JPH1064740A - Insulation transformer device for communication - Google Patents

Abstract

(57) [Summary] [PROBLEMS] When the structure is simple and easy to manufacture, and when the surge intrusion occurs, the electrostatic shield can exhibit its original shielding function well, and when interposed in an unbalanced transmission line. However, the present invention provides a communication isolation transformer device capable of expanding a usable frequency band while suppressing transmission loss in a steady state. In a communication insulating transformer device, an electrostatic shield inserted between a primary winding and a secondary winding is grounded via a ground terminal. A switching element is provided between the ground terminal and the ground terminal so as to conduct when the potential difference between the two terminals is equal to or greater than a predetermined value to electrically connect the electrostatic shield to the ground terminal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication insulating transformer device having an electrostatic shield interposed between a primary winding and a secondary winding.

[0002]

2. Description of the Related Art As is well known, in order to protect a communication device from a surge intruding into a signal transmission line due to induced lightning or the like, an insulation transformer is widely interposed between the signal transmission line and the communication device. ing. Insulating transformers used for such a purpose are usually provided with an electrostatic shield provided between a primary winding and a secondary winding, and the electrostatic shield is grounded.

FIG. 3 shows an example of an equivalent circuit in which an insulating transformer 3 is interposed between a signal transmission line 1 on the outside line and a signal transmission line 2 on the communication device side. The insulating transformer 3 includes a primary winding 4 and a secondary winding 5 wound around an iron core (not shown), and an electrostatic shield 6 between the primary winding 4 and the secondary winding 5.

[0004] Both ends of the primary winding 4 are connected to the center conductor and the outer conductor of the signal transmission line 1 constituted by a coaxial cable, for example, and both ends of the secondary winding 5 are constituted by a signal transmission line constituted by a coaxial cable, for example. 2 are connected to the center conductor and the outer conductor. The electrostatic shield 6 is grounded to the ground 8 via a ground terminal 7. In addition, the electrostatic shield 6
Is generally formed of a metal material having a low conductor resistance, such as copper, aluminum, and stainless steel.

If such an insulating transformer 3 is interposed in the middle of a signal transmission line, even if a surge (for example, common mode noise) enters the signal transmission line 1 on the outside line,
Most of this surge flows on the path between the distributed capacitance 9 between the primary winding 4 and the electrostatic shield 6, the electrostatic shield 6, the ground terminal 7, and the ground 8. Therefore, it is possible to suppress the surge from entering the secondary winding 5 and protect the communication device.

[0006] However, the insulating transformer 3 configured as described above has the following problems. That is, as shown in FIG. 3, when the signal transmission line 1 is an unbalanced transmission line composed of a center conductor and an outer conductor of a coaxial cable, the position A where the outer conductor is usually away from the insulating transformer 3 is usually used. Etc. are grounded. Therefore, a potential difference occurs between the primary winding 4 and the electrostatic shield 6 even in a steady state. Since the distributed capacitance 9 exists between the primary winding 4 and the electrostatic shield 6, a part of the transmission signal is transmitted in the steady state in a path from the distributed capacitance 9 to the electrostatic shield 6 to the ground terminal 7 to the ground 8. Flows in

As described above, when the signal transmission line 1 is an unbalanced transmission line, a part of the transmission signal flows through the electrostatic shield 6 even in a steady state, so that the signal transmission line is constituted by a balanced transmission line. However, there is a problem that the transmission loss in the steady state is larger than that in the case where it is performed.

When the frequency of the transmission signal coincides with the series resonance frequency f ₀ determined by the capacitance of the distributed capacitance 9 and the stray inductance 10 existing between the electrostatic shield 6 and the ground 8, FIG. As shown by the solid line therein, the transmission loss sharply increases. Furthermore, when the frequency of the transmission signal is, for example, in the region of 10 MHz or more, the impedance of the distributed capacitor 9 decreases with the increase of the frequency, so that the current flowing through the electrostatic shield 6 increases, and the transmission loss increases rapidly. To increase. From such a thing,
When the signal transmission line 1 is an unbalanced transmission line, there is a problem that the usable frequency band cannot be expanded.

Therefore, in order to solve such a problem, as shown in FIG.
1 is provided, an electrostatic shield 12 dedicated to the secondary winding is provided, and a main electrostatic shield 13 is provided between the electrostatic shields 11 and 12.
An insulating transformer 3a in which the ground 3 is grounded via a ground terminal 7 to the ground 8 has also been considered.

