JPS6077625A - Communication safety device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a communication protector used in an electronic exchange to protect in-office equipment from abnormal voltages and currents caused by lightning strikes, power lines, etc. coming into contact with external cables.

Conventionally, this type of communication protector has nonlinear resistance characteristics, including gas tube arresters 1 and 1', heat coils, fuses, and positive resistance coefficient thermistors 2° and 2', as shown in Figure 1. It is composed of MOVs (metal oxide varistors) 3 and 3' which are voltage limiting elements. As a protective element against abnormal currents that occur when power lines come into contact with communication lines, such protectors operate at relatively low currents, have fast response characteristics, and do not operate even when lightning surges are applied. In addition, the overcurrent protection element between the A and B lines is required to have a layer with little impedance unbalance.

In response to these requirements, each anti-poetry element has the following characteristics. DII Chi, heat coil,
If the surge resistance is large but the response characteristic is slow, the response characteristic is fast but the surge resistance is small, so it will melt due to the surge current caused by lightning surges.To prevent this, a device with a considerably large current capacity is required. It is not possible to protect station equipment from abnormal currents.

In addition, positive resistance coefficient thermistors are practically applicable in terms of response characteristics, surge resistance, and operating characteristics, but when compared with fuses and heat coils, the variation in DC resistance value is as large as about ±20%. For this reason, the amount of impedance unbalance increases, leading to a deterioration in call quality in electronic exchanges and the like.

Furthermore, although fuses and heating coils cannot be reused once they are activated by abnormal current, positive resistance coefficient thermistors have a self-recovery function and can therefore be used repeatedly.

As explained above, fuses have the disadvantages of insufficient surge resistance, heating coils have temperature dependence and slow response characteristics, and positive resistance coefficient thermistors have large variations in resistance.

An object of the present invention is to eliminate the above-mentioned drawbacks and provide a high-performance communication protector that operates reliably against power line interference.

That is, the present invention provides a communication protector for use in a communication device such as an electronic exchange, in which an overcurrent protection element is provided between a line side input terminal and a protected equipment side output terminal. A positive resistance coefficient thermistor is used as the pasting element, and the thermistor is connected in series with a thick film resistor formed on a ceramic circuit board, and the thermistor is connected in series between the input terminal on the line side and the output terminal on the protected equipment side. The thick film resistor is connected and trimmed so that the series resistance value of the thermistor and the resistor becomes constant.

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

FIG. 2 is a circuit diagram showing an embodiment of the communication safety device of the present invention. The protector of the present invention shown in the same figure has a line-side input terminal A.
Gas tube arresters 13 and 13' are connected in series between the line and line B, and the connection point is grounded.
A non-linear resistance element MOV (
(metal oxide varistors) 14, 14' are connected, and between them, a positive resistance coefficient thermistor 15, (15') and a thick film resistor 12, are connected to the A line and B line, respectively.
(12') are connected in series.

In this embodiment, the thick film resistors 12 and 12' are mounted on an Al2O3 ceramic circuit board with good thermal conductivity.
It is formed by screen-printing a 102 series resistance paste and firing it. The thick film resistors 12 and 12' are connected to positive resistance coefficient thermistors 15 and 15' in order to reduce the amount of impedance unbalance between the A and B lines.
, 12' is trimmed so that the series resistance value is approximately ±1 inch accurate.

In addition, in this embodiment, on the ceramic circuit board, cast tube lvstars 13, 13', MOVI 4° 14
', positive resistance coefficient thermistor l5, 15' are mounted in one solder reflow process. The characteristics of these elements are shown in FIGS. 3 to 5.

FIG. 3 shows the voltage-current characteristics of a gas tube arrester, which is one of the components of the present invention. This gas tube arrester utilizes a discharge phenomenon and has negative resistance. In other words, this type of element is normally in a high resistance region in the state of
When it exceeds , it has a characteristic of passing through a negative resistance region and transitioning to a low resistance region.

FIG. 4 shows the voltage-current characteristics of a nonlinear resistance element of which MO (metal oxide varistor) is a typical example. This type of element has a clear high-resistance region and a low-resistance region with a certain voltage (varistor voltage) as a boundary.

FIG. 5 shows the characteristics of a positive resistance coefficient thermistor.

In this type of thermistor, when the temperature exceeds the Curie temperature Tc (approximately 200° C. or less), the resistance value significantly increases.

Next, the characteristics and operation of the communication safety device of the present invention will be explained using the above embodiments.

The positive resistance coefficient thermistor 15.15' has the characteristic that it does not normally operate at the maximum signal current of the exchange (approximately 100 mA), but operates when the current withstand capacity of the subscriber circuit of the exchange exceeds (approximately 200 mA). Further, the thick film resistors 12 and 12' are set to have a rated power (approximately IW) that can withstand up to 1 current of the subscriber circuit of the exchange, and the positive resistance coefficient thermistors 15 and 15' The series resistance value of the thick film resistors 12 and 12' is set at a maximum of about 15 to 200, taking into account the insertion loss of the exchanger.

A communication protector with such characteristics protects against power line interference by applying high voltage (ACloov or 2) to the A line or B line.
00 V), the positive resistance coefficient thermistor 15
．． 15', the positive resistance coefficient thermistor self-heats and its resistance value increases rapidly due to this abnormal current, which protects the subscriber circuit and other equipment in the station. .

As explained above, the present invention is configured by combining a positive resistance coefficient thermistor and a thick film resistor, and by trimming the thick film resistor to obtain accuracy of the series resistance value. It is possible to ignore the large variation in resistance value, which is a drawback of Fuse, and to reduce the amount of impedance unbalance between wires A and B.
Even if the operating current is kept low, effects such as high surge resistance can be obtained. Furthermore, the positive resistance coefficient thermistor has the advantage of having lower temperature dependence and faster response characteristics than a heating coil, and can be used repeatedly compared to a fuse or a heating coil.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a conventional communication protector, FIG. 2 is a circuit diagram showing an embodiment of the communication protector of the present invention, and FIG. 3 is a graph showing voltage-current characteristics of a gas tube arrester. Figure 4 is a graph showing the voltage-current characteristics of a non-linear resistance element.
FIG. 5 is a characteristic diagram of a thermistor with a positive resistance coefficient. 12.12'... Thick film resistor 13.13'... Gas tube arrester 14.14'
...MOV (metal oxide varistor) 15.15'...
・Positive resistance coefficient thermistor applicant NEC Corporation Nippon Telegraph and Telephone Public Corporation

Claims (1)

[Claims] In communication protectors used in communication equipment such as electronic exchanges, an overcurrent protection element is provided between the input terminal on the line side and the output terminal on the protected equipment side, and a positive resistance coefficient is used as the overcurrent protection element. A thermistor is used, the thermistor is connected in series with a thick film resistor formed on a ceramic circuit board, and the thermistor is connected in series and disconnected between an input terminal on the line side and an output terminal on the protected equipment side, and A safety device for communication, characterized in that the thick film resistor is trimmed so that the series resistance value of the thermistor and the resistor is constant.