RU2124274C1 - Protection switching device for subscriber's line interface circuits - Google Patents

Abstract

FIELD: telephone communications. SUBSTANCE: since subscriber's line interface circuits are sensitive to overvoltage often caused by lightning affected subscriber's lines, their operations could be in danger. Overvoltage can be alleviated by means of switching circuits with expensive special-purpose elements and additional circuits. This invention discloses device design in which this is achieved by general-purpose power thyristor, which control electrode voltage or cathode voltage in blocked state or overvoltage in conducting state is compared to reference voltage by means of comparator. If overvoltage is detected subscriber's line interface circuits are switched on when no current runs through control input so that level of blocking thyristor is not reached. Current is supplied again, only if there is no overvoltage in blocked state. EFFECT: decreased cost, possibility of protection of multiple subscriber's line interface circuits. 1 dwg

Description

 The present invention relates to a switching protective device for protecting electronic subscriber circuits, which is used to eliminate overvoltage at the inputs of the electronic subscriber circuit. Such overvoltages occur primarily as a result of the effect of lightning on subscriber trunk lines. The subscriber circuits connected to them, which are increasingly being implemented with integrated circuits, the so-called Subscriber Line Interface Circuits, SLIC, are especially sensitive to overvoltages, which jeopardizes their operation.

 As for the power supply circuits with the usual grounded positive pole of the power supply source, the known option is the removal of positive overvoltage on subscriber connecting lines through diodes, and negative overvoltages through diodes and thyristor to the housing according to DD 281331 A7. In the case of such switching devices, it is necessary that the thyristor has a very large holding current to prevent the thyristor from conducting, which should occur only during overvoltages, by means of the current coming from the subscriber circuit, and thus regardless of the external overvoltage. This large holding current causes a large demand for current to control the valve circuit. To reduce the aforementioned current requirement for controlling the valve circuit in the switching device described in the patent DD 281331 A7, thyristor control is carried out through an additional thyristor circuit.

 Further, a device for protecting an electronic circuit of a device for interfacing subscriber connecting circuits is known in which the control current consumption of a special protective thyristor is reduced by an auxiliary thyristor installed before the input of the valve circuit, according to, for example, EP 0247319 B1. A large consumption of control current often occurs in the case when several subscriber connection lines are simultaneously under the influence of overvoltage resulting from lightning, as a result of which the control voltage source is under a very strong load.

 Known switching devices provide a protective effect, however, expensive special blocks or auxiliary circuits must be used for this.

 This implies the task of creating a switching protective device that implements using inexpensive publicly available elements and provides simultaneous protection of several subscriber circuits.

 This problem is solved using the switching device described in paragraph 1 of the claims.

 The essence of the invention lies in the fact that the thyristor, which is switched on during overvoltage, acts through the circuit of the comparison unit so that the protected subscriber circuits are switched on in a de-energized state. For this, it is necessary to have a control circuit in the subscriber scheme, which, however, with monolithic integration is not a problem. In this way, a situation where subscriber circuits supply a sufficiently large holding current to the thyristor can be avoided, so that a network thyristor with a small holding current can be used. The thyristor switches on automatically in the absence of overvoltage in the locked state, and the subscriber circuits in this case are again ready for operation. The thyristor used has a number of advantages, including low control power, as well as low cost, due to the large number of units produced and the simplicity of semiconductor manufacturing technology. The implementation of the protection of many subscriber schemes using only one protective switching device is real when using the solution in accordance with the invention.

 The invention is further explained in the description of an example of its implementation with reference to the accompanying drawing, depicting a diagram of a protective switching device.

 The drawing shows two subscriber circuits SLICI, SLICn with their subscriber trunk lines LtgI, Ltgn, which consist of core a and core b. Other subscriber circuits and connecting lines are not represented, but can be connected to a switching protective device in accordance with the claimed device. Positive overloads on the subscriber connecting lines Ltgl Ltgn are discharged through the first diodes D11, Dln and the second diodes D21, D2n to the housing, respectively. The switching protective device consists of the third diode D31, D3n, related to the subscriber connecting lines Ltgl, Ltgn and the fourth diode D41, D41, as well as the resistance RG, related to the input of the gate circuit, and from the comparator K.

In equilibrium mode, the thyristor Th is locked, the voltage at the control electrode is, for example, -100V and applied to the first input of the comparator K, and in magnitude it is greater than the reference voltage U _k applied to the second input of the comparator K, for example -5V, and the output of the comparator, connected to the corresponding control input ISt of the subscriber circuits SLICn is inactive. There is the possibility, instead of the voltage U _{G of the} control electrode, _to apply the cathode voltage U _{to the} thyristor Th to the first input of the comparator. The voltage U _{G of the} control electrode is supplied to the thyristor Th through the resistance RG from the first control voltage source USt.

If on the same subscriber line or on several subscriber lines Ltgl. .. Ltgn negative overvoltages appear, the absolute value of which is greater than the voltage U _{g of the} control electrode, for example, more than 100V, then the thyristor Th is triggered and forms with the third and fourth diode D31, D41; D3n, D4n low resistance circuit by weight. The voltage U _G at the control electrode and the cathode voltage U _k will then be U _G ≈ -1V and U _k ≈ -1V and will be less than the reference voltage U _{v of the} comparator K. In this case, a signal is generated at the input of the comparator, which is transmitted through the corresponding control input ISt subscriber circuits SLICl ... SLICn affects the interruption of the power circuit, that is, all connected subscriber circuits SLICl ... SLICn is mostly de-energized. In the absence of negative overvoltages, disconnected subscriber circuits SLICl ... SLICn can provide only a very small current, which is less than the holding current of the thyristor Th, and the latter goes back to the closed state. Thus, the voltage U _G or, respectively, U _k at the first input of the comparator becomes more negative than the reference voltage U _v at the second input of the comparator K, that is, (U _G )> (U _k ), so that through the output signal of the comparator, indicated at the top as inactive state, and through the control input ISt of the respective subscriber circuits SLICl ... SLICn, the power circuit is activated again. Thus, the working state is automatically restored again. Since in case of deenergized subscriber circuits SLICl ... SLICn a very small holding current flows through the thyristor Th, it is advisable to use cheap network thyristors with sufficient conductivity. Until now, the insignificant holding current of network thyristors has been a hidden reason for their use as protective thyristors for the described purpose.

Claims (1)

 1. A switching protective device for electronic subscriber circuits against overvoltages on subscriber lines, of which, respectively, one core through at least one diode and a thyristor connected in series to diodes, when overvoltages occur, forms a low-resistance connection between the residential subscriber line and ground, characterized in that to the first the thyristor cathode or the thyristor control electrode is connected to the comparator input, which is additionally connected to the control voltage source via resistance, and A reference voltage is applied to the second input of the comparator and the output of the comparator is connected to the control input of at least one subscriber circuit.