As shown in FIG. 6, a capacitor 14 is connected between an electrostatic shield 6 provided between the primary winding 4 and the secondary winding 5 and a ground terminal 7, and this capacitor 1
An insulating transformer 3b utilizing the property of transmitting the high frequency component 4 and the property of not transmitting the commercial frequency component well is also considered.

However, in the case of the insulating transformer 3a shown in FIG. 5, for example, when the grounding position A is far away from the insulating transformer 3a, the electrostatic shield 11 and the main electrostatic shield 13 are connected even in a steady state. , A potential difference occurs. Therefore, although the transmission loss is smaller than that of the insulating transformer 3 shown in FIG. 3, the transmission loss is still generated. Particularly, as the frequency increases, the transmission loss increases. Was difficult. In addition, in the insulating transformer 3a shown in FIG. 5, it is necessary to wind an independent electrostatic shield over so-called three systems, so that it is difficult to manufacture the insulating transformer 3a.
In addition, there is a problem that the insulating transformer 3a becomes large.

In the insulating transformer 3b shown in FIG. 6, in order to suppress the low frequency component from flowing to the ground 8 via the electrostatic shield 6, the connection between the primary winding 4 and the electrostatic shield 6 is required. The series combined capacitance of the capacitance of the distributed capacitor 9 and the capacitance of the capacitor 14 needs to be sufficiently small, and for this purpose, the capacitance of the capacitor 14 needs to be sufficiently small. But,
With this setting, when a surge enters the signal transmission line 1, the shared voltage of the capacitor 14 increases, and the potential of the electrostatic shield 6 rises. There was a problem that it could not be done.

[0013]

As described above, a conventional communication insulation transformer in which an electrostatic shield is interposed between a primary winding and a secondary winding and the electrostatic shield is grounded is provided. In particular, transmission loss in the steady state is large, and the usable frequency band can be widened, especially when interposed in an unbalanced transmission line composed of the center conductor and the outer conductor of a coaxial cable. There was a problem that it was not possible.

Further, it is difficult to manufacture a communication insulating transformer in which a dedicated electrostatic shield is provided for each winding in order to suppress the distributed capacitance between the winding and the electrostatic shield, and it is difficult to manufacture the transformer. In addition to this, the transmission loss still increases in the high frequency range, so that there is a problem that the usable frequency band cannot be expanded.

Furthermore, in a communication isolation transformer in which an electrostatic shield is grounded via a capacitor,
If the capacitance of the capacitor is set so as to suppress the current flowing through the electrostatic shield in a steady state, there is a problem that the electrostatic shield cannot exhibit its original shielding function when a surge enters.

Therefore, the present invention has a simple structure, is easy to manufacture, and allows the electrostatic shield to properly exhibit its original shielding function at the time of surge intrusion. It is an object of the present invention to provide a communication isolation transformer device capable of suppressing transmission loss in a steady state and expanding a usable frequency band.

[0017]

In order to achieve the above-mentioned object, the present invention provides an electrostatic shield which is interposed between a primary winding and a secondary winding so as to be grounded via a ground terminal. A switching element for electrically connecting the electrostatic shield to the ground terminal when the potential difference between the electrostatic shield and the ground terminal is greater than or equal to a predetermined value. Is provided.

The switching element may be any element that conducts quickly when the potential of the electrostatic shield is equal to or higher than a predetermined value, that is, when a surge enters, and a transistor can be used. A discharge tube, a Zener diode connected in series with two electrodes of opposite polarity, a varistor, and the like are preferable in terms of high current withstand capability, simple structure, and ease of assembly.

The communication insulating transformer device according to the present invention comprises:
In a steady state, the electrostatic shield is kept completely separated from the ground, and only when a surge enters, the switching element conducts and the electrostatic shield is electrically connected to the ground. For this reason, even when the signal is inserted into the unbalanced transmission line, a part of the transmission signal does not flow through the electrostatic shield in the steady state. Therefore, the transmission loss can be significantly reduced over a wide frequency band in the steady state, and the usable frequency band can be expanded with the transmission loss suppressed. In addition, when a surge enters, the switching element conducts, thereby electrically connecting the electrostatic shield to the ground, so that the electrostatic shield can properly exhibit its original shielding function.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a communication insulation transformer device 21 according to an embodiment of the present invention, which is connected to an external signal transmission line 2.
2 shows an example of an equivalent circuit interposed between the communication device 2 and the signal transmission path 23 on the communication device side.

