JPS6320091B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a communication protector, and more particularly to a communication protector suitable for use in a communication device such as an electronic exchange. Conventionally, as this type of protector, one shown in FIG. 1 has been used because of its simple configuration. Here 1
1 and 11' are carbon lightning arresters or self-recovering discharge tubes, and 12 and 12' are fuses, self-recovering heat coils, positive resistance coefficient thermistors, and the like. On the other hand, as the use of semiconductor elements in protected equipment progresses, the withstand voltage of the entire equipment decreases and the high-speed breakdown phenomenon peculiar to semiconductor elements becomes apparent, and the protector shown in Figure 1 becomes insufficient in terms of performance. There are drawbacks. There is also a method shown in FIG. 2 as a conventional technique that takes the above drawbacks into consideration. That is, in Figure 2, 2
1 and 21' correspond to, for example, the self-recovering discharge tubes 11 and 11', and 22 and 22' correspond to, for example, the fuses 12 and 11'.
12', and 23 and 23' indicate terminals connected to the protected equipment. 25 and 25' are semiconductor elements having nonlinear impedance, and MOV (metal oxide varistors) or Zener diodes are mainly used. As resistors 24 and 24', heat coils, fuses, etc. are used to provide current limiting characteristics. 2nd above
The protector with the configuration shown in the figure requires so-called voltage co-design, in which components are designed to match the voltage resistance of the protected equipment. In other words, when a high-energy surge such as induced lightning strikes, terminal 2 of the protected equipment
In order to suppress the voltage at terminals 3 and 23' below the withstand voltage of the equipment, for example, the terminal voltage at terminals 25 and 25' (for example, MOV) must be kept at the withstand voltage of the equipment until the self-recovering discharge tubes 21 and 21' operate. While keeping below,
The characteristics of each element are adjusted so that the sum of the voltage difference caused by the voltage drop of the current flowing through the resistors 24 and 24' becomes a value sufficient to start the operation of 21 and 21' (for example, a self-recovering discharge tube). must be selected. As a practical example, assume that the withstand voltage of the protected equipment is 350V,
For example, if the maximum voltage sent out from the protected equipment such as a switch is 210V, for example, MOV25, 25'
If the characteristics are as shown in FIG. 3, the design specifications for an induced lightning surge with a waveform as shown in FIG. 4 will be the values shown in Table 1.

