 and the protector 1 as shown by the ground 15 in FIG.
The method of connecting the three grounding lines 12 and 14 to each other and grounding to the ground at one place is adopted.

However, from the communication lines L1 and L2 to the ground line 14
If the lightning surge current I4 flowing into is too large or the wire length of the protector grounding wire 14 is long, the lightning surge currents I11, I21 sneaking into the communication equipment side increase due to the influence of the impedance Z of the grounding wire 14, Fuse F1 of protector 13
, F2 may be cut off or the communication device 11 may be broken. In addition, the protector 13 may differ due to manufacturing variations.
Since the lightning arrester ARR1 and the lightning arrester ARR2 in the device have different operation start voltages, a lightning surge current may flow into the communication device side from the communication line on the lightning arrester side that operates with a delay, and in that case as well, the fuse F1 of the protector 13 There were cases where F2 was cut off and communication device 11 failed.

[0005]

In order to prevent such a problem, as shown in FIG. 9, a protector 13 and a communication device 1 are provided.
The method of inserting the communication line isolation transformer 16 between the two is adopted. Further, there is a method of preventing the inflow of lightning surge current by using a common mode choke coil instead of this insulating transformer. However, in the case of the insulating transformer, the communication line is insulated in terms of direct current, so that there is a problem that it cannot be applied to a communication line such as an analog telephone or ISDN that supplies direct current.

Further, the common mode choke coil can be applied to a DC power supply line, but the one designed for a frequency band of several Hz to several 100 kHz such as lightning surge has a large shape and size. In addition, there is a problem that the lightning surge current suppression efficiency is low and that a communication signal in a high frequency band of several 100 kHz or more is greatly attenuated. Besides this,
There is a method of inserting a secondary lightning arrester into the communication line input part of the communication device as a measure against lightning surge secondary to the communication device via the protector, but even in that case, the secondary lightning arrester becomes conductive. When lightning surge currents I11 and I21 flow, the fuses F1 and F2 in the protector are blown and the communication line may be disconnected.

The present invention has been made to solve the above problems, and not only for analog telephone lines for direct current feeding but also for communication lines using high frequency signals such as ISDN lines and also for direct current feeding, An object of the present invention is to provide a communication line lightning surge current suppressing circuit that can efficiently suppress a lightning surge current flowing into a communication line.

[0008]

In conventional lightning arresters and semiconductors used in lightning protection circuits , many elements are turned from an insulated state to a conductive state when a predetermined voltage is applied. However, in order to solve the above-mentioned problems of the conventional lightning protection circuit, it is required to maintain a conductive state during normal communication and be in an insulating state when a lightning surge voltage is applied or a current flows. Therefore, in the present invention, when a voltage is applied to the gate, the drain-
A field effect transistor in which the current characteristic between the sources changes is used. Connect the input side of the communication line to the drain of the field effect transistor and the output side to the source of the field effect transistor so that the input and output of the communication line, that is, the drain and source of the field effect transistor become conductive during normal communication. A bias voltage is applied between the source and the gate. In the present invention, by connecting a resistance element or a current transformer to this communication line, the source-gate bias voltage of the field effect transistor is changed by utilizing the voltage generated in these resistance element and current transformer. A circuit that causes the above. The field effect transistor has a characteristic that the magnitude of the current flowing between the drain and the source is suppressed when the bias voltage between the source and the gate changes. Therefore, by varying the bias voltage between the source and the gate according to the magnitude of the lightning surge current flowing in the communication line, it does not affect the normal communication current, and the excess voltage such as the lightning surge current does not occur. A circuit that suppresses the current flowing through the communication line only when a large current flows into the communication line is configured. In this way, by constructing a circuit that becomes conductive during normal communication using field-effect transistors, a lightning surge current suppression circuit that does not have any effect on the communication line that supplies direct current is provided. realizable. Further, since the field effect transistor is used for suppressing the lightning surge current, it has a characteristic that it operates at high speed and can sufficiently cope with a lightning surge current that rises quickly. Furthermore, once the lightning surge is resolved, the original conductive state is restored, so there is no problem like a fuse that melts down with one lightning surge and disconnects the line.
The effect of withstanding lightning surges can be obtained repeatedly. Further, there is a feature that the circuit can be efficiently constructed in a small size.

The communication line lightning surge current suppressing circuit of the present invention is
A field effect transistor (3) connected between the drain and the source in series with the communication line, and a resistance element (R connected in series to a line other than the communication line such as a ground line or a pilot line).
3), and the bias voltage between the source and gate of the field effect transistor is changed by the voltage drop of the resistance element according to the current flowing into the line other than the communication line, and the lightning surge current flowing into the communication line is suppressed. It is a thing. Further, the communication line lightning surge current suppressing circuit of the present invention includes a field effect transistor (3-1, 3-2, 3-3, 3-4) connected between the drain and the source in series with the communication line. , A current transformer (6-1, 6-2) arranged to generate an induced voltage according to a current flowing into a line (14) other than a communication line such as a ground line or a pilot line, The source-gate bias voltage of the field effect transistor is changed by the induced voltage of the current transformer according to the current flowing into a line other than the communication line, and the lightning surge current flowing into the communication line is suppressed.

Further, in one configuration example of the above-mentioned communication line lightning surge current suppressing circuit, the drain is a first field effect transistor (3-1) whose drain is connected to the input side of the communication line, and the drain is the output side of the communication line. A second field effect transistor (3-2) connected to the first field effect transistor (3-2), one end connected to the source of the first field effect transistor (R1), and one end connected to the second field effect transistor. A second resistance element (R2) connected to the source, a positive electrode connected to the gates of the first and second field effect transistors, and a negative electrode connected to the connection point of the first and second resistance elements. And (4).

Further, in one configuration example of the above-mentioned communication line lightning surge current suppression circuit, the first field effect transistor (3-1) whose drain is connected to the input side of the communication line and the drain is the output side of the communication line. A second field effect transistor (3-2) connected to the source of the first field effect transistor and connected to the source of the first field effect transistor, and an induced voltage corresponding to the current flowing into the input side of the communication line. A first current transformer (6-1) whose one end is connected to the gate of the first field effect transistor, and is arranged so that an induced voltage according to the current flowing into the output side of the communication line is generated. A second current transformer (6−) having one end connected to the gate of the second field effect transistor and the other end connected to the other end of the first current transformer.
2) and a power source (4) whose positive electrode is connected to the connection point of the first and second current transformers and whose negative electrode is connected to the sources of the first and second field effect transistors.

In one configuration example of the above-mentioned communication line lightning surge current suppression circuit, the drain and source are connected in series with the communication line, and the gate is a line (7) other than the communication line such as a ground line or a pilot line. ), A resistance element (R3) inserted in series in a line other than the communication line so that one end is connected to the gate of the field effect transistor, and the positive electrode is the other end of the resistance element. Side communication line, the negative electrode has a power supply (4) connected to the source side communication line. Further, one configuration example of the above-mentioned communication line lightning surge current suppression circuit is the first field effect transistor (3-1, whose drain is connected to the input side of the communication line).
3-3), and a second field effect transistor (3-2, 3-4) whose drain is connected to the output side of the communication line and whose source is connected to the source of the first field effect transistor,
A first current transformer which is arranged so that an induced voltage corresponding to a current flowing into a line (14) other than a communication line such as a ground line or a pilot line is generated, and one end of which is connected to the gate of the first field effect transistor. And a second current transformer (6-1) which is arranged so as to generate an induced voltage according to a current flowing into a line other than the communication line and whose one end is connected to the gate of the second field effect transistor ( 6-2) and a power source (4) whose positive electrode is connected to the connection point of the first and second current transformers and whose negative electrode is connected to the sources of the first and second field effect transistors. is there. The first and second field effect transistors are provided for each communication line, each gate of the first field effect transistor is connected to one end of the first current transformer, and each of the second field effect transistors is provided. The gate is connected to one end of the second current transformer.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION [First Embodiment] Next, an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a circuit diagram of a communication line lightning surge current suppressing circuit according to a first embodiment of the present invention. The communication line lightning surge current suppressing circuit of the present embodiment is the same as the communication line L1 or L2 of FIG.
Between the source and the gate of the transistor 3, the drain D of which is connected to the input side communication line 1 and the positive electrode of which is connected to the gate G of the field effect transistor 3. A battery 4 for applying a bias voltage to the resistor 4, a resistor element R1 having one end connected to the source S of the field effect transistor 3 and the other end connected to the output communication line 2, and one end connected to the negative electrode of the battery 4. A resistance element R10 for preventing a short circuit of the battery 4, the other end of which is connected to the output side communication line 2, and one end of which is the field effect transistor 3
Is connected to the gate G of the transistor S and the other end is the source S of the transistor 3.
And a varistor 5 connected between the source and the gate to prevent an overvoltage from being applied.

In FIG. 1, I11 is a current flowing into the communication line, Vr1 is a voltage generated in the resistance element R1 by the current I11, E is a voltage of the battery 4, VSG is a field effect transistor 3.
Is the source-gate bias voltage of.

There are three types of field effect transistors, a deflection type, an enhancement type, and a deflection / enhancement type, all of which may be applicable to the present invention, but the drain-source current allowable value is large and the source is large. -The enhancement type, which has a large allowable value of the gate bias voltage fluctuation in the positive and negative directions, is optimal. A typical enhancement type field effect transistor is MO.
This is an S-FET, and in this embodiment, a MOS-FET is used as the field effect transistor 3.

In the MOS-FET, a current can flow from the source to the drain terminal regardless of the bias voltage between the source and gate terminals. However, in order to flow a current from the drain to the source terminal, it is a necessary condition that a positive bias voltage of a predetermined value (several V) or more is applied as the source-gate terminal bias voltage. That is, when the source-gate terminal bias voltage decreases below a predetermined voltage or becomes negative, the current from the drain to the source is suppressed.

In the circuit of FIG. 1, when a current I11 flows from the input side to the output side of the communication line L1, a voltage VSG given by the following equation is generated between the source and gate of the field effect transistor 3. VSG = E-R1 × I11 (1)

In normal communication, the current I11 flowing through the communication line is a direct current of several tens of mA to 200 mA. Therefore, if the resistance value of R1 is selected to be several Ω, the voltage VSG due to the current I11 during communication is set. Is a small voltage of about 1 V or less. Therefore, the bias voltage E of the battery 4 is set to 2 to 3
Set to a large V, and the drain-
If the current between the sources is not limited, it has almost no effect on the direct current flowing during normal communication.

On the other hand, an excessive current such as a lightning surge current (normally 1
When (A or more) I11 flows, the voltage VSG of the formula (1) decreases by several V or more, so that the current from the drain to the source direction can be suppressed. Further, even when the current I11 increases and VSG becomes negative, the excessive current can be suppressed.

2 uses 2SK906 (manufactured by Fuji Electric) as the field effect transistor 3 in the circuit of FIG.
It is a figure which shows the experimental result at the time of making E = 9V and R1 = 6 (ohm), and sending the electric current I11 with a waveform of 8x20 microseconds and a peak current value of 6 A to a communication line. FIG. 2 (a) is a diagram showing the communication line current I11 when the resistance element R1 is connected and not connected, and FIG. 2 (b) is a source of the field effect transistor 3 when the resistance element R1 is connected and not connected. FIG. 7 is a diagram showing a gate-to-gate bias voltage VSG.

As shown in FIG. 2A, when the resistance element R1 is not connected, a lightning surge current I11 having a peak current value exceeding 6 A flows. On the other hand, when the resistance element R1 is connected, the peak value of the lightning surge current I11 is about 1
It is suppressed to about A, and the effect of the present invention is clearly shown.

As shown in FIG. 2B, the source-gate bias voltage VSG of the transistor 3 when the resistance element R1 is connected decreases from 9V to 3V at the same time when the lightning surge current I11 begins to flow. It can be seen that the voltage drop continues according to the inflow of the lightning surge current I11 shown in FIG.

The varistor 5 is a lightning arrester for preventing a failure of the field effect transistor 3 so that an excessive voltage is not applied between its source and gate. Therefore, the varistor 5 can be omitted. Further, the resistance element R10 is a protection element for preventing the battery 4 from being short-circuited even when the field effect transistor 3 fails and the source and the gate become conductive. Therefore, the resistance element R10 may be omitted and the negative electrode of the battery 4 and the output communication line 2 may be directly connected.

[Second Embodiment] In the first embodiment,
Although it is possible to suppress the current from the input side to the output side,
Since the voltage VSG increases with respect to the current from the output side to the input side of the communication line, the inflowing current cannot be suppressed. Therefore, next, FIG. 3 shows a circuit in which the current in the direction opposite to that of FIG. 1, that is, the current from the output side to the input side can be suppressed.

FIG. 3 is a circuit diagram of a communication line lightning surge current suppressing circuit according to a second embodiment of the present invention. The communication line lightning surge current suppressing circuit of the present embodiment is the same as the communication line L of FIG.
1 or L2, the input side communication line 1 in which the drain D is connected to the input side communication line 1
From the output communication line 2 to the output communication line 2 in which the drain D is connected to the output communication line 2 and the field effect transistor 3-1 for suppressing the current I11 in the direction from the output communication line 2 to the output communication line 1
Field effect transistor 3-2 for suppressing the current I12 in the direction, and the positive electrodes are field effect transistors 3-1 and 3-2.
Transistors 3-1 and 3-2 connected to the gate G of
Battery 4 for applying a bias voltage between the source and the gate of the field effect transistor 3-1.
To the source S of the field-effect transistor 3-2, one end of which is connected to the negative electrode of the battery 4 and the other end of which is connected to the resistance elements R1 and R2.
A resistor element R10 for preventing a short circuit of the battery 4, which is connected to the connection point of, and one end connected to the gate G of the field effect transistor 3-1 and the other end connected to the source S of the transistor 3-1. It includes a varistor 5-1 and a varistor 5-2 having one end connected to the gate G of the field effect transistor 3-2 and the other end connected to the source S of the transistor 3-2.

In FIG. 3, Vr1 and Vr2 are voltages generated in the resistance elements R1 and R2 by the currents I11 and I12, respectively. In the present embodiment, one battery 4 is sufficient,
Sources for both field effect transistors 3-1 and 3-2
A gate-to-gate bias voltage can be applied. Along with this, the number of resistance elements R10 also becomes one.

When a current I11 flows from the input side to the output side, the bias voltage VSG1 of the field effect transistor 3-1 decreases due to the voltage Vr1 generated in the resistance element R1. Therefore, for the current I11, the field effect transistor 3-
1 has the effect of suppressing the current. Regarding the field effect transistor 3-2, since the voltage generated in the resistance element R2 is in the same direction as Vr1, the bias voltage VSG2 of the field effect transistor 3-2 increases and the current I
The effect of suppressing 11 cannot be obtained. Contrary to the current I11, when the current I12 in the direction from the output side to the input side flows, the resistance element R
A field effect transistor 3-
The bias voltage VSG2 of 2 is reduced and the current I12 can be suppressed.

Also in the present embodiment, the first embodiment
Similarly, the varistor 5-1 and 5-2 may be omitted.
Alternatively, the resistance element R10 may be omitted and the connection point between the negative electrode of the battery 4 and the resistance elements R1 and R2 may be directly connected.

[Third Embodiment] In the first and second embodiments, the resistance elements R1 and R2 are inserted in the communication line. However, the lightning surge current can be suppressed without inserting the resistance element. . FIG. 4 is a circuit diagram of a communication line lightning surge current suppressing circuit according to a third embodiment of the present invention.

In the communication line lightning surge current suppression circuit of this embodiment, a drain D is connected to the input side communication line 1, and a source S is connected to the output side communication line 2, and a field effect transistor 3 is connected at one end to the electric field. A current transformer 6 connected to the gate G of the effect transistor 3, a battery 4 having a positive electrode connected to the other end of the current transformer 6, one end connected to the negative electrode of the battery 4, and the other end connected to the output communication line 2 And a varistor 5 having one end connected to the gate G of the field effect transistor 3 and the other end connected to the negative electrode of the battery 4.

The current transformer 6 is attached so as to induce a voltage Vt in the direction of the arrow in FIG. 4 when a current I11 flows from the input side to the output side. As a result, the source-gate voltage VSG of the field effect transistor 3 is given by the following equation. VSG = E-Vt (2)

Therefore, also in this case, as in the first embodiment, when the source-gate voltage VSG of the field effect transistor 3 fluctuates due to the voltage Vt and the current I11 becomes excessive, the excessive current is suppressed. A circuit can be realized. In the circuit of this embodiment, a series resistor (see FIG.
In this case, since the resistance element R1) is not connected, there is a characteristic that it does not affect the transmission characteristics of the communication line.

In FIG. 5, the same MOS-FET as in FIG. 2 is used as the field effect transistor 3 in the circuit of FIG. 4, and the current transformer 6 is a model 287 manufactured by Pearson.
Using a current transformer of 7 and E = 9V, 8 × 20μ
It is a figure which shows the experimental result at the time of letting the electric current I11 with a peak current value of about 20 A in a waveform of s flow into a communication line. FIG. 5 (a) is a diagram showing the communication line current I11 with and without the current transformer 6, and FIG. 5 (b) is the source of the field effect transistor 3 with and without the current transformer 6. FIG. 7 is a diagram showing a gate-to-gate bias voltage VSG.

As shown in FIG. 5A, when the current transformer 6 is not provided, the lightning surge current I having a peak current value of 20 A is obtained.
11 flows. On the other hand, when the current transformer 6 is attached, the peak value of the lightning surge current I11 is suppressed to about 4 A, and the effect of the present invention can be clearly confirmed. Figure 5
As shown in (b), the source-gate bias voltage VSG of the transistor 3 when the current transformer 6 is attached.
4 from 9V at the same time when the lightning surge current I11 begins to flow.
It has fallen to about V.

Also in the present embodiment, the first embodiment
Similarly, the varistor 5 may be omitted. Alternatively, the resistance element R10 may be omitted and the negative electrode of the battery 4 and the output side communication line 2 may be directly connected.

[Fourth Embodiment] FIG. 6 is a circuit diagram of a communication line lightning surge current suppressing circuit according to a fourth embodiment of the present invention. In the communication line lightning surge current suppression circuit of the present embodiment, a field effect transistor 3-1 whose drain D is connected to the input side communication line 1, a drain D is connected to the output side communication line 2, and a source S is a transistor. 3-1 is connected to the source S of the field effect transistor 3-2, one end of the current transformer 6-1 is connected to the gate G of the field effect transistor 3-1, and one end of the field effect transistor 3-2. A current transformer 6-2 connected to the gate G and the other end of which is connected to the other end of the current transformer 6-1; and a positive electrode of the current transformer 6-1,
A battery 4 connected to the connection point 6-2, a resistor element R10 having one end connected to the negative electrode of the battery 4 and the other end connected to the sources S of the transistors 3-1 and 3-2, and one end having an electric field It is connected to the gate G of the effect transistor 3-1 and the other end is the battery 4
Of the varistor 5-1 connected to the negative electrode of the battery 4, one end of which is connected to the gate G of the field effect transistor 3-2 and the other end of which is the battery 4
And a varistor 5-2 connected to the negative electrode.

The current transformer 6-1 induces an induced voltage V in the direction of the arrow in FIG. 6 when a current I11 flows from the input side to the output side.
The current transformer 6-2 is arranged so that t1 is generated, and the induced voltage Vt2 is generated in the arrow direction of FIG. 6 when the current I12 in the input side direction flows from the output side.

In the third embodiment, a current transformer is used to suppress the current I11 from the input side to the output side. However, as shown in the relationship between the first embodiment and the second embodiment, By connecting the circuits of No. 4 in a left-right symmetrical manner and constructing them as shown in FIG. 6, it is possible to have an effect of suppressing the current in the opposite direction.

Also in this embodiment, the first embodiment
Similarly, the varistor 5-1 and 5-2 may be omitted.
Alternatively, the resistance element R10 may be omitted and the negative electrode of the battery 4 and the sources of the transistors 3-1 and 3-2 may be directly connected.

[Fifth Embodiment] FIG. 7 shows a fifth embodiment of the present invention.
2 is a circuit diagram of a communication line lightning surge current suppression circuit according to the embodiment of FIG. In the communication line lightning surge current suppression circuit of the present embodiment, the drain D is connected to the input side communication line 1, and the source S
Is connected to the output communication line 2 and the gate G is connected to the pilot line 7 and the field effect transistor 3 is connected in series to the pilot line 7 so that one end is connected to the gate G of the field effect transistor 3. An element R3, a battery 4 having a positive electrode connected to the pilot line 7 on the other end side of the resistance element R3, and a resistance element R10 having one end connected to the negative electrode of the battery 4 and the other end connected to the output side communication line 2. , One end of which is connected to the gate G of the field effect transistor 3 and the other end of which is the transistor 3
And a varistor 5 connected to the source S.

In FIG. 7, I3 is a current flowing through the pilot line 7, and Vr3 is a voltage generated in the resistance element R3 by the current I3. The communication line lightning surge current suppression circuit of the present embodiment detects a current flowing through a line other than the communication line such as a pilot line and suppresses the current of the communication line. Figure 7
When the current I3 flows through the pilot line 7 as shown in FIG. 5, the source-gate bias voltage VSG of the field effect transistor 3 is lowered by the voltage Vr3 generated in the resistance element R3. As a result, the current I11 flowing through the communication line can be suppressed.

Also in this embodiment, the first embodiment
Similarly, the varistor 5 may be omitted. Alternatively, the resistance element R10 may be omitted and the negative electrode of the battery 4 and the output side communication line 2 may be directly connected.

[Sixth Embodiment] FIG. 8 shows a sixth embodiment of the present invention.
2 is a circuit diagram of a communication line lightning surge current suppression circuit according to the embodiment of FIG. In the communication line lightning surge current suppression circuit of the present embodiment, the drain D is connected to the input side of the communication line L1, the field effect transistor 3-1 is connected, the drain D is connected to the output side of the communication line L1, and the source S is connected. Is a field effect transistor 3-2 connected to the source S of the transistor 3-1, a drain D is connected to the input side of the communication line L2, and a drain D is output side of the communication line L2. Is connected to the source S, and the source S is the source S of the transistor 3-3.
, A current transformer 6-1 having one end connected to the gates G of the field effect transistors 3-1 and 3-3, and one end having field effect transistors 3-2 and 3-. 4 is connected to the gate G and the other end is connected to the other end of the current transformer 6-1. The positive electrode is connected to the connection point of the current transformers 6-1 and 6-2. Battery 4
And a resistance element R10 having one end connected to the negative electrode of the battery 4 and the other end connected to the sources S of the transistors 3-1 and 3-2.
And a resistor element R10 having one end connected to the negative electrode of the battery 4 and the other end connected to the sources S of the transistors 3-3 and 3-4.
And a varistor 5-1 having one end connected to the gates G of the transistors 3-1 and 3-3 and the other end connected to the negative electrode of the battery 4.
And a varistor 5-2 having one end connected to the gates G of the transistors 3-2 and 3-4 and the other end connected to the negative electrode of the battery 4.
It has and.

The current transformer 6-1 is arranged so that the induced voltage Vt1 is generated when the current I4 in the direction of the arrow in FIG. 8 flows through the ground line 14, and the current transformer 6-2 is connected to the ground line 14. When the current flows in the direction opposite to the current I4, the induced voltage Vt2 is generated.

The communication line lightning surge current suppressing circuit of the present embodiment corresponds to that of FIG. 9, and it flows into the ground line 14 in order to suppress the current secondarily flowing from the protector 13 to the communication device 11. The lightning surge current is used as an induction source. When the lightning surge currents I1 and I2 flow from the communication lines L1 and L2, the lightning arresters ARR1 and ARR2 become conductive and the current I4 flows through the ground line 14, a voltage Vt1 is generated in the current transformer 6-1.

As a result, the field effect transistor 3-
The source-gate bias voltage VSG of 1, 3-3 decreases, and the output side currents I11, I21 of the communication lines L1, L2 are suppressed. When a current in the direction opposite to the current I4 flows through the ground line 14, the source-gate bias voltage VSG of the field effect transistors 3-2 and 3-4 decreases, and the communication lines L1 and L4.
The current flowing through 2 is suppressed.

In this embodiment, one biasing battery 4 and two current transformers 6-are provided for the communication lines L1 and L2.
1, 6-2 is used to cope with lightning surge currents in both directions, but the battery 4 and the current transformers 6-1, 6-2 are used.
Since the multi-connection is possible, it has a feature that it can cope with the case where the number of communication lines further increases.

That is, the first field effect transistor whose drain D is connected to the input side of the communication line (3-1 and 3-1 in FIG. 8).
3-3) and a drain D connected to the output side of the communication line, and a source S connected to the source S of the first field effect transistor (3 in FIG. 8).
(Corresponding to -2, 3-4) and resistors (corresponding to resistors R10 and R11 in FIG. 8) whose one end is connected to the sources S of the first and second field effect transistors are provided for each communication line. And
The gate G of the first field effect transistor is connected to the current transformer 6
−1, the gate G of the second field effect transistor is connected to one end of the current transformer 6-2, and the other end of the resistor is connected to the negative electrode of the battery 4.

Further, as in the present embodiment, the ground wire 14
Current is detected, and the induced voltages Vt1 and Vt2 are detected by the communication line L.
When feeding back to the source-gate bias voltage VSG of the field effect transistor connected to 1 and L2, the withstand voltage of the surge arresters ARR1 and ARR2 in the protective device is higher than the withstand voltage of the ground line 14 and the current detection circuit. However, since the current transformers 6-1 and 6-2 are used for current detection in the present embodiment, the withstand voltage can be easily realized.

Also in the present embodiment, the first embodiment
Similarly, the varistor 5-1 and 5-2 may be omitted.
Alternatively, the resistance elements R10 and R11 may be omitted, and the negative electrode of the battery 4 and the sources S of the transistors 3-1, 3-2, 3-3 and 3-4 may be directly connected.

In the above embodiments, the n-channel field effect transistors are used as the field effect transistors 3, 3-1, 3-2, 3-3 and 3-4, but the p-channel field effect transistors are used. An effect transistor may be used. In this case, the drains D and the sources S of the transistors 3, 3-1, 3-2, 3-3, 3-4 in FIGS. 1, 3, 4, and 6 to 8 are reversed and the battery 4 The polarity of can be reversed.

[0052]

According to the present invention, the source-gate bias voltage of the field effect transistor is varied by utilizing the voltage generated in the resistance element inserted in series with the communication line or the current transformer attached to the communication line. As a result, the lightning surge current of the communication line connected between the drain and the source can be controlled, and the lightning surge current component in a wide band from DC to several MHz can be limited by one circuit. Therefore, unlike a conventional lightning protection circuit that uses an insulating transformer, it can be applied to a communication line that supplies DC power. Also, unlike conventional lightning protection circuits that use common mode choke coils, lightning surge currents can be efficiently suppressed, so the circuit dimensions can be reduced, and in which frequency band lightning surges can be efficiently suppressed. It can be used without considering the limitation of the effective frequency band. Further, since the field effect transistor is used, it is possible to suppress an excessive current at a high speed, and it is possible to suppress a lightning surge current that rises quickly. Further, when the lightning surge disappears and the bias voltage of the field effect transistor returns to the normal state, the communication line also returns to the original conductive state. Therefore, like a fuse or an earth leakage breaker, a lightning surge current passes due to a slow operating time and communication equipment may fail, or once a lightning surge flows it may melt down and become unusable. It doesn't happen.

Further, an induced voltage may be generated according to a current flowing into a resistance element inserted in series with a wire other than the communication wire such as the ground wire or the pilot wire or a wire other than the communication wire such as the ground wire or the pilot wire. By using the current transformer arranged in, the current flowing in the lines other than the communication line is detected,
Since a circuit that suppresses the current of the communication line can be configured, it is possible to suppress the lightning surge current that flows around to the communication line side in conjunction with the current of the ground line, the pilot line, and the like.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a communication line lightning surge current suppression circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an experimental result in the communication line lightning surge current suppression circuit of FIG.

FIG. 3 is a circuit diagram of a communication line lightning surge current suppression circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a communication line lightning surge current suppression circuit according to a third embodiment of the present invention.

5 is a diagram showing an experimental result in the communication line lightning surge current suppression circuit of FIG.

FIG. 6 is a circuit diagram of a communication line lightning surge current suppression circuit according to a fourth embodiment of the present invention.

FIG. 7 is a circuit diagram of a communication line lightning surge current suppressing circuit according to a fifth embodiment of the present invention.

FIG. 8 is a circuit diagram of a communication line lightning surge current suppression circuit according to a sixth embodiment of the present invention.

FIG. 9 is a circuit diagram of a conventional lightning protection circuit.

[Explanation of symbols]

1 ... Input side communication line, 2 ... Output side communication line, 3, 3-1, 3
-2, 3-3, 3-4 ... Field effect transistor, 4 ... Battery, 5-1, 5-2, ... Varistor, 6, 6-1, 6-
2 ... current transformer, 7 ... pilot line, 11 ... communication device,
12 ... Grounding wire, 13 ... Protector, 14 ... Grounding wire, L1, L
2 ... Communication line, R1, R2, R3, R10, R11 ... Resistance element, ARR1, ARR2 ... Lightning arrester, F1, F2 ... Fuse, Vr1, Vr2, Vr3 ... Voltage generated in resistance element, Vt,
Vt1, Vt2 ... Voltage generated in current transformer, VSG, VSG1,
VSG2 ... Source-gate voltage of field effect transistor.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-178725 (JP, A) JP-A-10-323036 (JP, A) Actual development: 4-98841 (JP, U) (58) Field (Int.Cl. ⁷ , DB name) H02H 9/00-9/04

Claims (6)

(57) [Claims] 1. A field effect transistor having a drain-source connected in series with a communication line, and a resistance element inserted in series with a line other than a communication line such as a ground line or a pilot line . A communication characterized by varying the source-gate bias voltage of a field effect transistor by a voltage drop of a resistance element according to a current flowing into a line other than the communication line, and suppressing a lightning surge current flowing into the communication line. Line lightning surge current suppression circuit. 2. A field effect transistor connected between a drain and a source in series with a communication line, and an induced voltage according to a current flowing into a line other than a communication line such as a ground line or a pilot line. And a current transformer arranged, and changes the source-gate bias voltage of the field effect transistor by the induced voltage of the current transformer according to the current flowing into a line other than the communication line, and then flows into the communication line. Circuit for suppressing lightning surge current in a communication line. 3. The drain is connected to the input side of the communication line
A first field effect transistor and a second field effect whose drain is connected to the output side of the communication line
The transistor, one end of which is connected to the source of the first field effect transistor
The first resistance element and one end of which is connected to the source of the second field effect transistor.
The second resistance element and the positive electrode are connected to the gates of the first and second field effect transistors.
The negative electrode is connected to the connection point of the first and second resistance elements.
It has a separate power supply and responds to the current flowing into the input side or output side of the communication line.
It is possible to suppress the lightning surge current flowing into the communication line by varying the source-gate bias voltage of the first and second field effect transistors by the voltage drop of the first and second resistance elements. Characteristic communication line lightning surge current suppression circuit. 4. The drain is connected to the input side of the communication line
The first field effect transistor, the drain is connected to the output side of the communication line, and the source is the first
A second electric field connected to the source of the field effect transistor
An induced voltage is generated according to the current flowing into the effect transistor and the input side of the communication line.
And a first field effect transistor having one end
The first current transformer connected to the gate of the and the induced voltage according to the current flowing into the output side of the communication line
And a second field effect transistor arranged at one end
Connected to the gate of the first current transformer and the other end of the first current transformer.
A second current transformer connected and a positive electrode connected to the connection point of the first and second current transformers, and a negative
The pole is connected to the sources of the first and second field effect transistors
It has a built-in power supply and responds to the current flowing into the input side or the output side of the communication line.
It is possible to suppress the lightning surge current flowing into the communication line by varying the source-gate bias voltage of the first and second field effect transistors by the induced voltage of the first and second current transformers. Characteristic communication line lightning surge current suppression circuit. 5. The drain and source are connected in series with a communication line.
And the gate is connected to the ground line or pilot line.
Make sure that the field effect transistor connected to a line other than the signal line and one end is connected to the gate of the field effect transistor.
Connect the resistance element inserted in series to a line other than the communication line, and connect the positive electrode to a line other than the communication line on the other end side of the resistance element.
The negative electrode has a power supply connected to the communication line on the source side, and changes the source-gate bias voltage of the field effect transistor due to the voltage drop of the resistance element according to the current flowing into the line other than the communication line. A communication line lightning surge current suppression circuit, which suppresses a lightning surge current flowing into the communication line. 6. The drain is connected to the input side of the communication line
The first field effect transistor, the drain is connected to the output side of the communication line, and the source is the first
A second electric field connected to the source of the field effect transistor
The effect transistor and the electric current that flows into the lines other than the communication line such as the ground line and pilot line.
It is arranged so that an induced voltage according to the flow is generated, and one end is the first
A first electrode connected to the gate of the field effect transistor of
The induced voltage corresponding to the current flowing in the current transformer and the lines other than the communication line is
Is arranged so that one end has a second field effect transistor
A second current transformer connected to the gate of the current transformer, and a positive electrode connected to the connection point of the first and second current transformers,
The pole is connected to the sources of the first and second field effect transistors
And a first power source and a second power source transistor for each communication line.
And each gate of the first field effect transistor is
1 is connected to one end of the current transformer, and the second field effect transistor is connected.
Each gate of the transistor is connected to one end of the second current transformer.
A lightning surge current suppressor circuit for communication lines .