The communication insulating transformer device 21 includes a primary winding 24 and a secondary winding 25 wound around an iron core (not shown), and an electrostatic shield between the primary winding 24 and the secondary winding 25. 26.

Both ends of the primary winding 24 are connected to the center conductor and the outer conductor of the signal transmission line 21 constituted by a coaxial cable, for example, and both ends of the secondary winding 25 are constituted by a signal transmission line constituted by a coaxial cable, for example. 22 are connected to the center conductor and the outer conductor.

The electrostatic shield 26 is connected to a ground terminal 30 via a bidirectional regulated voltage conduction type switching element 29 formed by connecting zener diodes 27 and 28 in series with opposite polarities. Then, the ground terminal 30 is grounded to the ground 31.

The switching element 29 has a potential difference between the electrostatic shield 26 and the ground 31 of several volts.
For example, one that conducts when it exceeds 5 volts is used.

With such a configuration, in a steady state, the potential difference between the electrostatic shield 26 and the ground 31 is 5
Since the voltage does not exceed volts, the switching element 29
Maintain the off state. For this reason, even when the transmission signal is inserted into the unbalanced transmission line as shown in FIG. 1, a part of the transmission signal does not flow to the ground 31 via the electrostatic shield 26 in the steady state. .

Therefore, as shown by the broken line in FIG.
In a steady state, transmission loss can be significantly reduced over a wide frequency band, and a usable frequency band can be widened with transmission loss suppressed.

Further, the surge enters and the electrostatic shield 26
When the potential difference between the ground and the ground 31 exceeds 5 volts, the switching element 29 is turned on and the electrostatic shield 26 is connected to the ground 31.
, The electrostatic shield 26 can exhibit its original shielding function well.

In the above-described example, a switching element 29 in which two Zener diodes are connected in series with opposite polarities is used. However, a discharge tube 32 as shown in FIG. Varistor 33 as shown in (b),
Alternatively, a single element selected from semiconductor control elements such as transistors or a combination thereof may be used as the switching element. Further, in the above-described example, the transmission line is interposed in the unbalanced transmission line. However, it is needless to say that the transmission line can be used without any trouble even if the transmission line is interposed in the balanced transmission line.

[0029]

As described above, according to the present invention,
Since a switching element that conducts at a specified voltage is interposed between the electrostatic shield and the ground terminal, transmission loss is significantly reduced over a wide frequency band even when used in an unbalanced transmission path. , And the usable frequency band can be expanded while suppressing the transmission loss. In addition, when a surge enters, the electrostatic shield can be quickly connected to the ground, and the electrostatic shield can properly exhibit its original shielding function.

[Brief description of the drawings]

FIG. 1 is an equivalent circuit diagram of an example in which a communication insulating transformer device according to an embodiment of the present invention is interposed in a signal transmission path.

FIG. 2 is a diagram showing another example of a switching element.

FIG. 3 is an equivalent circuit diagram of an example in which a conventional communication insulating transformer is interposed in a signal transmission path.

FIG. 4 is a diagram showing a comparison between a transmission loss characteristic of a conventional communication insulating transformer and a transmission loss characteristic of a communication insulating transformer device according to the present invention.

FIG. 5 is an equivalent circuit diagram of an example in which another conventional insulating transformer for communication is interposed in a signal transmission path.

FIG. 6 is an equivalent circuit diagram of an example in which another conventional communication insulating transformer is interposed in a signal transmission path.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 ... Insulation transformer device for communication 22, 23 ... Signal transmission path 24 ... Primary winding 25 ... Secondary winding 26 ... Electrostatic shield 27, 28 ... Zener diode 29 ... Switching element 30 ... Ground terminal 31 ... Ground 32 ... Discharge Pipe 33 ... Barista

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hitoshi Kijima 3-19-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Masahiro Arima 3--19, Nishishinjuku, Shinjuku-ku, Tokyo No. 2 Nippon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. A communication insulating transformer device in which an electrostatic shield inserted between a primary winding and a secondary winding is grounded via a ground terminal, wherein the electrostatic shield and the ground terminal are connected. And a switching element for electrically connecting the electrostatic shield to the ground terminal when the potential difference between the two is greater than or equal to a predetermined value. 2. The communication insulating transformer device according to claim 1, wherein said switching element conducts when a surge enters. 3. The communication insulating transformer device according to claim 1, wherein said switching element is constituted by a single element or a combination selected from a Zener diode, a discharge tube, a varistor, and a semiconductor control element.