[Table] If this kind of design is possible, from the track side
Even if an electrical surge with a peak voltage of 1KV is applied as a power source with zero internal impedance, the voltage generated between the protected equipment terminals 23, 23' and the ground is suppressed to 340V, and after a certain period of operation delay. ,
21, 21' (for example, a self-recovering discharge tube) can be applied with a voltage sufficient to operate them. However, since this type of protector is inserted into the communication line of a switch, for example, increasing the resistance value as a characteristic element to 22Ω as in the design example above increases insertion loss in the transmission characteristics and the system performance will deteriorate. In addition, in order to lower this resistance value, it is necessary to allow an increase in the size of the MOV or to dramatically improve the characteristics at 25 and 25' in Figure 2, and also to use a Zener diode. In this case, since it is a unidirectional element, it has the disadvantage that it is difficult to realize a small and inexpensive high-performance protector due to the increase in the number of uses and the cost. An object of the present invention is to solve the above drawbacks by using a voltage limiting element having negative resistance, a nonlinear resistance element, and a positive resistance coefficient thermistor, and by thermally coupling the nonlinear resistance element and the positive resistance coefficient thermistor. It is small, inexpensive, and has sufficient protection performance.
The object of the present invention is to provide a high-performance protector that does not cause deterioration of device performance such as transmission characteristics. To explain the configuration of the present invention, the present invention has the following features:
In a communication protector used in communication devices such as electronic exchanges, a voltage limiting element having a negative resistance is connected between a line side input terminal and ground, and a voltage limiting element having a negative resistance is connected between the line side input terminal and the protected equipment side output terminal. A positive resistance coefficient thermistor is connected, a nonlinear resistance element having negative resistance is connected between the protected device side output terminal and ground, and the positive resistance coefficient thermistor and the nonlinear resistance element are thermally coupled. This is a communication safety device that is characterized by: The present invention will be explained below by way of examples with reference to the drawings. FIG. 5 shows the voltage-current characteristics of a voltage-limiting element having negative resistance, which is one of the components of the present invention.
Items with such characteristics include carbon lightning arresters, self-recovering discharge tubes, and SCRs that utilize electric discharge phenomena.
This type of element is in a high resistance region under normal conditions, but when the applied voltage exceeds a certain level (discharge starting voltage), it has the characteristic of passing through a negative resistance region and transitioning to a low resistance region. ing. FIG. 6 shows the characteristics of a nonlinear resistance element of which a metal oxide varistor (MOV) is a typical example. This type of element does not have a negative resistance region, but has a clear high resistance region and a clear low resistance region bordering on a certain voltage (limiting voltage). As something like this
There are MOV, Zener diode, etc. Figure 7 shows the characteristics of the positive resistance coefficient thermistor.
When the temperature exceeds the Curie temperature Tc (approximately below 200°C), a significant increase in resistance occurs. FIG. 8 shows an external view of an embodiment of the protector of the present invention using these components. FIG. 9 is a circuit diagram in this embodiment. In this embodiment, an MOV 33 produced by powder firing as an example of the nonlinear resistance element of the present invention and a positive resistance coefficient thermistor 34 are arranged close to each other on an Al ₂ O ₃ ceramic substrate 31 having good thermal conductivity. Achieving a combination. The resistance value of the positive resistance coefficient thermistor 34 is in a low resistance range against self-heating due to the current flowing when the communication line is used (usually about 20 mA to 200 mA in exchanges), and is such that the desired transmission characteristics can be obtained. A suitable value (for example, about 5Ω) is selected. When an induced lightning surge occurs in this state, current flows through the positive resistance coefficient thermistor 34 and it generates heat, but this alone does not raise the temperature at a sufficient rate. on the other hand
The same current flows through MOV33, but MOV3
Since the power consumed by the positive resistance coefficient thermistor 34 is much larger than that of the positive resistance coefficient thermistor 34 in a low resistance state, the temperature rapidly rises. Here, this temperature rise also causes the temperature of the positive resistance coefficient thermistor 34 to be thermally coupled to rise, causing a rapid increase in resistance beyond the Curie point as shown in FIG. Under the conditions explained in the conventional technology, the resistance required to obtain sufficient protection performance is about 22Ω, and the resistance is low resistance state 5.
While only about 5 times Ω is sufficient, the 7th
As shown in the figure, the temperature required to cause a 100 times resistance change in the positive resistance coefficient thermistor 34 is a temperature increase of about 20° C. relative to the Curie temperature. Therefore, by setting the operating point during normal use near the Curie point, it is possible to generate a resistance change at high speed. On the other hand, since the positive resistance coefficient thermistor 34 in a high resistance state applies sufficient voltage to both ends of the self-recovering discharge tube 32 to start the discharge, it is possible to start the discharge before self-destruction due to heat generation of the MOV 33 and the positive resistance coefficient thermistor 34 themselves. can. In addition to the voltage co-design, the ceramic circuit board 31 is used to create a positive resistance coefficient thermistor 34 as described above.
The MOV33's good thermal design allows it to achieve characteristics such as low resistance during normal use and high resistance when a surge occurs, making it possible to achieve both protection performance and transmission characteristics. As explained above, according to the present invention, a voltage limiting element having negative resistance, a nonlinear resistance element, and a positive resistance coefficient thermistor are used, and thermal coupling between the nonlinear resistance element and the positive resistance coefficient thermistor is achieved. By configuring the protector to be able to do so, it is possible to realize a high-performance protector that is small, inexpensive, has sufficient protection performance, and does not cause deterioration of device performance such as transmission characteristics.

[Brief explanation of the drawing]

Figures 1 and 2 are circuit diagrams of conventional protectors, Figure 3 is a characteristic diagram of a typical metal oxide varistor, and Figure 4 is a generally known electrical surge caused by induced lightning. Showing a wave graph. FIG. 5 is a characteristic diagram of a voltage limiting element used in the present invention, FIG. 6 is a characteristic diagram of a nonlinear resistance element having negative resistance, and FIG. 7 is a characteristic diagram of a positive resistance coefficient thermistor. FIG. 8 is a perspective view of a safety device for a communication device according to an embodiment of the present invention, and FIG. 9 is a circuit diagram thereof. The symbols used in the drawings indicate the following. 31... Ceramic circuit board, 32...
Self-resilient voltage limiting element, 33... Negative resistance coefficient nonlinear resistance element such as MOV, 34... Positive resistance coefficient thermistor, 35... Connection terminal.

Claims (1)

[Claims] 1. In a communication protector used in a communication device such as an electronic exchange, a voltage limiting element having a negative resistance is connected between a line side input terminal and ground, and a voltage limiting element having a negative resistance is connected between the line side input terminal and the protected equipment side output terminal. A positive resistance coefficient thermistor is connected to the output terminal of the protected device and a nonlinear resistance element having negative resistance is connected between the output terminal on the protected device side and ground, and the positive resistance coefficient thermistor and the nonlinear resistance element are thermally coupled. A communication safety device characterized by: